Synergistic effects of sustained loading and sulfate attack on the damage of UHPC based on lightweight aggregate

This paper presents an experimental study on the damage progress of lightweight ultra-high performance concrete (LUHPC) subject to sulfate attack under flexural loading. Two different loading environments (natural curing and 15% Na2SO4 solution immersion), which contain three different stress levels and both tensile and compressive regions, are applied in this test. The research results indicate that the damage of LUHPC was increased with the increasing stress level and loading age, which was manifested by the increase of sulfate ion content in the surface layer and the decline of the overall mechanical properties of LUHPC. The lightweight aggregate avoids the expansion damage of LUHPC by absorbing the surrounding excess sulfate ions. In the tensile region, loading accelerate the sulfate attack of the LUHPC, while in the compressive region, loading improve resistance of LUHPC against sulfate attack and this effect is more obvious with the increase of stress levels. Compared with the loading group, the mechanical properties of the LUHPC under loading-sulfate attack decreased less, and the microstructure was denser, indicating a significant synergistic effect between sustained loading and sulfate attack.