Freeze-thaw damage characteristics and evolution law of foam concrete based on acoustic emission-digital image correlation technique

To study the compression damage characteristics and damage evolution law of foam concrete under a freeze-thaw environment, a joint test combining uniaxial compression, acoustic emission (AE), and digital image correlation (DIC) technology was carried out on foam concrete with a density of 800 kg/m³. The strain evolution cloud diagram and acoustic emission parameter change characteristics of the foam concrete during the loading process were obtained. The results show that the compression damage process curve of foam concrete presents an obvious staged effect. The more freeze-thaw cycles the specimen experiences, the more pronounced the ductile damage characteristics become. With the increase in the number of freeze-thaw cycles, the area of the strain concentration zone of the specimen monitored by the DIC gradually increases, while the average value of the strain field gradually decreases. Meanwhile, the morphology of surface cracks in the specimen evolves from initial vertical single cracks to tilted shear-type multi-fractures. The proportion of shear cracks in the final damage of foam concrete specimens with 0, 20, 40, 60, and 80 freeze-thaw cycles are 52.5%, 57.8%, 59.2%, 65.3%, and 69.2%, respectively. The stages of decreasing acoustic emission b-value appear in 92.3%, 89.1%, 88.5%, 76.5%, and 72.3% of the loading process, respectively. The freeze-thaw environment can promote the transition from tensile to shear damage in foam concrete, exacerbates the internal damage of foam concrete, and thus induces large-scale rupture phenomena within the material. The results of AE and DIC complement each other, and their combination contributes to a comprehensive understanding of the developmental pattern of microcracks and damage mechanisms in foam concrete.