Experimental investigation on flexural toughness of hybrid fiber reinforced concrete (HFRC) containing metakaolin and pumice

•The mechanical properties for hybrid fibers reinforced concrete.•Investigation the effect of pumice and metakaolin on compressive strength and flexural toughness of concrete.•Effect of pozzolans on load versus deflection diagram of hybrid fibers reinforced concrete.•Modulus of rupture of hybrid fibers reinforced concrete containing pumice and metakaolin.

Fiber reinforced concrete (FRC) has been widely used due to its advantages over plain concrete. It can be an appropriate material for the repair of structures in a variety of situations. However there is a weak zone between fibers and paste in fiber reinforced concretes and this weak zone is full of porosity, especially in hybrid fiber reinforced concretes. Therefore, using of pozzolanic materials is required to reduce the porosity.Pumice and kaolin are two pozzolanic materials that have been found abundantly in some regions of the world. In this paper, the mechanical properties of concretes containing various amounts of the pozzolanic materials and steel and polypropylene fibers are investigated.At the first step of this paper, the flexural and impact resistance tests were carried out to choose the optimum percentage of steel and polypropylene fibers. Results showed that hybrid fiber reinforced concrete with 0.75% steel fibers and 0.25% polypropylene fibers had higher toughness indexes, modulus of rupture and impact resistance than other hybrid mixtures. Afterward, compressive strength and flexural tests on hybrid fiber reinforced concretes containing pumice and metakaolin were carried. Results showed that, metakaolin with highest substitution of cement had the best performance of mechanical properties of concrete. Moreover, this pozzolan caused increasing in compressive strength in comparison with control mixture. However, replacing pumice into the specimens had negative effect on the mechanical properties results.