African Design Magazine ADM #40 May 2018 | Page 51

TECHNOLOGY
pozzolanic reaction of fly ash is much
slower than the hydration of cement
[13].
The utilisation of fly ash not only saves
energy but also improves the properties
of concrete. With the fly ash addition,
the heat of hydration of high-volume
concrete is reduced [14–16]. Liu et al.
[17] proved that fly ash could improve
the fluidity of concrete. Fly ash also
can decrease the drying shrinkage
of concrete to some degree [18–21].
Furthermore, an appropriate addition of
fly ash could enhance the resistance of
concrete to sulphate attack and chloride
penetration [22–24], thus reducing
the risk of steel corrosion [25]. Other
properties such as strength [6], acid
resistance [26], wear resistance [27],
and leaching properties [28] could be
improved by replacing part of cement
with fly ash.
concrete by grinding.
In this research, pure cement and
ordinary fly ash were used as a
reference. With a variety of experimental
test methods, the effects of ground
fly ash and grade I fly ash on cement
hydration, pore structures of hardened
pastes, and strength of mortar were
comparatively studied. More importantly,
the mechanism of grinding fly ash in
hydration and hardening of cement-
based composite cementitious materials
was discussed.
2. Materials and methods
2.1 Raw materials
An ordinary Portland cement which is
used for testing admixtures was applied
in our research, and the specific surface
area of the cement is 346 m2/kg. Grade I
fly ash used was produced by a thermal
power plant in China, the specific surface
area of the fly ash is 384 m2/kg, and
water demand is 88%. The chemical
composition of cement and grade I
fly ash is shown in Table 1. Standard
sand was used as the aggregate for
mortar specimens. Polycarboxylate
superplasticiser with water reduction
rate 19.1% was used to adjust the flow-
ability and workability of fresh mortars
and pastes.
The specific surface area of the fly ash
used in current practical engineering is
between 300 and 400 m2/kg. Fly ash with
a specific surface area of 600 to 700 m2/
kg can be obtained from grinding. A large
part of the glass phase can be ground
up to pieces and the particle size of fly
ash is mainly distributed below 10 m by
grinding. The activity of fly ash depends
mainly on the structures and properties
of the amorphous composition and the
The ground fly ash was made of grade
filling effect of fly
Table 1: Chemical compositions of cement and fly ash.
ash depends mainly
on the particle
size. Therefore,
theoretically it
is practicable to
make fly ash play
a greater role in
AFRICAN DESIGN MAGAZINE © | MAY 2018
51