Soil-cement formation factor: methodological approach and relationship with unconfined compression strength

This study investigated the use of the Formation Factor of the material as an alternative way to estimate soil-cement strength involving no destructive tests. This factor is obtained from Archie’s Law and consists of the ratio of pore water electrical conductivity to saturated porous material electrical conductivity, being related to porosity by constant terms. In this study, the electrical conductivity of the pore solution was obtained from a soil-cement leaching test after curing, and the conductivity of the monolithic soil-cement, by applying continuous voltage between 12-35 V onto electrodes of 1 mm thick copper plates. The influence of cement content and dry density on the electrical properties and water absorption was studied and discussed for curing times of 7 and 28 days. The samples molded with higher dry densities and cement contents presented higher Formation Factor for Soil Cement and higher unconfined compression strength. The Formation Factor and the unconfined compression strength are linearly related. Due to the methodology adopted, the Formation Factor was predominantly influenced by the conductivity of the pore solution and was related to the open porosity by means of a power function. Therefore, the Archie’s Law can be applied to soil-cement. In this case, the cementation coefficient varies until 28 days of curing, tending to stabilize around 8 from that age onwards. The volumetric coefficient can be adopted as a constant with a value of 1012.