Pore structure and dynamic mechanical properties of geopolymer cement soil based on nuclear magnetic resonance technique

To study the effects of curing age and metakaolin (MK) content on its pore structure and dynamic mechanical properties, the dynamic uniaxial impact compression tests on the geopolymer cement soil are carried out with the help of the split Hopkinson pressure bar (SHPB) system, in addition, its pore size distribution and microstructure characteristics are studied by combining the nuclear magnetic resonance (NMR) and scanning electron microscope (SEM) analytical methods. The results indicate that with the increase of MK content, the dynamic compressive strength of the geopolymer cement soil exhibits a trend of first increase and then decrease, and the peak value appeares at 2% MK content. Moreover, its dynamic compressive strength increases slowly in the period of 7~14 curing days. The T₂ distribution curves of the geopolymer cement soil present bimodal characteristics, and the main peak accounts for large proportion. The incorporation of 2% MK can effectively improve the pore distribution and promote the conversion of small pores to micro pores. With the increase of porosity, the dynamic compressive strength of the geopolymer cement soil decreases exponentially. When the MK content is 2%, the internal pores of the geopolymer cement soil are greatly reduced, and the cementitious material produced by hydration can fill pores and connect soil particles.