Experimental Study on Mechanical Properties and Pore Structure Deterioration of Concrete under Freeze–Thaw Cycles

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.

Biomechanical Modelling for Tooth Survival Studies: Mechanical Properties, Loads and Boundary Conditions—A Narrative Review

“…Additionally, the results may vary depending on the conservation of the samples. Samples obtained from extracted teeth might have modified mechanical properties with time [ 93 ], which could be further affected with repetitive freeze-thaw cycles [ 69 , 94 , 95 ] and lack of moisture during experimentation [ 96 ].…”

The Freeze-Thaw Strength Evolution of Fiber-Reinforced Cement Mortar Based on NMR and Fractal Theory: Considering Porosity and Pore Distribution

“…Huang et al [ 21 ] suggested that in addition to elastic modulus and tensile strength, initial porosity was also an important parameter to describe the loss of freeze-thaw strength. Amirkiyaei et al [ 22 ] and Zhang et al [ 23 ] proposed damage models by using the change of porosity before and after freeze-thaw cycles to quantitatively describe the deterioration law of macroscopic mechanical properties. However, Li et al [ 24 ] believed that the porosity could only reflect the total number of pores, and proved through experiments that even if the porosity of the two samples was similar, the uniaxial compressive strength could be nearly doubled.…”

Both Plasticizing and Air-Entraining Effect on Cement-Based Material Porosity and Durability

“…According to Feng Yu's results, at 0.0055% air-entraining agent (AIR) dosage, the combination of 0.15% AF and 0.015% viscosity modifying agent (VMA) reduced the number of large bubbles in concrete by 57.96%. Afterward, the number of fine bubbles was increased by 16.55% and the spacing factor was reduced by 18.09%. A decrease in spacing factor increases freeze-thaw resistance of concrete.…”

“…Zheng [14] and Rodríguez [15] presented test results that show that frost resistance increases with increasing air content, which makes the space parameter decrease in the hardened concrete. Moreover, the experimental results indicate that, in air-entraining concrete, total air content is not the only factor that affects the final properties of the concrete; air void structure parameters, including void size, shape, and distribution, are key factors as well [16]. The research results of Lazniewska-Piekarczyk et al [17] on the influence of air-entraining admixture type have proved that a greater amount of micro pores in concrete is the effect of a synthetic air-entraining admixture.…”

“…Closed air pores perform the role of reserve pores and increase the frost resistance of concrete [20]. Zhang's [16] analyses concluded that as the number of freeze-thaw cycles increases, the repeated action of periodic freezing and expansion forces and hydrostatic pressure on the pores inside the concrete cause the pores inside the concrete to gradually expand, penetrate, and form connected pores. Shinichi [21] investigated pore structure in high-strength concrete at early ages via the BSE imaging technique assuming the Powers model.…”