Case Study on Ultra-High-Performance-Concrete-Reinforced Autoclaved Lightweight Concrete: Multi-Scale Optimization of Autogenous Shrinkage, Interface, and Structure

Autoclaved lightweight concrete (ALC) exhibits considerable potential as a wall material in prefabricated structures, but its high water absorption and limited mechanical properties limit its widespread application. Ultra-high-performance concrete (UHPC), which possesses superior mechanical strength and durability, presents a promising reinforcement strategy. This study proposes the development of a UHPC-ALC composite wall material to enhance structural performance. The effects of shrinkage-reducing agent (SRA) content and expansive agent (EA) dosage on UHPC properties were systematically investigated. Results indicate that increasing SRA content improves the fluidity of UHPC and significantly reduces early autogenous shrinkage while the optimal EA dosage enhances both its mechanical properties and volume stability. Furthermore, an interfacial agent was employed to enhance the bonding performance between UHPC and ALC resulting in an average bonding strength of 0.93 MPa which represents a 675% increase compared with the untreated group. Finite element simulations and mechanical tests revealed that the composite material demonstrates a compressive strength of 11.2 MPa and a flexural strength of 6.8 MPa which corresponds to increases of 111.3% and 325%, respectively, relative to monolithic ALC. The composite demonstrated ductile failure and the experimental damage modes were consistent with those of the simulation results. This study offers guidance for optimizing UHPC-based composite wall materials via the multi-scale regulation of shrinkage behavior, interfacial properties, and structural design.