ASSESSMENT OF USING AN OPTIMAL DOSE OF SUPERPLASTICIZER WITH THE OPTIMUM REPLACEMENT OF RICE HUSK ASH (RHA)ON CONCRETE COMPRESSIVE STRENGTH

Rice straw is one of the best sources of huge waste where governments try to get rid of it because it is harmful to the environment as the irregular burning of it by farmer's causes a lot of damage to the environment. This study aims to find the optimal dose of the plasticizer with the optimal replacement ratio of the Rice Husk Ash ( RHA ) and the optimum dose of superplasticizer (B-V-F) with ordinary Portland cement (OPC) concrete and comparing their results. Following is noted all researches agreed on the inevitability of using RHA without using a plasticizer, but no one studied the effect of added different doses of the plasticizer to RHA concrete or in other hand added it to different replacement percentages of RHA. In this study RHA generated by burning rice husk straw in a huge iron container for 24 hours. To improve pozzolanic activity, RHA was grinding in a flour mill. After the preparation of the material, we studied its chemical composition and physical properties. the Program consists of seven groups (A, C, A.13, A.15, A.2, A.1, and B) The first group mix (A) contained four mixtures of) OPC (by weight replacement (0, 10%, 15%, and 20%) from RHA, the second group contains six mixtures with a constant slump (15±3) and water-cement ratio (0.51), The first mixture is the control mix without any added of RHA or plasticizer the second mixture did not contain RHA, but it contained a dose of the plasticizer, the remaining four mixtures contained OPC by weight replacement (0%, 10%, 13%, 15%, and 20%) from RHA and different doses of the plasticizer. The group (A.1) contains six mixtures with a constant replacement cement ratio RHA and a constant slump of 23 cm, except the last mixture No( 21) that has a slump 8, and each mixture contains a different water-cement ratio and plasticizing doses. The seventh group (B) consists of three mixes of (OPC) cement with different doses of plasticizer and different water-cement ratio, all of which had a constant slump of 23cm. The result shows that the optimum replacement of RHA is equal to 10% at W/C ratio 0.51and (B-V-F) 6 L/ which increased concrete compressive strength by about 32% compared to the control mix. The optimum dosage of superplasticizer with optimal replacement was found to be 15 L/m^3 at W/C ratio 0.36, at which an increase in compressive strength by about 76% as compared to the control mix: The optimum dosage of superplasticizer (B-V-F) with (OPC) is 8 L/m^3 at W/C ratio equals 0.38 achieves an increase in compressive strength by 58% compared to (OPC) mix (control mix).