This report recommended a procedure for evaluating air-entraining admixtures used in highway concrete. The procedure involves the testing of non air-entrained concrete and concrete containing the air-entraining admixture under simulated field conditions, and proposes criteria for acceptance of admixtures for use in either highway pavements or structures.
Extensive laboratory testing and long-term field experience have demonstrated conclusively that concrete must be properly air entrained if it is to resist the action of freezing and thawing. For more than 50 years, neutralized vinsol resin has been used effectively for air entrainment. More recently, other air-entraining admixtures have been introduced and their use has increased primarily because of the higher cost and limited supply of vinsol resin. AASHTO T 157, Air-Entraining Admixtures for Concrete, sets limits on the effects that any given air-entraining admixture under test may exert on certain properties of the fresh and hardened concrete mixture in comparison with a similar concrete mixture containing a standard-reference air-entraining admixture such as neutralized vinsol resin. However, many concrete mixtures for bridge decks, pavements, and other highway structures incorporating these newer admixtures meeting AASHTO T 157 limits, have exhibited unacceptable properties when used in actual projects leading to a debate recently about the contribution of these admixtures to concrete properties and durability. Thus, research was needed to address the issues associated with the use of these air-entraining admixtures in highway concrete and to develop procedures for evaluating and qualifying air-entraining admixtures for hydraulic cement concrete for highway applications.
Research included an extensive laboratory testing that examined the properties of concrete mixtures containing a variety of air-entraining admixtures and related these properties to freezing and thawing durability. Based on analysis of test results, a procedure for evaluating air-entraining admixtures was developed. The procedure involves the testing of non air-entrained concrete and concrete containing the air-entraining admixture under simulated field conditions. Admixture evaluation is made by comparing the results from these tests against proposed evaluation criteria. The procedure includes two protocols: one for evaluating admixtures intended for use in highway pavements and the other for evaluating admixtures intended for use in highway structures. Validity of the recommended procedure was confirmed by laboratory tests conducted on concrete mixtures containing five air-entraining admixtures with known performance record. The recommended test method and proposed acceptance criteria will provide a good indicator of the expected concrete properties and resistance to freezing and thawing and can, therefore, be used to evaluate air-entraining admixtures intended for use in highway pavements and structures. The final report, without the appendices, has been published as NCHRP Report 578, and the appendices are available online as NCHRP Web-Only Document 101.