4.1.3. Setting time

This test was performed in conformity with the requirement of
ASTM-C191 (2008). This test method determines the time of setting of cement by
means of the Vicat needle. Two test methods are given; Method A is the reference
Test Method using the manually operated Vicat apparatus, while Method B permits
the use of an automatic Vicat machine that has, in accordance with the
qualification requirements of this method, demonstrated acceptable performance.
In this paper, the Method B is used. The initial setting time is the time
elapsed between the primary contact of cement and water and the time when the
penetration is measured or calculated to be 25 mm. The final setting time is
the time elapsed between primary contact of cement and water and the time when
the needle does not leave a complete circular impression on the paste surface.
Fig. 7 shows the change in initial and final setting time at different mixers.
The initial setting time shows an increase of 5% and 10% CWP and then decreases
slightly at 15% CWP before increasing further at 20% and 25% CWP. A similar
trend but more well defined is also observed for the final setting time. This
suggests that the CWP is contributing to and influencing hydration and setting
in a non-systematic manner. The Setting times of mortars do not show consistent
changes with increase in CWP content. The rather erratic behavior of setting
times of different mortars is attributed to the very complex interdependent
nature of the cement hydration (Snelson, Wild et al., 2011). Also, The CWP
mortar may contain less water as a consequence of the presence of CWP, and this
will influence the rate of stiffening.

                

 

4.2. Hardened mortar test

 

4.2.1. Dry bulk density

   Dry bulk density
of hardened mortar was obtained by dividing mass in dried conditions by its
occupied bulk while floating in water through saturation conditions.
The dry bulk
density (DBD) of mortars was determined following BS EN 1015-10 (1999). It
entailed weighing the mass of mortar prisms, which were dried in an oven at a
constant temperature of approximately 60 C constantly until consecutive weights
(within 2 h interval) were the same. Consequently, the average weight was
divided by the volume to obtain the DBD. The results of DBD of mortar specimens
are presented in Fig. 8. Although there was only slight variability in the DBD
of the mortars. However, the density of the control mortar (CP0) was higher
than those of other mixes, because the density of cement is greater than CWP.

 

                

Fig. 8. DBD of hardened mortar

4.2.3. Water absorption by capillary
action

   Water absorption of mortar by capillary
action is a key property as it helps to determine the rate of water ingress
into mortar through condensation from the atmosphere, capillary rise from
ground water and from driving rain. In this study, broken prisms (approximately
40 mm 40 mm 80 mm) arising from flexural strength tests were used for the
determination of coefficient of water absorption by capillary action. The test
was performed in conformity with the requirement of BS EN 1015-18 (1999). The
results for the water absorption coefficient by capillary action for all
mortars are shown in Fig. 9. It can be observed that mortars containing CWP
(CP5, CP10) present the lower values than control mortar. These reduced water
absorptions were an indication that there were few porous structures in the
mixes. Also, it can be observed that mortars containing CWP (CP15, CP20, CP25)
present the higher values than control mortar. Considering that these
compositions have lower dry bulk density than control mortar. On a general
note, Torres and Matias (2016) described the increase in the water absorption
of a mortar to be as a result of the small pore internal structure of the
mixture.