Flexural Resistance and Service Life Prediction of Lightweight Aggregate Concrete under Continuous Load and Corrosion

An accelerated corrosion test was conducted to examine the combined effects of sustained loading and acid exposure. Specimens were subjected to four-point bending under sustained load levels of 0, 0.2, 0.4, and 0.6 times the ultimate bending capacity, followed by immersion in a pH 4.0 acidic solution for 14, 28, 42, and 56 days, respectively. Subsequent flexural tests were performed, and the loss rate of bending strength was adopted to assess the corrosion resistance of alkali-activated lightweight aggregate concrete (ALWC). The results revealed that corrosion resistance progressively decreased with increasing load and immersion time, and the maximum strength loss was 38.5%. To determine the underlying mechanisms, microscopic examination, and X-ray diffraction (XRD) analyses were employed. The primary cause of strength degradation in lightweight aggregate concrete was identified as the accelerated propagation of internal cracks within the tensile zone. This facilitated the rapid diffusion of H+ and SO42− ions into the specimen interior, thereby disrupting the alkaline environment and decomposing preformed hydration products, including C─ A─ S─ H gel and Ca(OH)2. Concurrently, the process accelerated the decomposition of ettringite and the expansive hydration of gypsum, ultimately compromising the crystalline structure and degrading the performance of ALWC. Finally, a life-prediction model incorporating the decrease in bending strength and service safety was established. According to the model, the predicted failure times under acid rain corrosion for the 0ff, 0.2ff, 0.4ff, and 0.6ff groups were approximately 1,065, 350, 124, and 64 days, respectively.