Mechanical performance of high strength concrete made from high volume of Metakaolin and hybrid fibers

Among all construction materials, concrete made with Portland cement is one of the most used material all over the world. Reinforced concrete with short fibers distributed randomly was found to improve strength characteristics of cementitious matrices by controlling the initiation and/or spread of cracks. In this study, mechanical properties of high strength concrete with hybrid fibers were investigated. The properties included compressive strength, split tensile strength and bond strength of 21 mixtures containing hybrid fibers and Metakaolin. Combination of fibers, often called hybridization, refers to a composite of two or more types of fibers rationally combined in a matrix in order to produce a mixture that develops benefits from each fiber and shows a very good behavior. This study investigated the combination of different fiber proportions of steel and polypropylene in the presence of Metakaolin for a 60 MPa grade concrete at a total fiber volume fractions of 0.25% and 0.50%. It is concluded that the optimum percentage of cement replacement by MK is 15% either with the hybrid fiber fraction of 0.25% or 0.50%. The addition of different percentages of hybrid fibers to the concrete mixtures was effective for gaining strength at all testing ages. An increase in compressive strength of (13.62%, 24.17%, and 27.51%) for fiber content of 0.25% and (20.57%, 38.07%, 43.34%) for fiber content of 0.50% was observed at 28 days, respectively. A correlation between the compressive strength, split tensile strength, and bond strength were developed.