Figure 11 and Figure 12 illustrate X-ray intensities of CSH and ettringite with curing time. In similar to the characteristic curves of strength development and cement pastes, CSH and ettringite intensity characteristic curves
of the cement stabilized soil markedly increased during the first two weeks, then slightly increased and became almost constant at long term. In addition, as illustrated in Figure 13 and Figure 14, strengths were increased proportionally with amounts of CSH and ettringite that formed. It could therefore be concluded that these reaction products mainly contribute to strength development of the cement stabilized soils.
It was assumed that initial hardening effect was additionally enhanced due to formation of reaction product such as ettringite. Essential role of ettringite (3CaO.Al2O3. 3CaSO4. 32H2O) was attributed to the fact that large amount of water was initially combined in its crystals, resulting in significant decrease in moisture content at the early age. Extracting water that existed in the pore spaces by ettringite provided a reduced water to cement ratio that aided further hardening. In addition, CSH were thus formed simultaneously at the beginning course of reaction. Significant increase in strength of the stabilized soil was due to growth and hardening phases of CSH that bound soil particles together. Hardened and denser structure was gradually formed, resulting in a substantial increase in soil strength with progressive of
curing time.