Effects of Particle Size on Hydration Heat and Mechanical Performance of Cement

The particle sizes of oil well cement are closely related to its performance and use. Oil well cements of different particle size distribution obtained with three grinding methods have been studied for their early hydration exothermic rate (rate of hydration heat liberation), hydration product of set cement, pore structure and the micro-morphology of particles using ICC, XRD MIP and SEM experiments. It was shown that physical grinding cannot produce nano particles; it can only produce ultra-fine particles. Particles size distributions of cement slurries with the same water/cement ratio had no appreciable effect on the density of the slurries and the hydration products. On the other hand, cement slurries with smaller particle sizes had shortened thickening time, poor rheology, reduced percentage of free water, and better stability. Meanwhile, ultra-fine cement particles had enhanced hydration reactivity and higher hydration heat and hydration exothermic rate. The cumulative hydration heat released in 24 hours of a 0.013 mm ultra-fine cement (MC1000-0.5) was 91.03% higher than that of conventional class G cement (G-0.5) at the same water/cement ratio of 0.5. The ultra-fine particle cement produced more hydration products in a short period, and the set cement had improved early strength and impervious performance, and reduced total porosity. The set cement of a 0.013-mm ultra-fine cement (MC1000-0.7) had 1-d compressive strength and flexural strength that were 226.32% and 153.13% higher than those of the class G cement (G-0.7) respectively at the same water/cement ratio of 0.7. The MC1000-0.7set cement had 28-d total porosity and permeability that were 10.1% and 41.7% lower respectively than those of the G-0.7 set cement, while the late-stage compressive strength of the MC1000-0.7 set cement only slightly increased.