Abstract

This paper assesses the benefits of styrene-butadiene rubber (SBR), steel fibres (SF), and polypropylene fibres (PPF) to mitigate the brittle failure and drop in bond properties due to smooth surface geometries of carbon fibre-reinforced polymer (CFRP) bars embedded in ultra-high performance concrete (UHPC). A ready-to-use UHPC was employed to determine the bond stress vs. slip properties of CFRP and deformed steel bars. Test results showed that the incorporation of SBR is beneficial to alleviate up to 20% the detrimental effect of smooth CFRP geometry, which was attributed to enhanced adhesion along the spiral wounds. The ultimate bond improved by 45% and 87% when 1% of either PPF or SF was added, respectively, given the fibre bridging effect that limits the formation of radial cracks. Also, the ductility improved with fibre additions, reflecting their beneficial role for better transmitting the stresses along the cementitious matrix. The experimental bond strengths determined from the UHPC-Steel specimens are 3- and 3.5-times higher than those computed from EC2 and ACI 318-19 code provisions, respectively. Yet, such ratios dropped to 1.3- and 1.5-times for the CFRP bars, given their lower shear and lug indices that reduced the interaction with surrounding UHPC.

摘要

本文评估了丁苯橡胶 (SBR)、钢纤维 (SF) 和聚丙烯纤维 (PPF) 在减轻因碳纤维增强聚合物 (CFRP) 的光滑表面几何形状而导致的脆性破坏和粘合性能下降方面的优势嵌入超高性能混凝土 (UHPC) 中的钢筋。采用即用型 UHPC 来确定 CFRP 和变形钢筋的粘结应力与滑移特性。测试结果表明，SBR 的加入有利于减轻高达 20% 的光滑 CFRP 几何形状的不利影响，这归因于沿螺旋伤口的粘附性增强。考虑到限制径向裂纹形成的纤维桥接效应，当添加 1% 的 PPF 或 SF 时，最终粘合分别提高了 45% 和 87%。此外，随着纤维的添加，延展性得到改善，反映了它们对沿水泥基体更好地传递应力的有益作用。从 UHPC 钢试样确定的实验粘合强度分别比根据 EC2 和 ACI 318-19 规范规定计算的粘合强度高 3 倍和 3.5 倍。然而，考虑到 CFRP 条的较低剪切和凸耳指数降低了与周围 UHPC 的相互作用，这种比率下降到 1.3 倍和 1.5 倍。