定向钢纤维混凝土增强机理及力学模型研究

Compared to normal steel fibre reinforced concrete, the mechanical properties of Oriented Steel Fibre Reinforced Concrete (OSFRC) increase significantly due to the steel fibres inside have the same or similar orientation as designed. There is the necessity of investigating its mechanism and mechanical behaviour systematically..In the submission, firstly, by analysing the relation between the degree of orientation and reinforcement of steel fibres, the interaction between steel fibres and matrix, and energy dissipation in the progress of bonding, de-bonding, slipping and pulling out of steel fibres from matrix, the strength, constitutive relation and fracture energy of OSFRC are theoretically investigated, and hence the mechanism of reinforcement of OSFRC is proposed. In further, the mechanical properties of the OSFRC are modelled based on the reinforcement mechanism of oriented steel fibres. Secondly, the mechanical properties of OSFRC, including flexural strength, flexural toughness, splitting tensile strength, uniaxial tensile constitutive relation and fracture energy are experimentally tested. Then the theoretical models are validated according to test results. By comparing with the properties of normal steel fibre reinforced concrete, the mechanical characteristic of OSFRC is clarified. Finally, the technology of precast shield tunnel segment using OSFRC is developed. By determining the aim orientation of steel fibres in the segment according to the stress analysis, calculating other parameters according to previous theoretic analysis and trial tests, the approach of preparing shield tunnel segment using OSFRC is proposed. The segment prepared with OSFRC is tested and compared that with normal SFRC. Also the advantage of OSFRC and the segment made of OSFRC is assessed..The main benefit of this investigation is the interpretation of the mechanism, mechanical characteristic and application technology of OSFRC comprehensively. And it may lead to a significant progress of steel fibre reinforced concrete technology.

定向钢纤维混凝土中钢纤维按设计方向排列，其力学性能较普通钢纤维混凝土大幅度提高，有必要系统研究其机理和性能。.首先，通过分析钢纤维定向程度与增强作用的关系、定向钢纤维粘结滑移及拔出过程中与基体的交互作用及能量耗散，研究定向钢纤维混凝土的强度、本构关系及断裂能，揭示定向钢纤维增强机理，并建立基于机理的定向钢纤维混凝土力学性能模型。其次，试验研究定向钢纤维混凝土的强度、韧性、拉伸本构关系和断裂能等，分析钢纤维定向程度对力学性能的影响，对理论模型进行验证，掌握定向钢纤维混凝土的力学性能和特征。最后，研究定向钢纤维混凝土预制隧道管片，根据管片内力确定钢纤维设计方向，通过钢纤维方向控制参数分析和反复试验掌握制备方法，并对定向钢纤维混凝土预制管片进行力学性能测试，综合评估定向钢纤维混凝土的性能。.通过本项目研究，有利于掌握定向钢纤维混凝土的理论、性能及应用，从而获得钢纤维混凝土材料研究的重大突破。

传统钢纤维混凝土中，钢纤维随机乱向分布，任意方向的增强作用相同。而实际工程中混凝土构件的应力方向一般保持恒定，如梁、板等构件底部始终为纵向受拉。如果采用随机乱向钢纤维混凝土，只有与拉应力方向接近或一致的钢纤维发挥增强作用。理论上，发挥作用的纤维量只有40-50%，即大部分纤维被浪费了。如果能使所有钢纤维的增强作用得到发挥，钢纤维混凝土的性能将显著提高。.受指南针受地球磁场作用始终指向南北现象启示，对钢纤维混凝土拌合物施加定向磁场，驱动其中的钢纤维转动到设计方向，硬化后制备出定向钢纤维混凝土。定向钢纤维混凝土中，几乎所有纤维都能发挥作用，钢纤维方向有效系数达到0.90以上，即有效发挥增强作用的钢纤维比例从不到50%增加到90%以上，使增强效果大幅度提高。另一方面，定向钢纤维与拉应力方向一致，单根纤维的增强能力也显著提高。因此，定向钢纤维使混凝土的力学性能得到极大改善。据此，建立了定向钢纤维混凝土力学性能数学模型。.试验研究结果表明，钢纤维体积掺量0.5-2.0%范围内，如果保持钢纤维掺量相同，相对于传统随机乱向钢纤维混凝土，定向钢纤维混凝土的抗折强度提高50-100%，单轴拉伸强度提高20-40%，弯曲韧性提高80-150%，抗剪强度提高40-60%，断裂能提高20-50%，弯曲疲劳次数提高1-2个数量级。如果保持力学性能相同，采用定向钢纤维混凝土，钢纤维掺量可降低30-40%。试验结果与模型结果一致性较好。.定向钢纤维混凝土是将电磁学原理与混凝土技术结合，控制混凝土中的钢纤维分布方向，实现了混凝土材料中关键组分钢纤维分布方向的细观设计，促进了钢纤维混凝土技术的发展。