Hestbay Pty Ltd v One Sector Pty Ltd

[2024] QSC 180

Draft

SUPREME COURT OF QUEENSLAND

CITATION:	Hestbay Pty Ltd v One Sector Pty Ltd [2024] QSC 180
PARTIES:	Hestbay Pty Ltd
(Plaintiff)
v One Sector Pty Ltd
(Defendant)
FILE NO/S:	9563 of 2021
DIVISION:	Trial – Civil
PROCEEDING:	Claim
ORIGINATING	Supreme Court of Queensland
COURT:
DELIVERED ON:	22 August 2024
DELIVERED AT:	Brisbane
HEARING	9 – 13 October 2023
DATES:
16 – 17 October 2023
30 November 2023
1 December 2023
JUDGE:	Ryan J
ORDER:	The plaintiff’s claim is dismissed.
The defendant’s counterclaim is allowed in part.
The parties are to confer and produce a draft order which gives effect to my findings within 14 days.
I will hear the parties, and the third party, Excel Concrete Pty Ltd, as to costs.
CATCHWORDS:	CONTRACTS – BUILDING, ENGINEERING AND RELATED CONTRACTS – THE CONTRACT – GENERALLY – where the plaintiff engaged the defendant to construct an industrial warehouse with a concrete slab floor – – where the slab floor deteriorated – where the plaintiff
alleged that the defendant had constructed a deficient slab,
not in accordance with its contractual specifications – where
the plaintiff alleged that the defendant added too much water to the cement mix during the pour of the slab, causing it to be
understrength and of insufficient surface hardness – where
the plaintiff alleged that the slab was too thin at spot locations
– where the plaintiff alleged that the slab was not fit for
purpose – whether the contract was breached – whether any
breach was inconsequential/de minimus – turns on its own
facts.
RELATED CONTRACTS – THE CONTRACT –
CONTRACTS – BUILDING, ENGINEERING AND themselves (without lawyers or project managers) – where
the parties focus was on a series of Tender Letters, which set out the detail of the work to be performed and its cost but
which did not include broader contractual terms – where the parties did not sign a contract – where the parties disagreed
about whether the Australian Standards design and construct
contract terms applied – turns on own facts.
EVIDENCE – ADMISSIBILITY – OPINION EVIDENCE – EXPERT OPINION – GENERALLY – where the plaintiff relied upon the evidence of an expert engineer – where the expert’s opinion was based on identified factual assumptions
– where those factual assumptions were not proven by
admissible evidence – where the defendant did not apply to exclude the evidence of the plaintiff’s expert – weight to be
given to expert evidence where factual assumptions not proved.
Alexander v Cambridge Credit Corp Ltd (1987) 2 NSLR 310, considered Bellgrove v Eldridge (1954) 90 CLR 613, considered
Build Qld Pty Ltd v Pro-Invest Australian Hospitality
Opportunity (ST) Pty Ltd [2022] QCA 266, cited Elliott v Lawrence [1966] Qd R 440, cited Hestbay Pty Ltd v One Sector Pty Ltd [2023] QSC 154, noted McGhee v National Coal Board [1973] 1 WLR 1, considered PQ v Australian Red Cross Society [1992] 1 VR 19, cited R v Gibson [2022] QCA 151, applied R v Naidu [2008] QCA 130, applied
Sanrus Pty Ltd & Ors v Monto Coal 2 Pty Ltd & Ors (No 7)
[2019] QSC 241, applied
SHA Premier Constructions Pty Ltd v Niclin Constructions
Pty Ltd [2019] QCA 201, cited
Stockland Property Management Pty Ltd v Cairns City
Council [2011] 1 Qd R 77, cited Stone v Chappel (2017) 128 SASR 165, considered Tabcorp Holdings Ltd v Bowen Investments Pty Ltd (2009) 236 CLR 272, considered
COUNSEL:	S B Whitten & C Matthews for the plaintiff M D Ambrose KC & Dr A Greinke & S Lamb for the defendant
SOLICITORS:	Hickey Lawyers for the plaintiff Doyles Construction Lawyers for the defendant

Draft

Summary .............................................................................................................................. 7
Preliminary comments ........................................................................................................ 11

Context ............................................................................................................................... 13

Concrete and its strength ................................................................................................ 13
The concrete in this case ................................................................................................ 13

Strength testing ............................................................................................................... 14

Slump .............................................................................................................................. 14

Australian Standards relevant to the slab’s construction .................................................... 16

Authoritative documents other than Australian Standards ................................................. 23

Concrete Institute of Australia: Recommended Practice: The Evaluation of Concrete
Strength by Testing Cores .............................................................................................. 23
The Z11 document .......................................................................................................... 23
BS EN 13791:2019 ......................................................................................................... 28
European Standard EN 1992 -1-1 Eurocode 2 ............................................................... 28

National Construction Code Series 2015 ....................................................................... 29

The parties and early negotiations ...................................................................................... 31

The warehouses’ purpose ................................................................................................... 32

Warehouse completion, occupancy and maintenance ........................................................ 33

The Stage 1 contract ........................................................................................................... 34

The engineers’ specifications for the concrete slabs .......................................................... 38

The leases ........................................................................................................................... 40

Tenants’ complaints about the Stage 1 and Stage 2 slabs .................................................. 42

Viadux (Stage 1) ............................................................................................................. 42
Chempro (Stage 1) .......................................................................................................... 42
EZFurn (Units 10 and 11, Stage 2) ................................................................................. 43
Budget Pet Products (Units 12 and 13, Stage 2) ............................................................ 45

Budget Pet Products (Unit 9, Stage 2) ............................................................................ 48

Hestbay’s investigation of, and response to, the complaints .............................................. 49

Mr Ray’s observations of the Stage 2 units ........................................................................ 50

Unit 9 .............................................................................................................................. 50
Units 10 and 11 ............................................................................................................... 50

Units 12 and 13 ............................................................................................................... 50

Hestbay’s claim in brief ..................................................................................................... 52

One Sector’s response in brief ............................................................................................ 54

Testing of the Stage 2 slab in 2022 .................................................................................... 55
The Stage 2 contract ........................................................................................................... 57
The concrete used in Stage 2 .............................................................................................. 69
Flawed comparison between the Stage 1 and Stage 2 slabs ............................................... 73

Expert engineering evidence .............................................................................................. 76

Plaintiff’s expert: Dr Scott Woolcock ................................................................................ 77

Report 28 August 2022 ................................................................................................... 77

Defendant’s expert: Dr Inam Khan .................................................................................... 91

Report 6 April 2023 ........................................................................................................ 91

Defendant’s expert: Mr Lindsay Reid ................................................................................ 99

Report 26 April 2023 ...................................................................................................... 99

Dr Woolcock in reply ....................................................................................................... 102

Report 6 July 2023 ....................................................................................................... 102

Dr Khan in reply to Dr Woolcock’s report ....................................................................... 105

Report 29 August 2023 ................................................................................................. 105

Mr Reid in reply to Dr Woolcock’s report ....................................................................... 107

Report 4 September 2023 ............................................................................................. 107

Defendant’s expert: Mr Robert Munn .............................................................................. 109

Report 5 April 2023 ...................................................................................................... 109
Units 10 and 11 ............................................................................................................. 109
Unit 9 ............................................................................................................................ 110

Units 12 and 13 ............................................................................................................. 111

Mr Munn supplementary report (in response to Dr Woolcock’s report).......................... 114

1 September 2023 ......................................................................................................... 114

Joint report ........................................................................................................................ 115
Valuation evidence ........................................................................................................... 127

Main Issues ....................................................................................................................... 131

Issue 1: Whether the contract terms were those in an AS4902 – 2000 Design &

Construct sent by the plaintiff on 10 July 2015, or the terms of what the defendant says

is its “Commercial Contract”, which the plaintiff had a copy of as of 23 March 2016?

...................................................................................................................................... 133 problems, including by exhibiting degradation to parts of the surface, cracking in various areas and excessive dusting? ........................................................................... 136 Issue 3: If the contract was the AS 4902 contract, was the defendant aware of the

purpose of the slabs, and if so, whether the slabs as constructed were “fit for purpose”,

given that was required by cl 2.2(a) of that contract? .................................................. 138 version of the contract, which specified the depth and strength of the concrete to be constructed? .................................................................................................................. 141

Issue 5: If so, were those breaches the effective cause of the [plaintiff’s] loss and

damage, or were the defective durability and strength problems caused by the tenants identified by Dr Woolcock are reasonable and necessary? .......................................... 164

using non-pneumatic tyres on the flooring? ................................................................. 155

Counterclaim .................................................................................................................... 170

Inconsistent contractual terms ...................................................................................... 172

Qleave ........................................................................................................................... 174

Piling and piering ......................................................................................................... 174

The rock wall ................................................................................................................ 175

Appendix 1 ....................................................................................................................... 177

Leases and Tenants ....................................................................................................... 177

Appendix 2 ....................................................................................................................... 178

Vehicles in use .............................................................................................................. 178

Summary

1. Hestbay engaged One Sector to design and construct an industrial warehouse complex with a concrete slab floor in two stages, Stage 1 and Stage 2. After the complex was completed and tenanted, tenants complained about the state of the slab floor in Stage 2. Hestbay asserted that One Sector constructed a deficient Stage 2 slab, causing Hestbay loss and damage.

2. Hestbay asserted that the primary reason for the deficient Stage 2 slab was that One Sector added too much water to the cement mix during the pour of the slab, resulting in its being under-strength, or having an insufficiently hard surface, causing it to crack, deteriorate, and generate excessive dust. Hestbay also complained that the Stage 2 slab was not of its required thickness.

3. Hestbay brought a variety of claims against One Sector, including for breach of contract in failing to construct the slab in accordance with its specifications; and in failing to construct a warehouse which was fit for purpose because: (a) it was not fit for use by tenants of all kinds using pneumatic or non-pneumatic tyred vehicles; and (b) spot failures in the thickness of its slab did not allow tenants to put walls anywhere within the warehouse.

4. One Sector asserted that there was nothing wrong with the Stage 2 slab – even if more

   than the prescribed amount of water had been added to the cement mix during its pour. Hestbay was unable to prove that: (a) the slab was not built to its specifications; (b) the addition of excess or uncontrolled water to the cement mix during its pour led to its damage; (c) it was not of the thickness required; nor (d) that it was not fit for its purpose. The slab was designed for pneumatic tyred vehicles only. Any damage to

   it was caused by Hestbay’s tenants using non-pneumatic (or hard-wheeled) vehicles

on it. Further, One Sector counterclaimed against Hestbay for three amounts said to
be owing under the contract.

1. With respect to Hestbay’s claim, the parties identified the issues for me at the

   beginning of the hearing. At the end of the hearing, I re-framed the issues so that they better aligned with the way in which the case had been conducted. The table below briefly states my conclusions on the issues, as re-framed by me.

2. I found that, although One Sector may have breached its contract with Hestbay, the breaches were inconsequential; and the evidence did not persuade me that it was more probable than not that those breaches caused damage to Hestbay. It follows that

   Hestbay’s claim is dismissed.

Issue as drafted by the Issues as re-framed by Brief statement of my response.

plaintiff, pre-trial. me post-trial.

1. Whether the contract terms were those in	What contractual terms	The contract terms for Stage 2 included
governed the design and	those contained in AS4902-2000 and the
an AS 4902-2000	construction of Stage 2?	Tender Letter of 23 May 2015 itself. Both
Design & Construct	of those documents were included in the
sent by the defendant	contractual documents sent to the plaintiff
to the plaintiff on 10	on 10 July 2015.
July 2015, or the
terms of what the	This led to inconsistency between some of
defendant says is its	the contractual terms.
“Commercial
contract”, which the	I found that the terms of AS4902-2000
plaintiff had a copy	applied only to the extent that they were
of as of 23 March	not inconsistent with the terms expressly
2016?	agreed by the parties, including those spelt out in the Tender Letter.
One Sector’s terms and conditions did not
apply.
2. Whether the slabs in Stage 2 are defective	Were the Stage 2 slabs	I proceeded on the basis that the Stage 2
defective, in that they	slab was defective in that it was exhibiting
because of durability	were exhibiting	degradation, cracking, and excessive
and strength	degradation, cracking	dusting. The critical question was
problems, including	and excessive dusting?	“why?”.
by exhibiting
degradation to parts of the surface, cracking in various areas and excessive dusting?

3. If the contract was the AS4902 contract, (a) What was the (a) Mr Hutchins engaged Mr Ray to

intended purpose of build the sort of warehouses that he

was the defendant	the Stage 2 slab –	had built before on a speculative
aware of the purpose	stated or otherwise?	basis – that is a warehouse like the
of the slabs, and if so,	100 he’d built since 2009, all of
whether the slabs as	which specified slabs of 32 MPa.
constructed were “fit	Slabs of that strength were suitable
for purpose”, given	for “general industrial use” or a
that was required by	“broad range of industrial uses”.
cl 2.2(a)(iv) of that
contract?	I did not find that the Stage 2 slab’s
intended purpose included its being
able to accommodate hard-wheeled
vehicles.

(b) Would the Stage 2

slab’s specifications	(b) Yes.
render it fit for its
purpose?

(c) Was the Stage 2

slab built to its	(c)	See Issue 4.
specifications?

4. Whether the slabs	Was the slab built to its
were constructed in	specifications as to its –
breach of the terms
specified on either	(a) strength; (a) The defendant’s contractual
version of the	obligation was to construct a slab
contract, which	which was of a characteristic
specified the depth	compressive strength of 32 MPa at 28
and strength of the	days after its pour. It was more
probable than not that the slab was
concrete to be	not quite of a characteristic
constructed?	compressive strength of 32MPa at 28
days after its pour. It was more
probable than not that the slab was of
a characteristic compressive strength
of 32 MPa at practical completion.

(b) thickness;	(b)	Thickness was to be calculated as per
15.3.3 of the CCAA Guide to
Industrial Floors and Pavements.
Whether it was compliant with its
specification was to be determined as
per 15.2.4 of the Guide. There could
be no testing as per 15.3.3 because
the cores taken were not the right
size. Thus, I could not determine
compliance. If I “made do” with the
cores available, their average and
characteristic thickness exceeded
175mm and the slab met its thickness
specification. However, on a “spot
failure” approach, it did not.
(c)	slump; and	(c) No.
(d) water to cement	(d)	There was no evidence about the

ratio? water to cement ratio of the mix
when it left the supplier. Therefore,
one could not determine what the
water to cement ratio was at any
relevant point in time.

5. If so, were those (a) Was the addition of (a) I was not satisfied that it was more

breaches an effective	uncontrolled water	probable than not that the addition of
cause of the	an effective cause of	uncontrolled water to the Stage 2
plaintiff’s loss and	damage to the slab?	slab at pour was the cause, or an
damage, or were the	effective cause, of the damage to the
defective durability	slab.
and strength
problems caused by
the tenants using non	(b) Did the thickness of	(b) No.

pneumatic tyres on	the slab render it
the flooring?	unfit for purpose?
6. Whether rectification is required, and if so,	Not applicable, because of my findings on
which of the Options	Issues 1 – 5.
1, 2 or 3 identified by Dr Woolcock are reasonable and necessary?

1. With respect to the counterclaim, I found that Hestbay owed One Sector for the cost

   of the Qleave and piling and piering – but not for the rock wall. It follows that One

   Sector’s counterclaim is allowed in part.

2. My reasons in detail follow.

3. The parties are to prepare a draft order which gives effect to my findings within 14 days.

4. I will hear the parties and the third party, Excel Concrete Pty Ltd,[1] as to costs.

   [1]           Hestbay Pty Ltd v One Sector Pty Ltd [2023] QSC 154.

Preliminary comments

1. I found it difficult to make confident findings of fact about the state of the Stage 2 slab and the extent or seriousness of its deterioration, cracking, and dusting.

2. Stage 2 of the warehouse complex included Units 9 – 13. By the time of its inspection

   for the purposes of this trial, the whole of the slab in Unit 9 and the trafficked areas of the slab in Units 12 and 13 had been covered with an epoxy coating. Thus, none of the slab in Unit 9 and very little of the slab in Units 12 and 13 could be examined by experts for the purposes of this litigation.[2]

   [2]           The coating was applied to deal with the complaints of the Units 9 and 12 and 13 tenant – Budget Pet Products – about the slab.

3. The slab in Units 10 and 11 was uncoated and, at least in theory, provided the best evidence of the state of the slab, but the evidence about its condition was inconsistent, for example:

(a)	The most independent witness – the tenant of Units 10 and 11 – considered the dusting of the slab that he experienced to be “in the nature of the business”.
(b)	The plaintiff’s expert, Dr Scott Woolcock, considered the dusting to be so

excessive as to amount to a health hazard.

(c) Two of the defendant’s experts observed no dusting at all.

1. Nevertheless, when considering what caused the damage to the Stage 2 slab (its deficient construction or hard-wheeled vehicles), I was prepared to proceed on the basis that it was damaged beyond that which would be expected with ordinary wear and tear had it been traversed only by pneumatic-tyred vehicles.

2. Even though the evidence about it was vague and non-expert, I was prepared to

   proceed on the basis that the Stage 1 tenants’ use of the Stage 1 slab was similar to

   the use of the Stage 2 slab by the Stage 2 tenants, including in their use of similar, hard-wheeled vehicles, at similar intensity, and with similar loadings, during their diverse business operations.

3. Even though the evidence about it included little more than the impressions of lay witnesses, I was prepared to proceed on the basis that the Stage 1 slab was performing better than the Stage 2 slab.

4. Evidence from four engineers took up most of the reading and hearing time in this matter.

5. My reasons reveal my concerns about the evidence of the plaintiff’s engineering expert, Dr Scott Woolcock, including (but not only) because –

(a)	his approach to the issues was primarily theoretical. He did not link his opinions to the facts of the case. For example, his opinion about the effects of the addition of uncontrolled water on the slab was not supported by an examination of cores taken from the slab which did not reveal any sign of over-watering.
(b)	he was not a concrete technologist, which explained his limited understanding of the way in which concrete hardened in wet versus dry conditions.
(c)	he made several admitted errors in his evidence.

1. Additionally, the factual foundation for critical aspects of Dr Woolcock’s opinion was

   not established by admissible evidence. In offering his opinions, Dr Woolcock assumed that: (a) the Stage 1 slab had been constructed in accordance with its specifications (which were almost the same as the specifications for the Stage 2 slab);[3] and (b) that no uncontrolled water had been added to the Stage 1 cement mix during

   [3]           There were differences in the specification of their reinforcement and the application of a densifier.

   the Stage 1 slab’s pour. On that basis, Dr Woolcock concluded that the Stage 1 slab

   performed better than the Stage 2 slab (under similar conditions of use) because uncontrolled water had been added to the Stage 2 slab during its pour. Dr Woolcock concluded that it could not have been the hard wheeled vehicles of the Stage 2 tenants which were damaging the slab because hard wheeled vehicles had not damaged the Stage 1 slab. But the assumptions made by Dr Woolcock about the way in which the Stage 1 slab had been constructed were not proven by admissible evidence.

2. The failure to prove the factual assumptions which underpin an expert’s opinion

   renders the opinion liable to exclusion. As explained R v Naidu,[4] “It is unquestionably

   [4] [2008] QCA 130 at [68]. See also the footnote to that paragraph; R v Gibson [2022] QCA 151 at [10]; Makita (Aust) Pty Ltd v Sprowles (2000) 52 NSWLR 705; and Sanrus Pty Ltd v Monto Coal 2 Pty Ltd(No 7) [2019] QSC 214 at [99].

   the law that expert opinion evidence is inadmissible if the opinion is not expressed

   upon a state of facts both identified and proved in evidence”.

3. However, the defendant did not object to the admission of Dr Woolcock’s evidence

   to the extent to which it relied upon assumed facts which had not been proven. In

   those circumstances, it was for me to determine what weight to give it – see Naidu at

   [80].

4. Further, there was evidence that the slabs had been reinforced differently – which Dr

   Woolcock said might explain why the Stage 1 slab performed better, even on the assumption that uncontrolled water had been added to the Stage 2 slab only.

5. To the extent to which Dr Woolcock’s opinion relied upon assumptions which were

   not proven, I gave it no weight.

6. As will emerge in my reasons, evidential shortcomings in the plaintiff’s case, such as

those discussed above and others, prevented me from finding in its favour on the
critical issues.

Context

1. Before embarking on an outline of the evidence which I considered significant, it is important to put some context around the factual issues.

2. One of the primary factual issues for me was whether One Sector constructed the

   Stage 2 slab in accordance with the engineers’ specifications. Another was whether the slab was, in effect, “strong” enough and thick enough, to be fit for its “purpose”.

[28]    What “strength” meant; what the slab’s “purpose” was; and how to measure

“thickness” were also issues for me.

Concrete and its strength

1. Speaking in very broad terms, concrete is a mix of cement and water (plus aggregates or admixtures) which hardens over time because of a chemical reaction between the cement and the water.

2. As concrete hardens over time, it becomes stronger. How long concrete will continue to harden and how strong it ultimately becomes depends on several variables, including the environment in which it has been placed and the water available to it in that environment.

3. The compressive strength of concrete is a measure of the amount of force required to crush it in megapascals (MPa).

4. The stronger the concrete, the greater its resistance to abrasion and joint breakdown.

5. The characteristic compressive strength of a concrete structure is the strength below which not more than 5% of it is expected to fall. Determining the characteristic compressive strength of a concrete slab requires the taking of several samples from the slab; testing their individual compressive strengths; and calculating therefrom (by way of statistical analysis) the probable strength of the entire slab in terms of the

   “load” that at least 95% of it can bear.

6. The use to which concrete will be put will determine how strong it must be.

7. An Australian Standard, AS 3600, requires concrete slabs which are trafficked by

   vehicles to be of various characteristic compressive strengths – depending on the

nature of the traffic they are expected to bear. For example, and for obvious reasons,
the standard does not require residential driveways to be as strong as public roads.

1. The slab in the present case had an intended design or characteristic strength of 32

   MPa – based on AS 3600’s specified characteristic strength for slabs which will be

traversed by pneumatic tyred vehicles. AS 3600 requires slabs which will be traversed
by hard wheeled vehicles to be stronger, at 40 MPa.

The concrete in this case

1. Cement mixes are designed by concrete suppliers to achieve a certain design strength

   as measured 28 days after the concrete’s pour.

2. One Sector ordered Grade N32 concrete from a concrete supplier (“Excel”) for the

   warehouse slabs.

3. Grade N32 concrete is supplied by way of a cement mix designed to harden to a characteristic strength of 32 MPa after 28 days. Usually, concrete suppliers design and supply a cement mix which targets a higher concrete strength than design strength to minimise the risk that the concrete supplied will not meet its strength requirements after 28 days.

4. In this case, no one from Excel was called to give evidence about the strength targeted by their mix in either stage.

   Strength testing

5. AS 3600 anticipates that concrete will be tested, in a prescribed way, 28 days after its pour, to determine whether it has achieved its design, or characteristic, strength. It is reasonable to assume that the Australian Standards require concrete testing 28 days after pour because, whilst the concrete might continue to harden after that point in time, it hardens at an exponential rate and, if the mix supplied is appropriate, and it is cured appropriately, then it can be expected to achieve its design strength after 28 days.

6. In this case, the strength of the Stage 2 slab was not tested in accordance with the relevant Australian Standard at 28 days after its pour; or at any other subsequent time after its pour until 2022, when its strength was tested for the purpose of this litigation. It was then about six years old.

7. The strength of a hardened concrete slab may be tested by taking small samples from it (cores) and testing those samples. Each core will have a certain compressive strength. For several reasons (which need not be articulated), the compressive strength of individual cores may vary. Thus, one may not safely or reliably determine the strength of an entire concrete structure or slab on the basis of the compressive strength of one core only. Several of the documents tendered at trial, which included Australian and European standards, provide formulas for the calculation of the in-situ

   “strength” of a concrete structure (including a slab) based on the cores taken from it

   – in terms of either an average or mean compressive strength, or its characteristic

   compressive strength.

8. Some of the documents tendered at trial set out broad ranges for likely per centage

   increases in concrete’s strength over time – including beyond 28 days. But there is

   no generally accepted method or formula which would enable an engineer (or anyone else) to calculate the strength of concrete 28 days after its pour on the basis of its strength at a later date alone.

9. One of the issues for me in this case concerned the defendant’s contractual obligation when it came to the concrete’s strength.

   Slump

10. Slump is a quantitative measure of the consistency or workability of fresh concrete (the poured cement mix). Slump is determined by a test in which: (a) a cone shaped mould is filled with fresh concrete; (b) the mould is inverted; (c) the mould is lifted vertically, up and away from the concrete; and (d) the vertical height of the slumped concrete is measured against the height of the cone. The difference in millimetres is the slump.

11. Concrete with a higher slump is softer and wetter and easier to manoeuvre than

    concrete with a lower slump, which is harder and drier. A batch of concrete’s slump

    will be increased by the addition of water to the cement mix. Adding more water than intended for a mix will increase the workability of the concrete when it is wet; may reduce the strength of it when it has hardened; and may affect its surface hardness.

12. In designing a concrete slab, engineers will specify the slump of the concrete to be used. Australian Standards allow for a tolerance of 15 mm for a specified slump of

    80 mm. A tolerance of 20 mm is permitted for a 100 mm slump. One of Hestbay’s

complaints was that One Sector ordered concrete with a higher slump for the Stage 2
slab (100mm) than that specified by the engineers (80mm).

Australian Standards relevant to the slab’s construction

1. Several Australian Standards applied to the construction of the warehouse slabs and

   were referred to in this matter. They included –

(a)	AS 3600-2009 (and AS 3600-2018): Concrete Structures.
(b)	AS 1379-2007: Specification and supply of concrete.
(c)	AS 1012.9: Methods of testing concrete: compressive strength tests – concrete,

mortar and grout specimens.

(d) AS 1012.14: Methods of testing concrete: method for securing and testing cores

from hardened concrete for compressive strength.

1. To understand the evidence of the experts, it was necessary for me to achieve a reasonable level of understanding of the engineering principles behind their opinions. That required me to study the Australian Standards and other authoritative documents to which they referred in some detail.

2. The definitions used in the standards assumed some relevance because of the debate

   between the parties about the defendant’s obligation under the Stage 2 contract. One

   Sector submitted that it was under no contractual obligation to provide a slab which was of 32 MPa at 28 days after its pour.[5] In its outline of closing submissions it said,

   [5]           T 8-18 – T 8-19.

   “Hestbay has not identified any contractual basis for the concrete to be at a particular

   strength by 28 days after pouring, and before handover of the project works. No such obligation exists.” One Sector submitted that its obligation was to use N32 concrete

   and it did so. It was thus submitting, in effect, that it was not required to construct a slab which actually achieved its design strength. As will emerge, I found that its obligation was to construct a slab which was of a characteristic compressive strength of 32 MPa at 28 days after its pour.

3. The Preface to the 2009 version of AS 3600 (the version which was applicable when the slabs were constructed) includes the following statement of its objective:

   Objective of the Standard

   The principal objective of the Standard is to provide users with nationally acceptable unified rules for the design and detailing of concrete structures and members, with or without steel reinforcement or prestressing tendons, based on the principles of structural engineering mechanics. The secondary objective is to provide performance criteria against which the finished structure can be assessed for compliance with the relevant design requirements.

[54]    Clause 1.1.1 of AS 3600, Scope, states that the standard sets out “minimum

requirements for design and construction of concrete building structures and members

…”.

1. As per clause 1.1.2, the standard applies to structures and members in which the

   materials conform to the following: “Concrete with (i) characteristic compressive strength at 28 days … in the range 20 MPas to 100 MPas; and (ii) with a saturated

   surface-dry density in the range of 1800kg/m3 to 2800kg/m3.

2. By clause 1.3, the general principles of AS 3600 are to be applied when evaluating the strength or serviceability of an existing structure.

3. Definitions for the standard are contained in clause 1.6. They include the following:

   1.6.3.12. Characteristic strength

   Value of the material strength, as assessed by standard test, that is exceeded by 95% of the material (lower characteristic strength).

   1.6.3.56 Mean strength

   Statistical average of a number of test results representative of the strength of a member, prototype or material.

   1.6.3.74 Strength grade

   Numerical value of the characteristic compressive strength of concrete

   at 28 days (f’c), used in design.[6]

   1.6.3.85 Upper characteristic strength

   Value of the material strength, as assessed by standard test, which is exceeded by 5% of the material.

   [6]           Clause 1.7 ascribed meanings to the many symbols used in the standard, including “f’c” which stood

4. Section 2 is headed, “Design procedures, actions and loads”. Clause 2.1.1, “Design for strength and serviceability” states: “Concrete structures shall be designed for

   ultimate strength and serviceability limit states in accordance with the general principles and procedures for design as set out in AS/NZS 1170.0 and the specific

   requirements of Clauses 2.2 and 2.3”.

5. Clause 2.2 concerns design for strength and requires certain strength checks. Clause 2.3 concerns design for serviceability and requires design checks to ensure that a structure will perform in a manner appropriate for its intended function and purpose.

6. Clause 3.1.1.1 of AS 3600-2009 requires the characteristic compressive strength of concrete to be determined as follows:

   The characteristic compressive strength of concrete at 28 days (f’c)

   shall be either –

(a)	taken as equal to the specified strength grade, provided the appropriate curing is ensured and that the concrete complies with AS 1379; or
(b)	determined statistically from compressive strength tests carried out in accordance with AS 1012.9.

The characteristic compressive strengths of the standard strength grades are 20 MPa, 25 MPa, 32 MPa, 40 MPa, 50 MPa, 65 MPa, 80 MPa and 100 MPa.

1. Clause 3.1.1.2 “Mean in-situ compressive strength” states:

   In the absence of more accurate data, the mean value of the in-situ compressive strength (fcmi) shall be taken as 90% of the mean value of the cylinder strength (fcm) or shall be taken as those given in table 3.1.2.

2. According to the table, for concrete with a characteristic compressive strength of 32 MPa at 28 days, the mean in-situ compressive strength will be 35 MPa.

3. Table 4.6 of AS 3600 prescribes the “not less than” characteristic compressive strength required of concrete members subject to abrasion from traffic – such as the

   floor slabs in the present case.

   4.6 ABRASION

   In addition to the other durability requirements of this section, concrete for members subject to abrasion from traffic shall have a characteristic compressive strength not less than the applicable value given in Table 4.6.

TABLE 4.6

STRENGH REQUIREMENTS FOR ABRASION

Member and/or traffic Minimum characteristic Compressive strength

(ƒ′c)

MPa

Footpaths and residential driveways	20
Commercial and industrial floors not subject to vehicular traffic	25
Pavements or floors subject to:

(a) Pneumatic-tyred traffic	32
(b) Non-pneumatic-tyred traffic	40
(c) Steel-wheeled traffic	To be assessed

but not less than 40

NOTE: ƒ′c refers to the characteristic compressive strength of the wearing surface

1. My understanding of the standard is that concrete is to be tested for strength (and other

properties) always by the supplier – a production assessment – and sometimes also by

[7]           The distinction between production and project assessment is in AS 1379-2007.

the person to whom the concrete is supplied – a project assessment.[7]

1. Section 17 is entitled, “Material and construction requirements”. By clause 17.1.6.1, “Concrete, which is intended for use in structures designed in accordance with this

   Standard, shall be assessed in accordance with AS 1379 for compliance with the

   specified parameters.” The clause also contains the following note: “NOTE: When

   project assessment is required, the project specification should nominate responsibility for carrying out the relevant sampling, testing and assessment and, if these differ from or are not covered by AS 1379, should give details of how the

   assessment is to be made”.

2. In the present case, the engineers required project assessment for compressive strength and slump requirements, which required sampling on-site, on several occasions during the pour, and testing at certain intervals thereafter, with the results to be reported to the engineers. In the case of the Stage 2 slab, samples were taken on the first day of the pour only and the project assessment was not properly done.

3. Clause 17.1.6.2 sets out the criteria which must be satisfied for concrete specified by

   strength grade. It states: “… (a) For each strength grade of concrete supplied to a

   project, the mean cylinder compressive strength (fcm) as defined in AS 1379, shall be

   maintained within the limits specified in that Standard”.

4. A note to that clause explains that: “Strength grade” is defined in AS 1379 as the

   specified value of the characteristic compressive strength of the concrete at 28 days

   (f’c). The note continues, “The compressive strength of the concrete sampled, tested

   and assessed in accordance with AS 1379 indicates the potential strength of the supplied concrete, when placed, compacted and cured under optimum conditions; the responsibility of demonstrating rests on the supplier. The achievement of that potential on site is dependent upon the handling, placing, compacting and curing techniques actually used; the responsibility for which rests with the construction contractor …”[8] (AS 1379 is discussed below.)

   [8]           Page 5359 of Part E.

5. Appendix B of AS 3600-2009 is entitled “Testing of Members and Structures”. Its

   first paragraph (B1) explains its purpose, which includes setting out strength testing methods for hardened concrete in place, as detailed in part B6. The basis for the estimate of strength set out in B6.4.2, that is the multiplication of average core strength by 1.15, assumed some importance in the present case.

6. Relevant parts of Appendix B follow. It is important to note its application:

   B1 GENERAL

   This Appendix applies to the testing of a structure … to check that the

   strength and serviceability requirements of this Standard are met. Methods for testing hardened concrete in place are also detailed. Testing shall be undertaken by persons competent in, and with appropriate expertise for, performing such tests.

   B6 TESTING OF HARDENED CONCRETE IN PLACE

B6.1 Application

This paragraph applies to the assessment of strength and other properties of hardened concrete in place by non-destructive testing, by testing of samples cut from representative test panels, or samples cut from members.

…

B6.4	Tests on samples taken from the structure
B.6.4.1	Test requirements

Taking and testing of cores and beams from members and sample panels shall comply with the following:

(a)	Core and beam locations shall be selected so as to minimize any consequent reduction of strength of the structure.
(b)	The cores and beams shall be representative of the whole of the concrete concerned and in no case shall less than three samples be tested.
(c)	Cores and beams shall be examined visually before and after testing to assess the proportion and nature of any voids, cracks and inclusions present. These factors shall be considered in the interpretation of the test results.
(d)	Cores shall be taken and tested for compressive strength in

accordance with AS 1012.14 …

B6.4.2 Interpretation of results

The strength of the concrete in the member may be estimated –

(a)	as 1.15 times the average strength of the cores and beams; or
(b)	by using test data from cores or beams taken from another member for which the strength of the concrete is known.

1. The parts of AS 3600-2009 extracted above are identical to those in the later issued standard AS 3600-2018, apart from small changes to B6.4.2 including by replacing

   “may” with “shall” and tidying up the grammar.[9]

   [9]           In the 2018 version of the standard, B6.4.2 stated, “B6.4.2 Interpretation of results: The strength of the concrete in the member shall be estimated as either – (a) 1.15 times the average strength of the cores

2. In the present case, testing in accordance with AS 1012.14 was undertaken in 2022. The cores were tested for compressive strength in accordance with AS 1012.9.

3. Among other things, AS 1379-2007 sets out the minimum requirements for the sampling of, testing of, and compliance with specified properties of, plastic and hardened concrete.

4. It includes a definition clause which defines relevant concepts as follows:

   1.3.6 Cement

   A hydraulic binder composed of Portland or blended cement used alone or combined with one or more supplementary cementitious materials.

   1.3.7 Characteristic strength

   The value of the concrete strength, as assessed by standard test, which is exceeded by 95% of the concrete.

   1.3.8 Concrete

   A mixture of cement, aggregates, and water with or without the addition of chemical admixtures or other materials and defined as follows:

   (a) Plastic concrete Concrete in the state between completion of mixing and initial set as defined in AS 1012.18.

   (b) Hardened concrete Concrete after initial set, as represented by test

specimens that have been subjected to a specified process and duration of
curing.

(c) Normal class concrete Concrete that is specified primarily by a

standard compressive strength grade up to 50 MPa and otherwise in
accordance with 1.5.3.

(d) Special-class concrete …

1.3.10 Mean grade strength

The arithmetical mean of all relevant 28-day sample strengths taken in a production interval for the particular strength grade.

1.3.14 Production assessment

An assessment procedure for concrete defined by strength grade, carried out by the supplier and based on the statistical assessment of standard compressive strength tests on concrete, specified by compressive strength and produced by a specific supplying plant.

1.3.15 Project assessment

An assessment procedure for concrete defined by strength grade,

specified at the customer’s option, which provides additional test data

for the statistical assessment on concrete supplied to a specified

project.

1.3.21 Total free water

The mass or volume of water contained in liquid admixture and batch aggregates, in excess of their SSD [saturated surface dry] condition, plus the mass or volume of all water added to the batch before commencement of discharge.

1.3.22 Water-cement ratio (w/c)

The ratio of the mass of total free water in a batch to the mass of cement (as defined in 1.3.6) in the batch.

1. Clause 1.5.2 explains that standard strength grades and their corresponding design

   compressive strengths “shall be as given in Table 1.1”. According to Table 1.1, for “32” standard grade concrete, its design characteristic compressive strength after 28

   days of standard curing is 32 MPa.

2. Section 4 deals with production and delivery. Clause 4.2.1.2 “Water” requires “control” of the water added to a batch to be achieved by controlling the slump or by

   controlling the water-cement ratio, as follows:

   Where the ratio of total water to cement has been specified, the quantity of added water shall be controlled so that the ratio in the mix is maintained within + 10% of the specified value. If a maximum water-cement ratio has been specified, this value shall not be exceeded.

3. In the present case, the notes to the engineers’ drawings stated that the concrete was

   to have a “water/cement ratio of not greater than 0.65 …unless approved otherwise”.

4. Clause 4.2.3 deals with the addition of water to a mixed batch of concrete by the supplier. It requires slump to be tested after water is added.[10]

   [10]          Paragraph (c).

5. Section 5 requires concrete to be sampled and tested for compliance with, inter alia, slump (as per Clause 5.2) and strength (as per Clause 5.3). It requires slump to be determined in accordance with the slump test prescribed by AS 1012.3.1. Clause 5.2.3 sets out the permissible tolerances for compliant slump.

6. Clause 5.3.1 requires the sampling, testing and assessment of the strength of concrete specified by a compressive strength grade to be carried out in accordance with Section 6 of AS 1379-2007.

7. Clause 5.5.3 “Compliance” states: “For concrete specified by compressive strength,

   concrete represented by the strength samples shall be deemed to comply with the

   specified strength if the relevant requirements of Section 6 are satisfied”.

8. Section 6 is headed, “Sampling, testing and assessment for compliance of concrete

   specified by compressive strength”. The concrete in the present case was specified by

   the strength grade N32.

9. Section 6 deals with sampling and testing of plastic concrete, production assessment and project assessment.

10. Clause 6.2 deals with the sampling of plastic concrete samples. Clause 6.2.3 states that from each sample intended for strength grade assessment, at least two standard cylinder specimens are to be made and cured, in accordance with AS 1012.8.1 and AS 1012.8.2.

11. Clause 6.5 deals with the project assessment of the strength grade of cement, where it has been specified. In such a case, project assessment is to be in accordance with clauses 6.5.2 or 6.6. Among other things, clause 6.5.2 requires samples to be taken from each 50 cubic metres of concrete.

Authoritative documents other than Australian Standards

1. In addition to Australian Standards, the experts referred to other documents which they considered authoritative. They are discussed below.

Concrete Institute of Australia: Recommended Practice: The Evaluation of
Concrete Strength by Testing Cores

1. The experts referred to a document produced by the Concrete Institute of Australia

(the CIA) entitled “Recommended Practice: The Evaluation of Concrete Strength by
Testing Cores”.

1. It explains that the information it contains is intended for general guidance only. It is said to be based on recommendations of Australian Standards, Concrete Society

   reports and “new developments in this field”.

2. Its Part 2 deals with the obtaining of cores. Its Part 3 deals with the determination and evaluation of concrete strength by the testing of the cores.

3. Its appendices deal with the technical requirements of the testing process, including, for example, the need for correcting core strength for the length to diameter ratio of the core, or for age. Appendix 8 sets out the process for the evaluation of concrete strength.

   The Z11 document

4. The experts referred to another CIA document, “Z11 In-situ Strength Assessment of

   Concrete Structures and Components”, published in 2021.[11] Dr Woolcock and Dr

   Khan ultimately adopted the method suggested by this document in assessing the strength of the Stage 2 slab in 2022.

   [11]          Pages 5770 – 5835 of Part E.

5. The CIA makes it clear in its introduction to Z11 that the information contained in it

   is “for general guidance only”. It cautions that it was written as a “guide to the

   assessment in-situ (sic) strength of concrete structures and components in Australia”.

   It explains that it is based on established practice. It acknowledges that the science

   and knowledge of materials is “an evolving technology” and states that its content

   represents the state of knowledge at publication, which may be subject to change over time. The document was prepared by a working group of members of the CIA

   including Tony Thomas. Dr Woolcock relied upon Mr Thomas’ hearsay opinion in

   justifying his conclusions.

6. In its introduction, Z11 explains (my emphasis):

   In design, engineers generally use a cylinder characteristic

   compressive strength, which is defined by most design codes as: “The

   value of concrete strength as assessed by a standard test, that is

   exceeded by 95% of the material.

   After correction, core compressive strength data may be used to

   estimate characteristic concrete compressive strength and generally this testing is either: (a) to determine compliance of delivered concrete to the contract specification; or (b) to determine an appropriate strength to use in design or structural modifications or assessment.

   …

   Both methods require obtained core compressive strength data to be corrected to account for factors including diameter. Length/diameter ratio and possibly conditioning. Corrections for concrete age should

   be used with care as different cements and binders may have

   different aging properties.

   In order to determine the characteristic compressive strength (f’c)

   statistical analysis is conducted using the mean and standard
   deviation of the test data.

   This document provides appropriate techniques for sampling and testing of cores and analysis of data. It may be used by the concrete supplier, designer or other interested party to estimate compliance of delivered concrete or provide an estimate of the appropriate strength that may be used in design.

7. Z11 discusses core testing for compliance and explains why correction factors must be applied to the core samples taken for the purpose of evaluating strength. It explains why core compressive strengths must be converted to equivalent standard cylinder strengths to allow for an estimate of characteristic compressive strength. It continues (my emphasis):

   This is not a simple calculation as typically the mean of the core strengths are lower than that of the cylinders and the standard deviations are greater. This complication has led to a variety of

   methods being available internationally to calculate an appropriate design strength from in-situ strength assessment based on core compressive strength testing, and the choice of method may lead to considerably different estimates of design

   values …

   Practice Z11 is to assist engineers to assess the in-situ compressive

   strength of existing concrete structures as accurately as possible, utilising the latest published knowledge and research in the area and with the assistance of modern accepted technology and equipment such as NDT [non destructive testing].

8. The following definition was of some importance:

   In-situ characteristic compressive design strength

   The in-situ characteristic core compressive strength of a test region, converted to equivalent in-situ characteristic strength of standard specimens (e.g. cylinders), also known as equivalent design compressive strength or equivalent specified compressive strength, by either multiplying by 1.15 (AS 3600, 2018) or dividing by 0.85 (EN 13791: 2019) to account for several known factors that lead to weaker compressive strength when testing cores sampled from an existing concrete element compared to testing of standard specimens cast using the same concrete mix, cured under laboratory conditions.

9. On the basis of this definition, it seemed to me that the authors of Z11 considered the

   reference to “strength” in B6.4.2 a reference to in-situ characteristic compressive

   design strength as confirmed by the footnote to s 3.9, discussed below.

10. Chapter 3 of Z11 is entitled “Coring”. It begins with the following statement: Many Australian concrete testing laboratories are set up to test cores for compressive strength in accordance with AS 1012.14 (2018) and AS 1012.0 (2014), standards that have existed for several decades. Therefore, this document has been written to supplement provisions in existing Australian Standards for strength assessment of in-situ concrete and to not contradict relevant requirements of these Australian Standards except in exceptional circumstances.

11. I note, but will not discuss here, Section 3.8 which deals with the conversion of core

    strength to equivalent standard cylinder strength and Z11’s recommended practice for

    the application of correction factors.[12] By way of a footnote, the paragraph refers the

    reader to paragraph 3.9, “for recommendations on how to interpret and when to use

    AS 3600 (2018), Appendix B, clause B6.4.2 for characteristic strength assessment of existing concrete structures, and how this clause in AS 3600 compares to similar

    guidelines in AS 1379 (2007)”. Again, obviously, the authors of Z11 considered

    B6.4.2 to provide for the calculation of characteristic strength, although (as below) they cautioned against its use in certain situations.

    [12]          Page 5792 (1st column) of Part E.

12. Section 3.9 of Z11 is entitled “Discussion and recommendations on the application of AS 3600 (2018), Appendix B, Clause B6.4.2”. It makes the following points (emphasis

    in bold in original; my emphasis in underlining):

(a)

AS 3600 (2018) [and the earlier 2009 version] contains a multiplication factor of 1.15 to convert core compressive strength to an equivalent standard cylinder strength because core compression tests produce lower strength results than equivalent standard cylinder compression tests. However, the actual reason for choosing 1.15 is not clear. It is believed that this 1.15 conversion factor is based on the 0.85 (approximately 1/1.15) factor originally found in early US specifications.

(b)

As per AS 3600, the average of three corrected core strengths is considered to

satisfy the characteristic strength specified where they exceed 0.85 f’c (or 1.15

x average corrected core strength > f’c). This fits in with clause 6.5.2 of AS 1379

(2007) for “Project Assessment” where the average of 3 cylinder test sample

strengths must exceed f’c to be compliant provided that the concrete mix grade

has been tested and found to be compliant for AS 1379 (2007) rules as well. In

this regard –

(i)       AS 3600 clause B6.4.2 is a “deemed to comply” requirement and does

not aim to calculate the actual in-situ characteristic strength of an existing concrete member. It should only be applied when the design strength grade of the concrete under test is known.

(ii)      This does little to assist with cases where it is not known whether the concrete under review has been tested in accordance with AS 1379 and found to be compliant. In this case, clause B6.4.2 should not be relied

upon and the detailed procedures recommended in Z11 should be

followed to calculate an estimated in-situ characteristic strength.

(iii) …

(c) “Due to an unfortunate lack of clarification within AS3600 … or the

Commentary [to it], some engineers may incorrectly interpret AS 3600 clause B6.4.2 to be an appropriate method for determining the characteristic design strength of a single member in an old building or structure, especially where it

is highly likely constructed from just one batch of concrete … [A]s explained

above, using AS 3600’s Appendix B6 method to estimate the characteristic

strength in a single member of an old building or structure where one does not

know the design strength grade or whether the concrete used is AS 1379 …

compliant runs a very real risk of being unconservative”. An engineer using a

strength value calculated on that basis, may be over-estimating the characteristic strength and structural capacity of the member.
(d)	For in-situ compressive strength assessment of small test regions such as single members, where the design strength grade is not known; or it is not known

whether there was compliance with AS 1379, it is recommended that –

(i)	B6.4.2 ought not to be followed.
(ii)	Methods contained in BS EN 13791 (2019) specific for small test regions are followed, including all of the conditions they contain for their use, including the requirement for the spread of core compressive strength results to be < 15% of the mean otherwise more information about the members/region being assessed will need to be obtained.

(e)

Other international published standards may have similar and equally

appropriate procedures for in-situ characteristic strength assessment of small test regions or single members to BS EN 13791 (2019). Section 5.1.2 and 5.3 of this Recommended Practice provide further recommendations on the types of procedures to follow in these scenarios.

[100]   Chapter 5 is entitled “Procedure for Determination of Characteristic Compressive

Strength of Existing Concrete Structures of Unknown Strength”.

1. Section 5.1 is critical of clause B6.4.2 of Appendix B of AS 3600 (2018). It states that its use risks structural engineers erroneously using the value calculated from its procedure as the characteristic design compressive strength to use when completing a structural assessment of an existing structure. After explaining its issues with the procedure, Z11 recommends that a statistical procedure, such as one of the Z11

   tolerance methods it discusses, should be followed – especially where it is not known

   whether the concrete under review has been tested in standard test specimens according to AS 1379 and found to be compliant. (As will emerge, Dr Woolcock was unaware of this negative commentary about B6.4.2 when he wrote his first report. Indeed, he seemed unaware of B6.4.2.)

[102]   Z11 sets out a flow chart of the steps to be followed to determine characteristic compressive strength. It also refers the reader to a detailed discussion of current published international standards which contain methods for the calculation, on a statistical basis, of in-situ characteristic strength based on corrected core compressive strength, in its Appendix D. It recommends that the calculated in-situ characteristic core strength value should be converted into the equivalent for cylinder strength

results either by dividing by 0.85 or multiplying by 1.15 – whatever is recommended

in the jurisdiction of the standard followed. (As will emerge, Dr Woolcock applied
the wrong conversion factor in one of his later reports.)

1. Appendix D is entitled, “Further discussion of determination of in-situ characteristic

   compressive strength for structural assessment of an existing structure from core

   testing only”. It includes harsh criticism of Appendix B of AS 3600. It says its benefits are that it is “the ubiquitous Australian concrete structures design code” but

   that it has “unfortunately significant” drawbacks. They are that Appendix B6 does

   not calculate an in-situ characteristic strength for use in structural design. It calculates an in-situ mean strength which should not be directly used in structural design as it would potentially equate to a 50% probability of failure.

2. Appendix D made positive statements about BS EN 13791 (2019).[13]

   [13]          Page 5829 of Part E.

3. Appendix B is entitled “Additional corrections that can be applied for assessment of

   compressive strength class of supplied concrete that is in doubt”. Paragraph B2 is entitled “Strength Adjustment for Concrete Maturity”. That paragraph explained why,

in the current 2021 edition of Z11, no precise correction factor for concrete age was
provided (my emphasis):

In the previous version of [Z11] a correction factor was provided for concrete age, i.e. to relate the 28 day characteristic strength of concrete to characteristic strength measured at later ages. In this revision it has been decided that a precise correction factor for concrete age should not be provided and may provide uncertainty in design.

This is due to the rate of concrete strength gain after 28 days being dependent on many variables unique to each situation including environmental conditions, curing during service, cement (binder) system of the concrete and the water to binder ratio. It is noted that

most concretes obtain 90% of their ultimate compressive strength

within the first 28 days after placement and that the strength gains after this period are typically not as great as suggested by the correction factor table in the previous version of CIA Z11 (2002) where 20% to 30% further strength gains after 28 days were allowed to be considered for some blended cement system concretes.

…

1. B2 continued with a discussion of when an adjustment for maturity ought to be made. Maturity is something different from age and such an adjustment is not necessary when assessing the in-situ compressive strength of an existing structure which is likely several years old.

   BS EN 13791:2019

2. This is a standard of the British Standards Institute which is the “UK implementation of EN 13791:2007 and BS 6089:2010 which are withdrawn”. It is entitled

   “Assessment of in-situ compressive strength in structures and precast concrete

   components”.

[108] Its introduction states:

(1) This document covers two applications of in situ strength assessments. These are:

- to estimate in situ characteristic compressive strength of a
test region and/or in situ strength at specific locations;

- assessment of compressive strength class of concrete supplied to a structure under construction where there is doubt about the compressive strength based on results of standard tests or doubt about the quality of execution.

(2) Both applications have a number of common steps … but the assessment methods differ. The reason for this difference is that with the estimation of the in situ strength (Clause 8) there is no presumption as to what this should be and the uncertainty associated with the number of data are taken into account when estimating the value. The in situ strength determined in accordance with Clause 8 is a value based on testing a finished structure or element, as referred to by EN 1992-1-1:2004, A.2.3.

NOTE: Information may be available on the original quality of the supplied concrete, but the in situ strength may have changed over time.

1. Clause 8 is entitled, “Estimation of compressive strength for structural assessment of an existing structure”. It sets out formulas for this estimation based only on core test

   data at paragraph 8.1.

2. Clause 9 is entitled “Assessment of compressive strength class of concrete in case of

   doubt”. Paragraph 9.1(1) explains that doubt about the in situ quality of concrete may

   arise from doubts about the quality of the concrete supplied to the site, problems during the execution of the works or after some exceptional event on site. Paragraph 9.1 (4) explains that if the procedures of clause 9 are satisfied, the defined test region shall be accepted as having conformed to the specified compressive strength class. It

   continues, “From this it may be concluded that the concrete delivered to site, and any

   adjustments to the concrete on site and any deviation on the execution with respect to placing, compacting and curing as required by EN 13670 or EN 13369, as appropriate,

   were not significant with respect to compressive strength”.

   European Standard EN 1992 -1-1 Eurocode 2

3. This document is entitled “Design of concrete structures – Part 1.1: General rules

   and rules for buildings”. Among other things, it describes the principles and

   requirements for safety, serviceability, and durability of concrete structures.

4. Section 3 deals with “Materials”. When speaking of concrete’s strength, it speaks in

   terms of its compressive strength, which is denoted by its strength class, which relates to the characteristic (5%) cylinder compressive strength. Strength classes are based on the characteristic cylinder strength determined at 28 days. It sets out at 3.1.2 (4) the way in which to assess the compressive strength of concrete, before or after 28 days, on the basis of test specimens which have been stored under conditions other than those prescribed in EN 12390.[14]

   [14]          Page 5933 of Part E.

5. Section 3.1.2 (6) provides a formula (Expressions (3.1) and (3.2)) for the estimate of the compressive strength of concrete at a certain age for a mean temperature of 20° and curing in accordance with EN 12390. However, if the concrete does not conform to the specification for compressive strength at 28 days, the use of Expressions (3.1) and (3.2) is not appropriate. The clause should not be used retrospectively to justify a non-conforming reference strength by a later increase of the strength.

   National Construction Code Series 2015

[114]   The experts agreed that the National Construction Code Series 2015 Volume 1

“Building Code of Australia Class 2 to Class 9 Buildings” was the over-riding control

document in the building industry. Extracts from it were tendered. But, those extracts

did not include the Code’s “Application” or “Interpretation” chapters, which made it

very difficult for me to make sense of them. No expert evidence was called to assist
me.

1. The extracts that were included explain that the National Construction Code Series was developed to incorporate all on-site construction requirements into a single code

   in three volumes. Volume 1 was for class 2 to 9 buildings. Hestbay’s warehouses

   were Class 7b buildings. The extracts explain that the Building Code of Australia is

   “a uniform set of technical provisions for the design and construction of buildings and

   other structures throughout Australia whilst allowing for variations in climate and

   geological or geographical conditions”.[15] Its goal is “to enable the achievement of

   [15]          Page 7.

   nationally consistent, minimum necessary standards of relevant safety (including structural safety and safety from fire), health, amenity and sustainability objectives

   efficiently”.[16]

   [16]  

2. Part 1B contains Deemed-to-Satisfy structural provisions. However, because I was not provided with the whole document, I could not make sense of the Part. For example, B1.0 stated:

(a) Where a Building Solution is proposed to comply with the Deemed-to-Satisfy Provisions, Performance Requirements BP1.1 to BP1.4 are satisfied by complying with B1.1., B1.2, B1.3, B1.4, B1.5 and B1.6

(b) …

1. But I did not know if, or how, the phrases in italics in B1.0 (a) were defined. Nor was I provided with the Performance Requirements.

2. B1.1 sated that the resistance of a building or structure must be “greater than the most critical action effect resulting from different combinations of actions, where –

(a)	the most critical action effect on a building or structure is determined in accordance with B1.2 and the general design procedures contained in AS/NZS 1170.0; and
(b)	the resistance of a building or structure is determined in accordance with B1.4.

[119]   B1.4 is entitled “Determination of structural resistance of materials and forms of

construction. B1.4(b), the paragraph relied upon by the defendant, provides:

The structural resistance of materials and forms of construction must be

determined in accordance with the following, as appropriate … Concrete

construction …: AS 3600.

1. It was not clear to me what the phrase “structural resistance” meant – but it seemed

broad enough to encompass notions of strength, abrasion resistance, compressive
strength and characteristic compressive strength.

1. I will turn now to the evidence in the case.

The parties and early negotiations

1. The plaintiff company, “Hestbay”, became the owner of industrial land at Molendinar

   on which there were existing buildings. Hestbay wished to develop industrial

   warehouses on the site. John Hutchins is one of Hestbay’s directors.

[123]   The defendant company, “One Sector”, is an industrial design and construction

company. It specialises in “tilt panel light industry warehouses”. Nicholas Ray is its

director. He is a concreter by trade.

1. Mr Hutchins and Mr Ray met on 12 December 2013 to discuss a demolition and new build. According to Mr Ray, Mr Hutchins said that he wanted One Sector to build on

   the site “light industry warehouses” which had “the most lettable area possible”; and that he wanted to develop the site “as cheaply and quickly as possible”. Mr Hutchins said he did not use the phrase “cheaply and quickly”. Rather, he said he wanted to

develop the premises in the most economical way possible (which is probably the
same thing).

1. In 2015, Hestbay and One Sector agreed that One Sector would design and construct

   an industrial warehouse complex on Hestbay’s land. The construction was to be

completed in two stages: Stage 1 and Stage 2. Hestbay contracted separately with
One Sector for each stage.

1. One Sector engaged John Hooker, an architect, and Westera Partners, engineers, to design the warehouse and to prepare detailed drawings for its construction.

[127]   Hestbay engaged “GMP” – a project management company – to assist in the

development and to act as the Superintendent for Stage 1.

The warehouses’ purpose

1. Hestbay was a first-time, industrial warehouse developer, to Mr Ray’s knowledge.[17]

   [17]          T 5-17 lines 10-20. However, Mr Ray’s affidavit evidence was inconsistent on this point. In his affidavit of 18 May 2023, he said at [7], “There was no discussion of John Hutchins’ or the plaintiff’s industrial development experience, not on 3 September 2023, not ever.” In his affidavit of 7 March 2023 at [62] he said, “ … so far as I knew, John Hutchins had little to no experience with these types of contracts and was a new developer.” I preferred Mr Ray’s oral testimony and the position he took

   Hestbay asserted that it depended upon One Sector to design and construct the industrial warehouse complex in such a way as to render the units within it suitable for use by industrial or commercial tenants of all kinds (which would include those who used hard wheeled vehicles).

2. Mr Ray said that his instructions were to build light industry warehouses without any reference to prospective tenants, their businesses, or their needs. He considered the

   warehouses to be “speculative buildings” because neither he nor Mr Hutchins knew

   “what any future tenant’s requirements might be”. Nor was there any discussion

   during which Mr Hutchins told him that Hestbay was relying on him or One Sector to

   design and construct the warehouses “to ensure that they were fit for the purpose of

   leasing them to a wide variety of tenants for commercial use”.

3. In oral evidence, Mr Ray said that, since 2009, he’d built about 100 “light industry”

   warehouses. They had all been built with 32 MPa slabs. Having (now) read the

   engineers’ notes, he understood that such a slab was suitable for pneumatic tyred

   vehicles only. He could not remember whether he knew, when he constructed

   Hestbay’s warehouse, that the slab would need to be 40 MPa (that is, harder/stronger)

   if non-pneumatic tyred vehicles were traversing it. He knew that harder concrete was more expensive. He knew that some of the sheds he built were used for storing things and that some had racking.[18]

   [18]          Which was arguably relevant to his understanding of the vehicles which might be used in the units.

4. Mr Ray said that he told Mr Hutchins that the warehouses One Sector would build

   were for “light industry”, but he did not remember telling Mr Hutchins what that

   expression meant. He agreed that his tender for Stage 1 did not use the word “light”:

   the build “Type”, as per his tender, was “Tilt panel Design with Structural Steel

   Roof”.[19] He agreed that nothing in the tender identified any constraints upon the use

   [19]          Page 260 of Part C.

of the concrete slab. Nor did he recall any conversation with Mr Hutchins about the
need to limit the traffic in the warehouses to pneumatic tyred vehicles.

[132]   Mr Ray did not tell the architect or the engineers that the slab for the warehouse complex had to be 32 MPa.[20] He did not pass on to the architect or the engineers any other specifications for the complex because he did not have them.

[20]          T 5-27.

Warehouse completion, occupancy and maintenance

[133]   Stage 1 was completed on 17 June 2015. It included a warehouse of eight units, numbered 1 to 8.

1. Stage 2 was completed on 2 August 2016. It included a warehouse of five units and an office. Its unit numbers were 9, 9A (the office), 10, 11, 12 and 13.

2. The first of the Stage 1 leases commenced in September 2015. Stage 1 ultimately housed two tenants. Each tenant occupied more than one unit.

3. The first of the Stage 2 leases commenced in May 2017. Stage 2 ultimately housed three tenants. Each tenant occupied either one, two or three units. For a period of time, One Sector leased the Stage 2 office unit.

[137]   Hestbay subcontracted the maintenance of the warehouses and the tenant side of property management to a company (BNE Professional Services Pty Ltd) which employed Bruce Willmott. Tenants were to go to Mr Willmott with any concerns.

1. Mr Willmott attended to matters of routine maintenance himself and took instructions from Hestbay in relation to non-routine matters.

The Stage 1 contract

[139]   There is no dispute about the nature and terms of the Stage 1 contract made on 1 August 2014. Its terms came to be settled in the following way.

1. On 13 June 2014, GMP advised Mr Hutchins that the initial Design and Construct Contract, which had been sent from One Sector to Hestbay for Stage 1 and which

   included One Sector’s terms and conditions, was not suitable. GMP advised

Mr Hutchins that his financier would require a “suitable form of contract such as the
[Australian Standards design and construct contract] AS 4902”.[21]

[21]          Page 263, Part C.

[141]   On 20 June 2014, GMP provided Mr Hutchins with such a contract in draft. Mr Hutchins sent the draft contract to Mr Ray on 27 June 2014, noting that it was

“derived from Bank requirements and industry standard”.[22]

[22]          Pages 332 – 334 of Part C.

1. By 30 July 2014, the Stage 1 contract was at signing stage.[23] It was sent to Mr Ray by Mr Hutchins, by email, on that date.

   [23]          Page 347 of Part C.

2. The Stage 1 contract consisted of the following documents:[24]

   [24]          Pages 458A to 458PPP of Part C.

(a) An Australian Standards’ formal instrument of agreement, AS 4902 – 2000,

which listed at clause 6 the contract documents;

• Its recitals included the following at C: “The Principal has agreed to

engage the Contractor to carry out design and construction work in connection with the project [industrial development at Molendinar]

upon and subject to the terms and conditions set out in this Contract.”

(b) The AS 4902 – 2000’s “General conditions of a contract for design and construct”;

• The Preface to the general conditions included the following statement:

“If the project procurement method chosen by the Principal is: (a)

design and construct – the Principal would provide the Principal’s

1. In addition to its variation argument in response to this claim, Hestbay pleaded that

   the Tender Letters “did not provide an express agreement that the plaintiff would pay

   the defendant as an addition to the contract price the reasonable cost of … piling and

   piering works”.

[832]   As above, in my view, the only reasonable way to interpret the list of “Items not Included” was that their cost would be something additional to the contract price, and

payable by Hestbay.

[833]   I acknowledge that not all of the excluded items were payable by Hestbay to One Sector, such as, for example, GST or council fees. I acknowledge that the quotes for some of the excluded items could vary widely. And I acknowledge that, in the case of excluded work to be done by One Sector, the contract provided no mechanism for the determination of their cost. But I do not need to be troubled by that issue in this case, because the experts agreed upon a reasonable price for piling and piering.

1. I found that Hestbay owes One Sector for the cost of piling and piering.

   The rock wall

[835]   With respect to the Stage 2 rock wall: One Sector made an allowance for it of $120,000, as communicated to Mr Hutchins in June 2015.

1. One Sector engaged Australian Rock Walls (ARW) to do the rock wall work on 13 August 2015 for $110,910.

[837]   ARW sent One Sector two invoices for the work. One on 28 August 2015 for

$66,403.32; and another on 16 September 2015 for $55,087.37 – a total of

$121,490.69.

1. The rock wall had been built by 16 September 2015 and One Sector was aware of its cost (including the preparation costs) by that date.

[839]   One Sector pleaded that, as per the Tender Letters of 17 and 14 March 2016, the maximum height of the rock allowed for in the contract price was four metres and the

price was not inclusive of the height increase arising from the plaintiff’s variation

direction in 2015.

1. Its particulars referred to the clarification in the Tender Letters that the price included

   “Retaining required prior to design Western Boundary 4 m High”.

[841]   The Tender Letter dated 23 May 2015 – sent on 10 July 2015 by Mr Ray to Mr Hutchins as part of the Stage 2 contract documents – said under the heading “Clarifications”, in red type:

Please see attached list of contract variations for stage 1 we offer to absorb for the opportunity to move ahead on stage 2.

1. There was no list “attached” in a separate document.

[843]   The Tender Letters dated 14 March 2016 and 17 March 2016 included the same

clarification – but it is not in red type. Nor is a list attached. It also included, under

the clarification heading, the following statement about the wall:

This price includes Retaining required prior to design Western
Boundary 4 m High.

[844]   One Sector referred to correspondence revealing inter alia the architect’s decision

about an increase in wall height (as per his revised drawings); Mr Ray sending Mr Hutchins the revised drawings on 6 and 25 August 2015; and Mr Hutchins

“confirming the further revised site drawings by email to Mr Ray on 25 August 2015”.

1. One Sector argued that the statement in the Tender Letter about the rock wall ought to be interpreted as meaning that the cost of anything in excess of four metres was to be recovered.

2. Hestbay argued that the height of the rock wall was not specified in the Tender Letter

   as 4 metres high – rather that was the estimate. And One Sector was obliged to carry

   out that work as part of the lump sum fixed price contract. Also, One Sector did not comply with the contractual requirements for variation claims. It therefore did not accrue any right to payment of a debt under the contract for the variation. Nor was there any agreement with Hestbay about the additional cost for the rock wall.

[847]   Further, as Hestbay pointed out, One Sector allowed $120,000 in the contract’s

price.[251] The wall builder claimed a payment of $121,490.69. One Sector paid the wall builder only $115,656,10, after a remeasure. In other words, One Sector paid less than the amount it had allowed for the work in the contract price.

[251]  

1. I found that the amount allowed for the rock wall in the contract price, based on an estimated height of 4 metres, was, fortuitously, sufficient to cover the price of the wall as actually built.

2. I therefore dismissed this aspect of the counter claim.

Appendix 1

Leases and Tenants

(1)	Stage 1 was completed on 17 June 2015. It included a warehouse of eight units,
which were leased as follows –

Unit #	Tenant	Lease dates
1 – 5	Chempro	1 February 2016 – 1
February 2028; with 2 x 5-
Brad Markwell: The units were used as a storage and	year options
distribution centre for pharmaceutical supplies.
6 – 8	Viadux	29 September 2015 – 22
February 2024; with 2 x 3-
Karen Doblo: Viadux distributed civil, plumbing and	year options.
building goods. The units were used as a storage and distribution centre. Products were supplied in bulk, palletised form. Orders were picked, packed, and
despatched to clients, including on pallets and in boxes.

(2)	Stage 2’s construction commenced in early 2016 and was completed on 2
August 2016. It included a warehouse of five units and an office. Its unit numbers were 9, 9A (the office), 10, 11, 12 and 13 which were leased as follows
–

Unit #	Tenant	Lease dates
9	TNT: The units were used as an undercover transit and	1 March 2018 – 1 March
freight centre.	2021
9[252]	Budget Pet Products	1 March 2021, for a term of 3 years, with an option for a
Carla Vandepol: The units were used as a warehouse	further term of 5 years.
and distribution centre for pet and veterinary products.
10 – 11	EZFurn	1 August 2018 – 31 July
2026
Trevor Rex: EZFurn is a wholesale commercial furniture supplier, which used the units for the warehousing and light assembly of furniture, and as a
distribution centre.

[252]  

Appendix 2

Vehicles in use

(3) Stage 1 tenants –

Unit #	Tenant	Machinery and equipment
1 – 5	Chempro	Counterbalance gas powered forklift with solid rubber tyres. Used to load and unload trucks and to move stock in and around the warehouse
.	onto the racks.
2.5 T electric forklift with solid rubber tyres – free-standing weight of
1,470 kgs and a full load weight of 3,498 kgs. Used to load and unload trucks and to move stock in and around the warehouse onto the racks.
1.6 T electric forklift with solid rubber tyres – free-standing weight of
1.020 kgs and a full load weight of 4.185 kgs. Used to load and unload trucks and to move stock in and around the warehouse onto the racks.
4.5 T electric forklift with solid rubber tyres – free-standing weight of
2.040 kgs and a full load weight of 4,805 kgs. Used to load and unload trucks and to move stock in and around the warehouse onto the racks.
6 x pallet jacks with solid rubber tyres – free-standing weight of 70
kgs each and a full load weight of 2,300 kgs. Used to move stock in and around the warehouse.
As at 12 October 2022, Chempro continued to operate the 1.6 T forklift, the 2.5 T forklift; the 4.5 T forklift and the pallet jacks.
It ceased operation of the gas-powered forklift in early/mid 2016.
6 – 8	Viadux:	Gas powered forklift with solid tyres[253] – free-standing weight of 1,840
kgs and a full load weight of 4,350 kgs. Used to load and unload pipes
and pallets in the load bays.
Battery powered forklift with solid tyres – free-standing weight of
1,400 kgs and a full load weight of 2,480 kgs. Used to lift and move pallets within the warehouse and loading bays.
Battery powered forklift with solid tyres – free-standing weight of
1,600 kgs and a full load weight of 3,094 kgs.
2 x battery powered forklifts with solid tyres – free-standing weight of
1,600 kgs and a full load weight of 2,874 kgs. Used to lift and move pallets within the warehouse and loading bays.

[253]        Described elsewhere in evidence as hard plastic/polyurethane wheels.

(4) Stage 2 tenants –

Unit #	Tenant	Machinery and equipment
9	TNT	Ride-on forklift to unload and load trucks. Stand-up, ride-on, forklift to lift storage pallets and products onto
racking.

9	Budget	Pet	3 x battery powered Order Pickers, with Vulkollan tyres – free-standing
Products:	weight of 1,770 kgs and a full load weight of 2,770 kgs. Used to pick products from the bottom two levels of racking.
From 21 September 2021, another order picker (as above).
From 29 June 2022, an LPG powered. material handling forklift, with
pneumatic tyres – free-standing weight of 3,560 kgs and a full load
weight of 6,060 kgs. Used to load/unload trucks of pallets or parcel
cages.
10 – 11	EZFurn:	Forklift truck – with non-pneumatic tyres – free-standing weight of
3,560 kgs and a lift capacity of 2,500. In use for three hours per day.

Trevor Rex

Order picker with non-pneumatic tyres – free-standing weight of 3,700

kgs and a lift capacity of 972 kgs. In use for approximately 14 hours

per week.

(from February 2019) Narrow Aisle Forklift with non-pneumatic tyres

– free-standing weight of 6,500 kgs and a lift capacity of 1,500 kgs. In

use for approximately 24 hours per week.

(I note that according to Mr Ray, EZFurn operated 2 – 3 trolleys and 3

– 4 forklifts, with non-pneumatic tyres. This is an over-estimate.)

12 – 13	Budget	Pet	[All tyres non-pneumatic.]
Products
Petrol and LPG powered forklift with super-elastic tyres – free-
standing weight of 3,160 kgs and a full load weight of 5,660 kgs. Used to load and unload trucks of pallets or parcel cages.
2 x battery powered, work assist vehicles with polyurethane tyres –
free-standing weight of 590 kgs and a full load weight of 930 kgs. Used to enable a picker to operate in confined spaces. Used where small loads are handled at height.
On 12 May 2020, Budget Pet Products ceased operation of the work assist vehicles at Units 12 and 13.
Added on 30 November 2017: battery powered High Reach Forklift
with super elastic tyres – free-standing weight of 3.410 kgs and a full
load weight of 4,810 kgs. Used to load and unload pallets onto/from racking.
Added on 15 December 2017: battery powered order picker with
polyurethane tyres – free-standing weight of 1,264 kgs and a full load
weight of 1,964 kgs. Used to transport small loads around the warehouse.
Added on 1 June 2018: 2 x work assist vehicles with polyurethane
tyres – free-standing weight of 645 kgs and a full load weight of 985
kgs.
Added mid to late 2018: battery powered work assist vehicle with
polyurethane tyres – free-standing weight of 645 kgs and a full load
weight of 985 kg.
Added on 8 July 2019: battery powered high reach forklift with super
elastic tyres – free-standing weight of 3,470 kgs and a full load weight
of 5,070 kgs.
Added on 30 June 2020: LPG powered material handling forklift with
pneumatic tyres – free-standing weight of 3,560 kgs and a full load
weight of 6,060 kgs. Used to load/unload pallets onto/from racking.
Added on 22 July 2021: high reach forklift, which was battery powered
and with Vulkollan tyres – free-standing weight of 2,591 kgs and full
load weight of 4,190 kgs.
Infrequently, the tenant operates an order picker (from unit 9) to move
stock as required – free-standing weight 1,770 kgs and a full load weight
of 2,770 kgs.
Upon the commencement of the Unit 9 lease, the tenant ceased the operation of two of the work assist vehicles, the floor sweeper, a forklift, and a high lift forklift.
According to Mr Ray, in 2019: Budget Pet Products used 15 to 20 forklifts, with elastic or hard wheeled tyres; and trolleys with elastic or
hard wheels. This is an over-estimate.

for the characteristic compressive (cylinder) strength of concrete at 28 days

and beams; or (b) by using test data from cores or beams taken from another member for which the
strength of the concrete is known.

in his 7 March 2023 affidavit.

instructions to the client, the builder and ultimately to the contractor through the builder: T 7-5.

the premises were designed”.

to it as an Epoxy.

May 2015”. Paragraph 8 sets out the detail of the Tender Letter dated 23 May 2015. It does not include the statement contained in the actual tender letter itself that One Sector’s standard terms and conditions applied: Pages 611 and 612 of Part C. The Tender Letter is at 616 – 621 of Part C.

On my count, there were 51 dockets on which it was noted that water was added at the customer’s

request.

and the application of a densifier would “sort the issue” and he proposed such a solution to Mr Hutchins,

which did not proceed. Instead, Mr Hutchins arranged for certain areas of the Stage 2 slab to be covered

with an epoxy. Pages 209 – 210 of Part A & B.

he considered to be unnecessarily high, but he considered the Westera design suitable for the loading

criteria listed on the drawings. At [56] of his report, he discussed what would “normally” be included

in such a brief, such as the type of forklift and its wheels to be used on the slab.

amended his table after his evidence.

2016: one at 6.02 am and another at 8.38 am. No slump stand water was added to the 6.02 am delivery.

Nor was any water added at the customer’s request to that delivery. Nor was a maximum amount of

water per load specified. Twenty litres of slump stand water was added to the 8.38 am delivery. No

water was added at the customer’s request to that delivery. Nor was a maximum amount of water per

load specified.

the litres of slump stand water added per cubic metre when no water was added at the customer’s

request.

“MRTS70” which set out the conditions under which water might be added to concrete (see page 2823

of Part D). I appreciate the reason for Dr Woolcock’s reference to this document – that is, to illustrate

that Excel’s failing to state the maximum amount of water which might be added to a load on a docket

was inconsistent with best practice for the competent supply of concrete. But I also note that one of the conditions for the permissible addition of water to the mix on site was that the amount of water

added did not exceed 10 litres per cubic metre of mix – which was consistent with the Holcim document

but which suggested that anything less than 10 litres per cubic metre was permissible. Having made that observation, I took care not to give much weight to this statement in MRTS70 because it was not canvassed in evidence.

– 3257 of Part D and 3966 – 4467 of Part D. The core strength reports are at 3977 – 3979 of Part D.

explained in the Concrete Institute of Australia’s Z11 document – see page 5779 of Part E.

average corrected core strength in 2022.

by Mr Ray show (see pages 1696 – 1794).

(a)	The compressive strength of the cores tested by Testcrete ranged from 27.0 MPa to 36.5 MPa, with an average corrected core compressive strength of 32.1 MPa. That average, when converted to concrete strength in a member, applying AS 3600 Appendix B2 corresponded to a value of 36.9 MPa, which is 15% higher than the design strength of 32 MPa.
(b)	Applying Z11’s recommended practice and BS EN 13791, the core sample results met the 32

MPa concrete requirements.

(c)

Applying AS 3600 Appendix B to the CMT results to obtain values for concrete strength led to the following results:

(i)	37.03 MPa (Unit 9),
(ii)	36.45 MPa (Units 10 and 11) and
(iii)	37.37 MPa (Units 12 and 13),

which “in accordance with BS EN 13791 and CIA standards, demonstrate that the core sample results

met the 32 MPa concrete requirement”.

(a)	It was important to differentiate between concrete’s core strength and its cylinder strength.
(b)	Concrete’s core strength is its compression strength as determined from testing cores drilled

from existing slabs. Testing laboratories generally present the core compressive strength results as corrected core compressive strength results [as occurred in this case]. (The corrected compressive strength is generally calculated by using length to diameter factors for the cores where a length to diameter ratio of 2 after trimming is not achieved.)

(c)	Concrete cylinder strength is determined by testing standard cylinders, typically measuring 100 mm in diameter and 200 mm in height, which are cast in a well-controlled manner using concrete samples obtained during the pouring process and cured under controlled conditions.
(d)	Engineers generally use cylinder characteristic compressive strength.
(e)	Concrete core strength is generally lower than cylinder strength due to factors such as sample preparation, curing conditions, and surface preparation for testing. To account for these factors, and to compare in-situ strength with design strength, standards recommend applying correction factors when analysing core strength results.
(f)	AS 3600 (2018) clause B6.4.2 recommends using a factor of 1.15 when determining the strength of concrete using the average strength of cores. The recommended practice of the Concrete Institute of Australia in Z11 also recognises that in-situ concrete strength values based on the testing of cores are lower by an average of approximately 15% than the concrete strength obtained for the same structure at the same age from testing cylinders.
(g)	Dr Woolcock’s conclusion that the slab was understrength, assuming a conservative 10 per cent

gain over time, was based mainly on core compressive strength. The average core strengths had

not been converted to corrective strengths as per AS 3600 ([40] – [41]).

determination of characteristic strength – see 6-45.

demonstrated, either by calculation or testing in accordance with Appendix B, that the structural adequacy and intended use of the affected members are not impaired. Otherwise the concrete shall be

rejected.”

and over-estimated the characteristic compressive strength of the concrete: “… they consider that

factoring the average core test results by 1.15 provides an estimate of the characteristic strength of the in-situ concrete whereas it only provides an estimate of the average cylinder strength. Furthermore, both experts have then compared the factored average results with the specified 28-day characteristic strength of 32 MPa and concluded that the concrete was compliant without allowing for any increase in strength between placement and testing ([04]).

Dr Woolcock was of the view that the expression used in Clause B6.4.2, “the strength of the concrete”

was ambiguous. Recent commentary on it in “Z11” implied that it was outdated and in need of clarification. Z11 commented that “the strength of the concrete” might be incorrectly interpreted as an

appropriate method for determining characteristic design strength, leading to an over-estimate of
characteristic strength and the structural capacity of a member.

Dr Woolcock explained in detail the Z11 methods for determining compressive strength from core testing, including the formulas it proposed. Applying those formulas, and relying on BS EN 13791,

Dr Woolcock’s estimate of the characteristic core strength after 6 years was 27.77 MPa, which, when

factored by 1.15 resulted in an equivalent characteristic cylinder strength of 31.9 MPa.

Dr Woolcock then applied the percentage increase in strength over time as per a formula in the Eurocode 2 Part 1-1 (a European Code) or between 19% to 40%. Applying an increase in strength of 19% for a 32 MPa slab led to a characteristic strength of 38.1 MPa after 6 years. That was significantly higher than 31.9 MPa and, in his opinion, indicated that the uncontrolled addition of water prior to placement had weakened the concrete. Using a minimum increase in strength of 19% over time suggested that the concrete was only 26.8 MPa 28 days after pour, significantly less than the specified

32 MPa. However, in cross-examination, Dr Woolcock acknowledged that his “reverse calculation”,

based upon the Eurocode, was inappropriate (for reasons I do not need to elaborate upon).

(a) Z11’s criticism of AS 3600 Clause B6.4.2 and the risk of its leading to an over-estimate of a

structure’s “inherent” strength was “geared towards” older buildings without a defined design

strength and served as a precaution. Also, as Dr Woolcock recognised, the danger in this context

was likely in the assessment of suspended concrete structures, rather than slabs on ground.

(b)	Dr Woolcock’s assumed strength gain of between 19 to 40 percent was not based on evidence.
(c)	It was wrong/misguided of Dr Woolcock to use the European Standard EN 1992-1-1 to calculate the strength increase. The empirical equations in the standard were derived from extensive experimental data in Europe. They did not reflect the behaviour of concrete in Australia, with its crucial climate differences.
(d)	Also, the equation used by Dr Woolcock provided an estimate of mean compressive strength at any age, and not the characteristic compressive strength. Mean compressive strength over time should be calculated using mean equivalent cylinder strength.

… Concrete is generally poor in flexural strength and tensile strength. In other words, the compressive

strength is thumping the thing down, tensile strength is trying to pull it off … [T]he basic test that’s

used is they drill a hole in … and then they try to pull a piece out to find whether the coating fails or

whether it fails in the subbase underneath it …” He said a certain tensile strength was necessary so

that the coating which was applied would not lift off. A pull test was done to test tensile strength.
Relevant calculations for it were contained in AS 3600.

least in two cases, copied Dr Khan’s answer.

means that it is not only unsuitable for the specified pneumatic-tyred traffic from an abrasion

perspective in accordance with Table 4.5 of AS 3600 but also that the pavement’s structural capacity

is inadequate for the design forklifts loads by my calculations as demonstrated below. [Table 4.3 of AS 3600] shows the minimum characteristic concrete strength at 28 days and should not be interpreted as the strength at some time in the future, the underlying assumption being, in my opinion, that strength will increase with time.

60. Using the CC&AA software with a CBR of 11, I calculate by interpolation from the 80kN and 100 kN axle loads and the 25 MPa and 32 MPa concrete strengths that are required slab thickness for unlimited repetitions of the 94 kN axle loads (corresponding to twice the 4.8 tonne design wheel load) that the required slab thickness is 177 mm for a characteristic 28-day concrete strength of 26.8 Mpa at placement. The parameters I have adopted for the analysis are:

• Characteristic concrete strength 26.8 MPa

• K1 = 0.9 for wheel loads (adopting an intermediate value between 0.85 and 0.95)

• Unlimited repetitions, hence k2 = 0.5

• CBR 11, hence short term modulus Ess = 41 MPa (=29/07)

• Wheel spacing 1.45 m (typical for dual wheel front axle load of 10t, possibly smaller and if so, more severe)

• Depth of soil 3 m

• K3 = 1.2 for interior as opposed to edge loading

• Axle load 94 kN (= 9.6t x 9.82)

61. Note that using the same parameters except using 32 MPa rather than 26.8 MPa, the required

thickness is 168 mm which confirms that the Westera Partners’ design thickness of 175 mm is

adequate.”

By way of an example of the parties’ express terms applying in preference to the terms of AS 4902: It may be noted that the Scope of Works contained in Part F of Stage 2’s AS 4902 required the Stage 2

slab to be reinforced with “Helix Fibre Reinforcement”. The Tender Letter required its reinforcement

“to Engineering Design”. Mr Ray decided not to use Helix Fibre Reinforcement was not used in Stage

[2] – consistent with the Tender Letter and inconsistent with the AS 4902 contract.

than careful approach to contract formation.

traffic had to mean slabs of 32 MPa at 28 days, in accordance with AS 3600. Thus, this pleading was inconsistent with the submission made to me by Kings Counsel for the defendant that its obligation was only to use N32 concrete and that it was not obliged to create a slab which was at 32 MPa after 28 days (see below).

dusting, beyond that which would be expected with normal wear and tear.

time, were irrelevant to the question of its compliance. He simply applied Appendix B of AS 3600 to

the core test results and calculated the concrete’s strength as around 37 MPa, which meant it met its

compliance requirement.

(a) The plaintiff seemed to imply (at [234(a)]) that Mr Reid selected the highest k1 factor because it was

favourable to the defendant’s case.

(b) It submitted that because there had not been “careful construction control”, 0.90 should be the preferred

k1 factor.

(c) It submitted that Mr Reid ought not to have speculated about the loads and should have preferred Dr

Woolcock’s unlimited load assumptions.

(d)	It submitted that Mr Reid’s adoption of 1.5 m for the soil depth assessment factor was contrary to the
geotechnical analysis, which recorded rock depths of between 3.3 m and 4.9 m at bore hole 6, 10 and 11 on the eastern side, and 7 on the southern side.

ITEMS NOT INCLUDED GENERAL EXCLUSIONS

As per Tender Letter As per Annexure F

1.	GST not included	1.	GST not included
2.	No excavation allowed for in rock or reef	2.	No excavation allowed for in rock or reef
3.	Council fees, contributions and head works	3.	Council fees, contributions and head works
charges, Energex fees	charges, and Energex fees
4.	No allowance for water meter readers	4.	No allowance for water meter readers
5.	Furniture or window coverings	5.	Furniture or window coverings
6.	Qleave to be paid for by owner
7.	Racking to warehouse	6.	Racking to warehouse
8.	Piling or Piering
9.	Nature strip or footpath upgrade other than	7.	Nature Strip or footpath upgrade other than
required by council for approval	required by council for approval
10.	Traffic Control	8.	Traffic Control
11.	Air conditioning or ventilation to main	9.	Air conditioning or ventilation to main
warehouse area	warehouse area

12. Signage including power 10. Signage including power

13. Security	11. Security
14. Connection Fees	12. Connection Fees

15.    All works outside property boundary

excluded

16. Data or Phone systems installation 13. Data or phone systems installation

17. Data Cabling	14.	Data Cabling to office fit out
Please note:

• Quote Valid for 30 days

• Onesector Pty Ltd standard terms and conditions

• Final Design and plans to be approved by

client

Unit 9A, the office unit, was leased by Budget Pet Products from 1 July 2019 until 31 July 2026.