Selection of superplasticizer in concrete mix design by measuring the early electrical resistivities of pastes

Electrical resistivity measurement was used to study the early setting and hardening process of pastes, with different dosages, for 2 types of superplasticizer. The inflection point (Pi) was found on the differential curve of electrical resistivity for each sample. A time ratio, Kt, is defined as the inflection time ratio of the pastes with superplasticizer to the paste without superplasticizer and a resistivity ratio, Kr, is defined as the ratio of resistivity of the pastes with superplasticizer to the resistivity of paste without superplasticizer at 24 h. The results show that Kt is linearly positive to setting time and Kr is linearly positive to compressive strength at 24 h.The criterion for the selection of superplasticizer is proposed using these definitions. The most suitable superplasticizer is one which gives the mixture a higher Kt with a longer setting time and a higher Kr with a rapid strength gain in the hardening period for the saturation dosage at a fixed water cement ratio.