Materials used in this study consisted of Portland cement
type I, fine and coarse aggregates, fly ash, condensed silica
fume, superplasticizer, and water.
The coarse aggregate used was crushed limestone with
12 mm maximum size. The fine aggregate was natural river
sand, having a fineness modulus of 3.02. The coarse and
fine aggregates had a specific gravity of 2.67 and 2.61, and
water absorption of 0.3% and 0.8%, respectively.
The original fly ash from silo of Mae Moh power plant in
the northern part of Thailand was classified into different
particle sizes. It is known that fly ash with high fineness is
an excellent pozzolanic material to make high-strength
concrete [4]. However, this is not true for fly ash having a
large particle size. The mortar made from coarse fly ash,
having the average particle size of about 90–100 mm,
exhibited a strength activity index of 59% and 63% at the
ages of 7 and 28 days, respectively [3], which was very low
and did not conform to ASTM C 618. In this investigation,
the coarse fly ash (Sample C as shown in Fig. 1) was ground
by ball mill and reclassified. The ground fly ash, having an
average particle size of about 3.8 mm, was identified as
FAG. The refinement and separation process is shown in
Fig. 1.
Two imported brands of condensed silica fume, namely
SFI and SFII, in powder form were used in this experimental
program. Sulphonated naphthalene formaldehyde superplasticizer
was used in all concrete mixtures and tap water was
used throughout the experimental program.