Experimental study on the anti-seepage performance of modified mudstone fly ash geopolymer materials

The main challenge in the ecological reconstruction of open-pit mine waste dumps in arid areas lies in water conservation and restoration. However, the interior of the waste dump contains pores and has experienced non-uniform subsidence, resulting in reduced soil strength and expansion of cracks, thereby preventing the maximum utilization of water resources. Therefore, in the process of soil layer reconstruction of the waste dump, the mechanical properties and permeability of the impervious layer are particularly important. To enhance the efficiency of ecological restoration in open-pit mines located in arid regions, standard specimens were prepared based on the alkali-activated polycondensation reaction of geopolymers, with uniaxial compressive strength and permeability coefficient serving as key technical parameters. Uniaxial compressive strength tests and permeability tests were conducted to investigate the influence of varying material ratios and alkali activator mass fraction on the mechanical properties and failure characteristics of geopolymers materials. The relationships among material ratios, confining pressure, and alkali activator concentration regarding permeability performance were elucidated. Meanwhile, scanning electron microscopy (SEM) was employed to examine both mudstone and geopolymer samples, enabling a detailed analysis of their microstructural characteristics. Test results show that for every 10% reduction in the proportion of mudstone, the uniaxial compressive strength decreases by 25% to 30%. When the material ratio is 5∶3∶2, the uniaxial compressive strength reaches its lowest value among the three tested ratios. When the material ratio is 7∶1∶2 to 6∶2∶2, for every 10% increase in the concentration of the alkali activator, the uniaxial compressive strength increases by 12% to 20%. With the increase of confining pressure, the permeability and permeability coefficient of geopolymers generally show a downward trend. Under the same ratios and confining pressures, for every 10% increase in the concentration of alkali activator, the permeability coefficient of the geopolymer decreases by 20% to 30%. The influence of material ratio on the strength of geopolymer is greater than that of the concentration of alkali activator, and the concentration of alkali activator has a higher influence on the permeability coefficient of geopolymer. After a comprehensive comparison, when the ratio of mudstone∶slag∶fly ash is within the range of 7∶1∶2 to 6∶2∶2, the uniaxial compressive strength and permeability performance of the material are the best.