Author(s) :

OGORK, E.N., DANJA, Y.N..

Volume/Issue :

Abstract :

This paper presents an investigation on the effects of sorghum chaff ash (SCA) in cement paste and concrete as a supplementary cementing material. The SCA used was obtained by controlled burning of sorghum chaff to ash in a blast furnace at a temperature of 600 - 650 oC for five hours, and after allowing cooling, sieved through sieve 75 μm and characterized. The effects of SCA on cement paste and concrete were investigated at replacement levels of 0, 5, 10, 15, 20, 25, 30 and 40 % by weight of cement. The slump values of fresh concrete containing SCA as supplementary cementing material and of 1:2:4 mix ratio and water-cement ratio of 0.55 was determined. A total of ninety six numbers of 150 mm cubes of hardened concrete were tested for compressive strength at 3, 7, 28 and 56 days of curing in accordance with standard procedures. The concrete compressive strength was also modeled using Minitab statistical software based on linear regression technique. The results of the investigations showed that SCA has a combined SiO2, Al2O3 and Fe2O3 content of 79.56 %. The use of SCA as a substitute of cement increased consistency, initial and final setting times, as well as linear shrinkage of cement. The workability and compressive strength of concrete decreased with increase in SCA content. The 56 days compressive strength of SCA-concrete ranged from 40.6 – 105.2 % of control at SCA content of 5 – 40 %, with highest and least compressive strength occurring at 5 and 40 % SCA content, respectively. It is recommended that 25 % SCA content be used as replacement of cement in concrete, with 56 days compressive strength of 21 N/mm2. The compressive strength model of SCA-concrete was developed with R2 value of 0.846 and could be used to predict concrete compressive strength.

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