High performance concrete is known with its unique property of low water-binder ratio and thereby reported to be susceptible to autogenous shrinkage while the previous research efforts directed at incorporation of superabsorbent polymers (SAP) and pre-saturated lightweight aggregate (LWA) as internal curing (IC) agents in autogenous shrinkage mitigation and the incorporation resulted into an increase in the porosity of the HPC. This study seeks to fill the existing gap on proper understanding of the effectiveness of Nigeria pre-soaked pumice in comparism with SAP being a foreign material not available in Nigeria. While rice husk ash (RHA) on the other hand, affirmed to be an effective silica fume (SF) alternative replacement, a major requirement in HPC production. The work studied the sulphate resistance of HPC containing RHA as the SCM with Nigeria pre-soaked pumice and SAP incorporated as IC agents. HPC mixtures of designed C55/67 characteristic cube strength at 28 days were produced incorporating SAP at 0.2% (SHPC) by weight of binder (bwob) and pre-soaked pumice at 5% (PHPC1) and 7.5% (PHPC2) by weight of coarse aggregate at constant 10% RHA bwob using 100 mm cubes cured in water and magnesium sulphate solution. The gradual deterioration and resistance to sulphate of these specimens were examined via visual observations, mass loss and strength loss. The results revealed that the concrete cured in sulphate solution showed white sulphate crystals on both the reference HPC (CHPC) and the HPC incorporated IC agents at all ages except at 28 days where the specimens had grey colour and few precipitate. All HPC specimen studied suffered slight mass and strength losses but the losses decreased as the curing age increases as a result of a progressive hydration. The losses were observed to be higher in CHPC as compared to the internally cured HPCs. The study revealed that the RHA is a very reactive pozzolan and can be used as alternative to silica fume and the IC agents have effect on the strength property of the HPC. Pre-soaked Pumice of Nigeria origin’s utilization at 5% was observed to be better compared to other mixes in sulphate resistance behaviour and the study therefore recommend 5% Pre-soaked pumice as an IC agent in RHA based HPC production for good performance in sulphate environment.
Mohoro et al. (Wed,) studied this question.