Post-fire optimum mechanical properties of self-compacting mortar using Taguchi method and analysis of variance

Abstract

In this research, to investigate the impact of high temperatures on the mechanical properties of this mortar type, first, nine mix designs consisting of different limestone powder percentages and water to cementitious material ratios were considered. To explore the impact of polypropylene and steel microfibers, instead of 54 mix designs, 18 designs were considered using the algorithm proposed by Taguchi, bringing the total number of mix designs to 27. Three levels were considered for the water to cementitious materials ratio, limestone powder content, and microfiber ratio. After the sample preparation, they were placed in a furnace and exposed to three temperature levels of 200, 400, and 600 °C at a heating rate of 2 °C/min. Mortar specimens to each target temperature were kept for 6 h. Finally, considering the results obtained after conducting tests on the specimens without microfibers cooled under ambient environment, the optimum water to cementitious materials ratio and limestone powder percentage were 0.4 and 30% for all the target temperatures in the compression test, 0.4 and 10% in the flexural test, respectively. After exposure to 200 and 400 °C, in the specimens containing polypropylene microfibers, optimum values observed for the water to cementitious materials ratio, limestone powder percentage, and microfiber ratio in the compression test reached 0.45, 30%, and 0.15%, respectively. Furthermore, in the flexural test, the corresponding values were 0.45, 10%, and 0.15%, respectively. The results obtained for 600 °C were different only for the optimum ratio of polypropylene microfibers, which was 0.05% for both compressive and flexural strengths. Moreover, in the specimens containing steel microfibers, for all the exposure temperatures, the optimum values of the water to cementitious materials ratio, limestone powder percentage, and microfiber ratio were 0.4, 30%, and 1.0% in the compressive strength test and 0.4, 10%, and 1.5%, in the flexural strength test, respectively. Also, the results obtained from the analysis of variance indicating the compression and flexural tests consequences are reliable.