Nanomechanical characteristics of lightweight aggregate concrete containing supplementary cementitious materials exposed to elevated temperature

• Extensive nanoindentation tests were conducted on both interfacial transition zone and bulk paste.
• Grid indentation methodology was utilized to characterize nanomechanical properties of hydration phases.
• Effect of high temperature on hydration products of lightweight concrete with fly ash and slag was determined.
• High temperature damage on both interfacial transition zone and cement bulk were quantified.
• Lightweight aggregate alleviates the high temperature damage on bulk cement paste.

In order to determine the effect of elevated temperature on hydration products of lightweight aggregate concrete containing fly ash and ground granulated blast-furnace slag, nanoindentation characteristics of three different mixtures were investigated. The results indicated existence of porosity and two types of primary hydration products, Low Density and High Density Calcium–Silicate Hydrates (LD C–S–H and HD C–S–H), in the bulk cement paste. It was revealed that there is less degradation of mechanical properties of C–S–H phases in samples of lightweight aggregate concrete exposed to elevated temperature compared to those with conventional aggregate. Additionally, the interfacial transition zone of lightweight aggregate was investigated. It was revealed that because of internal curing caused by lightweight aggregate, mechanical properties of the interfacial transition zone in these samples were very similar to bulk paste. The effect of elevated temperature, however, was more pronounced in the interfacial transition zone of lightweight aggregate than in bulk paste. A dissipated energy parameter was introduced to use in the deconvolution method which demonstrated good correlation with indentation modulus and hardness as well as packing density of the C–S–H phases in general.