As 1379 Supp 1-1997 Specification and Supply of Concrete Sup

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AS 1379 Supp 1

AS 1379 Supp 1-1997 Specifica-1997 Specification and supply otion and supply of concrete - Commentaryf concrete - Commentary

(Supplement to AS

(Supplement to AS 1379-1997)1379-1997)

Licensed to E.S.SURESH on 04 Jun 2002 Licensed to E.S.SURESH on 04 Jun 2002

AS 1379 Supp1—1997

AS 1379 Supplement 1—1997

Speciﬁcation and supply of

concrete—Commentary

(Supplement 1 to AS 1379—1997)

w w o o r r k k p p r r o o h h i i b b i i t t e e d d . .

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AS 1379 Supplement 1—1997

Speciﬁcation and supply of

concrete—Commentary

(Supplement 1 to AS 1379—1997)

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AS 1379 Supp1—1997

AS 1379 Supplement 1—1997

Speciﬁcation and supply of

concrete—Commentary

(Supplement 1 to AS 1379—1997)

e e d d t t o o E E . . S S . . S S U U R R E E S S H H o o n n 0 0 4 4 J J u u n n 2 2 0 0 0 0 2 2 . . S S i i n n g g l l e e u u s s e e r r l l i i c c e e

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22 August 1997 and published on 5 October 1997. 22 August 1997 and published on 5 October 1997.

The following interests are represented on Committee BD/49: The following interests are represented on Committee BD/49:

Ash Development Association of Australia Ash Development Association of Australia AUSTROADS

AUSTROADS

Australasian Slag Association Australasian Slag Association

Australian Premixed Concrete Association Australian Premixed Concrete Association Cement & Concrete Association of Australia Cement & Concrete Association of Australia Housing Industry Association

Housing Industry Association Master Builders Australia Master Builders Australia

The Association of Consulting Engineers, Australia The Association of Consulting Engineers, Australia University of Newcastle

University of Newcastle

Revie

Revie w w of of AustraAustra lian lian StandStand ards.ards. TTo keep abreast of progress in industry, Australian Standaro keep abreast of progress in industry, Australian Standards are subject ds are subject to periodic review and are kept up to date by the issue of amendments or new editions as necessary. It is 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 important therefore that Standards users ensure that they are in possession of the latest edition, and any amendments thereto.

amendments thereto.

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Suggestions for improvements to Australian Standards, addressed to the head office of Standards Australia, 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 are welcomed. Notiﬁcation of any inaccuracy or ambiguity found in an Australian Standard should be made withou

without t delay in delay in ordorder that er that the matter the matter may be may be investiinvestigated and approprgated and appropriate action taken.iate action taken.

This Standard was issued in draft form for comment as DR 96017. This Standard was issued in draft form for comment as DR 96017.

n n s s e e d d t t o o E E . . S S . . S S U U R R E E S S H H o o n n 0 0 4 4 J J u u n n 2 2 0 0 0 0 2 2 . . S S i i n n g g l l e e u u s s e e r r l l i i c c e e

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AS 1379 Supp1 —1997

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

e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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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.

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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Care should be taken to ensure that material used is from the current edition of the Standard and that it is updated whenever the Standard is amended or revised. The number and date of the Standard should therefore be clearly identified.

The use of material in print form or in computer software programs to be used commercially, with or without payment, or in

n s e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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3 AS 1379 Supp1 — 1997

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.

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. n s e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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5 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.

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 Para-graph 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

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/m3to 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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7 AS 1379 Supp1 — 1997

(ii) 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.

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) Slum p.

(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.

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 special-class concrete, distinguishing it from N25, being a 25MPa strength grade normal-class 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 8a

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.

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. e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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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.

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 special-class 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). n s e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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AS 1379 Supp1—1997 10

(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.

(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) T he rel evant ‘Special-Class’ designation, in accordance with 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. e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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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 p re sc ri p t i on or de r a n d t h e i nf or ma t i on g i ve n i n 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).

(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) T he rel evant ‘Special-Class’ designation, in accordance with Clause 1.6.4, followed by the word ‘Prescription’.

(C) The particle density, maximum nominal size and grading of the coarse a ggregat e, wit hin t he ra nges provi ded 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. n s e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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AS 1379 Supp1—1997 12

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.

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.

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. n s e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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AS 1379 Supp1—1997 14

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 de-icing 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.

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. e d t o E . S . S U R E S H o n 0 4 J u n 2 0 0 2 . S i n g l e u s e r l i c e n c e o n l y . S t o r a g e , d i s t r i b u t i o n o r u s e o n n e t w o r k p r o h i b i t e d .

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S E C T I O N C 3 P L A N T A N D E Q U I P M E N T

C3.1 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

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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AS 1379 Supp1—1997 16

(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.

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 C 4 P R O D U C T I O N A N D D E L I V E R Y

C4.1 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

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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PREFACE

CONTENTS

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

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

S E C T I O N C 3 P L A N T A N D E Q U I P M E N T

S E C T I O N C 4 P R O D U C T I O N A N D D E L I V E R Y