Flexural strength of concrete made from Guınea Corn Husk Ash as partial replacement for cement

Abstract

Guinea Corn Husk Ash (GCHA) was a converted product of Guinea Corn Husk (GCH) that was incinerated up to a temperature of 600⁰C. The husk is a common agro-waste in Northern Nigeria. The GCHA was used to partially replace Ordinary Portland Cement (OPC) in concrete. The use was expected to reduce environmental nuisance and cost on cement. The replacement levels of 0%, 5%, 10%, 20%, 30% and 40% ash were used. The chemical constituents of the GCHA as determined from an X-Ray diffraction analyzer included SiO₂ (85.4%), K₂O (4.01%), Fe₂O₃ (0.64%), CaO (2.04%) and Na₂O (0.98%). SO₃ and AI₂O₃ were not detected. The combined percent of SiO₂, Al₂O₃ and Fe₂O₃ of 86.04% is above the 70% benchmark for a pozzolana material. Also, SO₃ and NaO₂ fall below the maximum allowable values of 4% and 1.5% respectively. The sieve analysis results show that GCHA has about the same fineness as OPC. The fresh concrete had slump values that ranged from 11mm for 0% cement replacement to 3.6mm for 40% replacement and lower densities. The hard concrete had flexural strength that was measured as Modulus of Rupture that ranged from the highest value of 4.61N/mm² at 0% replacement to the least value of 3.19N/mm² at 30% replacement after 56 days of curing. The density values equally decreased at an average of 3.3%. Relevant British and American standards procedures were used for the tests. The trend showed that GCHA neither improved flexural strength nor increased the density of concrete produced with it. The lower slump and fresh concrete values however makes for ease of fresh concrete handling.