Category: Uncategorized

CONCRETE:

 (AS 1379 Specification and supply of concrete) A mixture of Cement, aggregates and water with or without the addition of chemical admixtures or other materials.      

Cement: (AS 3972 Portland or blended cement) A hydraulic binder composed of Portland or blended cement used alone or in combination with one or more supplementary cementitious materials.

Concrete is defined as follows,

• Plastic concrete:

Concrete in the state between completion of mixing and initial set as defined in AS 1012.18 Methods of determining setting time of fresh concrete, mortar and grout by penetration resistance.

• Hardened concrete:

Concrete after initial set, as represented by test specimens that have been subjected to a specified process and duration of curing.

• Normal- Class Concrete:

Concrete that is specified primarily by a standard compressive strength grade up to 50 MPa and otherwise in accordance with Clause 1.5.3.

• Special- Class Concrete:

Concrete that is specified to have certain properties or characteristics different from, or additional to, those of normal-class concrete and otherwise in accordance with Clause 1.5.4.

SPECIFICATION OF CONCRETE:

Concrete shall be specified,

(a) as either

(1) Normal-class(N), or

(2) Special-class(S), or

(b) By strength grade or other readily verifiable parameter by which compliance with the specification can be assessed.

NOTE: Standard strength grades should be specified wherever possible.

• NORMAL-CLASS CONCRETE:

Normal-class concrete shall be specified only by the parameters given in Clause 1.5.3.2(Basic parameter), and shall have the following attributes:

• A mass per unit volume in the range 2100 kg/m³ to 2800 kg/m³ when determined in accordance with (AS 1012.12.1 Determination of mass per unit volume of hardened concrete) in the saturated, surface-dry condition.
• Acid-soluble chloride and sulfate contents within the limits given in Clause 2.7, when determined in accordance with Clause 5.5.2.
• A shrinkage strain not exceeding 1000 × 10⁻⁶, when determined in accordance with Clause 5.6 after 56 days drying.

NOTE: This maximum value of 1000 × 10⁻⁶ is consistent with the use for design purposes of a median basic shrinkage strain value of 850 × 10⁻⁶.

• A mean compressive strength at 7 days, assessed in accordance with Clause 5.7, of not less than the values of Grade designation for N20-9MPa, N25-12MPa, N32-16MPa, N40-20MPa & N50-25MPa.
• A cement complying with (AS 3972 Portland or blended cement) alone or in combination with one or more supplementary cementitious materials.
• No lightweight aggregate as defined in AS 2758.1 Aggregates and rock for engineering purposes Concrete aggregates.

Basic parameters of normal-class concrete:

The following basic parameters shall be specified by the customer:

• A standard strength grade selected from 20MPa,25MPa,32MPa,40MPa, 50MPa,65MPa,80MPa or 100MPa and designated as one of N20, N25, N32, N40 or N50.
• The slump at the point of acceptance, selected as one of 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, 110 mm or 120 mm.

NOTES:

1. The customer should carefully consider that the specified slump of concrete suits the placement method.
2. For residential slabs and footings, if the slump is not specified by the customer, the specified slump should be considered to be 100 mm.
3. The maximum nominal size of aggregate, selected as one of 10 mm, 14 mm or 20 mm. Unless otherwise specified, the default value shall be taken as 20 mm.
4. The intended method of placement, including relevant details of equipment.
5. If project assessment is required to be carried out by the supplier (see Note).

NOTE: If unspecified, it will be assumed that project assessment is not required.

• If required, a level of air entrainment up to a maximum of 5.0%.

(2) SPECIAL- CLASS CONCRETE:

Concrete other than normal-class concrete shall be specified by the customer as specialclass and, if applicable, by strength-grade. The parameters and attributes that should be specified for special-class concrete should be as set out listed below with reference to Appendix B and Table B1 on AS1379.

Special-class concrete commonly has the same basic parameters as normal-class concrete with some additions and(or) exceptions. Parameters or attributes that are different from, or additional to, those of normal-class concrete should be included in specification below. If the requirements of specification for any concrete are inconsistent with those for normal-class concrete then the requirements of specification take precedence for that concrete.

Where any parameter other than strength grade requires the specification of a special-class concrete, or the proportions of the mix are specified, the concrete should be identified by an appropriate code agreed to between the supplier and customer that identifies that particular mix.

Basic parameter for specification of special-class concrete:

• It is recommended to select from standard strength grades of S20, S25, S32, S40, S50, S65, S80 and S100.
• Where concrete is specified as special-class and a strength grade is applicable, the strength grade is designated by the prefix:

S, for compressive strength grades;

SF, for flexural strength grades; or

ST, for indirect-tensile strength grades.

Where concrete is special-class and any property other than strength grade is Specified as the principal criterion, or the proportions of the mix are specified, it is designated by an appropriate alphanumeric code, agreed between the supplier and the customer, to indicate the criterion.

• Special-class concrete should be subject to project assessment.
• Certain concrete exposure classifications may require special provisions for aggregate durability (AS 2758.1 Aggregate & Rock for engineering Purposes.)
• Any departures from the parameters or composition, or both, of normal-class concrete and any other criteria or limitations shall be specified by the customer in consultation with the supplier.

NOTE: A summary list of several such parameters, some or all of which may be specified for the production of special-class concrete for a project, is given in Appendix B on AS 1379.

• Other requirements additional to these parameters may be specified.