Cement-based grout has been used for ground improvement. Owing to environmental issues related to cement, its usage should be reduced. In this study, an inorganic binder is introduced to reduce the use of cement in grout. To evaluate the transient electrical and mechanical properties of the sand–cement admixture samples improved with the addition of inorganic binders, two non-destructive testing methods, the electrical resistivity and free–free resonant column tests, were adopted in addition to the unconfined compressive strength (UCS) test. Experimental tests were performed considering four different mixing ratios and three different cement contents, depending on the curing time. The results show that the mixing ratio and curing time have considerable effects on the electrical and mechanical properties of the mixture. The UCS decreases as the cement content decreases. However, sufficient UCS is expected to be obtained when the inorganic binder content is increased in the mixture. From the results, it is found that geotechnical properties of the mixture can be estimated in the field with proper non-destructive testing methods. It is expected that the data and trends proposed in this study can be used as a reference in predicting grouting quality in the field.