Experimental and theoretical study on the compressive strength of the high strength concrete incorporating steel fiber and metakaolin

In this paper, the effect of steel fiber (SF), Metakaolin (MK) and time of curing on the concrete compressive strength (fcu) was implemented. Cylinder specimens cast from concrete with SF (0, 0.25% and 0.5%) and MK (0%, 10%, 15%, 20%, 30%, 40% and 50% as replacement of cement content) were tested in compression at different ages of curing (3, 7 and 28 days). The results assured that; the concrete strength increased as MK% increased from 0% to 15% then decreased with further increase in MK%. Also, increasing the SF% from 0 to 0.5% increased the concrete strength. The optimum values of enhancement in fcu were obtained for concrete mix with 15% MK and 0.5% SF. The enhancement percentages in fcu of this mix at 3, 7 and 28 days were 26.53%, 33.04% and 44.65% over that of the control mix at the corresponding ages respectively. Moreover, a relation between fcu, SF%, MK% and curing age were predicted using two methods (the Central Composite Design, CCD and the Box Behnken Design, BBD). The two methods were also used to construct prediction equations for the cubic strength using experimental results from previous researches. The accuracy of these equations was verified to be a base of mix design for concrete with SF and MK.