Investigating properties of ultra-high performance cementitious composites made with gypsum-contaminated aggregates

The present work aimed to investigate the potential of using gypsum-contaminated fine aggregate in ultra-high performance cementitious composite (UHPCC) to enhance the economic efficiency of this outstanding composite and to provide detailed information on its resistance to internal sulfate attack. For this purpose, three groups of UHPCCs were designed at a constant w/b ratio of 0.174. Two groups of UHPCC mixtures were designed with binary and ternary cementitious blends of Portland cement, silica fume, and/or ground granulated blast furnace slag and were reinforced with 2% micro steel fibers by volume. The other group was designed with binary cementitious blends of Portland cement and silica fume and was prepared without fibers. Each group consisted of five mixes with different SO3 contents of between 0.11% and 4.5% by weight of natural sand. For each mix, the UHPCC samples were either standard cured or steam cured at 80 ˚C over a 48 h. The UHPCC samples were tested for compressive strength, splitting tensile strength, expansion, drying shrinkage and weight loss. The experimental findings were also supported by SEM, EDX, and XRD investigations. Besides, UHPCCs were compared to Portland cement mortars in terms of compressive strength, expansion, and microstructure. Test results indicated that UHPCCs generally showed an increase in compressive strength, particularly under steam curing and an insignificant expansion even in the presence of excess sulfates, in contrast to mortars thus suggesting the excellent resistance of UHPCC to the internal sulfate attack.