Assessment of effect of varying firing time and temperature on some physical properties of burnt clay bricks produced around jimma town

Abstract

Brick is one of the most widely used conventional construction materials throughout the World. The production cost of clay brick is significantly affected by the cost of energy required for firing; Different mechanisms have been used to reduce the energy required for clay brick production. For better energy utilization during brick production, controlling of firing temperature is a usual practice in the recent brick manufacturing technology. However, over and under firing clay bricks production and poor firing kiln management are major problem in traditional brick production. Generally controlling the firing temperature during clay bricks production plays a decisive role in both quality and production cost. The aim of this research is to study the effects of different firing temperature and time on the compressive strength, water absorption and saturation coefficients of fired clay bricks and evaluate effect of firing process in brick manufacturing on the properties, color and appearance of the brick.. The raw materials for this study were sampled from two quarries and clay bricks are produced from two soil samples. The physical property requirements of these clay bricks which dried clay bricks are fired at various temperatures of 700, 970 and 1200°C and fired for duration of 2h, 4h, 6h and 8h firing are tested and analyzed. Laboratory test and Interview questionnaires are designed to study the firing temperature management practices of some traditional brick production in and around Jimma. In addition to the interview, observational based study is conducted by visiting their production processes. During the production process effect of different heating rates on physical properties of firing standard bricks will be analyzed. In this investigation, different heating rates were used: slow heating rate and fast heating rate. Change will be checked with increment of firing temperature and all bricks were tested for their physical and mechanical properties. The results of this study show that with increment of firing temperature within the allowable firing temperature range; increase the compressive strengths and lower both the water absorptions and saturation coefficients of clay bricks. Increment of duration of firing slightly increases the compressive strength and lowers both the water absorption and saturation coefficient. The firing temperature control of the traditional brick factories surveyed during this study show that they have no temperature controlling device for their kiln but it is done with the observation of their kiln operator’s. Over and under firing of clay-bricks is their usual loss. Moreover, according to the response of the interviewee’s, the significance of firing temperature is less understood when compared to other stages in clay-bricks production. It was concluded that the allowable mechanical property for brick samples within the temperature range considered is obtained at 970 to 1200 oC and firing duration of 6hr to 8hr according to Ethiopian standard specification ES- 86:2001.