EFFECT OF COLLOIDAL NANO SILICA (CNS) ON PROPERTIES OF HIGH STRENGTH CONCRETE AT ELEVATED TEMPERATURE

Present research work was carried out to find the performance of HSC (M60) made with addition of fly ash and colloidal nano silica at elevated temperature. The variables used for test programme includes replacement of cement with fly ash from 10% to 35% along with addition of colloidal nano silica (CNS) from 1% to 5% b.w.c , temperature ranges from 270 c to 800 0 c . The mechanical behavior was studied from residual compressive strength; durability was assessed by RCPT test as per ASTM 1202-1991, mass loss at various temperatures was determined. Also to study behavior and crack pattern SEM (Scanning electron microscopy) on selected specimens was performed the two types of cooling methods are used as air cooling and water cooling. Test results shows degradation in the mechanical and durability properties of HSC at elevated temperature. It was observed that quick cooling exerts greater loss in compressive strength compared to slow cooling due to thermal shocks which is more predominant at 600o c temperature also it was observed that compressive strength has been increased at 400o c, where as it has decreased at 100o c and 2000 c, and beyond 6000 c temperature it has suddenly decreased, so concrete mixes containing CNS particles should be used by taking necessary care in structures which are subjected to temperature beyond 6000 c