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National Institute of Standards and Technology, Gaithersburg, MD USA
The degree of self-desiccation in field concrete depends on the availability of external water to replace that consumed due to the chemical shrinkage that occurs during cement hydration. As the cement hydrates, the capillary porosity depercolates, drastically slowing down this rate of external water ingress. In this paper, computer simulations are used to investigate the effects of cement particle size distribution (PSD) on capillary porosity percolation and the empty porosity created by chemical shrinkage. In addition, simulations are conducted with a single aggregate in the model microstructure to investigate the effects of cement PSD on interfacial transition zone (ITZ) microstructure at this aggregate interface. Because the largest pores empty first during self-desiccation, the ITZ region in systems containing aggregates is characterized by the presence of a large volume fraction of empty porosity relative to that found in the bulk paste. The cement PSD influences both the volume and size distribution of empty pores, which will in turn control the internal relative humidity reduction and autogeneous shrinkage for these materials. Thus, cement PSD is one material parameter available for engineering the self-desiccation and autogeneous shrinkage behavior of low water-to-cement ratio concretes.
Keywords: Chemical shrinkage, hydration, interfacial transition zone, microstructure, particle size distribution, percolation, self-desiccation, simulation.