English：

Under carbon peaking and carbon neutrality background, the research on the modification of alternative materials such as kaolin and coal gangue in cement mortar can effectively reduce the carbon emissions of traditional cement mortar and minimize its adverse impact on the environment. Using metakaolin and coal gangue as substitutes for 5%, 10%, 15%, 20%, and 30% cement to prepare sand specimens, this paper investigates the effects of different dosages on compressive strength, volcanic ash activity index, tensile strength, strength after sodium sulfate erosion, and electrical resistivity over time. The results are as follows: When the content of metakaolin is 20%, the compressive strength increases the most, and when the content of coal gangue is 30%, the compressive strength decreases the most. The compressive strength of the specimens increases with age; As the age increases, the activity index of volcanic ash tends to decrease with the increase of metakaolin and coal gangue content; The addition of metakaolin will increase the tensile strength of the specimen, while the tensile strength of the specimen mixed with coal gangue will firstly decrease and then increase. The maximum increase in tensile strength is achieved when the content of metakaolin is 15% and the content of coal gangue is 10%; The strength of the specimen after erosion increases with the increase of metakaolin content, while the opposite is true when coal gangue is added. The strength of the specimen is higher when the erosion frequency is less than 1 time, but lower when the erosion frequency is 2～4 times; After adding metakaolin and coal gangue, the electrical resistivity of the specimens generally shows an increasing trend with age. When the content of metakaolin is 20%, it is larger, while the addition of coal gangue has a smaller impact on the electrical resistivity..