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The air-void systems produced by two commercially available air-entraining admixtures (AEA), one a vinsol resin formulation and the other a tall oil formulation, were studied in mortars. Mortars were composed of four different portland cements and two Class F fly ashes (20 percent by mass) with concrete sand. The mortar proportions were based on Virginia Department of Transportation Class A4 concrete with a water-cementitious material ratio of 0.45. Foam index tests were conducted on all cementitious combinations, and the results were used to determine the dosage of AEA in the mortars. The air content of the mortars was determined gravimetrically, and specimens were cast for subsequent linear traverse analysis of the air-void system. With both AEAs, mortar air contents in the target range produced spacing factors much lower than necessary to provide resistance to freezing and thawing, suggesting that the ranges for air content currently used in VDOT specifications could be reduced to lessen the potential for acceptance problems associated with excessive air content. Further study is recommended to verify that the relationships observed in this study are also observed in concrete and to define improved air content specifications.
"This report presents a recommended 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. Criteria are proposed for acceptance of admixtures for use in either highway pavements or structures. The recommended procedure and acceptance criteria will guide materials engineers in evaluating and selecting air-entraining admixtures that should contribute to appropriate freeze-thaw durability and thus to good performance and long service life. The content of the report will be of immediate interest to materials engineers, researchers, and others concerned with the design of concrete mixtures for use in highway pavements and structures."--taken from Foreword, page [v].

Admixtures in Concrete

National Research Council (U.S.). Highway Research Board. Committee on Chemical Additions and Admixtures for Concrete

Published: 1971

Total Pages: 60


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An admixture is any material other than water, aggregates, and hydraulic cement that is used as an ingredient of a concrete or mortar mixture and added to the batch immediately before or during mixing. 4 types of admixtures are discussed: (1) accelerators, the most common of which is calcium chloride; (2) air-entraining, to protect the concrete against the damage it may suffer if the paste becomes saturated with water and then freezes; (3) retarders and water reducers, which extend setting time 30 to 50 percent to compensate for placement temperatures, to avoid cold joints, or to avoid undesirable effects of displacements and deflections; and (4) pozzolans, which react with hydroxides to form compounds with cementitious properties, and usually produce a lower cost concrete.
Three special water-reducing admixtures for concrete were evaluated according to test method CRD-C 87-72. Tests were made to determine the effects of these admixtures on the properties of concrete. Air-entrained concrete mixtures were made with and without these admixtures. All three of the admixtures permitted water reductions exceeding 15 percent. The admixtures met all the requirements of CRD-C 87-72 except for frost resistance. (Author).