MECHANICAL BEHAVIOR, PORE STRUCTURE AND ITS EVOLUTION MECHANISM OF CEMENT-BASED MATERIALS UNDER CRYOGENIC TEMPERATURE CONDITIONS

摘要

The properties of cement-based materials at cryogenic temperature are different from those at room temperature or low temperature.The mechanical behavior, pore structure and its evolution mechanism of cement-based materials under cryogenic temperature conditions are discussed in this paper.Cement-based materials show good cryogenic mechanical properties.Both cryogenic compressive and flexural strength increases 2～3 times, compared to room temperature strength.The strength increasing mechanisms are also discussed in this paper.A prediction model on mechanical performance at cryogenic temperatures is proposed.The deterioration of mechanical properties suffering cryogenic freeze-thaw cycles (-110 ℃～20 ℃) is much more rapidly than those suffering room temperature freeze-thaw cycles (-20℃～20℃).Cement-based materials gradually absorb water from the outside in the freeze-thaw process, and the amount of water absorbed is even greater than that absorbed by vacuum saturation.Around large pores where ice is formed, a great amount of micro-pores (5～20nm) appears, then micro-pores in this range increase rapidly and interconnect into larger pores, which results in deterioration of the mechanism properties.In addition, the pore structure and its evolution of cement-based materials under cryogenic temperature conditions using thermoporometry was analysed.