Potentials of using waste burnt clay as a pozzolanic material in Kenya

Samples of waste burnt clay were collected from various parts of the country to study their pozzolanic properties. The samples were ground into fine powder and taken for chemical tests. Results from the chemical tests on all the samples showed high silica content. In fact the combined percentages of Silica (SiO2), Alumina (Al2O3) and Iron Oxide (Fe2O3) was more than 70%, a requirement by the Kenyan standard for a suitable pozzolanic material. One sample from a major factory (being a large quantity) was mixed with various proportions of Ordinary Portland cement (OPC) and used for physical tests. Results showed compressive strengths way above the recommended for masonry cement when up to 50% OPC was replaced with burnt clay. For masonry works 50% OPC replacement with burnt clay will still give satisfactory results and reduce cost of binder by at least 20%.