A micro freeze-thaw damage model of concrete with fractal dimension

Abstract

Freeze-thaw damage is the leading damage in concrete structures. The damage model is a favorable method for researching the mechanism of freeze-thaw damage. However, at present, most freeze-thaw damage models of concretes are phenomenological models, which can characterize the deterioration of macroscopic mechanical properties of the concrete, but cannot present the damage morphology and evolution process inside the concrete at the microscopic level. The micro-structures determine the macro properties for the concrete. Hence, few damage models at the micro-scale have been proposed for attempting to exhibit the degradation of the micro-structure in concrete, which is subject to freeze-thaw cycles. Furthermore, the equations of damage parameters are too complex to calculate. In order to build a general and practicable micro freeze-thaw damage model for concrete, the tests for the freeze-thaw cycle and pore structure were developed based on the test results of eight mixes. The pore structures before and after freeze-thaw were qualitatively analyzed through a pore size distribution curve and pore volume histogram. The fractal model was employed to characterize the pore size distribution. This indicates that only fractal dimensions regularly change with the action of freeze-thaw among the pore parameters. A micro freeze-thaw damage model with fractal dimension as the independent variable was developed according to the definition of the damage parameter, and the relationship between durability factor and the damage parameter calculated by the damage model in the present study was analyzed. The results revealed that the damage model presented in the present study can quantitatively reflect the damage degree of concrete at the microscale, and the damage parameter has a good relation with the durability factor. Furthermore, research results have shown that damage on concrete at the microscale varies on the pore size distribution, but not on the pore volume. More researches should be conducted on the pore size distribution for digging the freeze-thaw damage mechanism in the future.