Experimental evaluation of microstructure durability interactions in UHPC exposed to diverse chemical environments

The ultra-high-performance concrete (UHPC) is becoming more popular in chemically demanding settings, although its long-term behaviour under equal exposure circumstances with acids and sulphates is undefined. This study examines the durability of UHPC mixes subjected to 5% acids (H2SO4, HCl and HNO3) and sulphate solutions (Na2SO4 and MgSO4) for 3, 7, 14, 28, and 90 days. Durability was evaluated through mass, area, volume loss and flexural strength retention, and morphological, microstructural densification of UHPC matrix supported by SEM and XRD microstructural analysis. Among all mixes, Mix-4 was incredibly durable. It had 15.69 MPa flexural strength before chemical treatment, with acid exposure, it showed the lowest compressive strength loss (−3.24, −2.24 and −2.15 MPa in H2SO4, HCl, and HNO3) and minimal decrease with sulphate exposure (−0.4 and −1.25 MPa in Na2SO4 and MgSO4) due to its optimised particle packing, homogeneous hydration, and decreased matrix breakdown make it outstanding. Microstructure showed a thick matrix, refined pores, and stable hydration products, limiting aggressive ion entry. UHPC deterioration in extreme chemical environments is compared and well-packed UHPC can withstand aggressive service conditions.