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Abstract
Understanding the evolution of mechanical properties and microscopic pore structure of concrete after freeze–thaw cycles is essential to assess the durability and safety of concrete structures. In this work, the degradation law of mechanical properties and damage characteristic of micro-structure of concrete with two water-cement ratios (w/c = 0.45 and 0.55) is investigated under the condition of freezing–thawing cycles. The influence of loading strain rate on dynamic compressive strength is studied. The microscopic pore structure after frost damage is measured by low-field nuclear magnetic resonance (LF-NMR) technique. Then, a damage model based on the porosity variation is established to quantitatively describe the degradation law of macroscopic mechanical properties. The test results show that the relative dynamic modulus of elasticity (RDME), dynamic compressive strength, flexural strength, and splitting tensile strength of concrete decrease with the increase of freeze–thaw cycles. Empirical relations of concrete dynamic increase factor (DIF) under the action of freeze–thaw cycles are proposed. Moreover, the experimental results of NMR indicate that the porosity as well as the proportion of meso-pores and macro-pores of concrete gradually increased with the increasing of freeze–thaw cycles. The research results can provide reference and experimental support for the anti-frost design theory and durability life prediction of hydraulic concrete structures in cold regions.
Highlights
Material degradation caused by freeze–thaw cycles is one of the major durability problems of concrete structures in cold regions [1,2,3], where many concrete structures located at the waterline fluctuation are suffer from severe deterioration, such as concrete dams, hydraulic power plants, and offshore structures [4,5]
The goal of this study is to investigate the mechanical properties and pore structure degradation of concrete with different water–cement (w/c) ratios under the action of freezing–thawing cycles
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Summary
Material degradation caused by freeze–thaw cycles is one of the major durability problems of concrete structures in cold regions [1,2,3], where many concrete structures located at the waterline fluctuation are suffer from severe deterioration, such as concrete dams, hydraulic power plants, and offshore structures [4,5]. The influential factors of material degradation during freezing and thawing are w/c ratios, porosity, air-content, cement, and aggregate. Surface scaling and the internal damage are the two typical characteristics under the freezing–thawing condition, which are caused by progressive expansion of the cement paste matrix from periodic freezing and thawing cycles [7,8]. It is necessary to further study the evolution of dynamic mechanical properties of concrete with different water–cement ratios after freeze–thaw
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