Studies on Salt Content Distribution in Concrete and Its Transition with Time, 1

Investigations have revealed that the damages due to corrosion of Re-bars in RC structures have been prevailing in Okinawa Prefecture and that the major cause of the damages is salt contained in concrete. There has been also disclosed that high values of salt concentration are found much frequently in concrete of RC structures mentioned above. The writers have started a series of experiments to disclose the causality between many causes and their effects on the above high values of salt concentration. The main one among the many causes is considered to be salt intrusion through concrete surface and water movement in concrete due to evaporation. Specimens were placed on some various places under different environments. One year has passed and the following results are obtained. 1. Specimens at coast have been intruded by a large amount of salt during one year period. The amount of 0.4 to 0.8 ％ salt by weight of mortar in concrete have been found. The effect of initial salt conent on salt concentration has been disappeared after one year. In some specimens at the point 500 m from coast, there have been also observed small increases of salt content in concrete. 2. The influence of W/C on salt concentration by penetration has been also founded in the specimens at coast. The smaller W/C is. the smaller quantities of salt are penetrated at the time one year has passed. The specimens at the point 500 m from coast have also shown the same tendency, but, only the specimen of W/C＝70％ has indicated a small increase in salt content. At coast, the differences among the quantities of intruded salt are relatively small and the quantities themselves are quite large. The structures at or near sea coast must be taken by some protective measures other than lowering W/C. 3. Coatings on concrete surfaces have some beneficial effects on salt penetration resistance, but there have been a large amount of penetrating salt in concrete of the specimens at coat. The lining of acril-gum coating material has been proved to have an excellent effect on preventing the intrusion of salt into concrete. 4. In all specimens, increases of salt concentration near the surfaces of concrete are observed at the biginning of this experiment. The movement of water toward surfaces in concrete specimens due to drying and evaporation is most responsible for this phenomenon. This phenomenon is termed "Edge effect". The salt concentration near surface amounts to 1.4 to 4 times the one of inside middle part of specimens