Research On Constitutive Relationship Of Frozen-Thawed Concrete And Mathematical Modeling Of Freeze-Thaw Process

Freeze-thaw resistance is an important aspect of durability of concrete structures. Hydraulic structures, offshore concrete structures and bridges in cold regions often suffer from surface scaling or internal cracking under freeze-thaw cycles.To study the complete compressive stress-strain curve of concrete subjected to freeze-thaw cycles, three groups of 85 concrete prism specimens with dimensions of 100mm×100mm×300mm were exposed to rapid freeze-thaw cycles in water according to the national standard GBJ 82-85. The parameters of the specimens were cubic strength of concrete and freeze-thaw cycle numbers. Then all specimens were tested under uni-axial compressive loading. Based on the test results the complete compressive stress-strain curve equations for frozen-thawed concrete with necessary parameters were suggested. The equations, which are suitable for concrete with cubic strength of 30MPa-50MPa, could be used for nonlinear analysis of concrete structural elements experienced to freezing-thawing cycles in cold regions.In order to simulate the physical processes involved in freezing and thawing of concrete, a mathematical model was developed based on thermodynamics and poroelastic theory. By using Comsol Multiphysics finite element program, the pore pressure, strain and temperature induced into saturated concrete specimens during freezing were predicted. The rationality of the numerical simulation was illustrated by comparing of the analytical results with available experimental data .The stress-strain relationship for stirrup-confined concrete after freez-thaw cycles was investigated. Two series of 54 concrete prism specimens with dimensions of 150mm×150mm×450mm and with stirrup characteristic value of 0.317 or 0.145 were exposed to rapid freeze-thaw cycles in water according to GBJ 82-85. The axial compressive loading tests of 46 specimens were carried out to obtain the complete stress-strain curves of confined concrete. Based on the test results, complete stress-strain curve equations for confined concrete subjected to freeze-thaw cycles were established. The equations could be used for nonlinear analysis of reinforced concrete structural elements experienced to freezing-thawing cycles in cold regions.Based on the stress-strain relationship of the frozen-thawed concrete, the sectional load-deformation response of three reinforced concrete elements subjected to freeze-thaw cycles were predicted by using Response-2000 program. The freeze-thaw resistance of these elements was analyzed .