Effect of FAG on compressive strength
A strength development of concrete containing FAG as a
cement replacement of 15%, 25%, and 35% was faster than
that of the 50% cement replacement, while 25% cement
replacement gave the highest compressive strength at all
ages as shown in Fig. 11. At 15–35% content replacements,
the compressive strengths were higher than that of control
concrete at all ages up to 180 days. For example, the 7-day
compressive strengths of FAG15, FAG25, and FAG35 were
71.0, 71.2, and 70.8 MPa or about 120% of the control
concrete (see Fig. 12). At 28 days, the compressive strength
tended to increase with the curing age for all mixtures and
varied from 77.3 MPa in sample FAG50 to 82.5 MPa in
sample FAG25. This is due to the extreme fineness of fly
ash that exhibits pozzolanic properties and packing effect.
These characteristics tend to improve concrete strength as
well as its density [4]. The results also confirm those of
Kiattikomol et al. [8] that the fineness of fly ash was the
major factor affecting the compressive strength of FAG–
cement mortar. In addition, no significant difference in
compressive strength was observed between mortars containing
classified fly ash and FAG of similar median particle
size. The sample FAG50, which contained 50% of FAG as a
cement replacement, had compressive strength at 7 days of
70.3 MPa or 119% of control concrete. Thereafter, the
compressive strength of FAG50 was almost the same as that
of control concrete as shown in Fig. 12.