Innovative Methods for Water Content Control of Recycled Aggregate Concrete: Rapid Absorption Test for Aggregate and Continuous Monitoring of Freshly-Mixed Concrete at Site

Abstract

Recycled aggregate concrete was used as structural concrete at site under the strict quality control system especially on water content in concrete. Two innovative methods were applied for this project: one is the rapid test method for water absorption of aggregate, and the other is the continuous real-time monitoring of water content of freshly mixed concrete at site using a radio isotope (RI) moisture meter. With regard to the rapid test method for water absorption of aggregate, hot water and pressure were applied for the test. By the rapid method, test results could be obtained within two hours. This method is very useful in water content control of concrete produced at mixing plants, especially for concrete with recycled aggregate, water absorption of which generally fluctuates more than that of normal aggregate. As for the water content control using RI moisture meter, water content of freshly mixed concrete transported to the site was being continuously monitored during pumping by a meter attached to the transporting pipe of the concrete pump. Neutron radiation intensity measured varies with the water content of concrete. Every 120 seconds, measurements were used for running mean of water content. According to some experimental studies on this method, standard deviation of the water content of concrete is about 3 kg/m3. In this paper, outline of above-mentioned methods and their application at site are described.