The Influence of Cement Content and Water/Cement Ratio on the Durability of Portland Cement Concretes exposed to Silage Effluent

Abstract

This paper outlines the findings of a study on the influence of cement content (275–425 kg/m3) and water/cement ratio (0·45 to 0·75) on the durability of concrete exposed to silage effluent. The test facility exposed concrete specimens to a controlled flow of effluent such that the volume of effluent in each 28 day cycle of exposure simulated one year's volume and expected period of effluent flow at the front of a well-drained 200 t horizontal silo. The relative performance of the concrete mixes was assessed over 10 cycles through measurement of saturated mass loss and surface depth change. The saturated mass loss measurement gave more consistent results. Optimum performance was recorded in concretes of cement content 325 and 375 kg/m3with water/cement ratios of 0·55 and 0·50, respectively. The studies indicate that water/cement ratio is a more critical variable than cement content. Deterioration increased significantly when the water/cement ratio exceeded 0·5. Increasing the cement content beyond the minimum recommended value in current national specifications (350 kg/m3) did not lead to a reduction in mass loss rate. The benefits of high cement content concretes is questioned, therefore, not least because of the increased risk of early-thermal cracking. It is postulated that specifications should limit the maximum water/cement ratio and both maximum and minimum cement content.