ASTM C494

ASTM C494 – Standard Specification for Chemical Admixtures for Concrete

Description:

Abstract

This specification covers the materials and the test methods for use in chemical admixtures to be added to hydraulic-cement concrete mixtures in the field. The seven types of admixtures are indicated as follows: Type A—water reducing; Type B—retarding; Type C—accelerating; Type D—water reducing and retarding; Type E—water reducing and accelerating; Type F—water reducing, high range; and Type G—water reducing, high range, and retarding. The materials used in the concrete mixtures shall include Type I or Type II cement, pozzolan, fine and coarse aggregates, and air-entraining admixture. Samples of freshly mixed concrete from at least three separate batches for each condition of concrete shall be tested in accordance with the slump, air content, time of setting, and water content tests. Physical properties retesting shall consist of uniformity and equivalence tests using infrared analysis which is intended to compare qualitatively the composition of different samples, residue by oven drying which shall be either a forced circulation type or one with provision for free access of air, and specific gravity determination using hydrometers. Test specimens of the hardened concrete shall be prepared in accordance to compressive strength, flexural strength, resistance to freezing and thawing, and length change.

Scope

1.1 This specification covers materials for use as chemical admixtures to be added to hydraulic-cement concrete mixtures for the purpose or purposes indicated for the eight types as follows:

1.1.1 Type A—Water-reducing admixtures,

1.1.2 Type B—Retarding admixtures,

1.1.3 Type C—Accelerating admixtures,

1.1.4 Type D—Water-reducing and retarding admixtures,

1.1.5 Type E—Water-reducing and accelerating admixtures,

1.1.6 Type F—Water-reducing, high range admixtures,

1.1.7 Type G—Water-reducing, high range, and retarding admixtures, and

1.1.8 Type S—Specific performance admixtures.

1.2 Unless specified otherwise by the purchaser, test specimens for qualifying an admixture shall be made using concreting materials as described in 11.1 – 11.3.

NOTE 1: As discussed in Appendix X2, it is recommended that, whenever practicable, supplementary tests be made by the purchaser using the cement, pozzolan, aggregates, air-entraining admixture, and the mixture proportions, batching sequence, and other physical conditions proposed for the specific work because the specific effects produced by chemical admixtures may vary with the properties and proportions of the other ingredients of the concrete. For example, Types F and G admixtures may exhibit much higher water reduction in concrete mixtures having higher cement contents than that listed in 12.1.1.

NOTE 2: The purchaser should verify that the admixture supplied for use in the work is equivalent in composition to the admixture subjected to test under this specification (see Section 6, Uniformity and Equivalence).

NOTE 3: Admixtures that contain sufficient amounts of chloride may accelerate corrosion of steel reinforcement. Compliance with the requirements of this specification does not constitute assurance of acceptability of the admixture for use in reinforced concrete.

1.3 This specification provides for three levels of testing.

1.3.1 Level 1—During the initial approval stage, proof of compliance with the performance requirements defined in Table 1 demonstrates that the admixture meets the requirements of this specification. Proof of compliance shall be based on comparisons of the average test results from the batches of test concrete and the average test results from the batches of reference concrete. Admixtures (except for Types B, C, E, and S) shall qualify for provisional compliance if the time of setting, length change, and durability factor meet the physical requirements and any of the alternative compressive strength requirements shown in parentheses in Table 1 are met through the date of provisional acceptance (see Note 4). If subsequent test results at six months or one year fail to meet the requirement of at least 100 % of reference strength, the provisional compliance of the admixture to this standard is withdrawn and all users of the admixture shall be notified immediately. Uniformity and equivalence tests of Section 6 shall be carried out to provide results against which later comparisons shall be made.

NOTE 4: Allowing for provisional compliance while retaining longer term compressive strength requirements promotes more rapid qualification of new materials, but also provides assurance that new admixture technologies will not exhibit unexpected longer term performance. The alternative compressive strength requirements in Table 1 are based on statistical analysis of 103 Specification C494/C494M evaluation tests. The alternative requirements shown in parentheses correspond to a 99 % probability of passing strength requirements at subsequent test ages,2 if any one of the requirements is met. There is no requirement that all be met.

1.3.2 Level 2—Limited retesting is described in 5.2 – 5.2.2. Proof of compliance with the requirements of Table 1 demonstrates continued conformity of the admixture with the requirements of the specification.

1.3.3 Level 3—For acceptance of a lot or for measuring uniformity within or between lots, if specified by the purchaser, the uniformity and equivalence tests of Section 6 shall be used.

1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined. Some values have only SI units because the inch-pound equivalents are not used in practice.

1.5 The text of this standard refers to notes and footnotes that provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.