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TECHNICAL PAPER

(a) Fly ash mortar (b) Calcined clay mortar

(c) Fly ash-Calcined clay mortar (d) Metakaolin mortar
Figure 1: Visual observation on mortar specimens before and after elevated temperature exposure;
BE (before exposure), 300, 600, and 900°C (from left to right)
2.0 1.8

1.5 1.6

Density (g/cc) 1.0 Density (g/cc) 1.4

1.2 P - FA
0.5
P - CC
P - FACC
P - MK
0
0.0 0 200 400 600 800 1000
FA CC FACC MK Temperature (°C)
(a) Density of binders after curing (b) Density of binders after elevated temperature exposure
Figure 2: Density measurements

of the specimens. Figure 2(b) shows that a significant reduction is shown in Figure 3, for paste, mortar as well as concrete. It
in density was observed in all the specimens when exposed could be evidently seen that the trend for various mixes did not
to 300°C possibly due to the expulsion of water, which formed show any variation among paste, mortar or concrete samples.
during the geopolymerization. Only a slight variation of density The loss in weight occurring upon exposure to 300ºC can be
was observed in specimens when exposed from 300 to 600°C. related to the dehydration of the structures present in the
When the temperature was increased to 900°C, no significant aluminosilicate gels of the geopolymers. Significant decrease
variations were observed in all the geopolymer mixes. From the in mass was observed when the temperature was increased to
results, a 30 % reduction in density of MK geopolymer concrete 600°C. However, the reduction was comparatively lower after
at elevated temperature exposure could be attributed to the 600°C irrespective of the differences in mix composition. The
decomposition of hydroxyl groups and water. Furthermore,
metakaolin geopolymer is having high acivator/binder ratio than mass loss above 600°C can be associated to the phase changes
other geopolymer mixes and experienced a significant reduction of the components. In general, geopolymers with MK and CC
in density [14] . have undergone the greater percentage of mass loss, attributed
to their high solution to source material ratio.
3.2 Mass changes
On comparing the mass loss along the various mix
Regarding mass loss, all the geopolymer specimens underwent compositions, fly ash geoloplymer exhibited the least mass
a loss in weight upon exposure to elevated temperatures, which loss at higher temperatures. From paste studies, noticeable

THE INDIAN CONCRETE JOURNAL | MAY 2022 21