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.
Supplement explanation on strength development due
to subsequent changes on soil structures should be further
elucidated. This could be accomplished by using the
advantage of Scanning Electron Microscopic observation
(SEM) of the cement stabilized soil. The results were
reported in a separate paper.