Experimental Study On Mechanical Properties And Durability Of Low Content Cement Red Clay In Cold Arid Regions

The seasonally frozen red clay widely distributed in cold arid regions of northern China belongs to a kind of special soil. It has some defects and deficiencies in engineering applications, which often needs artificial reinforcement and modification to satisfy normal engineering demands. As a relatively new green and eco-friendly material, cement red clay can be widely popularized and applied in hydraulic engineering, road engineering, geotechnical engineering, and constructional engineering, etc., but larger cement content often causes higher project costs. Reducing the cement content in cement red clay will save costs to a great extent, which however can give rise to such defects of some materials as easy cracking, high brittleness and poor durability, so it is very necessary to study how to keep the engineering properties in the premise of reducing cement content. It can provide a certain theoretical basis for engineering applications to improve the mechanical properties and durability of low content cement red clay by doping industrial waste fly ash and organic material polyacrylamide (PAM for short).First of all, the low content cement red clay doped with PAM only and doped with the mixture of PAM and fly ash were prepared, whose mechanical properties were measured by unconfined compressive strength experiment. Based on the laboratory experiment, different mixture ratios would make a difference in mechanical properties of low content cement red clay. As the proportion of PAM increased, the strength tended to first increase and then decrease, which showed that there was a relatively optimal proportion of PAM. The experiment indicated that, the strength of the soil containing mixture of 6%o PAM and 8% fly ash was significantly better than that in other experimental groups.Furthermore, the freezing resistance durability of low content cement red clay was further studied. Based on the laboratory experiment, the low content cement red clay doped with a proper mixture of PAM and fly ash was able to drastically reduce the quality loss and strength loss. The mass loss of the low content cement red clay doped with the optimal mixture of 6%o PAM and 8% fly ash was only 0.70% after the freeze-thaw cycle, which was superior to that in other experimental groups in varying degrees, revealing that this mixture ratio could improve the freezing resistance durability markedly.Finally, the mechanism of curing and durability was discussed from the mesoscopic and microscopic perspectives. On the basis of laboratory experiment results and theoretical analysis, the overall structure compactness, pore distribution and cracking development situation were identified on the micro level, and the macroscopic structure model of "aggregate-chain bar" was built. Under certain model assumptions, this model was used to explain the mechanical properties of the low content cement red clay, that is, under external influences and adverse environment, the "aggregate" structure itself was not likely to be destroyed, while the "chain bar" structure was more prone to getting damaged, eventually obtaining the mechanism of low content cement red clay curing and durability.