Impact of curing time on UCS-electrical resistivity relation of cement grouted sands

As the curing process proceeds, both the strength and electrical resistivity (ρ_mix) of cement-based (or cement-grouted) materials increase, leading to the nondestructive ρ_mix measurement technique is very appealing in the assessment/monitoring of the quality of cement-grouted materials. However, the strength gain of cement-grouted sands with time differs from the increase in ρ_mix with time. Thus, the relationship between unconfined compressive strength (UCS) and ρ_mix can be affected by the curing time. This study evaluated the effect of curing time on the relationship between ρ_mix and UCS of sands grouted with microcement. The ultimate goal of this study is to estimate UCS over time of cement-grouted sands based on ρ_mix. Three silica sands with different median particle sizes were grouted with microcement at different water-to-cement ratios (wc) of 1.0, 1.5, and 2.0. Both unconfined compression test and electrical resistivity measurement test were conducted. Results demonstrate that curing time, particle size, and wc influenced both ρ_mix and UCS of tested grouted sands in a similar manner; therefore, a direct relationship between ρ_mix and UCS can be established. However, the complex impact of curing time on the relation between UCS and ρ_mix and the nonlinear increase in UCS with time hinder the capture of adequate interplay between UCS, ρ_mix, and curing time. Because a nonlinear increase in UCS with time can be represented by hyperbolic model, an estimation method for hyperbolic model parameters is newly suggested in this study based on ρ_mix at early curing days.