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.

This lecture is about concrete - specifically, hydraulic-cement concrete. If one starts with the dry powder that is hydraulic cement - usually the particular class of hydraulic cement known as portland cement - and adds water, what results, depending on the amount of water added, is cement paste or grout. Grout can be poured like gravy. If fine aggregate is added, the result is mortar or sanded grout. If both fine aggregate and coarse aggregate are added, the result is concrete. As the Supreme Court of Pennsylvania once wrote in a decision dealing with cement-manufacturing plants, "cement is to concrete as flour is to fruitcake." My first point is, to get proper concrete, get the terminology right. There is no such thing as a cement mixer. And sand is not a synonym for fine aggregate; sand is a class of fine aggregate produced by nature rather than by rock crushers and grinding mills.

The Organizing Committee for this conference requested that we make some remarks and prepare some comments for inclusion in the Proceedings. These words are intended as a basis for the former and to serve as the latter. We observe that: Concrete is international; it is made locally; it has infinite variability; it can be made to be very uniform; and it can be made to last as long as you want it to. An unsolved problem is assessment of the nature and severity of the exposure, so that requirements can be graduated according to severity. Only when this problem is solved will we be able to stamp out specification overkill. The Organizing Committee also suggested we furnish biographical data and bibliographic data. The standard material accompanying this publication should suffice for the former. An appendix of selected items is provided for the latter purpose.

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.

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.