Study on mechanical properties and curing mechanism of metakaolin based geopolymer solidified soil activated by calcium carbide slag under low temperature curing

In order to address the issues about significant thermal disruption and carbon emissions associated with the use of cement for solidifying frozen soil, calcium carbide slag was used as an alkali activator to activate metakaolin based geopolymer for soil solidification. In this research, the impacts of metakaolin and calcium carbide slag contents, curing temperature and curing age on the compressive strength of the solidified soil were investigated. Geopolymer solidified soil and cement solidified soil were compared in parallel. The curing mechanism was studied by X-ray diffraction and electron microscope scanning. Test results indicate that there is an optimal content of metakaolin and calcium carbide slag. When the content is lower than the optimal content, it plays an active role. On the contrary, it will have a negative effect. The optimal content of metakaolin and calcium carbide slag is 10% and 6%, respectively. The compressive strength of the optimal content sample cured at 20 degrees C, -2 degrees C and -10 degrees C for 28 days is 3.783 MPa, 1.164 MPa and 0.901 MPa, respectively. The main products of metakaolin based geopolymer activated by calcium carbide slag are amorphous hydrated calcium silicate and hydrated calcium aluminate gel, which contribute to the improvement of compressive strength of solidified soil. The compressive strength of geopolymer solidified soil cured at -2 degrees C and -10 degrees C for 28 days is 69% and 76% lower than that cured at 20 degrees C, respectively. Due to the expansion of the pores in the frozen state which is related to the ice crystal, the growth of cracks is promoted, the efficiency of geological polymerization reaction is reduced and the amount of polymerization products is reduced. Compressive strength of the samples increases with the increase of curing age, because of the more silicon-aluminum grid structures produced by the geological polymerization reaction, the lower the porosity of the solidified soil and the internal structure of the soil is intertwined to form a denser structure. The geopolymerization reaction is less affected by low temperature. Compressive strength of geopolymer solidified soil cured at 20 degrees C, -2 degrees C and -10 degrees C for 28 days is 1.07, 1.13 and 1.19 times that of cement solidified soil, respectively. The research results lay a theoretical foundation for the application of geopolymer in subgrade soil reinforcement in frozen soil area.