Table after exposure to 550°C for 30 minutes

Table
1 provides the mixes and their compositions used in the study. Performance
indices were developed based on performances in compressive strength, flexural
strength, mass loss and abrasion resistance after exposure to 550°C for 30
minutes 10-20.  Mixes are then ranked
on a scale 1 to 8, for 1 being the best and 8 being the worst for limestone and
river sand mortars. For the geopolymer mixes the ranking was from 1 to 4 for
pastes and mortars separately. For both the types of aggregate, the cement
mortars with lower w/c ratios performed well in thermal in ranking. Similarly,
among the different types of cement, the performance of Portland pozzolana
cement was better in most of the cases. However, the relative performance of
river sand mortar was inferior to limestone mortars. The reductions in
compressive strengths after thermal exposure were 8.4, 9.1, 11.5, 16.1, 17.4,
12.9, 15.9 and 13.2 % for limestone mortars LS1 to LS8. The corresponding
values for river sand mortars were 12.3, 15.3, 18.1, 23.4, 22.4, 19.0, 19.1 and
17.6% respectively for the mixes RS1 to RS8. Similar trends were observed for
flexural strength and mass loss. However, abrasion resistance of river sand
mortars was better compared to limestone. This effect was resulted from the
mineralogy of river sand and limestone (calcite has a Mohs hardness scale
number of 3, whereas quartz is 7).  Geopolymer
pastes exhibited increase in compressive strengths upon heating at 550°C for 30
minutes.  Hence, for the geopolymer
pastes strength indices were based on absolute values. Among the different
pastes, the mix GM3 with 16 M ranked first. Increment in strength of
geopolymers may be due to the attainment of high level polymerization upon heat
treatment. Similar trends were observed for other indices, except for abrasion.
Further, geopolymer mortars with limestone aggregate were tested. The mixes
with lower molarities ranked higher indicating mixes becoming more brittle with
high molarities of NaOH. Moreover, the mix 18 M was severely cracked and broken
upon thermal exposure