The effects of nanoparticles on early age compressive strength of ash-based geopolymers

In the present work, compressive strength of ash based geopolymers containing 97 wt% rice husk ash + fly ash and 3 wt% nano alumina + nano silica has been designed by Taguchi method at 2 and 7 days of water curing. 4 factors including the percentage of nano silica (at 3 levels of 1, 2 and 3 wt%), oven curing temperature (at 3 levels of 25, 70 and 90 °C), oven curing time (at 3 levels of 2, 4 and 8 h) and NaOH concentration (at 3 levels of 5, 8 and 12 M) were considered. By utilizing L9 Taguchi array, 9 series of experiments were conducted on the prepared specimens. The alkali activating was done by a mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solutions. The obtained results were evaluated by analysis of variance (ANOVA) method to determine the optimum level of each factor. In all produced specimens, the optimum level of nano silica, oven curing temperature and oven curing time were 3 wt%, 90 °C and 8 h, respectively. The oven curing time was not an important factor for determining the compressive strength. To validate the accuracy of the optimum conditions suggested by ANOVA, compressive specimens were made and tested in accordance to the optimum conditions for each of 2 and 7 days water curing regimes. The obtained compressive strength acquired from this situation was higher than those of proposed in 9 series experiments for each of 2 and 7 days water curing regimes.