Browsing by Author "Olawuyi, Babatunde James"
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- ItemThe Mechanical Behaviour of High-Performance Concrete with Superabsorbent Polymers (SAP)(Stellenbosch : University of Stellenbosch, 2016-03) Olawuyi, Babatunde James; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: High performance concrete (HPC) is known to be of low water-binder ratio (W/B) and exhibits high strength, durability and elastic modulus amongst many other properties. HPC is susceptible to autogenous-shrinkage-caused-cracking under restraints while previous research efforts directed at mitigating autogenous-shrinkage in HPC by the introduction of IC agents have reported superabsorbent polymers (SAP) to be the most promising. This study seeks to fill the existing gap on proper understanding of the effect of SAP addition on the mechanical behaviour of HPC. The work studied the mechanical properties of HPC containing SAP as internal curing agent (IC-agent) using two grain sizes of SAP (˂ 300 μm and ˂ 600 μm) at varied SAP contents (0%; 0.2%; 0.3%; and 0.4% bwob) in four reference HPC mixtures (M1F, M1S, M2 and M3) after 7, 28, 56 and 90 days of curing in water. SAP absorption in cement pore solution (CPS) was determined using the tea-bag test and the 25 g/g absorption in CPS obtained after 10 minutes of immersion was used for provision of additional water in the HPC mixtures. Experimental works were carried to study the impact of SAP addition on the rheology of the HPCs, as well as identify and establish the effect of varying sizes and volume of SAP on rate of cement hydration and strength development. The work involved quantifying and modelling the mechanical behaviour (strength in compression, tension, elastic and fracture properties) of the low W/B (0.2 – 0.3) HPC (C55/67 – C100/115) with SAP. Microstructure and molecular interaction of the internal constituent of the HPC were also investigated using the X-ray computed tomography (CT) scanning and scanning electron microscopy (SEM). The study observed a slight decrease in the compressive strength of HPC as SAP content increases but there is no such effect on the elastic and fracture properties of the concrete. The 25 g/g SAP absorption result of the teabag test over-estimates the actual amount of water used up by SAP in the internal curing of HPC. The 3D void analysis of the HPC via CT scanning revealed that SAP created voids in the HPC is only about half (i.e.12.5 g/g) of the teabag test result of 25 g/g and affirms that the required additional water for SAP’s effective internal curing of the low W/B HPC is 12.5 g/g. The study concludes that the optimum additional water for SAP addition in the low W/B HPCs at no negative effect on mechanical properties is 12.5 g/g.