Non-Destructive Testing Methods for Quality Assessment of Mortar-Rich Pavement Surfaces

Abstract: The majority of concrete pavement construction in the United States utilizes slipform paving machines equipped with internal vibrators to consolidate the stiff concrete mixture while maintaining pavement edge and surface shape. A potential issue that may arise is the formation of mortar-rich surfaces, where coarse aggregate settles, and excess mortar accumulates at the surface. This condition is often caused by over-vibration, leading to segregation, or over-finishing, which draws excessive paste to the surface. Improper mixture designs, particularly those lacking optimized aggregate gradation, further increase the risk. Mortar-rich surfaces are problematic due to their higher porosity, which can reduce durability and lead to issues such as cracking, delamination, surface scaling, increased permeability, and lower wear resistance—all contributing to accelerated pavement deterioration. Therefore, identifying reliable non-destructive testing (NDT) methods to detect these surfaces is critical for quality assurance. This study evaluated several NDT devices on a full-scale test section constructed with controlled variations in mortar-rich surface depth. Devices tested included the rebound hammer, surface resistivity meter, impulse response system, and MIRA ultrasonic imaging system. Measurements were taken at early ages (1, 2, 3, 4, and 7 days) to assess early-age sensitivity and again at approximately one year to evaluate performance without the influence of hydration and moisture changes. Results showed that the rebound hammer and surface resistivity meter effectively distinguished between control and mortar-rich sections. The impulse response system also detected differences in areas with deeper mortar layers. However, the MIRA device was not able to quantify the mortar layer effectively. These findings indicate that several NDT methods are viable for evaluating pavement surface quality and can play an important role in ensuring long-term durability and performance in concrete pavement construction.