Variations of water absorption rate and porosity with depth from an exposed concrete surface: Effects of exposure conditions and cement type

Abstract

Small prisms of hardened cement paste were conditioned for 4 years within cavities in a uniaxially exposed, companion concrete cube. Four exposure conditions and three types of cement were used. The concretes and cement pastes were made with a water/cement ratio of 0.59 and were cured for three days prior to exposure. Water absorption rate, capillary porosity and gel porosity of the prisms were investigated as functions of the depth from the exposed concrete surface. The average water absorption rate and capillary porosity of the prisms in the 20 mm surface zone were generally greater than those of the underlying material. Carbonation reduced water absorption rates in prisms made with Portland cement due to associated reductions of capillary pore volume and continuity : carbonation increased the water absorption rate and capillary porosity of prisms made with OPC/fly ash or OPC/ground granulated blastfurance slag. When the capillary porosity reduces below about 0.2 the water absorption rate reduces markedly, suggesting that the pores are becoming less continuous.