【作者】 李海艳；

【导师】 武振宇； 郑文忠；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2012， 博士

【摘要】 活性粉末混凝土(Reactive Powder Concrete，简称RPC)具有超高的强度、高韧性、高耐久性和良好的体积稳定性，在石油、核电、市政、海洋、机械、航空、军事设施等工程领域具有广阔的应用前景。目前，RPC已成为国际工程材料领域的研究热点，但对其研究多集中于配制技术与常温力学性能方面，对其高温抗火性能的研究较少。本文在高强混凝土高温性能研究基础上，对RPC高温爆裂性能、纤维对爆裂抑制效果、高温后不同纤维种类和掺量的RPC力学性能及高温后RPC微观结构的变化进行试验研究，主要开展了以下几方面工作：(1)为摸清RPC的高温爆裂规律，试验研究了含水率、升温速度和试件尺寸对RPC爆裂性能的影响，对比分析了钢纤维、聚丙烯纤维和混杂纤维对RPC高温爆裂的抑制效果，基于试验结果，对RPC高温爆裂机理和爆裂抑制措施进行了探讨。试验结果表明：相对于升温速度和试件尺寸而言，含水率对RPC高温爆裂的影响最大，RPC爆裂临界含水率为0.80%~0.85%；单掺钢纤维体积率为2%或单掺聚丙烯纤维体积率为0.3%可有效防止RPC发生爆裂，钢纤维与聚丙烯纤维混掺对RPC爆裂的抑制效果更为显著；RPC高温爆裂机理可归因于蒸汽压、热应力和随机性裂纹三方面的耦合作用。(2)通过高温试验研究了RPC试件外观和质量损失随温度的变化情况。随经历温度的升高，钢纤维RPC、聚丙烯纤维RPC和混杂纤维RPC试件外观特征和质量损失具有相同的变化规律：试件表面颜色由青灰色→棕褐色→黑褐色→黄白色逐渐发生变化，600℃后出现明显可见长宽裂纹，且出现不同程度掉皮、缺角和疏松现象，800℃后出现大量网状长宽裂纹，掉皮疏松严重，钢纤维轻折即断，混凝土烧结；质量损失随加热温度的升高逐渐增大，200~400℃范围内质量损失最为严重，各对应温度下，聚丙烯纤维体积掺量大的RPC质量损失也相应较大。(3)对经历高温试验后的钢纤维RPC、聚丙烯纤维RPC和混杂纤维RPC进行强度试验，得到了高温后三种RPC对应的立方体抗压强度、抗折强度和轴心抗拉强度，考察了温度、纤维种类和纤维掺量对RPC各项强度的影响。试验结果表明：钢纤维的掺入可有效提高高温后RPC力学强度，聚丙烯纤维对RPC强度有削弱作用，相同高温作用后，RPC各项强度(抗压、抗折、抗拉)随钢纤维掺量的增加而增大，随聚丙烯纤维掺量的增加而减小；随经历温度的升高，高温后单掺钢纤维RPC与单掺聚丙烯纤维RPC的各项力学强度先增大后减小，混杂纤维RPC抗压强度先增大后减小，抗折和抗拉强度则基本呈线性规律降低；通过回归分析，拟合给出了不同纤维RPC各项强度随温度变化的计算公式，理论曲线与试验数据吻合较好。(4)为研究高温后钢纤维RPC与混杂纤维RPC单轴受压应力-应变关系，采用普通液压试验机附加刚性元件的方法对165个70.7mm×70.7mm×228mm的RPC试件进行单轴受压试验。实测了不同高温后钢纤维RPC与混杂纤维RPC的应力-应变关系曲线，分析了纤维掺量和经历温度对RPC轴心抗压强度、弹性模量、峰值应变和极限应变等力学指标的影响。试验结果表明：随经历温度的升高，钢纤维RPC与混杂纤维RPC应力-应变曲线渐趋扁平，峰值点明显右移和下移，轴心抗压强度和弹性模量先增大后减小，峰值应变和极限应变分别于600℃和700℃达到峰值，峰值点前二者增长迅速，峰值点后，二者基本呈线性规律降低，采用多项式回归方式，建立了轴心抗压强度、弹性模量、峰值应变和极限应变随经历温度的变化公式；相同高温作用后，RPC应力-应变曲线下的面积随钢纤维掺量增加而增大，说明钢纤维掺量大的RPC延性和韧性较好，300℃前，聚丙烯纤维掺量对应力-应变曲线的影响较小，300℃后，随聚丙烯纤维掺量的增加，应力-应变曲线下的面积逐渐增大；采用五次多项式和有理分式对钢纤维RPC与混杂纤维RPC应力-应变曲线的上升段和下降段进行拟合，并通过计算模拟确定了方程参数值，由方程确定的理论曲线与试验数据吻合较好。(5)利用SEM扫描电镜分析，研究了经历不同高温后的RPC微观结构变化和物相组成。结果表明：经历温度低于400℃时，水泥水化反应和火山灰反应互相促进，增加了C-S-H凝胶的含量，消耗了对强度有不利影响的Ca(OH)2，RPC的微观结构得到改善；经历400~800℃高温后，随经历温度的升高，C-S-H凝胶由连续块状形态变为尺寸较小的分散相，钢纤维与基体粘结界面处的裂纹逐渐形成并扩展，聚丙烯纤维融化后的孔道加剧了RPC的内部缺陷，RPC微观结构不断恶化。RPC微观结构的变化是其宏观力学性能发生改变的根本原因。本文对RPC高温爆裂性能、高温后RPC力学性能和RPC微观结构进行了系统研究，取得了阶段性的研究成果，丰富了RPC高温抗火性能方面的研究内容，为RPC构件、结构的抗火性能研究及理论分析提供了基础，对RPC的推广应用有重要意义。更多还原

【Abstract】 Reactive Powder Concrete (RPC) is characterized by the ultra-high strength,high toughness, high durability and excellent volume stability, so it has widelyapplication prospects in the fields of oil, nuclear power, municipal works, marineengineering, mechanical engineering, aviation and military facilities. At present,RPC has become the hot research spot in international engineering materials, andthere are many studies focused on its preparation technology and mechanicalproperties at room temperature, but there are few studies on its properties afterelevated temperatures. In this paper, based on the study of high temperatureperformance of high-strength concrete, the experimental studies were performed onthe high-temperature explosive spalling of RPC, effect of fiber on RPC spallingprevention, mechanical properties and microstructure of RPC with different fibersafter elevated temperatures. The main work of this study is as follows:To find out the explosive spalling law, the effects of moisture content, heatingrate and specimen size on spalling of RPC were studied. The prevention of steelfiber, polypropylene fiber and hybrid fiber on spalling of RPC were comparativelyanalyzed. Then, based on the experimental results, the mechanism and suppressionmeasures for high-temperature spalling of RPC were discussed. The results showthat the impact of moisture content on RPC spalling is greater than heating rate andspecimen size, and the critical moisture content is0.80%~0.85%. Mixing with steelfiber volume dosage of2%or polypropylene fiber volume dosage of0.3%caneffectively prevent RPC spalling, especially, blending with steel fiber andpolypropylene fiber together can prevent RPC from spalling more significantly. RPChigh-temperature spalling mechanism can be attributed to the combined effects ofvapor pressure, thermal stress and random cracks.Through high temperature test, variation of RPC specimen appearance andmass loss with temperature was studied. With the temperature increases, theappearance characteristics and mass loss of steel fiber-reinforced RPC, RPC withpolypropylene fiber and hybrid fiber-reinforced RPC have the same vary trend. Thespecimens appear to change in color with elevated temperatures as: slate-gray→grayish brown→darkish brown→yellow-white. After exposure to600℃, smallcracks and flaking come into being on the specimen surface. After exposure to800~900℃, a number of meshy cracks appear and the flaking and porosity becomeserious. Meanwhile the steel fibers can be easily broken off and the RPC sintering.The mass loss increases gradually with the increasing temperature, and the mass lossis most serious in200~400℃. For the same heat treatment, the higher polypropylene fiber content implies the higher mass loss.The mechanical strength tests were carried out on steel fiber-reinforced RPC,RPC with polypropylene fiber and hybrid fiber-reinforced RPC after undergoingelevated temperatures. The cubic compressive strength, flexural strength and tensilestrength corresponding three kinds of RPC were obtained. The effects oftemperature, fiber type and fiber content on RPC mechanical strength wereinvestigated. The results indicate that steel fiber can effectively improve themechanical strength of RPC after high temperature, but polypropylene fiber hasadverse effect on RPC strength. For the same heating treatment, the strength of RPC(compressive strength, flexural strength and tensile strength) increases with theincreasing steel fiber content, but decreases with the increasing polypropylene fibercontent. For steel fiber-reinforced RPC and RPC with polypropylene fiber, themechanical strength increases first and then decreases with the increasingtemperature. For hybrid fiber-reinforced RPC, with the temperature increases, thecompressive strength increases first and then decreases, while the flexural strengthand tensile strength reduce basically as linear law. Through regression analysis,equations to express the relationships between strength of different fiber-reinforcedRPC and heating temperature are established, and the theoretical curves are in goodagreement with the test data.In order to study the axial compressive stress-strain relationship of steelfiber-reinforced RPC and hybrid fiber-reinforced RPC, by the aid of the ordinarycompression testing machine with attached rigid auxiliary frame, the uniaxialcompression experiments were conducted by165specimens with the size of70.7mm×70.7mm×228mm. The stress-strain curves of steel fiber-reinforced RPCand hybrid fiber-reinforced RPC after different high temperatures were measured.The effects of fiber content and exposure temperature on the mechanical propertiesof RPC were analyzed, including the axial compressive strength, elastic modulus,peak strain and ultimate strain. The results indicate that the stress-strain curves ofsteel fiber-reinforced RPC and hybrid fiber-reinforced RPC become flatter with thetemperature increases, and the peak points of stress-strain curves move right anddownwards. The axial compressive strength and elastic modulus increase first andthen decrease with the temperature increasing. The peak strain and ultimate strainreach peaks at600℃and700℃, respectively, and they increase rapidly before thepeak points but decrease linearly after the peak points. Through regression analysis,the equations to express the relationship of the compressive strength, elasticmodulus, peak strain and ultimate strain with the exposure temperature are proposedto fit the test results. With the same heating treatment, the area under thestress-strain curves increases with the steel fiber volume dosage increases, whichmeans the greater the steel fiber content is, the better the RPC ductility and toughness are. When the temperature is lower than300℃, polypropylene fibercontent has less impact on the stress-strain curve; but when the temperature is higherthan300℃, with the polypropylene fiber content increases, the area under the RPCstress-strain curve increases. Quintic polynomial and rational fraction are used to fitthe ascending and descending of stress-strain curves, and the curves proposed byequation fit the test data well.By scanning electron microscope (SEM) technique, the microstructure andphase composition of RPC after different temperatures were studied. The resultsshow that after exposure to the temperature not higher than400℃, the cementhydration and the pozzolanic reaction promotes each other, which increases theamount of C-S-H gel, consumes part of the Ca(OH)2and improves themicrostructure of RPC. After exposure to400~800℃, with the temperatureincreases, the C-S-H gel shifts from continuous block-like form to dispersed phase,and the cracks at the bonding interface of steel fiber and matrix come into being andexpand gradually, meanwhile the melting channels of polypropylene fibersexacerbate the internal defects of RPC, so the microstructure of RPC deterioratesconstantly. The microstructure changes of RPC are the root causes of itsmacroscopic mechanical properties degradation.In this paper, the high-temperature explosive spalling, mechanical propertiesand microstructure of RPC were studied systematically. The stage achievementshave been achieved, which enriches the RPC high temperature resistance research,and provides basis for the fire resistance research and theoretical analysis of RPCcomponents and structures. This study has important significance for RPCapplication and promoting.更多还原