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AS 1379 Supp 1-1997 Specification and supply of concrete - Commentary
(Supplement to AS 1379-1997)
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AS 1379 Supp1—1997
Licensed to E.S.SURESH on 04 Jun 2002. Single user licence only. Storage, distribution or use on network prohibited.
AS 1379 Supplement 1—1997
Specification and supply of
concrete—Commentary
(Supplement 1 to AS 1379—1997)
This Australian Standard was prepared by Committee BD/49, Manufacture of
Concrete. It was approved on behalf of the Council of Standards Australia on
22 August 1997 and published on 5 October 1997.
The following interests are represented on Committee BD/49:
Ash Development Association of Australia
AUSTROADS
Australasian Slag Association
Australian Premixed Concrete Association
Cement & Concrete Association of Australia
Housing Industry Association
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Master Builders Australia
The Association of Consulting Engineers, Australia
University of Newcastle
Review of Australian Standards. To keep abreast of progress in industry, Australian Standards are subject
to periodic review and are kept up to date by the issue of amendments or new editions as necessary. It is
important therefore that Standards users ensure that they are in possession of the latest edition, and any
amendments thereto.
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Suggestions for improvements to Australian Standards, addressed to the head office of Standards Australia,
are welcomed. Notification of any inaccuracy or ambiguity found in an Australian Standard should be made
without delay in order that the matter may be investigated and appropriate action taken.
This Standard was issued in draft form for comment as DR 96017.
AS 1379 Supp1—1997
Licensed to E.S.SURESH on 04 Jun 2002. Single user licence only. Storage, distribution or use on network prohibited.
AS 1379 Supplement 1—1997
Specification and supply of
concrete—Commentary
(Supplement 1 to AS 1379—1997)
First published as AS 1379 Supplement 1 — 1997.
Incorporating:
Amdt 1—2000
PUBLISHED BY STANDARDS AUSTRALIA
(STANDARDS ASSOCIATION OF AUSTRALIA)
1 THE CRESCENT, HOMEBUSH, NSW 2140
ISBN 0 7337 1469 2
AS 1379 Supp1 — 1997
2
PREFACE
This Commentary (AS 1379—Supplement 1) was prepared by Standards Australia
Committee BD/49 on the Manufacture of Concrete. While it is intended for reading in
conjunction with AS 1379, Specification and supply of concrete, it does not form an
integral part of that Standard.
Objective
The objective of this Commentary is—
(a)
to provide background reference material to the Clauses in the Standard;
(b)
to indicate the origin of particular requirements;
(c)
to indicate departures from previous practice; and
(d)
to explain the application of certain Clauses.
The clause numbers and titles used in the Commentary are the same as those in AS 1379
except that they are prefixed by the letter C. To avoid possible confusion between this
Commentary and the Standard, clauses are cross-referenced within the text, while
Commentary clauses are referred to as Paragraph C ... in accordance with Standards
Australia policy.
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Gaps in the numerical sequence of Paragraphs in the Commentary indicate that the
committee considered that commentary on these Clauses was not needed.
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3
AS 1379 Supp1 — 1997
CONTENTS
Page
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SECTION C1 SCOPE AND GENERAL
C1.1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
C1.3 OTHER MATERIALS, PLANT OR METHODS . . . . . . . . . . . . . . . . . . . . 4
C1.4 DEFINITIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
C1.6 SPECIFICATION OF CONCRETE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
C1.7 METHODS OF ORDERING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8a
C1.8 BASIS OF SUPPLY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
SECTION C2 CONCRETE MATERIALS AND CONSTITUENT LIMITATIONS
C2.2 CEMENT CONSTITUENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C2.3 AGGREGATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C2.4 MIXING WATER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C2.6 BULK STORAGE OF MATERIALS . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C2.7 LIMITATIONS ON CHEMICAL CONTENT OF CONCRETE . . . . . . . . . .
13
13
13
13
14
SECTION C3 PLANT AND EQUIPMENT
C3.1 BINS AND SILOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C3.2 WEIGHING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C3.3 LIQUID DISPENSING EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . .
C3.4 MIXERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15
15
15
15
SECTION C4 PRODUCTION AND DELIVERY
C4.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C4.2 BATCH PRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C4.3 CONTINUOUS PRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C4.4 DELIVERY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17
17
21
21
SECTION C5 SAMPLING AND TESTING OF CONCRETE
C5.1 GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C5.2 SLUMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C5.3 STRENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C5.5 CHLORIDE AND SULFATE CONTENT . . . . . . . . . . . . . . . . . . . . . . . . .
C5.6 DRYING SHRINKAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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23
24
24
SECTION C6 SAMPLING, TESTING AND ASSESSMENT FOR COMPLIANCE OF
CONCRETE SPECIFIED BY COMPRESSIVE STRENGTH
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C6.1 GENERAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C6.2 SAMPLING AND TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C6.3 PRODUCTION ASSESSMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25
27
27
28
APPENDIX CB GUIDE TO THE SPECIFICATION OF SPECIAL-CLASS CONCRETE 31
AS 1379 Supp1 — 1997
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STANDARDS AUSTRALIA
Australian Standard
Specification and supply of concrete —
Commentary (Supplement 1 to AS 1379 — 1997)
S E C T I O N
C 1
S C O P E
A N D
G E N E R A L
C1.1 SCOPE The Standard was prepared for use in the specification and supply of all
concrete, whether or not it is addressed in the scope and application of AS 3600, Concrete
structures.
It is not intended to apply to mortars or grouts.
Requirements for mortars for masonry construction are given in AS 3700 and the methods
for sampling and testing mortars in AS 2701.
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Requirements for grouts to be used for the grouting of prestressing tendons in ducts, are
given in AS 3600.
The supply of concrete by the premix concrete industry has been expressly but not solely
contemplated in the preparation of the document.
It is not intended that this Standard should take precedence over existing Australian
Standards for the manufacture of specific concrete products.
The publication of this edition of the Standard is intended to complete the independence
of this Standard from AS 3600, Concrete Structures. Due to the lack of synchronization in
publishing dates, for many years concrete as a material relied on both Standards to one
degree or another. With the relatively recent revision of AS 3600 and the current edition
of AS 1379, it is intended that AS 1379 is now a ‘stand-alone’ document for the
specification and supply of concrete.
C1.3 OTHER MATERIALS, PLANT OR METHODS Where materials, plant or
methods not complying with this Standard are proposed and the intended use of the
concrete is subject to the control of a building or other regulatory authority, approval for
the use of those other materials, plant, or methods will need to be obtained from the
authority.
C1.4
DEFINITIONS
For the purpose of this Standard, the definitions below apply.
C1.4.4 Cement —the meaning of the term cement has been extended beyond its
traditional meaning of portland cement to include supplementary cementitious materials.
For the purpose of this Standard cement can be portland or blended cements as defined in
AS 3972, or a combination of these and fly-ash, silica fume or ground granulated iron
blast furnace slag.
C1.4.7 Customer — the terms ‘User’ and its derivatives have been replaced by
‘Customer’ for consistency with ISO 8402 terminology.
C1.4.11 Project assessment—Section 6 requires suppliers to continuously monitor the
strength of the concrete supplied by ‘Production assessment.’
Project assessment is an additional assessment that may be specified, and attracts an
additional cost.
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AS 1379 Supp1 — 1997
Currently AS 3600 requires project assessment to be specified for all special-class
concrete. Project assessment may also be specified for normal-class concrete.
The customer should not assume the supplier is aware of any liability to conduct project
assessment. It is the responsibility of the customer to commission an appropriate testing
body to carry out project assessment. The supplier may be an available choice for this
purpose. The customer may commission the supplier to carry out the specified project
testing, making appropriate arrangements for the recovery of the costs involved.
Project assessment is discussed further in the section of this Commentary dealing with
Section 6.
C1.4.16 Supply The terms ‘Manufacture’ and its derivatives have been replaced by
‘Supply’ for consistency with ISO 8402 terminology.
C1.4.17 Total free water—The only water considered to be available for hydration of
cementitious materials is the ‘total free water’, being ‘added water’ and the ‘surface
moisture’ of the aggregates.
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In this context, water separately added in the batching process, as distinct from water
introduced as moisture content in the aggregates, is referred to as ‘added water’.
The other component of total free water, the ‘surface moisture’ content of aggregates, is
defined as the total moisture content less the ‘absorbed moisture’ content. ‘Absorbed
moisture’ is that contained within capillary fissures in the aggregate particles. It is
considered to remain within the aggregates and not to be available to enter into chemical
combination with the cementitious materials. When aggregates are in a condition where
the only water they contain is that which can fully occupy the capillary fissures within the
aggregate particles, they are said to be in a ‘saturated surface dry’ condition. To bring
aggregates to this condition, they are slowly dried from a higher moisture content until the
surface water has evaporated. The ‘saturated surface dry’ moisture content can then be
determined. Any moisture the aggregates contain in excess of the absorbed moisture is
referred to as ‘surface moisture’.
C1.4.18 Water-cement ratio (w/c)— Water for this purpose is defined as the total free
water discussed at Paragraph C1.4.17 above, and cement as discussed in Paragraph C1.4.4.
C1.6
SPECIFICATION OF CONCRETE
C1.6.1 General ‘Normal-class concrete’ is presented as the specification method likely
to suit the majority of applications. Its properties are limited, albeit in reasonably wide
ranges, in respect of a number of key parameters such as strength grade, density,
aggregate size, slump, and chemical composition.
The quality compliance provisions of Section 6, originally promulgated in AS 3600
in 1988, anticipated that the majority of specifications would call up normal-class
concrete. The entire concept of production assessment is based on this assumption. In turn
the customer s level of protection also improves.
‘Special-class concrete’ provides the specifier with the opportunity to specify parameters
or values which are not permitted in normal-class concrete.
C1.6.2 Standard strength grades The majority of structural concrete lies in the range
of strength grades from 20 to 50 MPa. For such concrete, the committees responsible for
AS 3600 and this Standard recommend the selection of one of the values 20, 25, 32, 40,
or 50 MPa.
The advantages of standardizing strength grades lies in the consequent increase in the
volume of statistical information available for each mix and in avoiding a variety of
unnecessary mix designs.
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The use of standard strength grades whenever possible will result in more test results
being available for statistical analysis and will generate more reliable statistical
parameters with which to assess quality. This will enhance the effectiveness of suppliers
production assessment procedures, the principal tool for maintenance of the quality of
concrete production.
If special-class concrete is specified, it is preferable if the use of non-standard strength
grades is avoided. If the strength grade is one of the standard grades, test data can
sometimes be grouped with the data used for production assessment of normal-class
concrete of the same strength grade even though concrete may be special-class.
A technical distinction is introduced in this Clause with the use of the term ‘design’
characteristic strength. Characteristic strength is defined at Clause 1.4.5 as ‘that value of
the material strength, as assessed by the standard test, which is exceeded by 95 percent of
the material.’ The word ‘design’ is prefixed to it in this Clause to make clear that in this
context the value referred to is the value upon which the designer relies. It is not to be
confused with the value calculated from the test results for a particular grade which will
be expected to exceed the ‘design’ value.
C1.6.3
Normal-class concrete
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C1.6.3.1 General This Clause is an amalgamation of two clauses from the 1991
version of the Standard. It now contains all the surviving provisions from both clauses
dealing with limitations on cement types and lightweight aggregates.
Any restrictions on the use of fly-ash, ground slag or chemical admixture or a limitation
of basic shrinkage strain after 56 days drying to less than 1000 × 10-6, would change the
classification to special-class as follows:
(a)
Mass per unit volume The range of from 2100 kg/m3 to 2800 kg/m3 was chosen to
accommodate satisfactory dense aggregates commercially available. Lightweight
concrete (< 2100 kg/m3) would necessarily be special-class concrete.
(b)
Chemical content Limiting the chloride ion content to 0.8 kg/m3 reflects a
consensus of views as to a safe maximum to prevent corrosion of embedded ferrous
metals and any other deleterious chemical reactions from chlorides. Similarly, the
limit on sulfates of 50 g/kg of cement is consistent with all data on a safe maximum
to ensure long-term durability.
(c)
Basic shrinkage strain The maximum basic shrinkage strain, after 56 days drying,
of 1000 × 10-6 is a value to which suppliers of normal-class concrete in any area of
Australia are committed.
Two matters as follows are relevant when considering the appropriateness of this
limit:
(i)
Practicality In some areas the locally available aggregates and cement for
the production of concrete will result in concrete with a basic shrinkage
strain approaching this value. A lower maximum value for normal-class
concrete would, in such areas, preclude the use of economical and otherwise
satisfactory materials for use in normal-class concrete.
Many areas have materials economically available which will ensure the
basic shrinkage strain of concrete in those areas is considerably less than
1000 × 10-6. Designers should ascertain the shrinkage characteristics of
commercially produced concrete in any area by inspecting the records of
suppliers in that area.
It is preferable that such enquiries be made before the specification of lower
shrinkage strain limit is contemplated.
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(ii)
AS 1379 Supp1 — 1997
Consistency A median value of 700 × 10-6 is used in AS 3600 for the basic
shrinkage strain as an alternative to values determined from tests on the
concrete proposed to be used or similar local concrete.
The maximum to 1000 × 10-6 specified in AS 1379 includes allowance for
the range of values each side of the median and for the testing precision in
the determination of shrinkage.
The AS 3600 provision predated the drafting of AS 1379, but was based on a
similar body of experience of the values of shrinkage strain attained across
the nation.
Further discussion of basic shrinkage strain occurs in Clause C1.6.4.
(d)
Strength gain characteristics The needs for strength growth characteristics vary.
Relatively high early strengths are needed in some circumstances, for example,
when stripping time for suspended slabs is critical.
A minimum mean 7-day strength is included in the Standard to inform customers
what they may anticipate if normal-class concrete is specified.
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When higher early age strengths are needed special-class concrete should be
specified.
The previous edition of the Standard approached the minimum early strength issue
by imposing limits, expressed in a formula, on the allowable proportion of
supplementary cementitious materials to portland cement. With the changes to
AS 3972 ‘Portland and blended cements’ which allows up to 5% of ‘mineral
additions’ and the comparatively new use of silica fume, the formula approach
would become cumbersome and it is considered that a performance rather than a
prescriptive requirement is more consistent with current specification practice.
None the less it must be emphasized, especially in the absence of an additional early
strength specification parameter, that concrete takes some time to achieve its
potential strength. The importance of extended continuous curing to achieve the full
potential properties also needs to be emphasized in this context.
C1.6.3.2 Basic parameters The six (6) basic parameters that need to be specified
when ordering normal-class concrete are as follows:
(a)
Standard strength grades. The significance of standard strength grades is discussed
in Paragraph C1.6.2 above.
(b)
Slump.
(c)
Maximum aggregate size.
(d)
Method of placement.
(e)
Any requirement for project testing.
(f)
Level of air entrainment if required.
In the absence of specific advice, default values of maximum aggregate size and project
testing have to be established.
When a customer orders a specific value of slump, that slump becomes the supplier’s
target. The tolerances in Table 6 are to provide for the operator’s inability to precisely
assess slump in the production process.
The specification of slump of normal-class concrete is commonly established by the
designer in contractual documents, often without discussion with those responsible for
placing the concrete or certain knowledge of the details of the method of placement.
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There is merit in the alternative of allowing the customer to specify the slump to the
supplier, after considering the alternative methods of placement and finishing. The
customer may need to strike a balance between the higher cost of purchasing concrete
with a higher slump and the considerable cost associated with the difficulties of placing
concrete at lower slump. For example, it is usually more expensive to pump concrete at an
80 mm slump than a 100 mm slump.
Due to local aggregate characteristics, suppliers in some areas may not be able to meet the
shrinkage requirements of this Standard at a specified slump of >80 mm. In this case the
supplier cannot offer normal-class concrete of >80 mm slump, but only lower slump. It is
the responsibility of the supplier to decide if a >80 mm slump normal-class concrete can
be supplied.
C1.6.4
Special-class concrete
Shrinkage strain Special-class concrete may be specified as having maximum values of
basic shrinkage strain below or, indeed, above 1000 × 10−6.
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The specification of maximum basic shrinkage strains less than 1000 × 10−6 may carry
with it some disadvantages. Depending on the material resources available in the region, it
may be —
(a)
necessary to import distant materials, thus increasing the cost of concrete; and/or
(b)
unnecessarily deplete scarce resources.
Consultation with experienced suppliers in the region is advisable to determine what
shrinkage may be expected with normally used materials, and the cost, if any, associated
with specifying a limit less than 1000 × 10−6.
In the event that more restrictive values for basic shrinkage strain are specified, the
specification of a median value is recommended. A limit on the median is more capable
of rational assessment than a limit on the maximum. In view of the inherent variability of
the sampling and testing procedures, unusually high values may randomly occur. Where
maximum value is specified, irrational assessment may occur.
Proposed conventions for use in deciding prefixes to succinctly identify
mixes Identifying prefixes for special-class concrete should follow the following
conventions:
(i)
Mix codes such as S25 may be used to identify a 25 MPa strength grade specialclass concrete, distinguishing it from N25, being a 25MPa strength grade normalclass concrete.
(ii)
Codes SF ‘x’ and ST ‘y’ may be used to identify special-class concrete with a
design characteristic strength in flexure of ‘x’ MPa and indirect tension ‘y’ MPa,
respectively.
(iii) Appropriate alphanumerical codes agreed between the supplier and the user may be
used to identify concrete specified by properties other than strength; for example,
KC280 may be used to identify a kerb and channel mix with 280 kg cement/m3.
High strength/performance concrete Where concrete strength grades greater than
50 MPa, or other high performance parameters, are proposed, it is recommended that the
specification require the supplier to submit for approval to the customer or his agent a
quality plan specific to the project. The plan should confirm the supplier’s ability to
supply and deliver concrete conforming to the requirements of the specification. The plan
should also be implemented for the duration of the project.
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AS 1379 Supp1—1997
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Specifications of slump as a maximum value in lieu of the default mean value The
practice of specifying slump in accordance with the normal-class provisions is
encouraged. The specification of maximum slump or any non-standard method of slump
specification is discouraged to avoid confusion.
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C1.7 METHODS OF ORDERING The purpose of this Clause is to establish standard
guidelines for ordering concrete produced in accordance with this Standard, so that when
placing and accepting an order, there is a clear understanding between the purchaser and
the supplier, with regard to the expectations of the former and the responsibilities of the
latter.
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AS 1379 Supp1—1997
The Standard covers the specifications, manufacture (and delivery where applicable) of
plastic concrete containing certain basic ingredients and having specified plastic state
properties. Further, the purchaser should have confidence that the concrete supplied will
achieve specified hardened state properties at the nominated time when handled, cured and
tested in accordance with the relevant procedures.
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Whether or not the concrete placed into the structure achieves the same hardened state
properties as the test specimens is affected by the handling, placing and compacting
techniques employed, the methods and duration of curing used and the method, sequence
and timing of any formwork stripping. As these factors are outside the control of the
supplier, assessment of compliance of concrete on the basis of testing of the concrete in
the structure is outside the scope of this Standard. In fact assessment for compliance
based on testing the concrete in a structure is not covered by any Standard, however
AS 3600 does give a method of estimating the strength of concrete in a structure. In the
absence of test results on samples made from the fresh concrete, testing of concrete in the
structure can be undertaken, but only to provide guidance as to whether the concrete
produced by the supplier would have achieved the required hardened state properties.
In pursuance of the principles established when AS 1379 was first published, suppliers
will continue to classify orders as ‘performance’ or ‘prescription’ according to whether
the supplier accepts, or declines responsibility for selecting and proportioning the mix
ingredients to meet specified or ordered performance parameters. However, there is now
an additional requirement for specifying (and ordering) concrete as ‘normal-class’ or
‘special-class’, as distinguished by their respective specifications in Clause 1.6.3 and
Clause 1.6.4 of the Standard.
It is intended that normal-class concrete should provide a ‘standardized’ range of
concretes which are suitable for the majority of applications in domestic, commercial,
industrial and institutional buildings. There will of course be other areas, such as
particular civil engineering structures, where normal-class concrete would also be suitable.
The principal criterion for deciding whether normal-class concrete is appropriate for a
particular application, is to determine whether the limited number of parameters permitted
to be specified for that class (see Clause 1.6.3) is sufficient to ensure that concrete with
the desired properties can be provided. If it is considered to be insufficient, then specialclass concrete is required and the different or additional parameters needed to ensure the
desired results are to be specified (Clause 1.6.4) and noted in the order (Clause 1.7).
Apart from being an essential requirement for ordering, it is in the customer’s interest to
determine beforehand which class of concrete is the most appropriate for the project, as
there will usually be a cost difference between the two classes. If there is a ‘structural
specification’ for supply of the concrete, the decision as to which class is appropriate will
usually have been made by the specifier well before an order is placed. If there is no
specification, or the specification is not clear on which class is appropriate, it will be
essential for the customer and the supplier to reach an agreement on the appropriate class,
before any order is placed.
Having established which class of concrete is required, the following ordering procedures
of (a) or (b) should be followed as appropriate:
(a)
Ordering normal-class concrete Where normal-class concrete has been specified,
or it has been agreed between the customer and the supplier that normal-class
concrete is appropriate for the intended use, the order should contain only the
following information, as appropriate:
(i)
The quantity of concrete required and sufficient information to ensure that
the user receives the concrete ordered.
(ii)
The standard compressive strength grade, designated in accordance with
Clause 1.6.3.2(a).
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(iii)
A standard slump selected in accordance with Clause 1.6.3.2(b), at the point
of acceptance.
(iv)
The maximum nominal size of aggregate selected in accordance with
Clause 1.6.3.2(c).
(v)
The level of air-entrainment, if any in accordance with Clause 1.6.3.2(f).
(vi)
The intended method of placement (Clause 1.6.3.2(d)).
(vii)
Whether project assessment is to be carried out by the supplier.
Clearly Items (ii) to (v) above are performance requirements. Furthermore, apart
from the limitations imposed by Section 2 of the Standard, there is no restriction on
the supplier regarding the selection or proportioning of the mix ingredients. An
order for normal-class concrete is therefore a performance order.
It follows that in accepting an order for normal-class concrete, the supplier also
accepts responsibility for supplying concrete which will have both the specified
plastic-state properties, and the potential to attain the specified hardened-state
properties, and for ensuring that due account has been taken of the other
information contained in the order.
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(b)
Ordering special-class concrete Clause 1.6.4 of the Standard indicates that any
concrete which is not normal-class is classified as special-class. Clause 1.7 of the
Standard requires that if the concrete is special-class, the class is to be further
qualified as ‘performance’ or ‘prescription’.
At this point, it is important to remember that, like any other wholesaler or retailer,
it is the supplier’s prerogative to accept or decline an order for a product. Hence,
whether an order for special-class concrete is accepted as a ‘performance’ order or a
‘prescription’ order will depend entirely on agreement between the supplier and the
customer.
An order for special-class concrete may be accepted as either a performance order,
or a prescription order. If the order is in the form given in Paragraph C1.7b(i)
below, and it is agreed between the parties to the order that the supplier accepts
responsibility for proportioning the concrete ingredients so that the specified, or
otherwise agreed, properties or characteristics of the plastic and hardened concrete
can be achieved, then the order will be accepted as a ‘performance order’. If this
does not apply, it is understood that the supplier does not agree to accept
responsibility for achieving some or all of the specified, or otherwise agreed,
properties or characteristics of the plastic and hardened concrete. The order is then
classed as a ‘prescription order’ and the information listed in Paragraph C1.7b(ii)
below will be required. However, the supplier is still responsible for carrying out all
other applicable requirements of this Standard. Appendix B may be used as a guide
to the ordering of special-class concrete, subject to the limitations given above.
(i)
Special-class performance concrete A special-class performance order
should contain only the following information as appropriate:
(A)
The quantity of concrete required, and sufficient information to ensure
that the user receives the concrete ordered.
(B)
The relevant ‘Special-Class’ designation,
Clause 1.6.4, followed by the ‘Performance’.
(C)
The strength grade, if applicable.
(D)
The slump, quoted in multiples of 10 mm, and the point of acceptance.
(E)
The maximum nominal size of aggregate, selected from the standard
sizes specified in AS 2758.1.
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(F)
The level of air entrainment, if any.
(G)
The intended method of placement.
(H)
Whether project assessment is to be carried out by the supplier.
(I)
Any other construction, performance or quality criteria that may
influence the selection of materials or proportioning of the
ingredients. These criteria may include a minimum cement
content or a maximum water-cement ratio, or both, but if other
material proportions are specified, the order will be classed as a
prescription order and the information given in
Paragraph C1.7b(ii) will be required.
It can be seen that this is almost identical with an order for normal-class concrete, except
that the properties specified under Items (C), (D) and (E) do not have to be the
standardized normal-class values. The other important exception is the information to be
provided under Item (I). In the long run, this will determine whether the supplier accepts
the order on a ‘performance’ basis.
Information that would need to be included under Item (I) would include the following:
(1) Any early-age strength limitation.
(2) Any shrinkage strain limitation (see Clause 5.6.2).
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(3) The inclusion of additives such as fibres or colouring pigments.
(4) A requirement for colour control of the hardened concrete.
As indicated in Item (I) a requirement for specific material proportions will generally
preclude acceptance on a performance basis.
(ii)
Special-class prescription concrete A special-class prescription order
should contain at least the following information:
(A)
The quantity of concrete required and sufficient information to
ensure that the user receives the concrete so ordered.
(B)
The relevant ‘Special-Class’ designation, in
Clause 1.6.4, followed by the word ‘Prescription’.
(C)
The particle density, maximum nominal size and grading of the coarse
aggregate, within the ranges provided for in AS 2758.1, or
alternatively, the source of aggregate supply.
(D)
The particle density and grading of the fine aggregates, within
the ranges provided for in AS 2758.1, or alternatively, the source
of aggregate supply.
(E)
The type of portland or blended cement, selected from AS 3972.
(F)
The limitations, if any, on the use of other cement constituents.
(G)
The limitations, if any, on the type and proportions of admixtures that
may be used.
(H)
The proportions of aggregates and cement, by mass except as otherwise
permitted by Clause 4.1.2.
(I)
Either the maximum water-cement ratio, based on saturated surface-dry
aggregates and total water content; or the required slump at the point
of acceptance.
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Persons requiring special-class prescription concrete are reminded that concrete properties
are very sensitive to variations in the properties of the ingredients contained in the mix.
Because concrete properties can be achieved with particular proportions in one area, there
is no guarantee that these properties can be achieved in an area with different sources of
materials.
It is therefore incumbent on the specifier to ascertain whether all prescribed requirements
can be satisfied with the materials available to suppliers in the region in which the
concrete is to be supplied.
C1.8
BASIS OF SUPPLY
C1.8.2 Volume of plastic concrete This Clause addresses what the industry commonly
refers to as ‘yield’, i.e. the actual volume of concrete supplied, as against the volume
ordered and charged. There is an unavoidable variation in the volume of concrete
produced from any set of batch weights arising from batching deviations within the
allowed tolerances, variations in the moisture content of aggregates, density of aggregates
and to a lesser degree other factors such as slump variations and temperature.
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In order to achieve a minimum 98% yield, the mean value of the volumes yielded from
the batch weights for one cubic metre obviously has to exceed 98% and the volume of
concrete supplied over a long period will be at least equal to the cumulative volume
shown on the identification certificate.
The determination of volume of a batch of concrete involves measuring the weight of the
batch. This can be done by accumulating the batch weights of the ingredients used in the
production of the batch. If water is batched by a volumetric metre, a conversion to mass
will be necessary.
Several factors can cause the in situ measured volume to differ from the volume of plastic
concrete as determined above. These factors include handling and compaction, the effects
of hardening, temperature changes, formwork deflection and spillage. A quite small
unintentional increment in the thickness in a slab amounts to a significant percentage
increase in the volume of concrete used while proper compaction can reduce the delivered
volume by between 3% to 5%.
C1.8.3 Identification certificate A ‘delivery docket’ or similar document issued by
the manufacturer and containing at least the information specified in this Clause is
considered to be an ‘identification certificate’.
Where the customer is also the supplier, the records required by Clause 4.1.6 may be
considered to be an identification certificate.
The intent of recording water additions is to provide an audit trail to facilitate the analysis
of a nonconforming batch. For all the reasons discussed elsewhere it cannot be used as a
primary control of total water content at the time of delivery.
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S E C T I O N C 2
C O N C R E T E M A T E R I A L S
A N D C O N S T I T U E N T L I M I T A T I O N S
C2.2 CEMENT CONSTITUENTS Silica fume is included in this edition of the
Standard. Its use has been well documented in recent years and the requirements for its
properties are specified in AS 3582.3.
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The use of supplementary cementitious materials generally has progressively increased
over the last 20 years. There are good reasons to support this growth as follows:
(a)
Improvements in certain properties of both plastic and hardened concrete over those
achievable with portland cement alone.
(b)
Economy, since the supplementary cementitious materials are industrial by-products
which are often cheaper than cement.
(c)
Energy conservation, reducing the demand for the energy-intensive manufacture of
cement.
(d)
Reduced carbon dioxide emissions to the atmosphere due to reduced portland
cement manufacture.
(e)
Resource conservation, reducing the demand for the raw materials for cement
manufacture.
(f)
Reduction in the pressure on landfill for disposal of the otherwise waste materials.
(g)
There is usually the potential for enhanced strength gain after 28 days.
Good curing practice is essential to develop the strength potential of any concrete, and
this is especially so when supplementary cementitious materials are used. Generally
concrete made using mixtures of portland cement and supplementary cementitious
materials attains early strength more slowly than that made with portland cement alone.
C2.3 AGGREGATES Because the Australian Standard for aggregate, AS 2758.1,
includes a number of alternative options, it cannot be used on its own as a specification
for contract purposes. The options selected as appropriate to the intended use or
performance will therefore need to be separately specified. Usually it is the supplier s
responsibility to specify aggregate quality.
C2.4 MIXING WATER The range of impurities to be monitored has been reduced by
removing limits for chlorides, sulfates, sulfides and sodium equivalent. The rationale for
the change is that limits are elsewhere specified for chloride and sulfate ions in the
hardened concrete which embrace impurities introduced from all sources including water.
Test methods have been updated to include where appropriate, methods not previously
available.
C2.6
BULK STORAGE OF MATERIALS
C2.6.1 Cement constituents The requirement to use bagged cement in the same
chronological order as it was received has been eliminated. The requirement was absolute,
and as such could not be achieved in practice. It was considered the commitment to
achieve the specified quality requirements, particularly strength, would preclude any need
to expressly specify what is commonly known and observed as good practice in the use of
bagged cement.
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C2.7 LIMITATIONS ON CHEMICAL CONTENT OF CONCRETE Some small
amounts of chlorides can be introduced from water, cement, aggregates and admixtures.
The limit of 0.8 kg/m3 of concrete for chlorides was selected after a review of extensive
literature on the subject, especially from North America and Europe where the problem of
corrosion of reinforcement had reached alarming proportions, largely due to the use of deicing salts.
Experience indicates that sulfate levels above 5% by weight of cement may impair
durability.
The method of sampling for testing the chloride or sulfate contents is specifically intended
to exclude any contaminants introduced after the concrete has been discharged from the
mixer.
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If further contamination during or after placing is suspected, further samples of in situ
concrete should be tested. The issue of compliance of such samples lies beyond the scope
of this Standard.
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S E C T I O N
C3.1
C 3
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AS 1379 Supp1—1997
A N D
E Q U I P M E N T
BINS AND SILOS
C3.1.1 General Requirements have been reworded to include expressions such as ‘as
far as practicable’, as it was impracticable to comply with the previous wording expressed
in absolute terms. Bins and silos in most cases should carry prominent labelling of their
contents to prevent the accidental addition of material belonging to other storage.
C3.2
WEIGHING EQUIPMENT
C3.2.2 Accuracy The current clause allows calibration to be done by an ‘accredited’
rather than an ‘independent’ organization, reflecting the fact that many suppliers have
competent in-house calibration facilities.
C3.3
LIQUID DISPENSING EQUIPMENT
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C3.3.2 Accuracy of metering Water is usually added in two or more increments,
because the variability of moisture contents in aggregates storage precludes the exact prior
determination of the quantity of water necessary to produce a specified slump.
The first and principal addition of water is that added concurrently with the cement and
aggregates using weigh batching or rugged high capacity volumetric meters usually
protected by filters. This is regulated to produce a slump not exceeding the value
specified. In all cases an accuracy of at least ±2% can be relied upon from such
equipment.
The next addition is an adjustment decided upon after the mixing has proceeded
sufficiently for an experienced operator to assess the consistency of the batch and estimate
the further addition, if any, necessary to produce the specified slump. In larger pre-mixed
concrete plants this may be done through a different meter to that used for the first
addition, in order to make the loading station available to the next mobile mixer and
maintain production. A ‘slump stand’, being a freestanding standpipe with a suitable
platform for the operator to view the batch is a common installation used for this purpose.
The measuring device may be less accurate than that used for the first addition, but should
be sufficiently accurate to ensure that the total of the two increments is recorded to an
accuracy of at least ±2%. The second addition would usually be less than 10% of the first.
Again in a premix concrete operation, water may be added after the concrete leaves the
plant, and if so an estimate of the quantity added by the operator may be the only means
of assessing the quantity added due to the unreliability of truck-mounted water meters.
C3.4
MIXERS
C3.4.1(a) Performance The concept of testing for uniformity of mixing has been
substantially rationalized in this revision. The primary thrust now is to validate the
capacity for each different model of mixer in use to mix uniformly. Once a particular
model of mixer has been proven to mix concrete satisfactorily, it can safely be assumed
all such mixers of that model will continue to do so unless they are worn to a degree that
will preclude their continued performance or hardened concrete has been allowed to build
up in them.
Full uniformity tests are time consuming and expensive. To routinely do them when there
is no reason to expect that the mixer is not mixing efficiently has no value.
The thrust of the current clauses is —
(a)
to prove new mixer types by exhaustive testing of prototypes;
(b)
to validate existing mixer models by exhaustive testing of one of the series;
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(c)
to regularly inspect for wear and cleanliness in place of wasteful repetitive
uniformity testing at arbitrary intervals;
(d)
to effect necessary repairs and cleaning promptly when the need is perceived; and
(e)
to re-assess mixers by test after any major repair (e.g. design alteration).
The last item is in recognition that repair can involve the complete rebuilding of the
mixing vessel with its baffles and fins. A major repair is seen to be any which may have
the potential to reduce the mixer s uniformity of mixing. This would include a drum
rebuild under less stringent control than would be found at the original supplier’s factory,
but would not include the complete replacement of a drum with a new unit manufactured
by the original supplier.
An alternative and less rigorous uniformity test is called for after minor repairs, and in
cases where inspection raises doubt about the mixer’s capacity to mix uniformly. This
involves all but the comparison of coarse aggregate content and the mass per unit volume
of the air free mortar.
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The importance of good practice in charging the mixer correctly must be recognized as a
vital prerequisite for uniformity of mixing. Large mixers such as mobile mixers used in
the premix industry may have difficulty mixing uniformly if care is not exercised in the
sequence of loading materials. A reasonably uniform blending of the solid batch materials
should be achieved as they enter the mixer.
If poor uniformity is apparent without any clear reason indicating the condition of the
mixer, loading practice should be examined.
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S E C T I O N
C4.1
C 4
P R O D U C T I O N
AS 1379 Supp1—1997
A N D
D E L I V E R Y
GENERAL
C4.1.2 Method of measuring quantities of ingredients This edition amendment
removes some unintentional ambiguity present in the 1991 edition. The words
‘proportioned by mass’ have been replaced with ‘measured by mass’ and the words
‘directly or indirectly’ have been deleted.
Volume batching of solid ingredients is now only permissible for concrete with a
characteristic strength of 15 MPa or less.
The use of timed flow of material through a gate opening intermittently calibrated by
weight is not considered to constitute measurement by mass.
C4.2 BATCH PRODUCTION
C4.2.1 Tolerances on batch ingredients
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C4.2.1.1 Ingredients other than water Whatever tolerances apply, the supplier is also
constrained by the quality and yield requirements unequivocally expressed in Clause 1.8.
Indeed, given a philosophy of performance rather than prescriptive specifications, the
need for many of the prescriptive clauses still remaining in this 1997 Standard could be
debated.
Regardless of this argument, the barriers to compliance with the tolerances in the 1991
edition were identified and this edition addresses two issues which arose. These are as
follows:
(a)
Multiple cementitious materials and aggregates The 1991 edition was less than
clear as to whether the batching tolerances were applicable to each separate
aggregate size and cementitious material type of the total quantities.
This edition addresses this issue. It expresses explicit limits for the total of all
cementitious materials and for each individual cementitious material. It requires
compliance for the total mass of all aggregates, the total mass of fine aggregate and
the total mass of coarse aggregate. It does not call up limits on separate
components, if any, of fine or coarse aggregates.
(b)
The quantification of tolerances The provisions of the 1991 edition were
unattainable with current plant. Two issues are relevant, material in free fall and
variation in moisture contents of aggregates, as follows:
(i)
Material in free fall The flow of material into a weigh hopper does not stop
the instant a gate or valve is closed. Some material will be falling between
the gate and the surface of the material already in the weigh hopper, referred
to as material in free fall. The amount of material in free fall has to be
anticipated by both manual and computer controlled batching operations,
interrupting the feed of material before the intended mass has reached the
weigh hopper and registered on the scale or digital readout.
The allowance for free falling material is intuitive for a manual operation,
and preset for automated plants. The free falling mass for any one material
varies with the distance from the gate or valve to the surface of the material
already in the weigh hopper, the moisture content of aggregates, particularly
of fine aggregates, while humidity and fineness will affect the amount of
cementitious materials in free fall.
The efficiency of automated plants in anticipating the mass in free fall has
not been found to be better than that of an experienced manual operator,
although the human variability may be greater.
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Variation in moisture content of aggregates The weight of each aggregate
to be batched has to be adjusted to allow for its moisture content. No
sufficiently fast and accurate means of measuring moisture content of
aggregates has been developed to achieve this.
By compounding the moisture content inaccuracy (a percentage of the mass weighed) with
mass in free fall, (a constant for each weighing) a range was generated within which the
designed mass of material could be relied upon to fall.
Adverse combinations of tolerances for aggregates and cementitious materials, i.e.
overbatching aggregates and underbatching cement, were then examined. A tolerance of
+0.2 to -0.4 in the overall aggregate to the cementitious materials ratio was used to arrive
at the proposed figures. To achieve this it was necessary to ‘skew’ the tolerances,
allowing a greater negative tolerance in measuring aggregates and a greater positive
tolerance when measuring cement.
Suppliers have a further restraint imposed from Clause 1.8.2 which specifies minimum
‘yield’, i.e. the assurance that the volume of concrete supplied is substantially that stated
on the identification certificate (or delivery docket). Underbatching of both aggregates and
cement could result in breach of this Clause. Management of yield properly belongs in the
supplier’s quality management system.
C4.2.1.2
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(a)
Water
Two methods of control currently in use are as follows:
By control of slump The importance of water control in the production of quality
concrete is well and widely understood. The fact that the predominant method of
controlling water has been by achieving the desired slump and NOT by measuring
the water is not so well or widely understood.
This reality is due to the lack of any sufficiently responsive and accurate means of
measuring the moisture content of aggregates, discussed in Paragraph C4.2.1.1(b)(ii)
above in relation to the batching of materials other than water where it creates a
similar problem.
The control of slump is an indirect control of water, and in practice is more reliable
for making adjustments from batch-to-batch throughout a day than even the best
available measurements of water content. When accompanied by periodic checks
that the total batch water is within the tolerances set for the mix design, it has
proved for many years adequate to control the strength of concrete.
The tolerances specified in Clause 5.2.3 are intended to allow for human error in the
assessment of slump. The supplier should aim to achieve a mean slump that is close
to the specified slump. The supplier should not aim to achieve slump results higher
than the specified slump.
(b)
By control of water-cement ratio To meet a specification for water-cement ratio, or
total water content, it becomes necessary to measure and record the total water
content. Repetitive sampling and measurement is necessary to detect variations
within the stored material. This involves reliance on automatic devices of limited
accuracy or the attendance of additional personnel at additional cost. It may also be
necessary to restrict production rates in order to make the measurements.
It should be said that the value of the enterprise is questionable because of the limitations
to the frequency of sampling to detect variations in the moisture contents of material even
within a batch and the variation possible in the actual measurement, automated or manual.
Allowing for these variations in measurement accuracy and imperfect sampling, in the
best case measurements of moisture content cannot be relied upon to be more than ±1.0%
in fine aggregate and ±0.5% in coarse aggregates. The effect in a cubic metre of concrete
of these errors may be as much as 15 to 20L, or up to 10% of the total free water.
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Control of water by control of slump would usually result in less variation in total water
content than attempting to monitor added water. Any procedure involving control of water
content by measurement also has to be augmented by procedures to ensure the slump is
within the tolerances in Table 6.
The specification of the tolerance appropriate for water-cement ratio is dominated by the
achievable accuracy in the control of total water. The quantity of water per unit volume of
concrete is relatively constant over a wide range of mix designs. These considerations
gives rise to the logic that any tolerance for water-cement ratio is best expressed as a
percentage of the target water-cement ratio, and not as a constant. As discussed earlier the
water content per unit volume of concrete is estimated to be subject to a variation of 10%.
This possible variation determines the selection of a tolerance of ±10% of the target value
of the water-cement ratio. This neglects the compounding effect of variations in the
targeted cement content which would call for a greater tolerance.
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Examples of the absolute value of the tolerance are —
Specified value of w/c ratio
Tolerance
0.60
±0.06
0.35
±0.035
A difference in philosophy of the specification of water-cement ratio exists. The supply
industry prefers that the water-cement ratio be specified as a median value. Some public
authorities prefer to specify a maximum value. By way of compromise both practices were
admitted.
If the water-cement ratio is not specified to be a maximum value complying ratios will
range 10% either side of the specified value.
Alternatively if a maximum water-cement ratio is specified, complying ratios will range
from the specified value to 20% less than the specified value.
C4.2.2
Batch mixing
C4.2.2.1 General The 1991 edition required mixers to be completely discharged before
being loaded with a new batch. Although probably not the intention when drafted, this
could be construed to mean a complete washing out of the drum to remove even the
mortar coating remaining after a batch is discharged. Wording has been amended to
remove this possibility.
The coating of mortar remaining after all concrete has been discharged is arguably best
left in the mixer, as after discharge of the next batch a similar coating will remain, which
will be taken from the ingredients of the next load if the mixer is completely free of all
material prior to loading.
Special needs to completely empty and clean mixers occur in some circumstances such as
when fibre or colour are used intermittently in a mixer.
Aside from the debate, if any, on the mortar coating remaining in the mixer, if all mixers
were to be washed out completely prior to loading a new batch, existing waste disposal
units at all plants in Australia (with very few if any exceptions) would be grossly
overloaded, resulting in illegal discharges into drainage systems. Installing substantially
larger units is precluded by site area restraints in most plants and in any case their
economic viability is severely prejudiced by the capital and operating costs of
substantially larger disposal facilities.
The usage of water would also increase dramatically. If trucks are washed out after every
load, and without the recycling of water, the total use of water for washing and for
inclusion in the batch is approximately three times that contained in the batch.
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In some cases, even returned concrete can be allowed to remain in the mixer safely.
Suppliers’ quality assurance systems are designed to control the judgement and
procedures used. These are company specific, and would prove cumbersome to include in
this Standard. In the last analysis the supplier is constrained by the performance
requirements of all the other clauses in this Standard and the project specification.
In particular, the supplier has the obligations to —
(a)
satisfy the strength criteria;
(b)
deliver concrete with a truck life to ensure the ability to place and compact concrete
within a practical time; and
(c)
guarantee the yield.
Suppliers state that these constraints have in the past and will continue to provide the
protection needed to ensure the integrity of the concrete delivered, without breaching
environmental regulations or incurring a substantial and unnecessary cost burden on the
product to avoid the breaches.
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Admixtures recently available appear to prolong the life of plastic concrete for long
periods, such as overnight. Currently their use cannot be supported by sufficient data, but
in future their use may be permitted by an amendment or a revised Standard if adequate
documentation of their satisfactory performance becomes available.
C4.2.3 Addition of water or admixtures to a mixed batch Paragraph C3.3.2
discusses the various stages of water addition in the process of production of concrete.
For the purposes of this Clause, the batch is deemed to be ‘mixed’ after it leaves the
plant, and the addition of water en route to the site or after arrival at the site is dealt with
by this Clause. If water is added before the commencement of discharge either on site or
en route to the site, the Standard requires adequate mixing prior to commencement of
discharge. All such additions of water before commencement of discharge are deemed to
be at the supplier’s initiative and under his sole control.
The commencement of discharge is a contractually significant point in the process of
supplying a batch of concrete. Water added after commencement of discharge may be at
the initiative of the customer and negate the supplier’s warranty for the material. Such
additions also carry greater potential risks dependent on the time between the
contemplated addition and the original commencement of mixing.
For these reasons the commencement of discharge is critical and needs some definition.
On occasions a small amount of the batch may be discharged, say 0.2 m3, before it is
apparent that the slump is too low. Addition of water at this stage is considered to be no
different to the addition prior to any discharge. However, after discharge beyond this
point commencement of discharge is said to have commenced and the Standard calls up
additional assessment, testing and recording procedures.
This distinction between additions prior to and after commencement of discharge seeks to
regulate the irresponsible addition of water to facilitate handling, which will cause the
consistency of the batch to exceed the specified tolerances. To this end the Standard calls
for determination of slump when water is added after commencement of discharge.
In some regions industrial custom and practice requires the presence of an industrially
authorized tester on site to determine slump by the Standard method. Such an individual
may not be readily available.
It is also possible that timely availability of personnel or equipment preclude the
determination of slump by the Standard method.
In such cases an assessment is accepted in lieu of a measurement. In other circumstances
a measurement would always be preferred.
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The quality assurance intended to be provided by the Standard is lost if samples are taken
for the casting of test specimens, and then water added. Clause 4.2.3(c)(ii) precludes this
practice.
C4.2.4 Period for completion of discharge The Standard would be incomplete if no
limit was placed on the period for completion of discharge, however the ‘correct’ limit is
incapable of definition for all conditions. Temperature plays a great role in the speed of
the chemical reactions between cement and water, as do the properties of the batch
ingredients. The clause for these reasons does not prescribe 90 min as an inflexible limit.
C4.3
C4.3.1
CONTINUOUS PRODUCTION
Batching
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C4.3.1.1 Solid ingredients Periodic assessment of flow rates of solid ingredients from
storage into the production stream is not considered to constitute measurement of
materials by mass. A variety of acceptable procedures such as integrating belt weighers
exist. Continuous measurement by mass is critical as the flow characteristics of solid
ingredients change frequently.
C4.3.1.3 Accuracy of batching rates for cementitious materials To avoid adverse
combinations of tolerances for aggregates and cementitious materials, i.e. overbatching
aggregates and underbatching cement, a ‘skewed’ tolerance has been adopted as for batch
production to ensure maintenance of a tolerance of +0.2 to -0.4 in the overall aggregate to
cementitious materials ratio.
The discussion in Paragraph C4.2.1.1 on the need to sustain a conforming level of yield in
batch production applies equally to continuous production.
C4.3.1.4 Accuracy of batching rates for coarse, fine, and total aggregates The same
provisions for accuracy of component ingredients is used as in the clauses on batch
production.
C4.4
DELIVERY
C4.4.2 Temperature at point of delivery Where the ambient temperature is below
10°C or above 30°C, measures such as heating or cooling the water or aggregates may
need to be adopted in order to comply with the requirement that delivered concrete has a
temperature at the acceptance point of not less than 5°C nor greater than 35°C.
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C5.1
22
C 5
S A M P L I N G A N D
C O N C R E T E
T E S T I N G
O F
GENERAL
C5.1.2 Grouping of plants For some purposes of the Standard, different plants are
allowed to be grouped and considered as one plant.
For compliance with the statistical compressive strength criteria of Section 6, relatively
wide grouping is allowed. This grouping only prevails for the purpose of calculating a
standard deviation to apply to each of the plants in the group, where a minimum of 30
results is needed to obtain a value of standard deviation in which a fair degree of
confidence can be held.
Standard deviations for small groups would usually be less than for larger groups. Since a
higher standard deviation increases the values to be achieved to comply with the
acceptance criteria, a supplier s decision on grouping of plants will have to take account
of the disadvantages of large groups.
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A second permissible grouping is for chemical contents and shrinkage compliance. In this
case grouped plants are required to use similar materials to give confidence that the
measurement obtained from one plant will be those which would be obtained from others
in the group.
C5.2
SLUMP
C5.2.1 Frequency of testing Slump is almost always a parameter specified in the
order. Further, as discussed elsewhere in this commentary, assessment of slump is usually
the primary means of controlling the amount of water in concrete, an assessment being
made shortly after batching to fine tune the adjustment to water content.
For these reasons, slump needs to be assessed for every batch of concrete produced.
However, the measurement of slump in accordance with AS 1012.3 is not performed on
every batch, nor can it be without an expensive restructuring of manning levels in
concrete plants.
Experienced operators such as batchers or operators of truck-mounted mixers develop skill
in estimating slump from the appearance of the mix and the mechanical behaviour of
mixers to a point where satisfactory control is achieved without the need to measure the
slump of each batch. Alternatively, where the calibration of a slump meter is possible this
device may be used to complement the slump cone measurements and provide information
on each batch. Experience and skill is also vital when slump is determined in accordance
with AS 1012.3, as the test result can be corrupted by seemingly minor deviations from
the standard procedure.
It is uncommon for skill in estimation or measurement of slump to be developed by
people not continuously involved in observing and working with concrete.
When strength tests are to be taken from a batch containing superplasticizers slump
assessment before and measurement after the addition of superplasticizers is strongly
recommended.
C5.2.2 Determination of slump For some batches slump meters provide an alternative
method for slump assessment. Some slump meters are attached to the hydraulic system of
the truck-mounted agitator and measure the energy required to rotate the drum at mixing
speed. The slump meter reading is unique to the truck, batch size and mix proportions.
The slump meter may be useful for quality control rather than compliance testing and
should be supplemented by normal testing.
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C5.3 STRENGTH The parameter upon which to assess compliance for quality in
respect to strength is predominantly the 28-day characteristic strength, according to the
detailed criteria specified in Section 6.
When flexural or indirect tensile strengths are specified, rules are expressed to determine
an equivalent mean compressive strength by which the grade can be monitored. The
regime for monitoring characteristic compressive strength is so well established and
understood there is obvious merit in adopting a reliable conversion to enable flexural or
indirect tensile strengths to be monitored the same way.
Alternatively, when a strength other than 28-day characteristic strength is required as the
principal quality parameter, the specifier is free to develop a monitoring regime under
rules stipulated to achieve the same statistical operating characteristic as that upon which
Section 6 is based.
C5.3.4 Action to be taken on noncompliance for strength As a matter of policy
contractual issues are not included in Australian Standards. None the less Australian
Standards are frequently referred to or annexed in one way or another to contract
documents.
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This Standard is often directly referenced in the suppliers standard quotation forms and
hence becomes an element in the simplest contracts, such as those created by a letter of
offer and an expressed or implied acceptance.
Further it is caught by references to it, indirectly via AS 3600, in the Building Code of
Australia (BCA). Very little construction is not caught by the force of law attaching to the
BCA. As a result the majority of formal construction contracts will directly or indirectly
require compliance with this Standard.
The statistical process of production assessment in this Standard does not readily translate
into appropriate procedures in the event of noncompliance. While more sophisticated
contracts may specifically deal with procedures to apply in the event of noncompliance, it
cannot be expected that all contracts, expressed and implied, would be so carefully drawn.
It is desirable then that this Standard has some provisions that permit a linkage with the
contractual consequences of noncompliance while still maintaining the exclusion of
specifically contractual issues from the Standard intrinsically in compliance with policy of
Standards Australia.
In the event of noncompliance, the 1991 edition of the Standard was potentially very
onerous in its application. The principles of Section 6 represent a statistical process for
monitoring the quality of production on all projects within a particular production
interval. It could be construed that ALL concrete produced in the production interval of
the grade which did not comply should be rejected. This has the potential to span over a
period from one to several months and cover thousands of cubic metres of concrete. It
could not in any practical sense be enforced. In fact no instance is recorded of the matter
arising, although it is certain that in the 5 years of the Standard s application concrete
has failed to conform.
The problem to be addressed with this Standard was seen to be one in which that
compliance is determined for a production ‘lot’ of concrete of one grade produced in a
production interval of one or more months, without any relation to the projects on which
the concrete was used.
The potential interpretation of the 1991 edition that all concrete in a production interval
was to be rejected, or even made liable to rejection was completely unacceptable to the
supply industry.
This Clause addresses the problem by providing the supplier with procedures to be
implemented to restrict, where appropriate, the potential for rejection of concrete to a
subset(s) of the production of all the grade in the production interval.
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The burden of implementing these procedures rests on the supplier. None the less, if
calculations are necessary to determine if the noncomplying concrete is of sufficient
quality so as not to prejudice the durability or structural adequacy of the structure, the
designer will logically be expected to undertake such calculations.
C5.5 CHLORIDE AND SULFATE CONTENT There is a mismatch in the units used
to express chloride and sulfate contents in the Standard test procedures and those
generally used to express the accepted safe levels of each in concrete. It is hoped that
more compatible units may be adopted in the Standard test procedure in due course.
Meanwhile this Clause expresses the means by which the test results should be converted
to those units used to express permissible limits in this Standard.
C5.6
DRYING SHRINKAGE
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5.6.1 Drying shrinkage of normal-class concrete The test specimens for drying
shrinkage are easily damaged and care needs to be exercised when field sampling is
undertaken. The Standards for the test methods, AS 1012.13, specifically address all the
necessary issues in technique. Because of the particular sensitivity of this test procedure it
is especially important that the Standard is assiduously applied. Remote areas are
particularly prone to bad practices if experienced testing staff is in short supply.
The supply industry expresses a preference for control shrinkage sampling to be done in
accredited laboratories on laboratory mixes simulating the field mix, to reduce the
potential variation in results arising from sampling and handling procedures.
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S E C T I O N C 6
S A M P L I N G , T E S T I N G A N D
A S S E S S M E N T F O R C O M P L I A N C E O F
C O N C R E T E S P E C I F I E D B Y C O M P R E S S I V E
S T R E N G T H
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INTRODUCTION
(a)
Summary The assessment provisions in AS 3600 (1988) and AS 1379 (1991) were
strongly related to the concept of plant-based production control using a controlled
grade for which reasonable numbers of test data would be available. A complex
variety of provisions were given for other grades at the plant and for smaller plants
along with appropriate project control rules. Although technically sound there have
been practical problems. These provisions have been greatly simplified by
combining all the production control systems into one procedure that can deal with
a wide range of available sample numbers. This overcomes problems previously
encountered with very small production runs and production runs separated by long
periods of time. An important change is that the production interval length is
defined only for the controlled grade and the assessment of this grade and all the
other associated grades at the plant are made once only and at the same time — at
the end of that production interval.
(b)
Normal distribution In order to understand quality assurance testing and to
evaluate some of the alternative strategies, it is necessary to have some appreciation
of statistical concepts. The characteristic strength, fc′, is defined as the strength that
would be exceeded by 95 percent of the test results. Therefore, this definition
accepts that for satisfactory concrete 5 percent of results will be less than fc′. It has
been found that the long-term distribution of concrete test strengths approximates a
normal distribution. From the normal distribution, the definition of fc′ requires that
the target (average) strength be fc′ +1.65σ where σ is the standard deviation of the
concrete population. In terms of proportion of defectives the use of a normal
distribution may be a little severe as industry experience is that errors tend to be
more often on the high side rather than low.
The control method adopted compares the mean fcm of a group of results with a
threshold level in the form fc′ +kcs.
The definition of the threshold level has to consider the variability from determining
the mean of the population using a small sample and from the need to estimate the
standard deviation of the entire population, σ, using the standard deviation of the
sample, s. These uncertainties result in the acceptance threshold level fc′ +kcs being
dependent upon the number of tests.
(c)
Supplier’s and customer’s risk When a decision on the acceptability of a unit or
lot of concrete is made, based on limited data, there is considerable uncertainty and
the concept of who receives the benefit of the ensuing doubt becomes important.
The customer would like to receive cast iron assurances that the concrete is not less
than the specified strength. The supplier would expect that if the target strength is
just satisfactory then there would be no chance of noncompliance or rejection from
test results. Unfortunately, since testing is expensive and samples are limited, both
parties have to accept a compromise situation. However, since public safety is allied
with the customer’s interest, that compromise must take this into account. In the
production control methods in Section 6, the benefit is technically given to the
producer. However, basically the clauses are set up primarily to reject concrete that
is significantly defective, protecting the consumer and safety.
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The customer’s risk is defined in the alternative assessment procedures in
Clause 6.6(b) which are the basis of Section 6. This states that ‘concrete with a
proportion defective of 0.30 shall have a probability of rejection of at least 98%.
Ideally the customer would prefer a 100% chance that any concrete with more than
the specified 0.05 proportion defective should be rejected, but uncertainty prevents
such absolutes. Defective in this sense means test values below the specified grade
value of f ′c.
It may be thought that a value of strength so low that the proportion defective is as
high as 0.30 would be unsafe but a quick calculation using the normal distribution
would imply that such concrete would have a target of fc′+ 0.53σ compared with the
desired value of fc′ +1.65σ so the difference is only 1.12σ or, with a standard
deviation of say 3 MPa, only 3.4 MPa. Although by no means insignificant, such a
low strength is unlikely to seriously affect the safety of the structure. On the other
hand, there is little evidence to suggest that this is too severe on suppliers.
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The suppliers risk is also implied in Clause 6.6(a) as ‘concrete with a proportion
defective of 0.05 should have a probability of acceptance of at least 50% .
This means that the producer has to accept that if the concrete is up to the correct
grade, i.e. 0.05 proportion below the specified value, then there is still as much as a
50% chance of noncompliance. What is worse is that with low sampling rates the
chance of noncompliance may be higher and barely good concrete will more often
than not be rejected. Small samples create uncertainty and that uncertainty will lead
to risks for both suppliers and customers. To avoid these high risks some adjustment
in the target strength is necessary and suppliers will need to adapt to this trade-off,
particularly where low sampling rates are involved. On the other hand this
requirement infers that concrete that is just below grade still has a 50% chance of
acceptance. Other structural materials impose much more onerous statistical
conditions on suppliers.
As can be seen from the above discussion the distribution of risk is even-handed
with the consumer accepting the risk that the concrete could be a little below grade
but confident that concrete significantly below grade will be rejected, while the
producer has to accept the risk that even satisfactory concrete may be rejected,
particularly if sampling rates are low.
(d)
Basic principles of assessment clauses The basic principles of production
assessment for a particular grade are that where a large number of samples of a
grade are obtained during a production interval and their strengths determined, the
mean grade strength (fcm) should be not less than the specified characteristic strength
(f ′c) plus 1.65 times the standard deviation (s) of the sample strengths determined
for that interval.
Where a limited number of samples are obtained during a production interval, it is
not possible to directly confirm that the mean grade strength and an alternative is
taken of assuming it is correct unless the tests on available data are not consistent
with this hypothesis. Specifically if the strength is so significantly low that the
defective quantity could reach 30% then the concrete should almost certainly be
rejected. Thus concrete represented by the tests is deemed not to comply if the mean
grade strength for the relevant production interval falls below a threshold value
equal to the specified characteristic strength (f ′c) plus the standard deviation of the
sample strengths (s) multiplied by a factor (kc) which is dependent on the number of
samples obtained during the production interval. Hence compliance requires that —
fcm ≥ f ′c + kc s
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Since there are many mixes supplied by a plant the above requirement is applied
mainly to a frequently tested mix designated as the ‘controlled grade’ with the other
‘associated grades’ assumed to be subject to similar mix design and control
practices.
It must be appreciated that satisfactory concrete can fail this test and it may
sometimes be necessary for the average strength of the concrete to be even greater
than the minimum required to reduce the occurrence of random failures.
(e)
Production assessment vs Project assessment Production assessment using the
relatively large number of test data available to the supplier is the cornerstone of the
requirements of the Standard. Project assessment is also included, but the provisions
are less statistically rigorous, as such assessment is intended only as a
supplementary check rather than an assurance of quality. Engineers are strongly
recommended to rely generally on production assessment with project assessment
only used as an extra check for critical elements or special-class concrete.
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C6.1 GENERAL REQUIREMENTS The general requirement is that all concrete of
strength likely to be structurally important (grade 20 MPa or more) shall be assessed by
the supplier by a system of production assessment which invariably will involve
Clause 6.3. When project assessment is specified then additional assessment by Clause 6.5
will apply. Clause 6.6 allows for a rarely used alternative means of production and project
control.
Where project assessment is specified, then the testing and assessment is normally carried
out by the prime contractor or a subcontractor. The concrete supplier may be used for
project assessment if there is an agreement between the supplier and the party responsible
for project assessment.
C6.2
SAMPLING AND TESTING
C6.2.2 Sampling The point at which samples are taken is common to production and
project assessment. It is not intended that samples for production assessment be taken
prior to the normal point of discharge from the mixer.
C6.2.5 Test strength of samples Provision has been made for the rejection of test
specimens which differ significantly from results expected when good testing practice has
been followed. The two rejection criteria for individual test specimens are based on —
(a)
cylinder strengths which are significantly different from the expected average, i.e.
deviating by greater than ±3s: and
(b)
cylinder strengths from one sample which show excessive difference.
The first of these is a new requirement and effectively removes a result which has an
extremely low probability of belonging to the sample group, from being included in the
statistical analysis.
Recent test data should be used to calculate the expected average strength based on the
equation, fcm = f ′c + 1.65s.
The rejection criteria for the range of cylinder strengths within a sample is similar in
principle to that of AS 1480 except that the range has been halved, reflecting improved
testing practices.
The reduced acceptable difference between test specimens was evaluated from more that
3000 sets of test results, taken over a period of 3 years during the construction of the new
Parliament House. The data came from 3 separate testing laboratories, testing 5 grades of
concrete supplied to the project by 3 different manufacturers. Evaluation of the difference
between the 28-day strengths of companion specimens showed that, for a maximum
difference of 2 MPa, the probability of obtaining acceptable pairs of specimens is in the
range of 97% to 99%.
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When no cause can be determined for excessive range, the lowest cylinder strength is now
to be rejected. These modifications are designed to minimize dispute over which test
strengths are to be deleted from analysis of test data.
C6.3
PRODUCTION ASSESSMENT
C6.3.1
C6.3.1.1
Basic requirements of production control
General requirement
This Clause is mainly a directory to the other clauses.
C6.3.1.2 Designation of grades The system of control is based on the concept that only
one grade of a plant’s production is a controlled grade. This grade should generally be the
most commonly tested grade over 6 months but since this information is not known in
advance this Clause permits some latitude. Certainly it will be in the supplier’s interest to
adopt the most frequently tested grade. The controlled grade can vary from one production
interval to the next.
For this controlled grade, 10 samples per production interval which can be up to three
months, should be taken; but there is no actual minimum. However, the assessment is
structured so that there is an implied penalty for lower sampling rates.
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All other grades are associated grades.
C6.3.1.3 Frequency of assessment An important change is that all grades both the
controlled grade and the associated grades are assessed on the basis of the mean strength
at the end of the production interval of the controlled grade.
This has the disadvantage that some small sample sizes may result for the associated
grades but the advantage of a single clear-cut assessment period with no problems of
multiple assessment of the one lot of concrete.
C6.3.1.4 Assessment factor The Clause for compliance of a controlled grade is derived
from some complex statistics due to Manton-Hall using the recommendation for
compliance of Clause 6.6(b) discussed in the Introduction.
The compliance test is based on the mean grade strength determined each month from the
tests over the production interval being greater than a threshold value of f ′c + kcsc. The
value of kc is given in Table 7 where it can be seen to vary from 3.2 for 4 samples to 1.25
for 15 or more. (It effectively combines the earlier (AS 1379 1991) production assessment
criteria with that for non-standard strength grades.)
The use of a compliance criteria based on a defined probability of noncompliance of a
0.30 defective concrete using the mean and standard deviation determined from a limited
sample demands that the variability of the sample standard deviation must be taken into
account. Usually this can be done using the t-distribution which includes an allowance for
the variability of the standard deviation on the value of the mean of a sample. However,
as the criteria in terms of the 0.30 defective level also includes an estimate of the standard
deviation, a more complex non-central t-distribution is needed. Computations using a
program developed by Manton-Hall produced the numbers in Table 8 which were included
in AS 3600 (1988), but in the relatively obscure Clause 20.7.3. Certainly it is not possible
to verify these numbers using simple normal distribution, although it is possible to check
the results using simulation.
The same assessment factor is used for the associated grades as well as for the controlled
grade. This is based on the assumption that all grades at a plant are subject to a similar
process of control so that the standard deviations are related and any adjustments to the
controlled grade should be made to all grades. Because the numbers involved in the
associated grades are lower the risk that substandard concrete will be accepted is higher
than desired while the risk to the producer of satisfactory concrete being rejected is also
higher. This is not ideal but the alternative of spreading the assessment over a long period
in order to obtain sufficient data also presents problems.
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One important aspect is that the higher thresholds for the lower sampling rates implies
that unless the producers are to be plagued by noncompliance they should use higher
target strengths.
C6.3.1.5 Assessment of grade The assessment is based on the mean fcm of the test
results for the entire production interval. This assessment is carried out on all grades at
the same time — the end of the production interval for the controlled grade. Moreover the
threshold value given is based on the controlled grade and the number of tests available in
that grade.
C6.3.2 Grade being assessed The assessment procedure is based on the concept of
there being one population of concrete represented by a single mix. For practical reasons
some flexibility is needed in interpreting this ideal situation. The strength grade being
assessed has at least the common characteristic of the same required characteristic
strength. However, the clause permits considerable flexibility as to what constitutes a
strength grade. It can include variations in mix type aggregate size and cement types and
subject to Clause 6.3.6, can even come from different plants if operated by a single
supplier. It can include special-class concrete as well as normal-class and of course,
concrete with various slumps.
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It need not include all concrete of that grade as subsets are permitted. Note that for
sampling, compliance and all the other requirements of the Section, such subsets are
treated as a separate strength grade.
Ideally the assessment should be based on a single plant and a single mix. The extension
beyond this assumes certain common practices of adjusting and controlling the strength.
From the supplier’s point of view, widening the definition of strength grade will possibly
increase the standard deviation, although there are considerable advantages in threshold
levels for increasing the number of samples. Obviously the supplier is the appropriate
party to determine which mixes are to be included in the grade.
C6.3.3 Sampling frequency A sample consists of two or three cylinders. The cost of
sampling and testing is not insignificant and the rate is therefore a compromise between
cost and statistical accuracy while minimizing the volume of concrete at risk from failure
to comply.
A concession is offered for 20 MPa grade concrete where production is higher and
sampling rate is correspondingly high. However the reduction in sampling rate after 15
samples per month are achieved should still recognize the need for the sampling to be
random or at least uniform through the month.
C6.3.4 Production interval The choice of the production interval is a compromise
between the volume of concrete at risk, the need for frequent reports and the influence of
small sample sizes on rejection rates. If at least 10 samples are available the producer can
choose the production interval within wide limits of two weeks to three months. It must
be recalled that the production interval is set for the controlled grade but applies to all
associated grades as well.
Where the production is low so that 10 samples of the controlled grade are not expected
in the three months then the production interval is set at three months even though a
lower number of samples will result. The minimum sampling rate will influence the
number available.
Where the production interval exceeds one month the producer may choose to issue
interim assessment of the concrete based on the samples available over a period equal to a
production interval. Such reports would be advisory and could not lead to a situation of
noncompliance.
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C6.3.5.2 Sample size for the standard deviation of a controlled grade Clause 6.3.5.2
includes only minor modifications and provides a practical method of determining the
standard deviation. The basic calculation is on the controlled grade. If the number of
samples in the production interval is 30 or more then the calculation is based on the
current production interval. If there are less than 30 results then past production interval
results can be included up to a total of 30 results but not back further than 6 months. This
is a compromise between the need for large samples and the requirement that the samples
should represent the concrete being assessed.
If there are only five or fewer samples available they shall be used but in this case the
standard deviation shall be taken as not less than 3 MPa.
The use of standard deviation over a period longer than the current production interval is
somewhat inconsistent with the statistical basis of the compliance, but limited simulation
studies indicate that the results would be more conservative. This means unsatisfactory
concrete would have an even higher chance of rejection.
The sample standard deviation (sc), is determined from the statistical expression with
‘n − 1’ as the denominator. This is of course only an estimate of the true standard
deviation σ. The difference is significant when compliance is being considered. The
formula is as follows:
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sc =
(x − x )2
n − 1
where
sc = standard deviation of a controlled grade
x = sample strength
x = mean strength
n = number of samples
C6.3.5.3 Standard deviation for an associated grade For an associated grade, the
standard deviation, sa, is computed from the results if there are 30 in the current
production interval. Otherwise the standard deviation is computed using relative factors.
For example, if 25 MPa was the controlled grade for which a standard deviation of
3.0 MPa was found, then the value for 40 MPa grade would be given by:
s40 = 3.0 × 1.3/1.1
= 3.5 MPa
where 1.1 and 1.3 are the relative factors given in Table 8 for 25 and 40 grade
respectively.
C6.3.6 Grouping of plants to determine nc and s The need for large sample sizes is
in conflict with the requirement that the sample should represent one population of
concrete. In some circumstances a single supplier may elect to pool results from different
plants and this is permitted. Ideally such pooling should only be used when the materials
and control processes at the plants are similar.
C6.3.7 Action on noncompliance Where the concrete does not comply with
Clause 6.3.1 or even Clause 6.5, then it is important to realise that no further testing or
assessment can change that condition of noncompliance. However, the action to be taken
should recognize two aspects. Firstly, satisfactory concrete can often fail to comply, and
secondly even if the concrete is not entirely satisfactory it may still be suitable for its
intended purpose. Consumers should take a long term view on the reliability of concrete
from a producer.
C6.3.8 Early age assessment of controlled grades The industry practice of early age
testing resulted in this Clause which is intended to provided additional assurance to the
consumers that the strength is being maintained and that any major errors will result in
early action.
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APPENDIX CB
GUIDE TO THE SPECIFICATION OF SPECIAL-CLASS CONCRETE
CB1 GENERAL The specification options listed in Table B1 of Appendix B are
generally limited by practical considerations of available materials and plant capabilities.
These limitations are in some cases specific to a region or a plant configuration. The
ranges of practically available options are discussed below. Additional costs may be
incurred complying with special-class concrete parameters compared with those incurred
in complying with normal-class concrete parameters.
Attention is directed to Clause 5.8 which calls for the method of production control and
the criteria for compliance which shall be specified for ‘other parameters’. This applies to
some of the parameters discussed below.
NOTE: Values other than shown may be negotiated between the supplier and the customer.
TABLE
CB1
ALTERNATIVE VALUES FOR CONSIDERATION
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Parameter, Clause, normal-class
default value
Mass per unit volume of hardened
concrete
Clause 1.6.3.1(a)
2100-2800 kg/m3
Alternative values for consideration
Lightweight aggregates can be used to reduce the deadweight of the members.
The aggregates available and the weight reduction achievable with them are
region specific and should be identified with the concrete and aggregate
suppliers.
Dense concrete has occasionally been required, e.g. for nuclear shielding.
Region specific comment applies as above.
Chloride content
Clause 1.6.3.1(b)
0.8 kg/m3
The level of chloride present in the regionally available materials, notably
water, will set achievable limits.
Sulfate content by weight of cement
Clause 1.6.3.1(b)
50 g/kg
As for chlorides, achievable sulfate limits are region specific.
Shrinkage strain
Clause 1.6.3.1(c)
1000 × 10-6
Characteristics of available aggregates make shrinkage strain a region specific
parameter. The subject has been discussed in some detail in Clause C1.6.4.
The Commentary on AS 3600 1994 (AS 3600 Supplement 1 — 1994) includes
[Table 6.1.7(A)] the typical values achieved at some capital cities, reproduced
below.
Data on typical shrinkage values for commercial structural concrete, suitable
for pumping at a slump of approximately 80 mm.
Location
Brisbane
Sydney
Melbourne
Adelaide
Perth
Range of basic strain values
10-6
500 to 900
500 to 900
600 to 1000
700 to 1100
600 to 1200
(continued)
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TABLE
Parameter, Clause, normal-class
default value
Cement type
Clause 1.6.3.1(e)
as required within Clause 2.2
CB1
(continued)
Alternative values for consideration
Normal-class concrete may contain any combination of cements and supplementary cementitious materials, an implied control being achieved with
compliance with the 7-day strength specification.
Special-class concrete may specify a cement type to achieve results appropriate
for the structure, e.g. low heat, sulfate resistance and the like.
Licensed to E.S.SURESH on 04 Jun 2002. Single user licence only. Storage, distribution or use on network prohibited.
f ′c
Clause 1.6.3.2(a)
20, 25, 32, 40 or 50 MPa
Strengths higher than 50 MPa can be supplied. The upper limit is both plant
and region specific.
Slump
Clause 1.6.3.2(b)
20 to 120 mm in intervals of 10 mm
As required
Maximum nominal aggregate size
Clause 1.6.3.2(c)
10, 14, or 20 mm
As required
Project assessment
Clause 1.6.3.2(e)
subject to specification
As required
Air entrainment
Clause 1.6.3.2(f)
≤ 5%
As required
Flexural strengths
Clause 1.6.4(b)
nil
As required
Indirect-tensile strength
Clause 1.6.4(c)
nil
As required
Testing of constituents
Clauses 2.2 to 2.4
nil
In normal-class concrete the onus is entirely on the supplier to maintain records
to establish compliance with the Standard and this is commonly incorporated in
the supplier’s contracts with the material supplier.
If required, reports on the quality of constituents can be incorporated in a
special-class concrete specification. The tests required (preferably by reference
to a Standards Australia reference) and their frequency should be specified.
Records and additional information
Clause 4.1.6 and Clause 1.8.3
(Identification Certificate)
Provision of batch information as required in addition to that specified in
Clause 1.8.3 may be specified.
Computerized plants, becoming more common in metropolitan areas and on
large projects, can readily provide a wide range of information. Smaller, lowcapacity plants are more limited in what can be readily produced.
The identification certificates are limited in size, and usually additional
information has to be presented in a supplementary document, and if so
specified, attached to the identification certificate where practicable.
(continued)
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TABLE
Parameter, Clause, normal-class
default value
Tolerances on batching
Clause 4.2.1
CB1
AS 1379 Supp 1 — 1997
(continued)
Alternative values for consideration
The batching tolerances specified in Clause 4.2.1 are consistent with the
capabilities of plant used in the industry.
The onus of achieving the minimum criteria specified by the customer is
discharged by the supplier, by means of targeting mean performances
sufficiently above those minima to satisfy the compliance criteria.
Some customers have expressed a desire to control the range between minima
and maxima values achieved for the performance parameters in addition to the
specification of minimum values.
Standard deviation is a traditional statistical measure of variability and is
considered appropriate in this context.
Licensed to E.S.SURESH on 04 Jun 2002. Single user licence only. Storage, distribution or use on network prohibited.
The level of control exercised in the operation of a plant together with the
nature of the plant itself and the availability of the material determine the
standard deviation achieved in production from that plant. The standard
deviation also increases, as the strength grade increases, although not linearly.
However a difficulty arises if a maximum standard deviation is specified. The
number of samples used to calculate the value is critical. With six values the
Standard deviation computed could range over ±2 MPa of the value computed
from 1000 results. This is such a large percentage of any value likely to be
specified as to render impractical the definition of an acceptance criterion for
anything but a very large number of samples.
A practical approach may be to establish by inspection of plant records the
Standard deviation achieved over a long period for the most commonly
produced mix and either rely on that value being sustained or specify that it be
sustained. Indicative values for a variety of strength grades and levels of
control are:
Level of control
Strength grade
20 MPa 25 MPa
Laboratory
High level commercial plant predominantly one mix
Typical commercial plant
Low production remote plant
w/c
Clause 4.2.1.2(b)
nil
2.0
2.6
3.0
4.0
2.2
2.9
3.3
4.4
32 MPa
2.4
3.1
3.6
4.8
40 MPa 50 M
Pa
2.6
3.4
3.9
5.2
2.8
3.6
4.2
5.6
As required
Addition of water or admixtures to a
mixed batch
Clause 4.2.3
The provisions of Clause 4.2.3 are those universally achievable in practice.
Any variation to those would generally involve additional cost.
Period for completion of discharge
Clause 4.2.4
The 90 minutes specified in Clause 4.2.4 is qualified by reference to prevailing
temperatures.
90 minutes, subject to qualifications
If project considerations indicate a need for more precision in the specification
of allowable times they may be appropriately specified.
Temperature at point of discharge (t)
Clause 4.4.2
5°C<t°C<35°C
Project considerations, e.g. size of members, may dictate the specification of a
lower maximum temperature.
Testing of concrete
Section 5
If a frequency and type of concrete testing more extensive than that specified
in Section 5 is required, it should be specified and if the supplier is required to
carry out that additional testing, this should also be specified.
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AS 1379 Supp1 — 1997
34
REFERENCES
MANTON-HALL A.W., Comparison of Operating Characteristic of Overlapping and
non-overlapping ‘Means of N’ type specification Uniciv Report R-171 August 1977.
MANTON-HALL A.W., Tables of the Operating Characteristic of Overlapping Means of
N type specification Uniciv Report R-176 March/August 1978.
Licensed to E.S.SURESH on 04 Jun 2002. Single user licence only. Storage, distribution or use on network prohibited.
STANDARDS AUSTRALIA Concrete Structures: AS 3600 — 1994, Sydney 1994.
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