Effect of high temperature on the properties of ternary blended cement pastes and mortars

This paper presents experimental study to investigate the effect of high temperature up to 800 °C on the properties of ternary blended Portland cement, lime sludge (LS), a residual solid from paper and pulp industry, with silica fume (SF) and nanosilica (NS). Physicochemical properties and mechanical behavior of ternary blended cement are studied. The replacement of cement by LS is fixed throughout as 20 % except control paste/mortar. In addition to the replacement of LS, SF by 3 and 6 % and NS by 1.5 and 3 % are incorporated in cement paste and mortar. The phase changes due to the thermal effect of all the 28-day water-cured composite pastes are monitored by XRD and thermal analysis by TG-DTG. Unstressed residual compressive strength tests are used in this study for the mortars. Results show that the incorporation of LS–SF cement composites with cement replacement level up to 26 % increases the compressive strength significantly at ambient temperature as well as after 2-h exposure to 500 °C compared to control mortars, but spalling of mortars occurs at 800 °C after 28 days of water curing. In the case of LS–NS cement composites, the residual compressive strength reduces considerably at all the temperatures, but there is no occurrence of spalling.