Influence of supplementary cementitious materials on sulfate resistance of ultra-high-performance concrete

The study presented herein investigated the effect of supplementary cementitious materials (SCMs) on the sulfate resistance of ultra-high-performance concretes (UHPCs) made with ASTM Type III and Type V cement. Three types of UHPCs were prepared for each cement type, namely, one with 100 % cement (C100) and two others with 20 % cement replaced by fly ash (FA20) and a combination of silica fume and fly ash (FA15SF5). These UHPCs were exposed to a 5 % sodium sulfate solution for 365 days to evaluate their sulfate resistance. In addition to the sulfate-induced expansion, the compressive strengths of the studied UHPCs were evaluated under two curing conditions: continuous water curing and curing under exposure to the 5 % sulfate solution. The Rapid Sulfate Permeability Test (RSPT) was also conducted at 28 and 90 days to assess rapid sulfate ions penetration into the studied UHPCs. The results revealed that the addition of supplementary cementitious materials (SCMs) significantly enhanced sulfate resistance in both Type III and Type V cement UHPCs. However, Type V cement UHPCs consistently showed reduced sulfate-induced expansion by approximately 20.4 % compared to Type III cement UHPC, primarily due to its lower C3A content. The Rapid Sulfate Permeability Test (RSPT) results revealed that, at both 28 and 90 days, Type V UHPCs consistently displayed lower penetrability compared to Type III UHPCs. Furthermore, Type V cement UHPCs incorporating SCMs exhibited an average surface penetration reduction of about 6 % relative to their Type III cement counterparts.