Repair of Heat-Damaged RC Beams Using Micro-concrete Modified with Carbon Nanotubes

This paper investigates the use of micro-concrete modified with carbon nanotubes (CNTs) for the repair of heat-damaged reinforced concrete (RC) beams. Ten RC beams were cast and then subjected to elevated temperature of 550oC for two hours. The damaged beams were then repaired using micro-concrete integrating CNTs and tested under four-point bending. Different factors were taken into consideration in this research: CNTs modification, depth of repair, aggregate size of the repair material, and curing period. The repair material was applied on the tension side of the beam. Test results showed that micro-concrete with a larger aggregate size was more effective as a repair material than smaller sized aggregate micro-concrete. CNTs modification had little impact on the flexural strength of the repaired beams, but clearly enhanced the stiffness. The increase in the repair depth improved the strength recovery of the repaired beams but did not influence the failure mode. Curing period of the repaired beams significantly affected their stiffness but not their ultimate load and toughness. To investigate the mineral composition of repair material, scanning electron microscopy (SEM) was conducted for the micro-concrete with and without CNTs modified cementitious. The SEM image showed the CNTs are uniformly dispersed in the cement matrix. The CNTs and the products of the hydration process formed a meshwork structure. The CNTs acted as fillers to the voids, leading to an increase in the compressive strength.