Properties of beam.

The utilization of rice husk ash (RHA) as a cement substitute in concrete can mitigate the environmental issues caused by concrete production. This study is the first investigated the effect of different concentrations of multiwall carbon nanotubes (MWCNTs) on the shear behaviour of RHA-reinforced concrete (RC) beams. Three RHA RC beams incorporating different MWCNTs concentrations (0%, 0.1%, and 0.2%) were subjected to shear failure tests, with shear behaviour evaluated based on load-deflection capacity, failure load, strain distribution, and crack development morphology. The results indicate that the incorporation of well-dispersed MWCNTs (0.1%) significantly enhances the shear resistance of RHA RC beams. Specifically, with the addition of 0.1% MWCNTs, the first crack load, initial stiffness, and ultimate shear capacity increased by 34.78%, 38.4%, and 4.76%, respectively, while midspan deflection and ductility improved by 23.19% compared to the control specimen. However, excessive MWCNTs incorporation negatively impacted shear capacity, as the inclusion of 0.2% MWCNTs led to an 8.57% reduction in the ultimate shear capacity of the RHA RC beam. Additionally, the experimental results were compared with predictions from several models, including the ACI 318 model, Eurocode 2–05 model, Canadian standard, Bazant and Kim, Zsutty, and Collins and Kuchma models. The comparison revealed that the Eurocode 2–05 model, Canadian standard, and Zsutty models provide reliable predictions of the shear behaviour of RHA RC beams, with an error margin within 20%. The findings suggested that well-dispersed MWCNTs can play a role in improving the initial stiffness and ductility of RHA RC beams, enhancing the shear resistance of the beams, delaying shear failure, and preventing brittle failure of the beams. Furthermore, the improvement of the performance of RHA sustainable concrete components by MWCNTs contributes to the sustainable development of the construction industry.

稻壳灰（rice husk ash, RHA）作为水泥替代材料应用于混凝土中，可缓解混凝土生产带来的环境问题。本研究首次探究了不同掺量的多壁碳纳米管（multiwall carbon nanotubes, MWCNTs）对稻壳灰增强混凝土（RC）梁抗剪性能的影响。试验共制备3根掺加不同MWCNTs掺量（0%、0.1%和0.2%）的稻壳灰增强混凝土梁，开展抗剪失效试验，并通过荷载-挠度性能、失效荷载、应变分布以及裂缝发展形态对抗剪行为进行评价。研究结果表明，掺加分散性良好的0.1% MWCNTs可显著提升稻壳灰增强混凝土梁的抗剪承载力。具体而言，相较于基准试件，掺入0.1% MWCNTs后，梁的初裂荷载、初始刚度和极限抗剪承载力分别提升了34.78%、38.4%和4.76%，跨中挠度与延性则改善了23.19%。然而，过量掺加MWCNTs会对抗剪承载力产生负面影响：当掺量达到0.2%时，稻壳灰增强混凝土梁的极限抗剪承载力降低了8.57%。此外，本研究将试验结果与多个模型的预测结果进行了对比，包括ACI 318模型、欧洲规范2-05（Eurocode 2–05）模型、加拿大标准、巴赞特-金模型（Bazant and Kim）、祖蒂模型（Zsutty）以及柯林斯-库奇马模型（Collins and Kuchma）。对比结果显示，欧洲规范2-05模型、加拿大标准与祖蒂模型可对稻壳灰增强混凝土梁的抗剪行为做出可靠预测，误差范围控制在20%以内。研究结论表明，分散性良好的MWCNTs可有效提升稻壳灰增强混凝土梁的初始刚度与延性，增强梁的抗剪性能，延缓抗剪失效进程，避免梁发生脆性破坏。此外，通过MWCNTs改善稻壳灰基可持续混凝土构件的性能，有助于推动建筑业的可持续发展。