Mechanical and physical properties of stabilised compressed coal bottom ash blocks with inclusion of lateritic soils in Niger

Abstract

This paper describes the results from an investigation on the production of compressed block made with coal combustion by-products and local clayey soil in Niger. Stabilisation with Portland cement and a mixture of Portland cement and lime was adopted. Mechanical, physical, hydric, and thermal characterisation of the produced bricks was carried out. Blocks with satisfactory compressive strength were produced, with samples consistently exceeding the compressive strength of 4 MPa. Stabilisation with Portland cement proved to be the most effective in terms of strength development. However, satisfactory results were obtained with partial substitution of cement with lime (up to 30%). Porosity was found to be in the range 33% to 40% for all samples. The low thermal conductivity (in the range 0.31 to 0.48 W/m·K) was presumably influenced by the high porosity. Water absorption of the bricks was found to be very fast, although total water absorption (in the range 20.6 to 28.7%) was lower than the calculated porosity, suggesting that some of the pores were not accessible by water. Samples subjected to heating showed very promising results in terms of strength and mass loss. An increase in compressive strength was recorded up to temperatures of 400 °C. This might be due to the triggering of other reactions in the binding matrix due to the chemistry of the bottom ash. A change in colour of samples (from grey to red) was observed, due to the dehydroxilation of iron hydroxide turning into ferric oxide. Keywords: Coal bottom ash, Compressed earth blocks, Lime stabilisation, Water absorption, Fire resistance