Ramon L. Carrasquillo

Temperature Rise and Durability of Concrete Containing Fly Ash

This paper describes how a research program was conducted in which the temperature rise of mortars and the durability of concrete containing fly ash were studied. The study of the effect of fly ash on the temperature rise of mortars included the use of both ASTM C 618 Class C and Class F fly ashes. Control tests were conducted on mortars containing ASTM C 150 Type I, Type I-II, and Type III cements, and comparison tests were conducted on mortars containing 20, 27.5, and 35 percent fly ash by volume of cement. It was found that the use of Class F fly ash resulted in a reduction in the temperature of the mortar, whereas the partial replacement of cement with Class C fly ash did not lower the mortar temperature, regardless of the type of cement used. Resistance to scaling in the presence of deicing salts and abrasion resistance tests were conducted on concrete samples cast from 21 batches of concrete. Variables studied included fly ash type, fly ash content, and curing conditions. Both ASTM Class F and Class C fly ashes were used to replace 25 or 35 percent of the cement by volume, and curing conditions included combinations of 50, 75, and 100 F with 50 and 100 percent relative humidities.

Alkali-Aggregate Reaction in Concrete Containing Fly Ash

This paper depicts the first steps taken to answer the urgent need of developing guidelines for proper, economical and efficient use of fly ash to reduce alkali-aggregate reaction damage in concrete. More than 1300 mortar-bars were cast and tested according to the mortar-bar test method, ASTM c 227, with 0, 17, 26, 34, 45 and 62 percent replacement of the volume of cement in the mixture with fly ash. The effect of silica fume in the mixture was compared to that of fly ash at 17, 34 and 45 percent cement replacement. The variables studied included: type of aggregate, alkali content of the cement, type of pozzolan, percent of cement being replaced and blending of the cement with the fly ash. Both ASTM class c and class f fly ashes were investigated. The test results indicate that the replacement of a portion of the volume of cement with fly ash may reduce the alkali-aggregate expansions, regardless of whether the fly ash is blended or not with the cement at the time of mixing, depending on the proper combination of the following factors: fly ash alkali content and cement replacement with fly ash. The test results also suggest that the replacement of a portion of the volume of cement with silica fume is equally or more effective in reducing the alkali-aggregate expansions. For the covering abstract of the conference see IRRD 811982.

Effects of Withholding Mixing Water and Retempering on Properties of Concrete

The effects of withholding mixing water at initial batching followed by retempering of the mix at the jobsite on the properties of the concrete produced for highway applications was examined in an experimental program. Additionally, the effects of redosage with water above and beyond that called for in the specified mix design was examined. Tests were performed to determine the effects on slump, air content, unit weight, compressive strength, flexural strength, abrasion resistance, and freeze thaw resistance. The effects of varying the withholding amount, withholding time, and cement content on the fresh and hardened concrete properties mentioned above were examined. The concrete examined was produced at a ready mixed concrete facility in order to duplicate as closely as possible job site conditions arising in typical concrete construction. The results of the study show that significant detrimental effects occur when mixing water is withheld and concrete is retempered at a later time. Slump, air content, abrasion resistance, and freeze thaw resistance are all adversely affected. The effects were found to vary with variations in both withholding time and cement content. The strength was not affected when water was withheld and concrete was retempered, but a reduction in strength accompanied an increase in water cement ratio above design values at redosage. The properties changed lead to concrete of reduced quality and questionable performance (A).