Abstract
This paper presents a contribution to the modeling of the chemical shrinkage of the slag-blended cement paste (binder) at early age. Assuming that the chemical shrinkage is a direct result of hydration, the hydration modeling of slag-blended cement was studied by considering the interaction between the hydrations of blast furnace slag (BFS) and ordinary Portland cement. The reaction of BFS in the presence of calcium hydroxide CH (Portlandite) produced from the hydration of the cement was investigated. The kinetic hydration of cement was developed, and the volume phases in the cementitious material during the hydration process were calculated. The chemical shrinkage, which is the negative volume balance between the reactants and the products formed, is then calculated. In parallel with this numerical modeling, an experimental study was conducted to investigate the effect of slag’s addition (0%, 30%, 50% and 80%) on the heat of hydration and chemical shrinkage at early age (maturation up to 7days). The proposed hydration model incorporates the effect of following variables; the chemical composition of the binder, the fineness, the water to binder ratio (w/b), the curing time and the temperature.
Highlights
Autogenous shrinkage is considered as one of the phenomena clearly identified as the origin of the cracking of cementitious materials used in the design of civil engineering structures
The presence of the slag contributes clearly to the reduction of the heat of hydration which is very beneficial for mass concrete to minimize the risk of cracking
The interactions between the cement hydration and slag reaction were considered through the available calcium hydroxide amount in the system
Summary
Autogenous shrinkage is considered as one of the phenomena clearly identified as the origin of the (micro) cracking of cementitious materials used in the design of civil engineering structures. When, is prevented, the shrinkage is responsible for the formation of microcracks in the area surrounding the aggregates and through cracks in the binding matrix. This leads to an increase of the porosity and loss containment characteristics of material and an increase in its permeability. The autogenous shrinkage is a physico-chemical phenomenon coupled to mechanical capillary effects due to consumption of pore water during the hydration. The origin of this deformation has been studied extensively in the literature [1,2,3]. At early-age, these stresses are often higher than the breaking stress of the material, the occurrence of (micro) cracks
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