Effect of Pozzolana on the Compressive strength of Concrete in Chemically Aggressive Environment.

Abstract

Concrete deteriorates considerably when exposed to aggressive chemicals such as sulphates and acids. Incorporation of pozzolana to concrete can ameliorate its effectiveness in these chemicals but this has to be experimentally established. This paper therefore investigates the effect of pozzolana; (rice husk ash (RHA), powdered burnt brick (PBB) and saw dust ash (SDA)) on the compressive strength of concrete in chemically aggressive environment. This was achieved by partially replacing concrete with 10 percent (%) of each pozzolana to produce three different concrete samples. Samples of 100% concrete were equally produced to serve as the control. The quantities of cement, fine aggregate and coarse aggregate used for the production of the specimens were obtained through absolute volume method of calculation. A mix ratio of 1: 2: 4 with watercement (w/c) ratio of 0.65 was adopted for the various specimen. 150x150x150mm twenty-seven (27) concrete cubes were produced for each pozzolana and the control specimen. The specimens were cured for 28 days in ordinary water after which they were equally and completely immersed in chemical solution of 5% H2SO4, 10% MgSO4 and ordinary water for another 28 and 56 days. The specimens in ordinary water were used as the control during the chemical test. The percentage reduction in strengths of RHA, PBB, SDA and the control specimens in 10% MgSO4 at 56 days were observed to be 2.09%, 3.26%, 23.03% and 10.06% respectively. In 5% H2SO4, the percentage reductions in strengths of RHA, PBB, SDA and the control at 56 days were also observed to be 25.13%, 21.27%, 52.19% and 33.61% respectively. The results show that RHA and PBB concrete exhibit better strength than SDA and the control specimen in MgSO4 solution. All the specimens tested in H2SO4 performed poorly at 56 days. The study concludes that RHA and PBB concrete are highly resistant to MgSO4 and can be recommended as sulphate resistant additive in concrete production.