Effect of Pumice pozzolan and Metakaolin on the durability of recycled concrete and its bars corrosion

This study investigate the effect of Pumice and Metakaolin Pozzolans on properties of recycled concrete. In order to build the specimens, 10 percent of Taftan Pumice, 15 percent of Metakaolin and combination of both Pozzolans were replace to the cement. Compressive strength, water absorption, the penetration depth at the age of 28 days and 90 days for all specimens are obtained. The results of the tests indicate that the single use of Pozzolan operates better when it used in a composition. The specimen with 15 percent Metakaolin increased the compressive strength by 5.2 and 11.73 percent on days 28 and 90 in comparison with the recycled concrete specimen, respectively. Also in water absorption 27 percent decrease was caused on day 28 and 30 percent decrease was caused on day 90. And the 10 percent Pumice specimen performed better on day 90. On day 90 the water absorption was decreased by 25 percent and the remarkable decrease of penetration depth which was decreased by 53 percent. The reason of this reduction could be caused by the low hydration speed of Taftan Pozzolan and also the completion of Pozzolan and Morphology reactions. In the case of corrosion testing, the addition of Pozzolan alone increases concrete’s resistance against corrosion, so the specimens with 15 percent Metakaolin and with 10 percent Pumice Taftan perform better in comparison with the combined specimen. The reason is that the uniform structure and also the presence of Hydrated Calcium Silicate gel(C-S-H), which decreases the cavities and the passing electrical flow which causes more corrosion resistance.