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Twenty materials, representing eight different classes of mineral admixtures, were evaluated, using both chemical and mortar-bar test methods, for their effectiveness in preventing excessive expansion of concrete due to alkali-aggregate reaction. It was found that the chemical tests cannot be used with reliance to evaluate effectiveness. Each of the replacement materials evaluated will prevent excessive expansion if a sufficient quantity is used. Correlations were found between effectiveness and: fineness, dissolved silica, and percentage of alkali retained by reaction product. Five of the materials tested (a fly ash, a tuff, a calcined shale, a calcined diatomite, and an uncalcined diatomite) showed a reduction in alkalinity of 40 percent or more when tested by the quick chemical test. All of these except the fly ash met the requirement proposed by Moran and Gilliland for the relationship between reduction in alkalinity and silica solubility. Six of the materials tested (two slags, a fly ash, a pumicite, and two calcined shales) reduced mortarbar expansion at least 75 percent with high-alkali cement and Pyrex glass aggregates when used as 50, 45, 35, and 30 percent replacements of the cement. Calculations were made that suggest that the minimum quantity of each material required for effective prevention of excessive expansion ranged from 10 percent for the synthetic silica glass to 45 percent for one of the slags. By groups, these calculated minimum percentages were: calcined shales, 19 to 29; uncalcined diatomite, 22; volcanic glasses, 32 to 36; slags, 39 to 45; and fly ashes, 40 to 44. The investigation of mineral ad-mixtures as cement-replacement materials was initiated by the Office of the Chief of Engineers in 1950 as part of the Civil Works Investigations Program with the purpose of ascertaining the degree to which portland cement may be advantageously replaced by other materials, considering cost and the quality of the resulting concrete. This paper deals with that part of the investigation that was concerned with the ability of these materials to prevent excessive expansion of concrete due to alkali-aggregate reaction.

Concrete is international, but made locally; has infinite variability, but can be made very uniform; and can be made to last as long as you want it to. Therefore, what is needed to more fully realize its potential as a construction material is to understand what we want it to do, learn how to make it so it will do so, use available methods to restrict undesired variability, consider the ethical and environmental aspects of its use, and help the people who are making it to do it better.

A property of aggregate is "significant" from the viewpoint of this publication only if it has a significant effect on the behavior of portland-cement concrete in service. Similarly, a test of aggregate is "significant" only if it yields useful information about a significant property or group of properties. The behavior of concrete in service is determined by the interaction of certain of its properties and the significant characteristics of the exposure to which it is subjected. Variations in shape and surface texture of, or the presence of coatings on, aggregate particles may significantly affect properties of concrete that are important to its behavior in service. No ASTM methods exist by which quantitative determinations of particle shape, surface texture, or coatings can be made. Few satisfactory data are available concerning the relations between variation in these properties of aggregates and behavior of concrete. These properties have not been adequately defined, and adequate definition is necessary before satisfactory information can be obtained regarding the degree to which aggregates differ with respect to them. The nature and degree of differences among aggregates with respect to these properties must be satisfactorily determined before their effect on the behavior of concrete can be properly evaluated. The absence of satisfactory data is not due to failure of previous writers to suggest the probable significance of these properties. These properties are mentioned or discussed in the 1943 ASTM "Report on Significance of Tests of Concrete and Concrete Aggregates" in the papers by Gilkey [1], Hubbard [2], Kriege [3], and Lang [4]; and in the 1948 ASTM Symposium on Mineral Aggregates in the papers by Allen [5], Rhoades and Mielenz [6], Rockwood [7], Sweet [8], and Woolf [9]. Reports of work done in Australia, Denmark, France, Germany, Great Britain, Japan, Sweden, Switzerland, and the United States are cited in the list of references at the end of this paper. Standardized test methods have been developed by Markwick [10,11] and Shergold [12,13] of the Road Research Laboratory in Great Britain; by Schiel [14-16], Walz [17], Schulz [18-20], Schulze [21], Pickel and Rothfuchs [22], Pickel [23], and the Forschungsgesellschaft fiir das Strassenwesen [24], in Germany; by von Matem [25] in Sweden; by Feret [26,27] in France; and by Goldbeck [28], Huang [29], and the Corps of Engineers [30-32] in the United States. The most careful studies of concepts and definitions of particle shape and surface texture have been made by sedimentary petrologists, notably Wentworth (33-35], Wadell [36-38], Zingg [39], Krumbein [40-42], Pettijohn [43], and Sneed and Folk [44]. However, the relation of their work to aggregates for portland-cement concrete has received little attention, especially in the United States.

Crystals are found in some entrained-air voids of all concrete that has been "left out in the rain" or stored while damp. These crystals can be observed through petrographic examination of thin or ground concrete sections at normal magnification. If the concrete was made using a cement with a high tricalcium aluminate (C3A) content (over 8%), it is likely that areas in it will be covered with ettringite crystals - secondary ettringite.

Concrete will be immune to the effects of freezing and thawing if (1) it is not in an environment where freezing and thawing take place so as to cause freezable water in the concrete to freeze, (2) when freezing takes place there are no pores in the concrete large enough to hold freezable water (i.e., no capillary cavities), (3) during freezing of freezable water, the pores containing freezable water are never more than 91 percent filled, i.e., not critically saturated, (4) during freezing of freezable water the pores containing freezable water are more than 91 percent full, the paste has an air-void system with an air bubble located not more than 0.2 mm (0.008 in.) from anywhere (L = 0.2 mm), sound aggregate, and moderate maturity. Sound aggregate is aggregate that does not contain significant amounts of accessible capillary pore space that is likely to be critically saturated when freezing occurs. The way to establish that such is the case, is to subject properly air-entrained, properly mature concrete, made with the aggregate in question, to an appropriate laboratory freezing-and-thawing test such as ASTM C 666 Procedure A. Moderate maturity means that the originally mixing water-filled space has been reduced by cement hydration so that the remaining capillary porosity that can hold freezable water is a small enough fractional volume of the paste so that the expansion of the water on freezing can be accommodated by the air-void system. Such maturity was shown by Klieger in 1956 to have been attained when the compressive strength reaches about 4,000 psi.