Effect of Cement Type, Curing Conditions, and Selected Admixtures on Hardened Concrete Properties

Abstract

This report presents a multi-part study investigating the effects of cement type, curing conditions, and selected admixtures on the strength, permeability, and shrinkage characteristics of concrete. Phase I of the study included compressive strength (ASTM C39) and permeability testing (ASTM C1202 and NT Build 492) of four mixtures, with Type I/II portland cement or Type IL portland-limestone cement, and slag cement. Two combinations of chemical admixture packages were used. Half of the specimens from each mixture were moist-cured at 23°C (73°F) and half were moist-cured at 15.5°C (60°F). Curing temperature had a significant influence on the tested concrete properties, but neither the cement type nor admixture package had any significant effect. Phase II of the study compared eight mixtures with Type IL portland-limestone cement, with variables including w/cm (0.42 and 0.48) and the use of two colloidal silica admixtures, one of which replaced slag cement when used, and the other was intended to provide a means of internal curing. Specimens from each mixture were subdivided into those that were moist-cured at 23°C (73°F) and those that were dry-cured in air at 23°C (73°F) and 50% relative humidity. Each mixture was tested for compressive and split-tensile strength (ASTM C496), permeability, and drying shrinkage (ASTM C157). Two additional mixtures (3R and 7R) were prepared using both colloidal silica admixtures in combination, with results reported in an addendum following the initial eight Phase II mixture results. The type of curing and w/cm had the most significant influence on the tested concrete properties with permeability being most affected. The mixtures with slag cement were more sensitive to the negative effect of dry curing. The colloidal silica admixtures had no consistent positive or negative effect on concrete properties.