多尺度下混杂纤维轻骨料混凝土増韧机理及梁受剪性能研究

Lightweight aggregate concrete (LWAC) has a prominent advantage of “lightweight”, but also shows high brittleness which is prone to shear failure. Under the premise of ensuring this material feature, the project proposes using high-elasticity modulus carbon/glass and high-tenacity polypropylene hybrid fibers to toughen the LWAC. On the material level, the influence factors analysis of hybrid fiber reinforced lightweight aggregate concrete (HFRLWAC) is firstly carried out at macro-scale to determine the optimum proportion of hybrid fibers. The uniaxial tension and compression constitutive models as well as the bond-slip relationship with reinforcement for this type of concrete are suggested. At micro-/submicro-scale, the interaction between fiber and cement matrix interface is studied, by introducing the fiber spacing theory, to clarify the toughening mechanism of hybrid fibers. At meso-scale, the mesomechanics-based finite element method adopting the random aggregate structure is employed to establish the constitutive relationships, which can reveal the relation between microstructure and macro-mechanical properties. Additionally, on the component level, the experimental investigation on the shear behavior of HFRLWAC beams is further completed to examine the shear mechanism and effect factors. Based on the modified compression field theory, a section analysis model for this kind of beams subjected to combined bending and shear is proposed, and the shear design method is presented. The research is of both theoretical significance and practical value for promoting the high-performance improvement and engineering application of LWAC.

轻骨料混凝土最突出的优势是“轻”，但也存在脆性突出，易发生剪切破坏等不足。本项目基于材料“轻”的特性，提出采用高弹性模量的碳纤维/玻璃纤维与高韧性的聚丙烯纤维混杂改性轻骨料混凝土。在材料层次，首先在宏观尺度开展混杂纤维轻骨料混凝土影响因素分析，给出混杂纤维最佳掺量，提出该类混凝土的单轴受拉、受压及与钢筋的粘结滑移本构模型；在微观—亚微观尺度研究纤维与水泥基体界面的相互作用，引入纤维间距理论，揭示混杂纤维的增韧机理；细观尺度下基于细观力学有限元法采用随机骨料模型建立本构关系分析模型，揭示微观结构与宏观性能的联系；构件层次完成混杂纤维増韧轻骨料混凝土梁受剪性能试验研究，揭示其受剪机理及影响因素，基于修正压力场理论建立该类梁在弯剪复合作用下的截面分析模型，给出梁的受剪设计方法。相关研究对于推动轻骨料混凝土高性能化及工程应用均具有重要的理论意义和实用价值。

轻骨料混凝土最突出的优势是“轻”，但也存在脆性突出，易发生剪切破坏等不足。本项目基于材料“轻”的特性，提出采用高弹性模量的碳纤维/玻璃纤维与高韧性的聚丙烯纤维混杂改性轻骨料混凝土，采用试验研究与理论分析相结合的方法，从不同尺度系统开展了混杂纤维轻骨料混凝土增韧机理及构件受力性能研究。材料层面，首先在宏观尺度开展了混杂纤维轻骨料混凝土影响因素分析，给出了建议混杂纤维最佳掺量，建立了该类材料的单轴受压本构模型；在微观—亚微观尺度研究纤维与水泥基体界面的相互作用，分析了微观结构特征对宏观力学性能指标的影响；细观尺度下基于细观力学有限元法建立了能够反映轻骨料混凝土特性、具有普遍适用性的二维单轴受拉分析模型，明确了关键因素对轻骨料混凝土拉伸强度尺寸效应影响的显著性。构件层面，完成了30根CFRP布约束混杂纤维轻骨料混凝土柱和20根箍筋约束混杂纤维轻骨料混凝土柱轴压性能试验，明确了纤维种类和掺量对约束柱承载力和延性的量化影响，提出了考虑不同约束形式和纤维增韧叠加效应的混杂纤维轻骨料混凝土约束柱轴压本构模型；完成了15根FRP筋纤维增韧轻骨料混凝土梁和8根无粘结部分预应力FRP筋纤维增韧轻骨料混凝土梁受力性能试验，重点分析了纤维掺量、FRP筋配筋率和直径等关键因素对构件承载力、弯矩-跨中挠度曲线和裂缝宽度的耦合影响，建立了修正的构件承载力计算公式和考虑纤维影响的梁挠度与裂缝宽度计算模型，提出了相适应的设计方法。相关研究成果可为轻骨料混凝土的高性能化改性及工程应用推广提供理论依据和可行性建议。