This paper assesses the use of ‘‘Katsi’’ (dye residue ash) as an admixture in Ordinary Portland Cement (OPC) concrete in normal and aggressive environments. The ‘Katsi’ used was obtained from local dyers in Kano city and was sieved through a 425 μm sieve. The ‘Katsi’ was used as an admixture to Grades 20 and 30 concrete at percentage additions of 2.5%, 5%, 7.5% and 10% of the mass of cement respectively, with 0 % serving as control. Mix design was carried out in accordance with the Department of Environment (DoE) U.K (1975) method to determine the mix proportions of the two grades of concrete. Concrete mixes of the two Grades, 20 and 30 were prepared and the properties of fresh and hardened concrete assessed. The compressive strength of the samples of ‘Katsi’ concrete grades (cured by immersion in clean water for 3 days, 7 days and 28 days respectively) was determined in accordance with BS 1881, part 116, 1983. Some samples of the two grades of concrete (with various percentage addition of ‘Katsi’) were further cured in 0%, 5%, 10% and 15% concentration of NPK, super phosphate and urea solution respectively for 28 days after initially cured in water for 28 days. Then the compressive strength of the samples was determined to assess the effect of ‘Katsi’ on the resistance of ‘Katsi’ concrete to aggressive environment. Water absorption test was also conducted on cubes of the two grades of concrete cured at 28 days. There was a significant increase in the compressive strength of concrete with addition of up to 5% ‘Katsi’, for all ages of curing in water. The increase in 28 days compressive strength of 5 % ‘Katsi’ concrete was 15.7 % and 11.3 % that of control samples for grades 20 and 30 respectively. The use of up to 5% addition of ‘Katsi’ improved the resistance of concrete and sustained the durability of concrete cured in various concentration of fertilizer solution. The results also showed that the slump of ‘Katsi’ concrete increased slightly with increase in the percentage addition of ‘Katsi’. Addition of up to 10% ‘Katsi’ does not have any significant effect on the water absorption of concrete. .It is therefore recommended that 5% ‘Katsi’ should be used as an admixture to improve the compressive strength and durability of concrete in normal and aggressive environments.
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