PSI - Issue 64

Hamzeh Shdeifat et al. / Procedia Structural Integrity 64 (2024) 1360–1368 Shdeifat at al. / Structural Integrity Procedia 00 (2019) 000–000

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2.4. Experimental methods To simulate fire conditions, electrical horizontal Tetlow furnace was utilised as shown in Fig. 4.a. The furnace heating rate was fabricated to follow the nominal fire curve in ISO 834 (ISO, 1999). The nominal fire curve and furnace time-temperature curves are depicted in Fig. 4. (a) Electric furnace; (b) nominal fire curve vs furnace temperature. All mixes were subjected to fire exposure with the duration of 1 hour (1H) and 2 hours (2H) to capture the changes in thermomechanical performance at different firing periods. All mixes were naturally cooled down after firing with exception of mix KC14R.6, it was subjected to natural cooling and water quenching, separately.

(a)

(b)

Fig. 4. (a) Electric furnace; (b) nominal fire curve vs furnace temperature.

All mixes were tested for compressive strength using tecnotest compression machine with a loading rate of 900 N/s as per ASTM C109/C109M (Standard, 2008). Changes in volume were measured using vernier calliper with an accuracy of up to two decimal places in mm. All measurements were taken before and after firing. Thermal shock was carried out by quenching samples in water for 5 minutes, but for 1 cycle only (Rashad and Zeedan, 2011). Thermal shock impact was assessed in terms of residual compressive strength, volume change and careful visual inspection of sample’s surfaces for any signs of deterioration. All results are reported as the mean values of at least three samples for each tested parameter. 3. Results and discussion The results of bulk densities and compressive strength at ambient temperature and post firing are listed in Table 4.1. When comparing KC14R1.2 to KC14R.6, It is noted that reducing the molar oxide ratio from 1.2 to 0.6 while fixing the total activator oxides content at 14% increases the ambient compressive strength significantly. In contrast, when fixing the oxides ratio and lowering the alkali activator oxides content from 20% to 14%, the compressive strength was found to decrease. Furthermore, the influence of changing the oxides ratio on the reference strength was much more significant than when changing the activator total oxides content. The significant increase in compressive strength when lowering the oxides ratio is ascribed to the increased hydroxide content. It is noted that increasing the concentration of hydroxide in the activator to a certain extent enhances the quality of the structural reorganisation of geopolymer gel, leading to a robust microstructure and a remarkable increase in compressive strength (Leong et al., 2016, Cheng and Chiu, 2003, Duxson et al., 2005). It is also reported that the reduction in the activator oxides content could compromise the productivity of geopolymer gel, resulting in a decreased compressive strength at ambient temperature (Lin and Chen, 2022, Leong et al., 2016).