Development of a Device for Continuous Automatic Monitoring of Consolidation of Fresh Concrete.

摘要

Quality of portland cement concrete can be increased if water/cement ratios are reduced;however,this increase is only achieved if concrete is adequately consolidated. This study was conducted to develop a device to permit continuous automatic monitoring of the degree of consolidation during pavement construction. A literature search identified several candidate techniques,the most feasible being a nuclear backscatter technique to measure concrete density. A prototype instrument was developed with a 500mCi source of Cesium (137) and a sodium iodide/photomultiplier sensing unit. The sensor head is located 1inch (25.4mm) above the concrete. It is moved back and forth across the width of the pavement by a traversing mechanism mounted to the back of a slip-form paver. Density is recorded on chart paper. The CMD (Consolidation Monitoring Device) is capable of sensing and displaying changes in density while traversing over the pavement surface at 17 fpm (0.086 m/s). It can duplicate core density measurements within a +or -2-1 pcf (+or -36kg cu m) confidence range (95% confidence limits).