Abstract:
With the envisaged structural applications of nano-modified cementitious matrices, it is imperative to characterize their behavior under different service conditions. As fire is one of the most severe hazards to which structures are threatened with during their service life, the requirement to characterize the mechanical and material performance of such nano-modified matrices at elevated temperatures becomes important. Thus an experimental program was developed to evaluate the effect of nano-modification on elevated temperature properties of normal weight concrete (NWC) and lightweight concrete (LWC) which is one of the best fire enduring concretes. The mechanical performance was assessed by conducting material property tests namely compressive strength, tensile strength, mass loss, elastic modulus and stress-strain response under unstressed and residual conditions in the range of 23 to 800℃. Results show that the inclusion of highly dispersed MWCNTs in cementitious matrices enhanced the fire endurance. The relative retention of mechanical strength and mass of concretes modified with MWCNTs was higher. Thermal conductivity of the modified samples was increased appreciably. The formed hydrates in nano-modified mixes were more stable indicated by the endotherm shift in DTA. The stress-strain response of specimens modified with MWCNTs was more ductile showing increment in peak stress and ultimate strains at both ambient and elevated temperatures. Microstructural study of cyrofractured samples evidenced the homogenous dispersion of MWCNTs in host matrix, the nano-reinforcements were found effective in bridging the microcracks. Heat treated samples were also visually inspected. Furthermore, the data obtained from high temperature material property tests was utilized to develop simplified empirical relations for expressing mechanical properties of modified mixes as a function of temperature.
