Research on capillary water absorption characteristics of aeolian sand concrete under sulfate freeze-thaw coupling based on fractal theory

Northwest China, represented by Inner Mongolia, is rich in desert resources, and the reasonable use of aeolian sand (AS) as fine aggregate for the preparation of aeolian sand concrete (ASC) can not only reduce land desertification but also alleviate the shortage of river sand (RS) resources. At the same time, more salt lakes in Inner Mongolia lead to concrete structures often accompanied by salt corrosion and freeze-thaw cycle (FTC) and other erosion effects. Therefore, this paper carries out the capillary water absorption (CWA) test on ASC under the coupling of sulphate FTC, and analyses the effects of different erosive environments (5 %Na₂SO₄, 10 %Na₂SO₄, 5 %Na₂SO₄+3.5 %NaCl) and the amount of AS dosage (0 %, 20 %, 100 %) on the CWA performance of ASC. The results show that, under the coupling effect of sulphate FTC, the expansion stress produced by moisture phase change and erosion products increases continuously, the initial defects inside the concrete develop continuously, the percentage of gel pores and less harmful pores decreases gradually, the compressive strength, relative dynamic elastic modulus (RDEM) and mass decrease gradually, and the concrete is damaged most seriously in the composite salt environment. The CWA of ASC mainly occurs before 2 h^1/2, and there is a good correlation between the initial water absorption rate (IWAR) and the depth of CWA and the degree of freeze-thaw damage. The cumulative water absorption and the IWAR of ASC became smaller with the increase of AS dosage. By applying the fractal theory to the pore structure, it was found that the relationship between the fractal dimension and the IWAR and damage degree was good, and that a reasonable increase in the proportion of small pores below 50 nm was more favourable to the frost durability of ASC.