Combined effect of silica fume and steel fiber on the mechanical properties of high strength concretes

In this experimental study, the changes on some mechanical properties of concrete specimens produced by using silica fume and steel fiber were investigated. The main objective of this work is to obtain a more ductile high strength concrete produced by using both silica fume and steel fiber. Two types of steel fibers with aspect ratios (fiber length/fiber diameter) of 65 and 80 were used in the experiments and volume fractions of steel fiber were 0.5% and 1%. Additions of silica fume into the concrete were 0%, 5%, 10% and 15% by weight of cement content. Water/cement ratio was 0.38 and the reference slump was 120 ± 20 mm. Slump test for workability, air content and unit weight tests were performed on fresh concretes. Compressive strength, splitting tensile strength and flexural strength tests were made on hardened concrete specimens. Load–deflection curves and toughness of the specimens were also obtained by flexural test performed according to ASTM C1018 standards. Flexural tests on beam specimens were achieved using a closed loop deflection-controlled testing machine.The use of silica fume increased both the mechanical strength and the modulus of the elasticity of concrete. On the other hand, the addition of steel fiber into concrete improves toughness of high strength concrete significantly. As the steel fiber volume fraction increases, the toughness increases, and high values of aspect ratios give higher toughness. The toughness of high strength steel fiber concrete depends on silica fume content, the fiber volume fraction and the fiber aspect ratio.