L. O. Ettu, J. C. Ezeh, O. M. Ibearugbulem, U. C. Anya, K. O. Njoku
Abstract: This work investigated the strength characteristics of binary blended cement composites made with Ordinary Portland Cement (OPC) and Coconut Husk Ash (CHA). 105 concrete cubes and 105 sandcrete cubes of 150mm x 150mm x 150mm were produced at percentage OPC replacement with CHA of 5 %, 10 %, 15 %, 20 %, and 25 % and crushed to obtain their compressive strengths at 3, 7, 14, 21, 28, 50, and 90 days of curing. The 3-28 day compressive strength values of OPC-CHA binary blended cement concrete were found to be much lower than the control values; the 50 day strengths were comparable to the control values; while the 90 day strengths were higher than the control values especially at 5-10 % replacements of OPC with CHA, ranging from 24.00N/mm2 for 10 % replacement of OPC to 25.10N/mm2 for 5 % replacement of OPC compared with the control value of 23.60N/mm2. This same trend was observed for OPC-CHA binary blended cement sandcrete. The variation in density was not significant. Mathematical models were developed for predicting compressive strengths of OPC-CHA binary blended cement composites using polynomial regression analysis. The model values of compressive strengths obtained from the various model equations were found to be either exactly the same as those of the equivalent laboratory values or very close to them, especially at ages 28-90 days, with differences ranging from 0 to 0.5N/mm2. Thus, OPC-CHA binary blended cement composites could be good for civil engineering works and the developed model equations can be easily used to estimate their strengths for various curing ages and percentage OPC replacement with CHA.
Keywords: Binary blended cement, composites, compressive strength, concrete, pozzolan, sandcrete