Abstract: To tackle the problems of strength loss and poor durability of concrete in high geothermal tunnel, we examined the mechanical properties of composite concretes undergone thermal curing mixed with steel fiber, polypropylene fiber and vitrified microspheres, hence revealing the variation of compressive strength, tensile strength and failure characteristics of composite concretes with curing temperature. Furthermore, we deduced the formula of uniaxial compression strength of composite concretes considering the thermal-force relationship based on the homogenization theory. Results unveiled that the composite concretes are of higher compressive strength and tensile strength compared with ordinary concrete with no such mixtures, and have smaller strength loss after thermal curing. Failed sample is cracked but not separated, implying higher residual strength. The inclusion materials in the composite concretes attribute to the strength and durability after high temperature curing. The concrete strength model based on the homogenization theory fits well with the experimental results. The research findings offer theoretical basis for the design and evaluation of lining structures in high geothermal tunnel.

Key words: composite concrete, thermal curing, high geothermal environment, mechanical property, failure characteristics, homogenization theory, thermal stress