Ali Akbar Kafash Bazari - Chief of research and development of Tehran cement Co, Tehran, Iran
Mehdi Chini - Assistant Professor of Road, Housing and Urban Development Research Centre, Tehran, Iran

Common methods of controlling setting, hardness, process of strength concrete are tests for determining the setting time of mortar and concrete and determining the compressive strength of concrete It seems that these physical methods, do not fully reflect the behavior of concrete and the process of changing phase states during the hydration process; however, with the method of the electrical resistance of concrete, this observation is possible. Therefore, in this study, at the first stage, ۱۱ samples of cement were prepared, the phases of which varied, but due to laboratory cementation, their fineness and grading conditions were almost the same. Physical and chemical analysis of cement samples was performed. In the next step, ۲۲ concrete mixtures with ۱۱ cement samples were prepared, so that ۱۱ mixtures without additives and ۱۱ mixtures with constant dosage of commercial super plasticizer. Also in the all concrete mixtures, the slump kept constant about ۸ cm. Compressive strength tests of ۷, ۲۸ and ۹۰ days hardened concrete were performed on concrete mixtures. Also, an electrical resistance test was performed, which was performed regularly from the time of cement contact with water until ۳۱ days later. The results showed that at least three peaks of ۸, ۱۶ and ۲۳ days in the electrical resistance curve are seen along the test time. In almost all samples, the electrical resistance is reduced to about ۳ hours, which indicates the setting time of the concrete. Based on the results of this study, formula was presented.

Electrical resistance, cement, Concrete, additives