An Evaluation of Selected Instruments used to Measure the Moisture Content of Hardened Concrete.

摘要

Six types of gages for measuring moisture content of hardened concrete were studied to determine their behavior in long-term service. They were evaluated with respect to stability of measurement and response to moisture change. The gages were mounted in a 12- by 12- by 18-in. copper box and the box was filled with concrete and a copper lid soldered to it. The gages were monitored for a period of 800 days. For the first 194 days the gages were read in a hermetically sealed environment, then for 326 days (194 to 520 days) the copper lid was removed and the box was exposed to a 50 percent relative humidity atmosphere. From 520 to 722 days, the concrete specimen was exposed to 50 percent relative humidity after being entirely removed from the copper box, and for the last 78 days of the test, from 722 to 800 days, the bare concrete block was monitored in a 100 percent relative humidity atmosphere (fog room). The results of the test indicated that two gages (the ionic barrier moisture gage and the Bouyoucos moisture gage) reacted the most favorably during the entire 800-day test period. Both types of gages gave results that were responsive to environmental changes and stable with respect to time. (Author)