The reduction in density of about 13.4% of ET8 compared to ET1
which had no POFA content might be attributed to specific gravity,
particle shape & size and water demand. In the case of POFA, particles
cannot easily roll over one another due its agglomerated and
crushed shape, increasing inter-particle friction. Thus, this illuminates
the need for more evaporable water in mixes with high POFA
content in order to obtain a workable mix. However, this additional
water leads to more pores, which reduces density. As seen in
Table 3, the additional water required by mix ET8 to achieve a
workable mix was higher than other mixes. Similar findings on
the requirement for more water to achieve workable mixes with
POFA as replacement material for OPC have been reported
[34,35]. In contrast, the spherical shaped FA particles reduce the
friction between the binder and fine aggregate resulting in an increase
in workability of fresh mortar [36]. The spherical shape also
minimizes the particle’s surface to volume ratio, resulting in low
fluid demand. The most common reason for poor workability is
that the addition of a fine powder increases demand for water as
the surface area has increased [37]. A higher packing density was
obtained with spherical particles compared to crushed particles
in a wet state, resulting in lower water retention in the spherical
case and a subsequently lower water demand for specific workability’s
[38]. The specific gravity of POFA is about 94% that of FA and
hence the use of a higher dosage of POFA decreases specimen density.
In addition, the relatively smaller size of spherical FA particles
fills the voids and makes for denser packing. In the cases of specimens
containing POFA and FA, increase in POFA content shows an
approximately linear decrease in the specimen density.