Water Vapor Transmission and Electrical Resistivity of Concrete

摘要

This is the final report of a study of water vapor transmission (WVT) of plain concrete and of San Gabriel rock, corrosion of steel grids, and electrical resistivity of concrete. The WVT studies involved San Gabriel rock and plain concrete with water-cement ratio, type of reinforcing steel grid, aggregate size, relative humidity, two admixtures (sodium chloride and oleic acid), and position of slice as variables in one or more of three phases of investigation. WVT rates decreased with an increase in age of concrete, in strength of concrete, in maximum aggregate size, and with the presence of 1.5 percent sodium chloride. Two kinds of steel grids--mild reinforcing steel and high-strength prestressing wire--were embedded in the 2-inch-thick concrete disks of some of the WVT specimens. Upon completion of the test, a higher percent of corrosion of steel was found in the higher water-cement ratio concrete disks; nearly all of the grids in concrete containing sodium chloride showed some corrosion. In order to determine the electrical resistivity of concrete, using the twopoint method, sixteen concrete prisms were cast with carbon grids. Electrical resistivity increased with age and decreased with increased salinity of mixing water. (Author)