Punching Shear Behavior of Engineered Cementitious Composites Flat-Plate Slabs Incorporating Cement Kiln Dust and Crumb Rubber

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This study experimentally investigated the punching shear behavior of engineered cementitious composite flat-plate slabs incorporating cement kiln dust and crumb rubber. The considered criteria included replacing 50% of the rubber without treatment and treating the rubber at the same percentage; the flexural reinforcement ratio, whether in the bottom tensile reinforcement ratio or in the top compressive reinforcement; and the ECC cube compressive strength (fcu). For this purpose, thirteen reinforced flat-plate slabs were cast and tested. All slabs had the same dimensions of 1100 × 1100 × 100 mm, with a central square column that had dimensions equal to 160 × 160 × 160 mm. The flexural RFT ratios in the tension and compression zones were 1.0, 1.2, and 1.6%. The tested slabs were cast with different values of fcu of 50, 65, and 70 MPa. The study first presented and discussed the first cracking load, ultimate load, crack pattern, load–deflection response, stiffness, and RFT strain. The experimental results demonstrated that increasing the tensile reinforcement RFT ratio significantly improved punching shear capacity by up to 33%, while the concrete cube compressive strength only contributed an approximately 14.2% increase. Treated crumb rubber engineered cementitious composite slabs showed greater initial stiffness and reduced deflections under the same loads, along with higher post-cracking stiffness degradation compared to crumb rubber concrete engineered cementitious composite slabs. Increased tension reinforcement improved initial and post-cracking stiffness and reduced deflections, with more significant effects in crumb rubber concrete engineered cementitious composite slabs. The flexural tension had a more substantial impact on punching shear behavior than compression. Comparisons with building design codes (ECP 203-2020, ACI 318-25, and Eurocode 2) revealed that while these codes could estimate shear capacity, they were conservative, with Eurocode 2 providing the best predictions by considering flexural tension.

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