Olawuyi, Babatunde James (2016-03)
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.
AFRIKAANSE OPSOMMING: Hoë verrigting beton (HVB) is bekend as ‘n beton met ‘n lae water/binder (w/b) verhouding en vertoon ‘n hoë sterkte, duursaamheid en elastiteitsmodulus. HVB is egter geneig om krake te vorm weens outogene krimp wanneer dit verhinder word om te krimp. Vorige werk het gewys dat die gebruik van superabsorberende polimere (SAP) hierdie outogene krimp kan verminder as dit gebruik word as ‘n interne kuur metode. Hierdie studie poog om die gebreke in die navorsing van HVB met SAP te vul, naamlik die verstaan van die meganiese eienskappe van hierdie materiaal. Hierdie werk het die meganiese eienskappe van HVB met SAP van twee groottes (< 300 μm en < 600 μm) ondersoek teen verskillende inhoude (0%; 0.2%, 0.3%, 0.4% bgvb) met drie verskillende meng klasse (M1F, M1S, M2, M3) na 7, 28, 56 en 90 dae van kuur in water. Eksperimentele werk was uitgevoer om die impak van SAP byvoeging op die reologie van die HVB, die effek van verskillende groottes SAP, die volume van SAP op die hidrasie tempo en sterkte ontwikkeling te ondersoek. Die werk het behels die kwantifisering en die modellering van die meganiese gedrag (sterkte in druk, trek en die elastiese en fraktuur eienskappe) van lae W/B HVB (0.2 tot 0.3) (C55/67 tot C90/C105) wat SAP bevat. Die mikrostruktuur en molekulêre interaksie van die interne bestanddele was ook ondersoek met twee nie-destruktiewe toetsmetodes naamlik CT skandering en elektronmikroskopie. Die studie wys ‘n minimale verlaging van die druksterkte van HVB indien die SAP inhoud verhoog word, maar geen effek was opgemerk op die elastiese en fraktuur eienskappe van die beton nie. Die 25 g/g SAP absorpsie kapasiteit bepaal deur die sogenaamde teesakkie-toets oorskat die eintlike hoeveelheid water opgeneem deur SAP in HVB. Die 3D leemte bepaling d.m.v. die CT skandering het getoon dat die leemtes veroorsaak deur die SAP is nader aan die helfte as verwag, naamlik 12.5 g/g. Dit bevestig die addisionele water wat benodig word vir interne kuur met SAP is eerder 12.5 g/g. Indien meer as 12.5 g/g water addisioneel bygevoeg word sal dit ‘n verlaging van die druksterkte veroorsaak. Die optimale addisionele water byvoeging vir interne kuur doeleindes vir HVB met SAP is dus 12.5 g/g.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98352
Doctoral Degrees (Civil Engineering)61