4.1.3. Setting timeThis test was performed in conformity with the requirement ofASTM-C191 (2008). This test method determines the time of setting of cement bymeans of the Vicat needle. Two test methods are given; Method A is the referenceTest Method using the manually operated Vicat apparatus, while Method B permitsthe use of an automatic Vicat machine that has, in accordance with thequalification requirements of this method, demonstrated acceptable performance.In this paper, the Method B is used.
The initial setting time is the timeelapsed between the primary contact of cement and water and the time when thepenetration is measured or calculated to be 25 mm. The final setting time isthe time elapsed between primary contact of cement and water and the time whenthe 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 decreasesslightly at 15% CWP before increasing further at 20% and 25% CWP. A similartrend but more well defined is also observed for the final setting time. Thissuggests that the CWP is contributing to and influencing hydration and settingin a non-systematic manner. The Setting times of mortars do not show consistentchanges with increase in CWP content.
The rather erratic behavior of settingtimes of different mortars is attributed to the very complex interdependentnature of the cement hydration (Snelson, Wild et al., 2011). Also, The CWPmortar may contain less water as a consequence of the presence of CWP, and thiswill influence the rate of stiffening. 4.
2. Hardened mortar test 4.2.
1. Dry bulk density Dry bulk densityof hardened mortar was obtained by dividing mass in dried conditions by itsoccupied bulk while floating in water through saturation conditions.The dry bulkdensity (DBD) of mortars was determined following BS EN 1015-10 (1999). Itentailed weighing the mass of mortar prisms, which were dried in an oven at aconstant temperature of approximately 60 C constantly until consecutive weights(within 2 h interval) were the same. Consequently, the average weight wasdivided by the volume to obtain the DBD.
The results of DBD of mortar specimensare presented in Fig. 8. Although there was only slight variability in the DBDof the mortars.
However, the density of the control mortar (CP0) was higherthan those of other mixes, because the density of cement is greater than CWP. Fig. 8. DBD of hardened mortar4.2.3. Water absorption by capillaryaction Water absorption of mortar by capillaryaction is a key property as it helps to determine the rate of water ingressinto mortar through condensation from the atmosphere, capillary rise fromground water and from driving rain.
In this study, broken prisms (approximately40 mm 40 mm 80 mm) arising from flexural strength tests were used for thedetermination of coefficient of water absorption by capillary action. The testwas performed in conformity with the requirement of BS EN 1015-18 (1999). Theresults for the water absorption coefficient by capillary action for allmortars are shown in Fig. 9. It can be observed that mortars containing CWP(CP5, CP10) present the lower values than control mortar. These reduced waterabsorptions were an indication that there were few porous structures in themixes.
Also, it can be observed that mortars containing CWP (CP15, CP20, CP25)present the higher values than control mortar. Considering that thesecompositions have lower dry bulk density than control mortar. On a generalnote, Torres and Matias (2016) described the increase in the water absorptionof a mortar to be as a result of the small pore internal structure of themixture.