Experiment on the Effect of Freezing–Thawing Cyclic on Mechanical Properties of Solidified Sludge

The solidification technology of sludge can effectively solve the problem of environmental pollution and resource shortage. Whereas, the current study lacks the exploration of the durability of solidified sludge. The freeze–thaw cycle test and the moisture transfer test were carried out to test the freeze–thaw resistance and the failure mechanism of the solidified sludge. The results showed that the content of fly ash has a significant effect on the freeze–thaw cycle of the mechanical properties of the solidified sludge. The stress–strain relationship of different dosage samples tends to approach the number of freeze–thaw cycles increases. The stress–strain curve of the samples under all confining pressures is strain-hardening type, which failure mode is ductile failure. The incorporation of fly ash can improve the failure strength and cohesion of cement–lime solidified soil, and gradually increase with the increase of fly ash content. The freeze–thaw cycle test is carried out under the closed system. The moisture in the sample migrates under the temperature load, causing the water content to increase and decrease the partition distribution. The sample with lower fly ash content has smaller static pressure density, which is beneficial to water migration. And increasing the range of water increase zone, the effect of the sample on the freeze–thaw cycle is relatively small. However, the influence of the number of freeze–thaw cycles on the internal friction angle of each soil sample depends largely on the distribution of water in the soil sample, it does not appear regular changes. During the freezing and thawing process, the effects of fly ash content and water redistribution on the mechanical properties of the solidified sludge are simultaneous. In short, the samples with different ratios and freeze–thaw cycles have different factors influencing the change of strength.