Probing Optimal Blends of Pozzolans to Develop Supplementary Cementing Material within Busia County, Kenya
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Date
2024-04
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Kenyatta University
Abstract
Usage of pozzolanic materials in cement production has increased in the recent past years. This is because of the high expense of material, high energy requirement and high emission of green-house gases accompanied with manufacture of Ordinary Portland Cement (OPC). Utilization of pozzolanic material is advantageous because it utilizes local agricultural waste materials. This work focused on the use of natural pozzolans within Busia County, that is; broken bricks (BB), rice husks ash (RHA), clay and bagasse ash (BA), to make Pozzolana Cement (PC). These materials contain active Silica and Alumina necessary for a pozzolanic reaction to take place. BA was obtained as a by-product of controlled burning of Bagasse and limestone in a kiln. The lime obtained in this process was slaked to get calcium hydroxide. RHA was produced by burning rice husks at temperatures of 700 - 900°C. Using different ratio, we prepared RBC, BBC and RBBC samples. RBC comprised of RHA, BA and clay. BBC was made of BB, BA and Clay. RBBC comprised of RHA, BA, ground BB and Clays. The binder was made by mixing each Pozzolana ash with lime at different intervals. Mortar was prepared and tested for physical cement tests. Chemical composition tests demonstrated that the Pozzolans studied met pozzolanicity standards for use in supplementary cement production, with a total percentage of Iron(iii) Oxide (Fe2O3), Alumina (Al2O3) and Silica (SiO2) being greater than 70%. SiO2 had the highest percentage. The levels of MgO were less than 2.8% which comply with ASTM C (618) specifications. The electrical conductivity test showed that RHA had the highest rate of decrease in the electrical conductivity by 77% followed by BB 64%, Clay 56% and least was BA 26%. RHA had the highest pozzolanicity value and BA had the least though all of them had great change in electrical conductivity an indication that they are active pozzolans. In addition, optimal Pozzolana: Lime ratio was 2:1, and the best blend of the pozzolana ashes was RBC comprising of RHA, BB and Clay which gave a 28 days compressive strength of 2.88N/mm2 cured in air. The optimal blend obtained, for instance RBC falls under cement type CS ii as classified by BS EN 998-1; Classification For Hardened Rendering and Plastering Mortar. The others; BBC and RBBC fall under cement type CS i. The optimal Pozzolan: Lime binder had 677 minutes final setting time with 139 minutes initial setting time demonstrating that the binder takes a prolonged duration reaching peak hydration temperature comparing with Lime Pozzolana Cement. It implies that compared to PPC cements hydaration, the binder hydration is very low. The study provides an alternative method for making cement which is ecofriendly, of low cost and uses locally available materials in Kenya. It also has positive input on solving waste disposal problem which is of great environmental and health concerns.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Masters in Science (Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, April 2024.