Effect of Silica Fume on Fly Ash Cement Bricks - An Experimental Study

Abstract

This investigation is done to study of the effect of silica fume on fly ash cement bricks. The experiments are conducted in two phases to observe the variation in properties i.e. compressive strength, density and water absorption of fly ash-cement brick. In first phase the fly ash, stone dust percentage are kept constant and cement is replaced with silica fume in different proportion, whereas in second phase, silica fume is added as a admixture in same proportion of weight of cement. The entire experimentation is done S.M. Nawle & Company fly ash - cement brick plant in Dhule. The fly ash cement - bricks are tested after 7 days, 14 days and 28 days curing in concrete material testing laboratory of the institute. The experimental results showed that in the compressive strength of fly ash cement brick decreases with increase in content of silica fumes as replacement of cement whereas increases with increase in content of silica fume as addition. The water absorption % in first phase of experimentation increases whereas in second phase of experimentation decreases. Keywords - Bricks, Compressive Strength, Fly Ash, Silica Fume, Water Absorption. I. Background India is the second largest producer of bricks after china. The estimated brick production during 2011- 12 was close to 200 billion. The Indian brick industry is unrecognized with small production units clustered in rural and peri-urban areas. There are more than 100,000 brick kilns operating in the country. The brick making consumes about 24 million tons of coal and several million tones of biomass fuels per year. The coal consumption by the brick industry is approximately 8% of the total coal in the country. The share of energy cost in total costs of brick production is 35 to 50 %. Several types of brick kilns are used for firing bricks. The choice of technology depends generally on factors such as scale of production, soil and fuel availability market conditions and skills. II. Fly Ash - Cement Brick Making Process The process for manufacturing fly ash - cement/lime brick requires fly ash, sand/stone dust, and cement/lime and gypsum which are mixed in proper proportion. Firstly lime and gypsum mixed in pan-mixer with optimum quantity of water. Then fly ash and sand/stone dust are further mixed in to pan-mixer to form homogeneous mixture. In the place of lime and gypsum if cement is used, initially in pan-mixer fly ash and sand/stone dust are mixed and after this cement is added into pan-mixer to form homogeneous dry mixture. The optimum quantity of water added in to pan-mixer until homogeneous dry mixture of fly ash, sand/stone dust and cement are achieved. The mixture is then transferred to the molding machine via belt conveyor and is pressed or compacted. If hydraulic press is used, the bricks are formed at a pressure of 150-200 kg/cm 2 . The pressed bricks are taken out manually and are laid on wooden pallet in 4-5 layers. The brick laden pallets are transported on hydraulic trolley from press area to stack yard. If vibratory press is used, the mix is manually brought from the pan-mixer and filled into the moulds. The table, on which the moulds are kept, is vibrated. The mix is also pressed lightly. The pallets from the table with the bricks are taken manually to stack yard. The bricks are air dried for about 1 to 2 days and then cured at least for 14 days to achieve its required strength. The curing is carried out by sprinkling water manually or by any other means. It is recommended that the curing period may be extended during cold/wet weather. The process of making the fly-ash cement brick is shown in Figure - 1.