Simulation of the effect of nano-CaCO3 agglomeration on the hydration process and microstructural evolution of cement paste

In this study, three-dimensional simulations of cement hydration are conducted to investigate the effect of nano-CaCO3 (NC) agglomeration on the hydration process and microstructural evolution of cement pastes (CPs). Few experimental studies have reported on the effect of NC agglomeration on the properties of CPs because the degree of NC agglomeration is difficult to control in experiments. Herein, NC agglomeration was first investigated in a simulation by assigning different contents of NC in water-filled voxels in a three-dimensional cement hydration and microstructure development model (CEMHYD3D). CPs containing 3 wt.% NC with a water-to-cement ratio (w/c) of 0.3 were considered in the simulation. Four levels (1, 2, 3, and 4) of NC agglomeration were investigated by assigning 8.5, 13.7, 19.8, and 27 vol.% of NC in a C–H voxel, respectively. Agglomeration level 0 refers to the condition in which no NC particles are deposited in a water-filled voxel. An isothermal calorimetry test was conducted to validate the simulation results obtained for plain CPs. A comparison of experimental data and simulation results in terms of heat flow rate and heat formation revealed that level 3 showed better agreement than the other levels. The effect of NC agglomeration on cement hydration was more evident in the early stages of the process than in the later stages. Lower levels of agglomeration resulted in a faster hydration rate, a higher degree of hydration (DOH), and higher C–S–H and CH contents at an early age. However, the addition of NC particles did not result in an increase in ultimate DOH.