Experimental and theoretical investigations on the flexural behavior of RC slabs with steel-PVA hybrid fiber reinforced cementitious composite (HFRCC) permanent formwork

From the perspective of optimizing the construction process, the steel-PVA hybrid fiber reinforced cementitious composite (HFRCC) permanent formwork, which can take full advantage of the mechanical properties of HFRCC and factory prefabrication, was presented. Firstly, the fiber hybrid ratio of HFRCC was determined based on the slump flow tests and four-point bending tests. It was found that the HFRCC containing 0.25 % PVA fiber and 1.5 % steel fiber exhibited excellent workability and flexural behavior, and was adopted to manufacture the permanent formwork. Subsequently, the mechanical properties of prefabricated HFRCC formwork subjected to the construction load were studied. The results showed that the ratio of the maximum elastic load to the design load was 1.38-1.66 and the prefabricated HFRCC formwork with a thickness of 10 mm can ensure the safety of construction. Then, seven reinforced concrete (RC) slabs with 10 mm thick HFRCC permanent formwork (composite slabs) and one RC slab were tested under four -point loading to explore the impact of span length, depth of cast-in-place concrete, reinforcement ratio, and HFRCC-RC interface treatments. The results showed that the addition of HFRCC formwork can improve the flexural behavior of RC slabs. The cracking load of such composite slabs was increased by 20.1-31.7 % compared with the reference RC slab. Due to the favorable bonding properties between HFRCC and concrete, the flexural behavior of composite slabs with different interface treatments (manual smoothing, isometric grooves, and surface scratching) was similar, and negligible interfacial slip occurred. Moreover, a theoretical method was put forward for estimating the flexural strength and deflection of composite slabs. The feasibility of the developed model was verified by the comparisons between the estimated value and test data.