In order to study the influence of nano-clay on the crack resistance of cement-based materials, two kinds of nano-metakaolin (NMK) and two kinds of nano-attapulgite clay (NMA) were considered. The early cracking process and mechanical properties of nano-clay cement mortar (NCM) was studied by using a plate knife-edge constraint test. Based on fractal theory, the distribution characteristics of NCM surface cracks were revealed, and the calculation method forNCM maximum crack width was given. The results show that the cracking time of the NMK-3 specimen is 2 and 6 h later than that of NMK-1 and NMA-2, respectively; the smaller the particle size of nano-clay, the earlier the cracking time of the specimen. However, nano-clay effectively inhibited the expansion of mortar cracks, and the cracks on the surface of NCM were thin and sparse. At 28 days, the maximum crack width of NMK-3 was 46.7% and 33.3% lower than that of NMK-1 and NMA-2, respectively. NMK hadthe best improvement effect on the mechanical properties cement mortar. The smaller the particle size, the more pronounced the improvement effect.The flexural strength ratio and compressive strength ratio at 7 and 28 days are 76.7%, 67.4%, and 61.2%, respectively.The distribution of surface cracks on NCM has fractal characteristics, and the fractal dimension of surface cracks is smaller than that of ordinary cement mortar. The larger the particle size of nano-clay, the smaller the fractal dimension of cracks. The quantitative relationship between fracture fractal dimension and NCM elastic modulus and shrinkage tensile stress is established.

To explore the effect of nano-attapulgite clay (NAC) on the durability of concrete, two kinds of NAC (calcined raw ore and calcined high viscosity ore: calcination at 650 °C for 2 h) were used to study their effects on the durability of concrete, mainly discussing the changes of chloride ion permeability and the resistivity of concrete with NAC. The effect of NAC on the strength of concrete was analyzed by testing the compressive strength of concrete. The two-electrode method, four-electrode method, and concrete resistivity tester were used to analyze the relationship between the testing method and concrete resistivity, and the effect of NAC on concrete resistivity was analyzed. The influence of NAC on the chloride corrosion resistance of concrete was analyzed by measuring the chloride diffusion coefficient, and the relationship between the chloride diffusion coefficient and resistivity was established. The diffusion process of chloride ions in concrete was analyzed by theoretical derivation and numerical simulation. The results show that: calcining raw ore NAC can improve the compressive strength of concrete, while calcining high-viscosity ore reduces the compressive strength of concrete. At the age of 28 days, the strength of concrete mixed with calcined raw ore is about 7.10% higher than that of ordinary concrete, while the compressive strength of concrete mixed with calcined high-viscosity ore is about 4.32% lower than that of common concrete. The resistivity of concrete mixed with calcined raw ore increases the fastest, and the 56 days age is about 15.8% and 29.6% higher than that of ordinary concrete and calcined high-viscosity ore. There is a good negative correlation between concrete resistivity and chloride diffusion coefficient. At 28 days, the incorporation of calcined raw ore concrete decreased by about 19.9% and 49.4% compared with ordinary concrete and calcined high-viscosity ore, respectively. After 10 years of decline, the chloride ion content is 11.1% and 23.2% lower than that of ordinary concrete and concrete mixed with calcined high viscosity ore.