Experimental evaluation of the mechanical performance and compressive stress–strain response of normal-strength concrete incorporating densified silica fume and local materials

Abstract

In this study, the effect of densified silica fume on the fresh properties, mechanical performance, and ascending compressive stress-strain response of normal-strength concrete using local Iraqi materials was investigated. Densified Sika® Fume S92 D was used as the replacement for Portland cement at 10% and 15% by total binder mass. Three mixtures were studied: control concrete (NC), concrete containing 10% silica fume (SF10), and concrete containing 15% silica fume (SF15). The total binder content and water-to-binder ratio were kept at 350 kg/m³ and 0.55, respectively, without chemical admixtures. The slump increased from 130 mm for NC to 180 mm for SF10 and 160 mm for SF15. While this is in contrast to the commonly reported decrease in workability of silica fume, it could be due to the combination of saturated surface dry aggregates, high effective water content, very fine Zone 4 sand, and an incomplete deagglomeration of the densified silica fume. No visible bleeding or aggregate segregation was observed during the workability test. The compressive and splitting tensile strengths of SF15 increased by 22.6% and 24.0%, respectively, compared to NC. The peak compressive stress of the instrumented cylinders increased from 24.0 MPa for NC to 28.2 MPa for SF10 and 33.8 MPa for SF15, while the corresponding peak strain was increased from 0.00102 to 0.00116 and 0.00126. The secant modulus at 40% of peak stress also increased from 32.3 GPa for NC to 36.0 GPa for SF10 and 42.8 GPa for SF15. The descending branches of the SF10 and SF15 curves were not captured reliably, and therefore, no reliable conclusions could be drawn regarding ductility or post-peak behavior. In this range, SF15 had the best overall mechanical performance.