3.3.4. Weight Loss of Concrete

The effect of elevated temperature on the weight loss of geopolymer concrete for all curing regimes is depicted in Table 11. The initial weight of the samples is expressed as the density of the sample exposed to a 25 ◦C temperature. The weight loss of Csample and Asample increased as the temperature increased. The weight loss increased significantly from 200 ◦C to 400 ◦C where the mass loss observed was a result of moisture movement out of the geopolymer matrix. The reduction in weight loss gradually decreased from 11.96% to 10.83% for AC to WC, respectively, in Csample at 600 ◦C. However, a greater loss is to be found at 800 ◦C with ranges of 12.3% (AC) and 10.79% (WC). Apart from that, the weight loss for Asample was slightly higher compared to Csample at 800 ◦C, having reached 12.62% (AC) and 11.28% (WC). The exposure to elevated temperature can lead to changes in the stiffness and mechanical properties of geopolymer concrete. It was proved that high temperature can affect the stiffness and mechanical properties of geopolymer concrete [48].

In addition, an increase in temperature and weight reduction lead to deterioration of the structural integrity of geopolymer concrete. Asample yielded a higher weight loss compared to Csample. Furthermore, weight loss was observed to be lower in WC compared to AC regime. This may be due to water being absorbed during the application of water-cooling to make sure the temperature of the concrete was under control.


**Table 11.** Weight loss of concrete samples.

The experimental results indicated that Csample had a lower confidence level i.e., R2 = 0.8949 (Figure 7a) that lay outside of the recommendation range (0.90–1.00) whereas Asample (Figure 7b) showed a strong relationship between these two parameters with a high confidence level i.e. 0.9939. From this result, it is illustrated that the experimental results show fitted well for Asample but not for Csample. Thus, it can be concluded that the presence of 5% bamboo ash in 95% fly ash gives a better confidence level compared to the control sample.

**Figure 7.** Ultrasonic pulse velocity (UPV) value of (**a**) Csample and (**b**) Asample as a function of weight loss.
