Abstract
This study was conducted to propose a design of cementitious material containing Ordinary Portland Cement (OPC) with Blast Furnace Slag (BFS), anhydrite (AH : CaSO4) and lime stone powder (LSP : mostly CaCO3), with improved sulfate resistance. This study was also focused on the influence of adding BFS, AH and LSP on sulfate resistance of OPC paste and mortar specimens at temperatures of both 23°C and 40°C and investigated the mechanism of sulfate attack on cementitious materials at both temperatures. The sulfate resistance was improved by adding BFS, AH and LSP; the best sulfate resistance was found for BFS 59.5%-OPC 25.5%-AH 5%-LSP 10% (BFS/OPC ratio = 70 : 30), at 40°C. It was concluded that (a) the amounts of substances responsible for expansion, CH and residual C3S, could be decreased with increasing the BFS replacement ratio (especially by adding more than 55% BFS) (b) a large amount of ettringite instead of monosulfate was produced before immersion in sulfate solution when 5% AH was added and (c) adding 10% LSP resulted in production of monocarbonate, which was stable in sulfate solution, instead of unstable monosulfate. AH and LSP could also improve early age strength. In addition, sulfate resistance of specimens was almost the same at both 23°C and 40°C when the BFS replacement ratio was more than 55%.
