The heterogeneous characteristics of the microstructure in cement stone under the effect of self-weight segregation

Under the influence of self-weight segregation, the microstructure of cement stone exhibits significant heterogeneous characteristics, but the mechanisms of these variations have not been revealed. In this study, the pore size distribution and porosity of the cement stone with various water-to-cement (w/c) ratios and the initial height were measured using NMR methods. The relationships between cement stone porosity and height position were fitted using a simplified self-weight consolidation finite model and a small strain model. The results show that under the same w/c ratios, the density and porosity of the stones formed at the bottom of cement grout columns with different initial heights are essentially consistent. As the height increases, the amount of ettringite increases while the formation of C-S-H gels decreases, leading to a higher content of transitional and capillary pores, which primarily contributes to the overall increase in the porosity of the cement stone. The variation trend in the porosity of cement stone with a lower w/c ratio, such as 0.8, aligns with the predictions of the finite strain model. As the w/c ratio increases, like 1.0 or 1.2, the reduction in effective stress between particles delays the self-weight consolidation process, enhancing the influence of cement hydration. This ultimately makes the porosity change more consistent with the small strain model.