School of Management Engineering, & Engineering Research Center Program of Development & Reform Commission of Jiangsu Province, Jiangsu Urban and Rural Construction Vocational College, Changzhou, 213147, People's Republic of China.
Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, 200240, People's Republic of China.
Sci Rep. 2022 Dec 30;12(1):22612. doi: 10.1038/s41598-022-27122-w.
Concrete structures in cold regions are usually suffer from froze and thaw action. A combined investigation of nanoindentation technique and X-ray diffraction were adopted to demonstrate the microstructure change and micromechanical properties deterioration of concrete subjected to freeze-thaw (F-T) cycles in this study. The results showed that the indentation modulus and hardness of the main compositions in mortar, such as calcium-silicate-hydrates and calcium hydroxide, both gradually decreases as the F-T cycles increase, with the greatest reduction approximate 38% after 1500 F-T cycles, while the corresponding greatest reduction of the main compositions in interfacial transition zone (ITZ) is close to 50%. In addition, the micropores in mortar and ITZ both gradually converge and connect to form larger diameter pores, and the thickness of ITZ increased rapidly from 25 to 50 μm after 1500 F-T cycles. On this basis, the effective modulus of elasticity under different F-T cycles are analyzed through Mori-Tanaka scheme with consistent variation tendency of dynamic modulus of elasticity test. Subsequently, the mechanical properties deterioration of concrete under F-T cycles is mainly attributed to the decrease of mechanical properties (such as modulus and hardness) of microscopic components, and the increase and propagation of the internal micropores especially for micropores in ITZ.
寒冷地区的混凝土结构通常会受到冻融作用的影响。本研究采用纳米压痕技术和 X 射线衍射的联合研究，证明了混凝土在冻融循环下的微观结构变化和力学性能劣化。结果表明，随着冻融循环次数的增加，水泥砂浆中主要成分（如硅酸钙水化物和氢氧化钙）的压痕模量和硬度逐渐降低，最大降幅约为 38%，经过 1500 次冻融循环后，界面过渡区（ITZ）中主要成分的相应最大降幅接近 50%。此外，水泥砂浆和 ITZ 中的微孔逐渐收敛并连接形成更大直径的孔隙，ITZ 的厚度在经过 1500 次冻融循环后迅速从 25μm 增加到 50μm。在此基础上，通过 Mori-Tanaka 方案分析了不同冻融循环下的有效弹性模量，与动态弹性模量试验的变化趋势一致。随后，冻融循环下混凝土的力学性能劣化主要归因于微观组分力学性能（如模量和硬度）的降低，以及内部微孔，尤其是 ITZ 中微孔的增加和扩展。
