Pullout test in steel fiber reinforced concrete

Abstract

Use of steel fibers in cement-based composites has become popular due to possibility of using that material as total or partial replacement of conventional reinforcement, as in floor slabs or tunnel cover. This reinforcement aims to improve composites properties with regard, mainly, to cracks propagation. It’s known that concrete has high compressive strength and durability, but its toughness is low, being considered a fragile material. The performance of the fiber as stress bridge depends on several factors, among them bond strength between fiber and matrix. Interfacial Transition Zone (ITZ) is one in which first cracks that lead to material failure appear. Some researches with mineral additives, such as rice husk ash (RHA), are aimed at ITZ densification. RHA has a high content of amorphous silica, which gives it high potential for its pozzolanic activity. That RHA characteristic is able to potentiate new hydration products formation, especially C-S-H, giving a higher density to cement matrix and pores and voids reduction. Research’s objective was to evaluate the effect of cement substitution by RHA, aiming to densify cement matrix to point where the adhesion stress with steel fiber was higher than in conventional mixture. For this, control specimens were produced and 15% of the cement replaced by RHA. Through the single fiber pullout test it was possible to measure the adhesion stress between steel fiber and cement matrix. Results indicate an increase in the adhesion strength with a long curing time, which confirms that the RHA hydration occurs late in relation to cement.