Digital Image Correlation Technique for Measurement of Surface Strains in Reinforced Asphalt Concrete Beams under Fatigue Loading

Geosynthetic products are routinely used to reinforce pavement overlays to control crack propagation under repeated vehicular and varying thermal loads. Many experimental methods are available to measure the potential of geosynthetic products in controlling reflective cracks. Among all methods, the four-point beam (4PB) fatigue test is commonly used as an effective method to evaluate the performance of asphalt concrete beam specimens with geosynthetics. Three types of geosynthetic products made of GlasGrids (SGT), coir (CGT), and jute (JGT) were used to reinforce the asphalt concrete beam specimens in the current research study. Conventional linear variable differential transformers (LVDTs) were used to measure the vertical deflections during the 4PB fatigue tests. The digital image correlation (DIC) technique, being a noncontact measurement method, has undoubted advantages over the conventional measurement methods in asphalt concrete (AC) testing. The analysis of sequential images captured during the test aids in measuring the strain or displacement field over a region of interest (ROI). This method is most suitable for the study of cracks and their propagation where random damages are expected. The flexibility in postprocessing the measured data eases the analysis of results. This research study explains the different phases of the DIC method adopted for measuring the crack growth pattern during the 4PB fatigue tests on geosynthetic reinforced beams. The analysis of results showed that all the reinforcement layers assist in mitigating the cracking potential, by diverting the crack path along the interface of the geosynthetics. The parameters that influence the accuracy of the DIC analysis are also discussed in this paper.