BFRP-MPCM复合材料加固混凝土阻裂性能试验研究

Experimental Study on Crack Resistance Performance of Concrete Strengthened with BFRP-MPCM Composite Materials

摘要

磷酸镁水泥砂浆(MPCM)具有凝结硬化快和黏结性能好等优点,在快速加固领域具有广阔的应用前景．基于材料-结构一体化设计思想,提出玄武岩纤维增强聚合物改性磷酸镁水泥砂浆(BFRP-MPCM)复合材料,包括微筋增强MPCM和复合增强MPCM；通过BFRP-MPCM薄板4点弯曲试验,揭示玄武岩微筋和BFRP网格的协同增强机制,初选加固混凝土用复合材料类型及配比；通过外贴BFRP-MPCM薄层加固既有混凝土梁并开展3点弯曲试验,基于混凝土断裂理论,量化分析复合材料类型和被加固混凝土强度对BFRP-MPCM加固混凝土阻裂性能的影响规律,探究BFRP-MPCM对既有混凝土的阻裂加固机理．试验结果表明：纤维掺量2.0%(体积分数)的微筋增强MPCM流动度可达178 mm,纤维掺量2.0%(体积分数)并配置BFRP网格的复合增强MPCM薄板(龄期3 d)弯曲峰值荷载比素MPCM提高了128%,峰值韧性指数为173.65,适用于快速加固既有混凝土；复合增强MPCM中的玄武岩微筋主要影响试件弯曲受力前期,使试件破坏形态向延性破坏转变,BFRP网格主要影响试件开裂后性能,显著提高BFRP-MPCM薄板的弯曲峰值荷载和韧性；BFRP-MPCM加固试件的混凝土起裂滞后,配置BFRP网格使复合增强MPCM加固试件的起裂荷载应力强度因子比微筋增强MPCM加固试件提高22%,复合增强MPCM加固试件的裂缝失稳扩展破坏过程显著延长,荷载-裂缝口张开位移曲线呈现双峰形态；复合增强MPCM加固混凝土阻裂性能提高,起裂荷载应力强度因子、阻裂荷载应力强度因子和断裂能相比未加固混凝土分别增大了3.9倍、18.9倍和37.2倍；复合增强MPCM加固层对不同强度混凝土阻裂性能均具有良好的提升效果．

Abstract

Owing to its advantages of fast setting and hardening, as well as a good bonding performance, magnesium phosphate cement mortar(MPCM) has a broad application prospect in the field of rapid reinforcement. Based on the idea of material-structure integrated design, basalt fiber reinforced polymer modified MPCM(BFRP-MPCM) composites including basalt minibar reinforced MPCM and combined reinforced MPCM were proposed in this paper. Four-point bending tests on BFRP-MPCM sheets were carried out to reveal the collaborative enhancement mechanism between the basalt minibar and BFRP grid, and the types and proportions of composites for strengthening concrete were preliminarily selected. Afterwards, the existing concrete beams were strengthened by bonding BFRP-MPCM sheets, and three-point bending tests were conducted. Based on the fracture mechanics of concrete, the effects of BFRP-MPCM sheet types and the existing concrete strength on the crack resistance performance of strengthened concrete were quantitatively analyzed, and the reinforcement mechanism of BFRP-MPCM for the existing concrete was also studied. Experimental results show that the fluidity of basalt minibar reinforced MPCM with fiber content of 2.0%(volume fraction) was 178 mm, and the flexural peak load of combined reinforced MPCM sheet(age 3 d) with fiber content of 2.0%(volume fraction) and BFRP grid was 128% higher than that of the plain MPCM, with a peak toughness index of 173.65. Therefore, the composite materials were suitable for rapid reinforcement of the existing concrete. The effects of basalt minibars in the combined reinforced MPCM were mainly at the early stage of the stress development process, causing the failure mode of the specimen to transit into a ductile failure. In comparison, the BFRP grid mainly affected the post-cracking performance of the specimen, which significantly improved the flexural peak load and toughness of the BFRP-MPCM sheet. The concrete crack initiation of specimens strengthened with BFRP-MPCM was delayed. For the specimen strengthened with combined reinforced MPCM, its stress intensity factor under crack initiation load was 22% higher than that of the specimen strengthened with basalt minibar reinforced MPCM owing to the configuration of BFRP grid. In addition, the corresponding failure process of crack instability propagation was significantly prolonged, and the load-crack mouth opening displacement curves presented a double-peak shape. The crack resistance performance of the concrete strengthened with combined reinforced MPCM sheets were improved; for example, the stress intensity factor under crack initiation load, the stress intensity factor under crack resistance load and the fracture energy of the concrete specimen strengthened with combined reinforced MPCM sheet were improved by 3.9, 18.9 and 37.2 times respectively compared with those of the concrete specimen which was not strengthened. By bonding the combined reinforced MPCM sheet to concrete, the crack resistance performances of the existing concrete with different types of strength were all well improved.

关键词

磷酸镁水泥砂浆 / 玄武岩微筋 / BFRP网格 / 混凝土加固 / 阻裂性能

Key words

magnesium phosphate cement mortar(MPCM) / basalt minibar / basalt fiber reinforced polymer(BFRP) grid / concrete reinforcement / crack resistance performance

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基金资助

国家自然科学基金资助项目(52068043)

甘肃省建设科技攻关项目(JKR2021-07)