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TECHNICAL PAPER

30 30 30
Paste Mortar Concrete
25 25 25
(%) 20 (%) 20 (%) 20
Mass loss 15 Mass loss 15 Mass loss 15

10
10
10
P - FA M-FA C-FA
5 P - CC 5 M-CC 5 C-CC
P - FACC M-FACC C-FACC
P - MK M-MK C-MK
0 0 0
0 200 400 600 800 1000 0 200 400 600 800 1000 0 200 400 600 800 1000
Temperature (°C) Temperature (°C) Temperature (°C)
(a) Paste (b) Mortar (c) Concrete
Figure 3: Mass loss associated with elevated temperature exposure in pastes, mortars, and concrete

volume shrinkage of the geopolymer specimens was observed from room temperature to 300°C. However, the exposure to
after 900°C exposure (Figure 3). Volume shrinkage was more 600°C triggered a sharp decrease in residual compressive
pronounced in the case of MK and CC. When exposed to higher strength for all the specimens tested. Compared to other
temperature above 600°C, extensive damage was visible in MK samples, fly ash geopolymer experienced a noticeable strength
geopolymer, from Figure 3 (a). This observation points towards reduction. When temperature increased to 900°C, the residual
the limitation in the application of geopolymers with high Al/Si compressive strength of all samples continued to decrease. And
ratio at elevated temperatures. this time fly ash geopolymer maintained the higher residual
strength.
3.3 Compressive strength
Table 3 presents a detailed summary of change in residual
The variation in compressive strength is shown in Figure 4 for compressive strength in all the specimens exposed to different
each of the mixes after being exposed to the different test elevated temperature. In all exposure condition, FACC recorded
temperatures, for paste, mortar as well as concrete samples. greater strength than CC. CC and FACC geopolymers follow
In paste samples, at room temperature, the geopolymer with a similar trend in the variation of compressive strength. In the
fly ash-calcined clay blend recorded the highest compressive case of MK geopolymer, compressive strength variation upon
strength, while calcined clay geopolymer showed the lowest. It heating follows a different route. Even though MK geopolymer
is also indicative of the improved mechanical performance of possesses a compressive strength comparable to others at
geopolymers when used with 50 % calcined clay substitution for ambient temperature, it's performance at higher temperatures
fly ash, compared to the other mixes. was poor, which can be related to the large wide cracks
observed.
A significant increase in compressive strength was observed in
all specimens except MK geopolymer. The rise in compressive Clearly in paste, mortar and concrete samples, MK geopolymer
strength was found maximum for FA geopolymer when heated was found to have the least strength at all the high temperatures

Compressive Strength (Mpa) 70 Compressive Strength (Mpa) 70 Compressive Strength (MPa) 70
Mortar
Concrete
Paste
60
60
60
50
50
50
40
40
40
30
30
30
20
20
20
C-CC
P-CC
M-CC
10
C-FACC
P-FACC
M-FACC
C-MK
M-MK
P-MK
0 P-FA 10 0 M-FA 10 0 C-FA
0 200 400 600 800 1000 0 200 400 600 800 1000 0 200 400 600 800 1000
Temperature (°C) Temperature (°C) Temperature (°C)
(a) Paste (b) Mortar (c) Concrete
Figure 4: Compressive strength of geopolymer systems exposed to higher temperature
22 THE INDIAN CONCRETE JOURNAL | MAY 2022