Investigation of shrinkage in industrial concrete slabs on ground

Abstract

Concrete slabs on ground are used widely in engineering construction design. However many problems lie with the crack susceptibility and therefore durability reduction created from shrinkage in concrete. The performance of slabs on ground can be significantly influenced by early age shrinkage. Through previous research, and this current study, tensile stresses are shown to occur in concrete slabs, and will cause an increase in concrete cracking. Slabs experience many conditions resulting in early age shrinkage and minimal research exists to incorporate the early age effects on slab shrinkage strains and cracking. Crack prevention is critical in designing and constructing concrete slabs. Concrete mixes with low 56 day standard drying shrinkage levels are generally used as an attempt to control cracking. It is often assumed that a low selection of a 56-day shrinkage level is adequate to reduce shrinkage strains and hence cracking. However this is not necessarily the case. This thesis researches the relationship between different shrinkage levels of concrete mix and experimental data. It is found that ‘stronger’ concrete does not mean less cracking, and therefore other methods and factors need to be incorporates to prevent early age shrinkage. Curing method and the addition of evaporation retardants are used to prevent the onset of cracking in concrete slabs. Moist curing and curing-compound application are compared relative to its effect on early age shrinkage strains. Evaporation retardants are discovered to significantly reduce the early age shrinkage strains in concrete slabs. Current concrete shrinkage prediction models are studied, and have little relevance to the experimental data. This is predominately due to the early age effects of strain, and the lack of inclusion of early age shrinkage when the models were formulated. Early age shrinkage has major effects on the formation of cracking in slabs on ground. Important measures need to be taken to help prevent these detrimental effects of early age shrinkage strains (cracking). Evaporation retardants are found to be very effective along with the moist curing of concrete.

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