Research on flexure and impact performance of functionally-graded two-stage fibrous concrete beams of different sizes

Abstract

This research focuses on developing functionally-graded two-stage fibrous concrete (FGTFC) comprising steel and polypropylene fibres to enhance impact resistance and alleviate the damage. The FGTFC was developed based on the bionic-inspired impact resistance of turtle shells. This research examines the flexural and impact performance of FGTFC beams of three sizes. Three different beams were prepared of size 250 × 50 × 50 mm, 400 × 100 × 100 mm and 550 × 150 × 150 mm with a 2.4% average dosage of steel and polypropylene fibres. Additionally, steel and polypropylene used in this study are the new types of fibres which are not used by researchers and not found in the literature. Totally twelve mixtures were prepared; one was Two-Stage Concrete (TSC) and considered a reference specimen. Two-Stage Fibrous Concrete (TSFC) was another two with fully reinforced single layer cross-sectional beams, with their fibres constituents being dispersed evenly. The remaining were two and three-layered FGTFC beams with evenly dispersed fibre constituents. Uneven dispersion in the current research meant that the fibre dosage was more in the peripheral layers and less in the inner layers, despite the fibre dosage being used remains the same in all beams. The fabricated FGTFC beams were synchronously cast using cement grout and tested against the three-point bending and falling mass impact. All beams were tested through the falling mass impact as per the guidelines of ACI Committee 544. Compressive strength, first crack and peak stress, flexural toughness, initial crack impact number, failure impact number, impact ductility index, and failure patterns were examined. Findings indicated that the peak load, flexural toughness and impact strength increased significantly with increased beam size. Additionally, steel fibre significantly contributed to increasing flexural toughness and impact strength than the polypropylene fibre. Thus, the proposed three-layer FGTFC beams had greater efficacy and exceptional fiber usage in the peripheral layers, despite the exact fibre dosage in all TSFC beams.