Creep behavior of lightweight concrete containing fly ash ceramsite aggregate after exposure to high temperatures

To investigate the influence of aggregate types on the long-term deformation performance of concrete after disasters, this paper takes normal-weight aggregate concrete (NWAC) and light weight aggregate concrete (LWAC) as the research objects, and conducts uniaxial step-wise compression creep tests after being subjected to high-temperature treatment ranging from 20 °C to 800 °C. The focus is on comparing and analyzing the effects of aggregate types on total strain, load-induced thermal strain (LITS), creep deformation, and rate patterns. The results show that below 200 °C, LWAC has a higher LITS than NWAC by approximately 83.3% due to its lower lightweight aggregate modulus; above 400 °C, NWAC experiences a rapid increase in creep strain due to the thermal expansion mismatch between the aggregate and the paste at the interface transition zone (ITZ). In contrast, the porous structure of the fly ash ceramic aggregate within LWAC plays a “thermal mitigating” effect, effectively inhibiting the propagation of microcracks. LWAC can maintain a longer steady-state creep period compared to NWAC. SEM confirmed that at high temperatures, the ITZ of NWAC developed tensile cracks of several micrometers, while LWAC maintained a relatively intact structure. Moreover, the fitting degree of the Burgers model for the creep data of LWAC was high ( R 2 = 0.99), verifying the applicability of this model in describing the deceleration and constant-speed creep behavior of LWAC after high-temperature treatment. The research results reveal the deformation mechanism of fly ash ceramic aggregate in the high-temperature environment, providing a theoretical basis for the design and post-disaster assessment of the fire resistance of LWAC structures.