Applicability of Electrical Resistance Method to Moisture Transfer Measurement in Paste Using Mineral Admixture

Abstract

AbstractConcrete is a porous material which has the ability to hold moisture stably inside. Since moisture is closely related to the deterioration of concrete structures, it is important to understand the moisture transfer in concrete in order to maintain the concrete structure appropriately. The electrical resistance method is one of non-destructive methods to investigate the moisture in concrete and the moisture transfer can be assessed with time by using one specimen. However, the electrical resistance may be affected by mineral admixtures in concrete. Although previous studies on the effects of mineral admixtures on the electrical resistance have been conducted, there are still many unclear points. Therefore, the purpose of this study is to assess the applicability of the electrical resistance method to moisture transfer measurement in paste containing mineral admixtures by focusing on the moisture transfer in the drying process. The moisture transfer in the hardened cement paste using fly ash and blast furnace slag with water-to-binder ratios of 0.35 and 0.55 was investigated by the electrical resistance method. Stainless steel rods of 0.9 mm in diameter were placed at an interval of 4 mm in the specimen. The calibration test was also conducted to obtain the relationship between the electrical resistivity and the internal relative humidity of the specimen. The result showed that the specific resistance of the specimen containing mineral admixtures was higher than that of the specimen without mineral admixtures. It was observed that at the drying period of 70 days, the internal relative humidity at a depth of 4 mm from the exposed surface was almost the same as the surrounding relative humidity. It is possible to know the change in the internal relative humidity distribution in the cement paste using mineral admixtures during the drying process by performing the calibration test appropriately.KeywordsMoisture transferElectrical resistanceMineral admixtureStainless steel rodRelative humidity