Title: Laboratory and Field Evaluation of Nuclear Gage for Measurement of Water and Cement Content of Fresh Concrete
Author(s): D. Whiting and M. Nagi
Publication: Symposium Paper
Appears on pages(s): 69-80
Keywords: calibration; cement content; concretes; entrained air; nuclear gage; testing; water content
A laboratory and field test program was undertaken to determine the perfromance of a nuclear water/cement content gauge for fresh concrete. The laboratory evaluations included study of the effects such variables as air content, pozzolans, hold time, coarse aggregate, and temperature on gauge response. The laboratory testing demonstrated that the gauge is sensitive to materials compositions and other factors, and therefore must be calibrated with exactly the same materials as will be used on the job in question. With proper calibration in a laboratory setting, the cement gauge is capable of determining cement content of fresh concrete to within approximately 10 to 20 lb/yd3 (6 to 12 kg/m3). The water gauge is capable of determining water content to within approximately 2 to 4 lb/yd3 (1 to 2 kg/m3). Field tests at two locations are described. Favorable results were acheived where calibrations were carefully carried out using the same materials as to be used in actual construction. In these cases, avearge water content determinations for a series of samples using the nuclear gauge were comparable to those obtained using a microwave oven drying technique.The gauge is well-suited for use at construction sites. Technicians (having proper radiation safety training and certification) can successfully operate the gauge after a brief period of training, and the gauge can be transported in construction vehicles and set up on-site with a minimum of effort. The test period is short, requiring approximately ten minutes per sample, including consolidating of concrete into a test bucket.