Flexural Behavior of One-Way Lightweight UHPC-NC Superimposed Sandwich Slabs

A novel type of ultra-high-performance concrete–normal concrete (UHPC-NC) superimposed sandwich slab is introduced, which eliminates the need for conventional longitudinal reinforcement. This sandwich slab consists of a prefabricated thin UHPC layer at the bottom, a cast-in-place NC layer at the top, and an extruded polystyrene foam core that provides both acoustic and thermal insulation. The resulting lightweight composite sandwich structure is integrated with web walls reinforced by a three-dimensional truss reinforcement system. The flexural performance is examined through four-point bending tests and compared with that of a fully UHPC sandwich slab of identical structural configuration and casting progress. Relative to the fully UHPC slab, the UHPC-NC slab demonstrates superior flexural structural integrity, significantly reduces costs and improves construction efficiency. The ductility coefficient of the UHPC-NC slab reaches 3.23, which is superior to the UHPC slab. This indicates that it has a stronger collaborative working ability with the rebars and the compressed concrete. Comprehensive analytical, numerical, and experimental investigations into the flexural behavior of the proposed UHPC-NC sandwich slab yield accurate evaluation of cracking and ultimate load capacities, thereby offering valuable guidance for the engineering application of this innovative superimposed sandwich slab system.