SULFATE RESISTANCE OF ROLLER COMPACTED CONCRETE

This paper presents the results of a study on sulfate resistance of pl ain and fly ash roller compacted concretes (RCC). A total of 12 plain, 24 cement-replaced and 12 fine aggregate-substituted fly ash concrete s were used in this investigation. laboratory-made RCC specimens were prepared at their optimum moisture content and were fabricated in acco rdance with ASTM C 1170, Procedure A. The rest samples were initially moist-cured for 28 days after casting, prior to immersion in a 5 perce nt sodium sulfate solution. Length change, mass loss, and compressive strength were monitored for a period of 180 days to evaluate the perfo rmance of specimens exposed to ''very severe'' sulfate attack. The inf luence of mixture variables (cement, coarse aggregate, and fly ash con tents) on bulk characteristics and sulfate resistance were evaluated. The study shows that good sulfate-resistant roller compacted concretes can be attained with the use of Type V portland cement with or withou t low-calcium fly ash. The resistance to sulfate attack improves with increases in cement or coarse aggregate content, as concrete becomes m ore dense and impermeable. Length change of RCC samples increases with increasing immersion age and stabilizes within 3 to 4 months after th e initial contact. No mass of concrete residues is found for any speci mens tested in this study However; after six months of immersion in a sodium sulfate solution, RCC mixtures with cement content of 12 percen t or less (by mass of total dry solids) experienced slight reduction i ii strength. A 20 to 40 percent replacement of cement by low-calcium f ly ash increases the sulfate resistance of RCC samples (excluding mixt ures made with 9 percent cementitious binder and 20 percent fly ash), whereas 10 percent replacement has a contrary effect. Mixtures with 10 to 20 percent fine aggregate-replaced Class F fly ash exhibit lower s ulfate expansion and higher compressive strength than those of plain a nd cement-substituted-fly ash I-oiler compacted concretes.