Concrete pore sizes are in the range of a few nanometers to a few millimeters, and these pores directly affect the cracking characteristics of concrete. In this study, the influence of the pore size distribution on concrete cracking damage was evaluated. Low-field nuclear magnetic resonance (LF-NMR) was used to test the effects of curing age and air-entraining agent (AEA) content on the pore structure of concrete. Three sets of concrete samples with different AEA dosages (0%, 0.7%, and 1.4% of the cementitious material) were prepared, and standard curing was carried out for 3, 7, 28, and 90 days before the tests. During the uniaxial compression test, the cracking signal of the concrete specimen was collected with an acoustic emission (AE) system. The results show that as the curing age increased, the proportion of macropores decreased and the combined proportion of gel pores and transition pores increased. The proportions of macropores and capillary pores increased with AEA content. During the compression process, the relative ringing count at low strain levels was positively correlated with concrete cracking damage. Based on the AE and LF-NMR data, a mathematical model between concrete cracking and the pore size distribution was established, and the effect of the pore size distribution on concrete cracking was quantitatively described by multiple regression equations.

混凝土的孔隙大小在几纳米到几毫米的范围内，这些孔隙直接影响着混凝土的开裂特性。在这项研究中，评估了孔径分布对混凝土开裂损伤的影响。采用低场核磁共振（LF-NMR）测试养护龄期和引气剂（AEA）含量对混凝土孔隙结构的影响。制备了三组不同AEA用量（胶凝材料0%、0.7%和1.4%）的混凝土试样，并在试验前进行了标准养护3、7、28和90天。单轴压缩试验时混凝土试件的开裂信号用声发射（AE）系统收集。结果表明，随着养护龄期的增加，大孔比例降低，凝胶孔和过渡孔的组合比例增加。大孔和毛细孔的比例随着AEA含量的增加而增加。在压缩过程中，低应变水平下的相对振铃计数与混凝土开裂损伤呈正相关。基于AE和LF-NMR数据，建立了混凝土开裂与孔径分布的数学模型，并通过多元回归方程定量描述了孔径分布对混凝土开裂的影响。