The partial loss of subgrade support associated with voids under portland cement concrete (PCC) pavements leads to increased deflections and increased load stresses. This can cause a significant reduction in the fatigue life of the pavement. This paper presents the findings of a comprehensive research study to establish the performance capabilities and limitations of the following methods and equipment for detection and measurement of voids beneath PCC pavements: (a) Proof Roller, (b) Deflection Equipment, (c) Ground Penetrating Radar Equipment, and (d) Transient Dynamic Response (TDR) Equipment. The records of grout quantity, based on field tests conducted by the highway agencies of several states during undersealing projects, were the prime source to verify the presence of voids.
All methods required extensive manual data analysis and output interpretation. Deflection methods are the least satisfactory because pavement deflections are significantly influenced by daily and seasonal variation of temperature. The TDR method is very labor intensive and relies on subjective interpretation. Radar methods hold good promise if the data interpretation and processing is enhanced.