Investigating the Effects of Variability in Pozzolanic Properties of Rice Husk Ash on Compressive Strength of Concrete

Rice husk ash (RHA) is an agro waste and a natural pozzolana which is rich in silica and found in
abundance globally. This research considered the pozzolanic properties of RHA from Seven different
sources in Nigeria (Ogoja, Abakaliki, Adani, Adikpo, Obubra, Makurdi and Vandikya). It is discovered
that the elemental chemical composition of this natural pozzolan varies based on their location.
Samples from Ogoja were found to have the highest pozzolanic properties followed by Abakaliki,
Adani, Adikpo, Obubra, Makurdi and Vandikya. Their silica content was found to be84.55%, 76.3%,
70.12%, 70.11%, 64.67%, 55.55%, and 48.4% respectively. Four out of the seven samples with the
highest pozzolanic values were used as partial replacements for ordinary Portland cement at 5, 10,
15, 20, 25, and 30% replacement levels. Concrete mix ratio of 1:1.5:3 was adopted and the
compressive strength values at 28 days were found to be in the range of 37-42N/mm2 at 5%RHA, 35-
39.5N/mm2 at 10%RHA, 30-34.5N/mm2 at 15%RHA, 27-29N/mm2 at 20%RHA, 22-25.6N/mm2 at
25% RHA and 21-24N/mm2 at 30% RHA compared to the controlled sample with a strength value of
42.64N/mm2.