Zhou Jiguo, Wang Guihua, Xu Jun
College of Civil Engineering, Baicheng Normal University, Baicheng 137000, China.
College of Civil Engineering and Architecture, Jiangsu University of Science and Technology, Zhenjiang 212003, China.
Materials (Basel). 2022 Jun 24;15(13):4454. doi: 10.3390/ma15134454.
Herein, ordinary silicate concrete specimens are prepared to study the damage law of a cement-concrete material under the effects of salt erosion and a freeze-thaw environment. NaCl, NaHCO, and NaSO solutions are separately produced, according to the characteristics of saline soil, to conduct an experimental study on the concrete characteristics during quick salt freezing cycles, and to analyse the changes in its compressive strength, mass loss, and dynamic elastic modulus (DEM) under freeze-thaw cycles. Low-field nuclear magnetic resonance (NMR) and scanning electronic microscopy are used to investigate the change in the microstructure of concrete specimens under salt freeze-thaw cycles (FTCs). The results show the loss in compressive strength, mass, DEM, and NMR spectrum signal increased by 1.5-3 times, 3-5 times, 1.5-2.5 times, and 2-4 times, respectively, for concrete specimens under 50-100 FTCs in 6.8% composite salt solution, in comparison to fresh water. Apparent spalling, decreases in the DEM, and reductions in the compressive strength occur in concrete when increasing the number of salt FTCs. The number of internal cracks in the concrete structure increase under the combined action of salt crystallization, moisture absorption, and freeze-thaw. The changes in the internal microscopic pore volume in concrete structures exhibit the same trend with changes in the macro mechanical properties of concrete. The correlation coefficients between the changes in each peak in the NUR spectrum and the changes in the compressive strength of concrete specimens under FTCs in freshwater or low-concentration salt solutions are both larger than 0.7, calculated using the grey correlation degree method. Therefore, these changes could be used as a potential evaluation index for salt frozen damage to concrete structures.
本文制备普通硅酸盐混凝土试件，研究水泥混凝土材料在盐侵蚀和冻融环境作用下的损伤规律。根据盐渍土特性分别配制NaCl、NaHCO₃和Na₂SO₄溶液，对混凝土在快速盐冻循环过程中的特性进行试验研究，分析其在冻融循环作用下抗压强度、质量损失和动弹模量（DEM）的变化。采用低场核磁共振（NMR）和扫描电子显微镜研究盐冻融循环（FTCs）作用下混凝土试件微观结构的变化。结果表明，与淡水相比，6.8%复合盐溶液中50 - 100次FTCs作用下的混凝土试件抗压强度损失、质量损失、DEM损失和NMR谱信号损失分别增加了1.5 - 3倍、3 - 5倍、1.5 - 2.5倍和2 - 4倍。随着盐冻融循环次数增加，混凝土出现明显剥落、DEM降低和抗压强度减小。在盐结晶、吸湿和冻融共同作用下，混凝土结构内部裂缝数量增加。混凝土结构内部微观孔隙体积变化与混凝土宏观力学性能变化趋势一致。利用灰色关联度法计算得出，淡水或低浓度盐溶液中冻融循环作用下混凝土试件NUR谱各峰变化与抗压强度变化之间的相关系数均大于0.7。因此，这些变化可作为混凝土结构盐冻损伤的潜在评价指标。
