Figs. 3 and 4 show the role of ash content on unit weight and
strength development in the FA blended cement admixed Bangkok
clay cured for 28 days. It is noted from Fig. 3 that for all water contents
tested, the unit weight and strength increase with fly ash
content and achieve the peak values at a = 25%. The unit weight
and strength gradually decrease with the ash content when
a > 25%. For the same combination of cement content and fly ash
content, the higher the water content, the lower the unit weight
and the strength. The peak unit weight and strength are also found
at a = 25% for different cement contents (vide Fig. 4). This characteristic
is also found for the BA blended cement admixed Bangkok
clay for all tested water contents, cement contents, and curing
times. To conclude, the optimal ash content is 25%. It is independent
of cement content since the ash content is determined in proportion
to the cement content.