Abstract
Thermal stresses are generated in concrete during the accelerated curing process in precast concrete. These stresses may cause concrete to crack, which would have a negative effect on the general concrete performance. This paper provides the results of the thermal stress analysis of concrete containing 25% replacement of ordinary Portland cement (OPC) by ground granulated blast-furnace slag cement (GGBFS) with 3000 cm2/g fineness. A total of 2.5% of limestone powder and 1.75% of fine gypsum by mass of OPC were incorporated in the other concrete mix proportion to check their effect on the cracking tendency of concrete. The concrete was subjected to heat curing. JCMAC, a 3D finite element analysis software developed in Japan, was used in this study for the thermal stress analysis. The heat curing period of one day, similar to generally used in the precast concrete industry for civil engineering products consisting of 3 h preheating period, heating to a peak temperature of 65 °C and this temperature was kept for 3 h, and lastly cooling was used in the study. A standard precast box culvert model member together with some experimental results obtained in the laboratory were used in the analysis. Lower cracking resistance at 1 day was observed in both mix proportions that would lead to cracking at demolding time. Curing sheets were then introduced in the analysis to cover the precast mold during accelerated curing and this showed improvement in cracking resistance of concrete containing limestone powder and fine gypsum.
Highlights
Cracks may develop in concrete structures at different ages due to several reasons, but the main principle is the fact that concrete is a quasi-brittle material with a low capacity for deformation under tensile stresses [1,2,3]
There was an increase in the setting time in both concrete mix proportions in relation to the general time concrete made with N cement
The results from the fresh, mechanical, shrinkage properties of concrete made with BFS cement as main mineral admixture and subjected to accelerated curing by heating provided some input parameters for 3D FEM analysis
Summary
Cracks may develop in concrete structures at different ages due to several reasons, but the main principle is the fact that concrete is a quasi-brittle material with a low capacity for deformation under tensile stresses [1,2,3]. Cracks that may occur either at early or later age are often attributed to concrete shrinkage and their extent has a negative effect on concrete durability. It has been recognized that control of concrete cracking caused both by temperature change and shrinkage can be achieved through the selection of proper materials, mix proportions, curing conditions, and construction practice [4]. These measures promote concrete produced with desirable strength and durability. Many factories in the precast concrete industry use accelerated curing methods and various concrete mix proportions to achieve desirable early strength and minimize crack development at early and later age [5]. Various supplementary cementitious materials (SCMs) such as ground granulated blast furnace slag cement (GGBFS) are often used in precast concrete products [7]
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