Evaluation of equipment for measuring voids under pavements

This report documents the research performed on evaluation of equipment for measuring voids under portland cement concrete pavements. The following equipment was evaluated based on field tests conducted by several state dot's: proof roller, the benkelman beam, dynaflect, falling weight deflectometer (fwd), ground penetrating radar (gpr) equipment developed by gulf applied radar and donohue and associates inc, and transient dynamic response (tdr) equipment. The devices were evaluated through information obtained from a literature search, synthesis of field test data provided by the states and additional telephone contacts conducted for this study. The field tests were performed on pcc pavements in these states during undersealing projects. Records of grout quantity were the prime source to verify voids. Cores and, in some cases, lifting of the entire pcc slabs provided further evidence of the presence of voids. Gpr and tdr data were interpreted by their participants. Deflection data were interpreted by the states or analyzed in this study using standard procedures. The report concludes that, based on the interpretation of field test data and field verifications, none of the methods or equipment can yet be classified as an excellent tool to measure voids. Deflection methods are the least satisfactory because pavement deflections are influenced by daily temperature cycles and load transfer deficiencies across transverse joints. All methods require extensive manual data analysis and data interpretation. The tdr method is very labor intensive and needs further study in relation to the influence of slab curling due to temperature cycles and the effect of load transfer inadequacy. Ground penetrating radar methods hold good promise if the data interpretation techniques are enhanced and their subjective and time consuming reporting aspects are improved (a).