Evaluation of coupled hygro-mechanical behavior of heat-damaged mortars during post-heating water absorption using DICM

In this study, one-dimensional water absorption tests were performed on heat-damaged mortar specimens following their exposure to elevated temperatures of 200°C, 400°C and 600°C. During water absorption, real-time surface deformations were simultaneously monitored using surface strain gauges and the Digital Image Correlation Method (DICM). Water absorption characteristics were evaluated in terms of the initial absorption rate and maximum expansion strain based on DICM-derived strain response, whereas the residual mechanical properties, the compressive strength (f′ cm ) and the Young’s modulus (Eₘ), were subsequently determined through uniaxial compression tests on the same specimens. Finally, the relationships between the DICM-derived absorption characteristics and residual mechanical properties were analyzed. The experimental results revealed that increasing exposure temperatures significantly altered both the water absorption and moisture-induced expansion behavior. Compared with unheated/oven-dried mortars, the initial water absorption rate and maximum expansion strain increased by approximately 3.4 and 2.5 times, respectively, after exposure to 600°C. Beyond these changes, full-field strain visualization revealed distinct patterns of spatial deformation and heterogeneous swelling, progressing from relatively gradual expansion at 200°C and 400°C to highly localized and abrupt deformation at 600°C. The latter behavior is consistent with the increased contribution of CaO rehydration-induced expansion in severely heat-damaged mortars during post-heating water absorption. Furthermore, the DICM-derived absorption and expansion characteristics exhibited an inverse relationship with the residual mechanical properties, demonstrating that mortars with greater loss of mechanical integrity were generally associated with faster water ingress and greater wetting-induced deformation. Overall, the findings demonstrate the potential of DICM to simultaneously characterize spatial deformation associated with water ingress and relate it to the residual mechanical condition of heat-damaged mortars, thereby providing a useful framework for post-heating durability assessment of cementitious materials.