【作者】 何锐；

【导师】 陈拴发；

【作者基本信息】 长安大学 ， 道路与铁道工程， 2013， 博士

【摘要】 普通水泥混凝土具有抗拉强度低、韧性差和开裂后裂缝发展迅速等缺点，给结构物的耐久性带来极大的影响，尤其是随着混凝土强度的提高其固有缺点更加突出。随着我国交通基础设施建设的快速发展，重轴载和高速化的交通流特点给混凝土的弯拉强度和变形性能提出了更高的要求。本文采用混杂纤维增强体系，综合考虑从工作性到宏观力学性能的多维度因素，制备出具有应变硬化和多缝开裂特征的高韧性水泥混凝土铺装材料，采用室内试验与数值模拟相结合的方法，对其材料性能和结构特征进行了深入研究。论文从原材料性能分析入手，对聚乙烯（PE）和聚丙烯粗合成纤维（CPP）的耐酸碱性能进行了测试，结果表明所选纤维均具有优良的抗腐蚀性能。为提高拌合物的流动性并保证纤维的均匀分散及其与基体的粘结，自主配制了纤维分散助剂（M1）和功能复合粉体材料（M2），M1的加入能显著提高纤维分散均匀性，M2的加入则大幅提高了纤维与基体的粘结，在单掺M1与复掺M1和M2的情况下，拌合物的流动性和均匀性均较好。为检测两种纤维的分散性能，采用数字图像处理与分析技术，建立了CPP纤维识别与分散性评价系统，并提出了相应的评价指标。该评价方法不仅适合有机粗合成纤维，对于钢纤维同样适用。采用SEM微观观测对PE纤维的分散性进行了定性评价，结果表明M1与M2的配合使用可以促进PE纤维的均匀分散，CPP和PE纤维的分散性具有相同的规律。采用四点弯曲试验和落锤冲击试验对制备的高韧性混凝土强韧化特性进行了评价。在弯拉荷载作用下制备的高韧性混凝土具有明显的变形硬化特征，试件的开裂模式均较曲折，且在开口附近都可观察到大量微细裂缝。在冲击荷载作用下高韧性混凝土的初裂和破坏冲击次数均远大于普通混凝土，根据冲击开裂发展规律推荐了冲击韧性指标，该指标与纤维混凝土的变形能力有较好的相关性，抗弯变形能力强的纤维混凝土其冲击抗力也大。基于纤维水泥基复合材料的桥联法则，对高韧性混凝土裂缝发展规律进行了分析。采用SEM测试手段分析了CPP纤维/基体界面的微结构，结果表明，CPP纤维与水泥基体的粘结较差，界面区内部有少量的孔隙和微裂缝，同时有大量板状C-H晶体聚集。功能材料M2的加入导致C-S-H凝胶的大量产生并提高了界面区的密实性，应力和变形的传递效果得以改善，界面区力学特征由脆性转变成韧性，纤维增韧效应范围增大，所以混凝土的韧性性能被明显提高。采用单轴拉伸和压缩试验对高韧性混凝土的单轴受力特征进行了评价，其弹性模量约是同等抗压强度普通混凝土的2/3，极限抗压和抗拉应变均大大提高；六组推荐配比在单轴受拉条件下出现明显的应变硬化和多缝开裂现象。根据应力-应变全曲线特点，建立了高韧性混凝土本构关系模型，该模型在峰值前和峰值后均能准确拟合高韧性混凝土的变形特征。结合材料弯曲与受拉力学特征，推荐出高韧性混凝土单轴极限抗拉强度和拉应变的简易反算公式。基于细观层次建立了高韧性混凝土弯曲、受压与受拉试件的二维数值模型，并对这三种试验过程进行了数值模拟，模拟结果能够较好的反应出高韧性水泥混凝土在三种受力状态下的应力-应变特点以及开裂损伤发展规律。采用弯曲疲劳试验对高韧性混凝土的疲劳性能进行了评价，在疲劳荷载作用下高韧性混凝土试件的跨中挠度-循环次数比曲线同样符合3阶段模式。基于威布尔分布模型，建立了在0.05和0.50失效概率下的双对数疲劳方程，并推导得出高韧性混凝土面板的疲劳应力系数计算公式。建立三维有限元模型对高韧性混凝土路面结构力学行为进行了分析，结果表明，在设计参数常规变化范围内，高韧性路面板的受力特征变化较小；高韧性混凝土面板抵抗荷载和温度应力综合疲劳作用的能力要远高于普通混凝土。根据计算结果，并结合工程实际，推荐出高韧性混凝土面板的横缝间距以及各交通等级下高韧性混凝土面板的厚度范围。更多还原

【Abstract】 Due to its low tensile strength, poor toughness and cracking potential, ordinarycement concrete has caused a great influence to the durability of concrete structures,which is more prominent with the increase of concrete strength. As the construction ofChina’s transportation infrastructures develops, the traffic flow with heavey axle loadand high speed has put forward higher requirements to the flexural strength anddeformation performance of concrete. Considering the multi-dimensional factors fromworkability to macroscopic mechanical properties, hybrid fiber were adopted toprepare high-toughness cement concrete paving material featuring the characteristicsof strain hardening and multiple cracking, the material properties and structuralfeatures of which was analyzed intensively in this paper with the combination ofindoor experiment and numerical simulation.This paper was started from analyzing the performance of raw materials. Thechemical stability of polyethylene (PE) and coarse polypropylene fibers (CPP) wastested, with the results showing that the employed fibers have good resistance tochemical corrosion. A fiber dispersing agent (M1) and a functional composite powder(M2) was invented to enhance the flowability of concrete mixture and improve thebond strength between fiber and matrix. It’s shown that the addition of M1cansignificantly improve the dispersion of fibers, while M2causes better interface bondto fiber and matrix. The flowability and fiber dispersion are preferable with the use ofM1or compound M1and M2.For the detection of the dispersion properties of these two fibers, digital imageprocessing and analysis technology was employed to establish a recognition anddispersion evaluation system of CPP fiber, with the evaluation index presented. Theevaluation method is not only suitable for coarse synthetic fiber, but also suitable forsteel fiber. The qualitative evaluation of PE fiber was conducted with the use of SEMobservation. Results show that the compound use of M1and M2can promote theuniform dispersion of PE fiber, and the dispersion of CPP and PE fibers have the samerules. Four point bending test and impact test were adopted to evaluate the toughnesscharacteristics of prepared high-toughness concrete. Obvious strain hardeningcharacteristics were observed under the flexural load and large amounts of fine cracksCPPeared near the opening surface. The initial crack and failure impact numbers ofprepared concrete are far higher than that of normal concrete under impact load. Theimpact toughness index was proposed according to the development of impactcracking, which has a good correlation with the deformation performance of fiberreinforced concrete.The cracking development law of high-toughness concrete was analyzed basedon the bridging law of fiber reinforced cementitious composites. SEM method is usedto analyze the microstructure of the interface between CPP fiber and matrix. Theobservation results show that the adhesion is poor, and there are a small number ofpores and micro-fractures in the interface zone with a large number of plate-likeaggregations of C-H crystals. The addition of M2leads to a large number of C-S-Hgel and improve the compactness of the interfacial zone. Thus, the stress anddeformation of the transfer effect can be improved, the mechanical characteristics ofinterface transform from brittle into toughn, and fiber toughening effect rangeincreases, leading to the significantly improvement of toughness in concrete.The uniaxial performance of high-toughness of concrete was evaluated inuniaxial tensile and compression tests. The elastic modulus is approximately the2/3of ordinary concrete with the same compressive strength, and the compressive andtensile strain capacity is greatly improved. The unique multiple cracking and strainhardening phenomenon occur for the six recommended mix proportion. According tothe features of stress-strain curve of high-toughness concrete, the constitutive modelwas built which can accurately fitting the deformation characteristics of concrete bothbefore and after the peak load. In the combination of bending and tensioncharacteristics, the inverse formula for determining the tensile strength and straincapacity of high-toughness concrete was recommended.Two-dimensional numerical models were established for the bending,compression and tensile concrete specimens at the mesoscopic level. The three kind of test process was simulated. The simulation results can better reflect the stress-straincharacteristics and the law of cracking damage development for the high-toughnessconcrete.The fatigue performance of high-toughness concrete was evaluated by bendingfatigue test. The curves of mid-span deflection-cycle ratio under fatigue load alsoaccord with the3stage model. The double logarithm fatigue equations with0.05and0.50of the failure probability were established based on the Weibull distributionmodel. The formula of fatigue stress coefficient in high-toughness slab is also derived.A three-dimensional finite element model was established for the analysis of thecharacteristics of high-toughness concrete pavement structure. It’s shown that thevariation of design parameters in the conventional range has less influence on themechanics characteristics of high-toughness concrete pavement which has superioranti-fatigue performance to the combination action of load and temperature fatigueeffect than that of ordinary concrete. According to the calculation results, combinedwith the engineering practice, the slab length and thickness under different trafficlevels were recommended for the high-toughness concrete pavement.更多还原