Combined effect of metakaolin and hybrid fibers on the strength properties of high performance concrete

Abstract

This study aims to investigate the combined effects of Metakaolin (MK) and Hybrid fibers on High-Performance Concrete's (HPC) mechanical properties. A constant proportion of 0.25% for polypropylene fibers (PF) and varying proportions of 0%, 0.5%, 0.75% and 1.0% for steel fibers (SF) making a total fiber volume fractions of 0%, 0.75%, 1.0% and 1.25% were used to develop hybrid fiber-reinforced high-performance concrete (HFRHPC). Four replacement levels for hybrid fibers by volume of the binders and four partial replacement levels for Metakaolin (0%, 10%, 20% & 30%) by weight of cement have been considered for three different water binder ratios (0.275, 0.325 & 0.375). An aggregate binder ratio of 1.75 was kept constant. The test results reveal a maximum increase of 31.83%, 37.05%, and 36.53% in compressive strength for curing periods of 7, 28, and 56 days, respectively. The split tensile strength, flexural strength, and impact strength test results show an increase of 42%, 74.41%, and 68.32% for a curing period of 28 days, respectively. Additionally, linear regression analysis was performed, and plots of compressive strength v/s tensile strength and compressive strength v/s flexural strength have been obtained to develop a relationship between compressive strength, tensile strength, and flexural strength. With the incorporation of metakaolin and hybrid fibers into the concrete matrix, very high mechanical properties could be achieved. The results indicate that a combination of 1.25% hybrid fibers and 10% Metakaolin gains all the water-binder ratios' highest strength.