Effect of silica fume on the mechanical properties of crushed brick concrete

This paper presents an experimental investigation on the effect of silica fume on the mechanical properties of concrete obtained by replacing 50% of weight of stone aggregate by crushed clay-brick. The only variable considered in this study was the dosage of silica which it is a percent of cement weight, the percent values of replacement silica fume are (0%, 2%, 4%, 6%, and 8%) of cement weight. The comparative study is focus on the effect of the silica fume on this type of concrete not the effect of replacement of crushed brick. The added silica fume has active effect on the strength of crushed brick concrete. The effect of using silica fume on compressive strength is different for the different replacement of silica fume and it is more active for the 2% replacement at 7 days age, while the replacement that yield best enhancement at 28 days is 4%. The compressive strength for 28 days age is about 27.5 MPa,29.5 MPa, 38.5 MPa,31.4MPa, and 10MPa,for (0%, 2%,4%,6%, and8%) of replacement silica percent .Further more the best increasing in tensile strength is at 2%while there is a small gradually increasing in gain in modulus of rupture with using silica fume until 6%, which beyond the least value it starts to drop.The high level which is observed in this study beyond 6% reduces the gain in strength of compressive at 28 days and it gets a compressive strength less than the control value at 7 days. Furthermore it gets a reduction in tensile strength and modulus of rupturein at 28 days.