Preparation of self-compacting ultra-high toughness cementitious composite

A self-compacting ultra-high toughness cementitious composite (UHTCC) reinforced by discontinuous short polyvinyl alcohol (PVA) fibers, which exhibits self-compacting performance in the fresh state and strain-hardening and multiple cracking behavior in the hardened state, was developed through controlling flow properties of fresh mortar matrix at constant ingredients concentrations determined by micromechanical design and ensuring uniform fibers dispersion. The superplasticizer was utilized to adjust its flow properties in the fresh state. A series of flow tests, including deformability test, flow rate test, and self-placing test, were conducted to characterize and quantify the fluidity performance of fresh mortar matrix and self-compactability of fresh UHTCC. It is revealed that the utilization of superplasticizer is efficient in producing the fresh mortar matrix with desirable fluidity and the resulting self-compacting UHTCC. In addition, results of four point bending tests on the developed self-compacting UHTCC confirm the insensitivity of mechanical performance of self-compacting UHTCC to the presence of external vibrations as well as the flexural characteristics of deformation hardening and multiple cracking.     

带肋钢筋与超高延性水泥基复合材料的黏结性能

超高延性水泥基复合材料(UHDCC)是新型纤维增强混凝土,受拉时表现出超高的延性和应变硬化能力.为提供UHDCC应用于受力构件的界面黏结理论依据,进行了45个钢筋在UHDCC中锚固的拉拔试验,考察了锚固长度、浇筑方式、保护层厚度、90°弯钩等对黏结性能的影响.试验结果表明:由于纤维约束作用,试件未发生劈裂破坏;UHDC...     

活性矿物掺合料对超高性能水泥基材料的影响

通过复掺粉煤灰和硅灰,制备一种抗压强度超过200 MPa的超高性能水泥基复合材料(UHPCC),采用扫描电镜、微区能谱分析、X射线衍射、汞压入法和差示扫描量热分析等现代测试手段,研究了活性矿物掺合料对UHPCC微观结构及性能的影响.实验结果表明,UHPCC水泥石主要以低mCa/mSi、结构致密的C-S-H凝胶和许多未水化颗粒组成;活性矿物掺合料的火山灰效应使水泥浆体与集料间界面过渡区得以改善;矿物掺合料的微集料效应使体系颗粒级配优化,致使基体内部结构致密,总孔隙率减小,孔尺寸得到细化,孔结构得以优化,材料性能得以提高.     

Dynamic mechanical behaviour of ultra-high performance fiber reinforced concretes

Ultra-high performance fiber reinforced concretes （UHPFRC） were prepared by replacing 60% of cement with ultra-fine industrial waste powder. The dynamic mechanical behaviour of UHPFRC with different fiber volume fraction was researched on repeated compressive impact in four kinds of impact modes through split Hopkinson pressure bar （SHPB）. The experimental results show that the peak stress and elastic modulus decrease and the strain rate and peak strain increase gradually with the increasing of impact times. The initial material damage increases and the peak stress of the specimen decreases from the second impact with the increasing of the initial incident wave. Standard strength on repeated impact is defined to compare the ability of resistance against repeated impact among different materials. The rate of reduction of standard strength is decreased by fiber reinforcement under repeated impact. The material damage is reduced and the ability of repeated impact resistance of UHPFRC is improved with the increasing of fiber volume fraction.     

纤维混杂对超高性能纤维增强水泥基复合材料力学性能的影响

采用最紧密堆积理论对UHPFRC进行配合比设计,并通过应用Excel Solver Tool进行编程求解,实现了UHPFRCC符合体系的理论设计,利用石灰石粉改善流动性的作用得到最终配合比。基于基准配合比,研究了钢纤维与合成纤维混杂对UHPFRCC的力学性能的影响。试验结果表明：基于Dinger-Funk模型可实现自密实UHPFRCC的配合比设计;混杂纤维可增强UHPFRCC的抗压强度,但抗折强度有所降低;相比于单掺2%钢纤维的UHPFRCC,合成纤维的取代掺入均降低了UHPFRCC的抗压强度和抗折强度。     

超高韧性水泥基材料的制备技术

分别采用活性粉末混凝土（RPC）和渗浇钢纤维混凝土（SIFCON）两种制备工艺,根据水泥基材料结构的多尺度特征,研究了由碳酸钙晶须和微钢纤维复合增强的超高韧性水泥基材料（Ultra-High-Toughness Cementitious Composite,简称UHTCC）的制备技术,测试UHTCC不同配比的抗压强度、抗折强度、抗弯强度以及单轴拉伸性能,采用折压比、韧性指数等多个指标对UHTCC的韧性进行了评价。试验表明：UHTCC的抗压强度、抗折强度、抗弯强度以及延性和韧性都远高于普通钢纤维混凝土,其抗弯强度最高达65.1 MPa、韧性指数I₂₀最高达49.21,单轴拉伸试验时呈现明显的假应变硬化行为,极限拉应变可达4%~8%。相对而言,利用SIFCON工艺制得的水泥基材料韧性更高。     

绿色韧性水泥基复合材料力学性能

为了研究绿色尾矿砂PVA纤维增强水泥基复合材料的韧性,参考国内外试验方法开展了立方体抗压、薄板拉伸和冲击韧性等力学性能试验研究.分析了纤维与基体的相互作用及增韧机理,讨论了纤维掺量和水胶比二元因素对增韧性能的影响.该研究获得了复合材料相应的强度和韧性指标,为高性能尾矿砂PVA纤维增强水泥基复合材料的制备和工程应用提供了参考.     

Experimental investigation and analysis on flexural performance of functionally graded composite beam crack-controlled by ultrahigh toughness cementitious composites

Based on the concept of functionally graded concrete, UHTCC (ultrahigh toughness cementitious composites) material with excellent crack-controlling ability is strategically substituted for part of the concrete, which surrounds the main longitudinal reinforcement in a reinforced concrete member. Investigations on bending behavior of such a functionally graded composite beam crack-controlled by UHTCC (abbreviated as UHTCC-FGC beam) have been carried out. After establishing a theoretical calculation model, the paper discusses the results of four-point bending experiment on long composite beams without web reinforcement, and validates the theoretical formulae through experimental results of UHTCC-FGC beams with different thicknesses of UHTCC layer. Besides improving bearing capacity and saving steel reinforcements, the results indicate that UHTCC-FGC beams can also effectively control the deformation and enhance the ductility of members. At last, the optimal thickness of UHTCC layer in UHTCC-FGC beams has been confirmed, which can not only save materials and improve mechanical performance of members, but also be very effective in preventing corrosion-induced damage and enhancing the durability of members by controlling crack width below 0.05 mm under service conditions. Supported by the Key Program of the National Natural Science Foundation of China (Grant No. 50438010) and the Research and Application Programs of Key Technologies for Major Constructions in the South-North Water Transfer Project Construction in China (Grant No. JGZXJJ2006-13)     

Theoretical analysis and experimental investigation on flexural performance of steel reinforced ultrahigh toughness cementitious composite (RUHTCC) beams

UHTCC (ultrahigh toughness cementitious composite), which is a kind of ultrahigh toughness cemen- titious composites material, exhibits pseudo strain hardening feature when subjected to tension load, and has enormous ductility and prominent crack dispersal ability. Accordingly, UHTCC can improve mechanical behavior of ordinary concrete structure especially its durability, and has been regarded as historical breakthrough to traditional cementitious materials. In this paper, the study focuses on flexure behav...     

聚乙烯醇纤维强化水泥基复合材料的抗盐冻性能

通过氯盐环境中的快速冻融试验研究了纤维体积率、冻融循环次数、粉煤灰、硅粉对聚乙烯醇(PVA)纤维水泥基复合材料抗盐冻性能的影响。通过扫描电镜观察内部微观结构随盐冻作用的变化规律、PVA纤维在水泥基体中分布情况和界面结合状况。试验结果表明:PVA纤维的掺入可明显改善水泥基复合材料的抗盐冻性能;PVA纤维在基体中分散性较好,且与水泥基体界面结合状况较好;而粉煤灰、硅粉的掺入未明显改善PVA纤维水泥基复合材料的抗盐冻性能。     

Uniaxial compressive properties of ultra high toughness cementitious composite

Uniaxial compression tests were conducted to characterize the main compressive performance of ultra high toughness cementitious composite (UHTCC) in terms of strength and toughness and to obtain its stress-strain relationships. The compressive strength investigated ranges from 30 MPa to 60 MPa. Complete stress-strain curves were directly obtained, and the strength indexes, including uniaxial compressive strength, compressive strain at peak stress, elastic modulus and Poisson’s ratio, were calculated. The comparisons between UHTCC and matrix were also carried out to understand the fiber effect on the compressive strength indexes. Three dimensionless toughness indexes were calculated, which either represent its relative improvement in energy absorption capacity because of fiber addition or provide an indication of its behavior relative to a rigid-plastic material. Moreover, two new toughness indexes, which were named as post-crack deformation energy and equivalent compressive strength, were proposed and calculated with the aim at linking up the compressive toughness of UHTCC with the existing design concept of concrete. The failure mode was also given. The study production provides material characteristics for the practical engineering application of UHTCC.     

绿色韧性水泥基复合材料碳化性能试验

为了研究绿色韧性水泥基复合材料(GCC)的耐久性,进行了快速碳化试验,研究了GCC的抗碳化性能以及水胶比和纤维掺量对抗碳化性能的影响规律.结果表明:随着碳化时间的增加,GCC的碳化深度逐渐增加,但其碳化速率逐渐减小;掺加一定量的纤维可以改善GCC的抗碳化性能,但当纤维掺量超过一定临界值时,GCC的抗碳化性能反而有所降低;水胶比对于GCC的抗碳化性能有明显影响,随着水胶比的增加,GCC材料的抗碳化性能逐渐降低.     

PVA纤维增强水泥基复合材料的抗拉性能

通过单轴拉伸试验,研究了粉煤灰种类、掺量、水胶比和砂胶比对聚乙烯醇(PVA)纤维应变硬化水泥基复合材料(SHCC)拉伸性能的影响.研究结果表明:粉煤灰替代部分水泥会降低SHCC的抗拉强度,随着粉煤灰掺量的增加,SHCC的应变硬化和多缝开裂特性能得到更好的发挥;在相同掺量下,Ⅰ级粉煤灰相较于Ⅱ级粉煤灰而言,能使SHCC具有更好的拉伸性能;水胶比的增加与砂胶比的减小,都会使SHCC的初裂强度和极限拉伸强度降低,但其极限拉伸应变会有所提升,较高的水胶比与较低的砂胶比更利于SHCC应变硬化和多缝开裂特性的发挥.     

微胶囊对水泥自修复复合材料微观结构的影响

在环氧树脂微胶囊的制备实验基础上,制备水泥自修复复合材料,研究养护龄期和微胶囊掺量对水泥自修复复合材料微观结构的影响,采用多种测试仪器对复合材料孔结构特性、电性能、抗渗透性能和水化热进行了分析.结果表明,随着养护龄期的增加,复合材料电阻值显著增大,而累积孔体积和吸水性系数减小;随着微胶囊掺量的增加,电阻值增大,而累积孔体积、吸附量与脱附量、吸水性系数以及水化放热速率与放热量减小.     

水泥基复合材料单轴受力特性研究

通过圆柱体聚乙烯醇纤维增强水泥基复合材料（PVA—FRCC）试件单轴受压试验,对其力学性能进行系统研究．分析其破坏形态、峰值应力、极限应变、弹性模量、泊松比、应力一应变曲线．通过试验发现聚乙烯醇纤维增强水泥基复合材料与普通混凝土相比,具备极限应变大、延性好、峰值应力、变形能力及韧性明显增加、弹性模量、泊松比基本不变等优点．通过改变聚乙烯醇纤维增强水泥基复合材料中水、水泥、砂、纤维的配比进而讨论纤维掺量、水胶比、砂胶比对其力学参数的影响．     

生态型工程水泥基复合材料的制备与性能研究

ECC选用磨细石英砂的最大粒径不超过110μm,极大地制约了它在实际工程中的推广应用.采用多重复合技术并利用矿山尾砂制备出生态型工程水泥基复合材料--ECO-ECC.ECO-ECC同样具有应变硬化和多缝开裂的特性,其极限拉应变值可达2%以上,薄板四点受弯时试件最大裂缝宽度仅为0.06 mm,平均裂缝间距为1.43 mm,主要性能指标优异.对ECO-ECC的原材料优选原则和制备工艺进行了研究与介绍,制备的ECO-ECC可实现自流平.同时系统分析研究了ECO-ECC耐久性能.ECO-ECC其优越的性能使得其可用于混凝土板面层的维修、桥梁的连接板、框架结构的节点等,具有广泛的应用前景.     

超高性能轻质混凝土的循环拉伸力学性能

超高性能轻质混凝土(ultra-high performance lightweight concrete,UHPLC)是一种具有高拉压比和拉伸应变强化特性的轻质水泥基材料.为了阐述UHPLC与钢筋在钢筋屈服点之前的协同受拉机制,针对一种密度为1789 kg/m3、抗压强度为63.1 MPa、极限拉伸应变约为2.4×1...     

碱渣复合胶凝材料制备无熟料混凝土

碱渣作为氨碱法制备纯碱过程中产生的固体废弃物,目前无较好的大规模处理利用方法.本文以最大限度利用碱渣为目的,利用碱渣、矿渣、钢渣和脱硫石膏为复合胶凝材料,铁尾矿砂和废石为骨料制备无熟料混凝土.胶凝材料中碱渣掺量30%、矿渣45%、钢渣15%、脱硫石膏10%时,无熟料混凝土的28 d抗压强度可达38.33 MPa.通过XRD、SEM-EDS、TG-DSC和IR等表征方法研究了复合胶凝材料体系的水化产物及水化过程,结果表明该复合胶凝材料的水化产物主要为C-S-H凝胶、钙矾石（AFt）和 Friedel盐（FS）.对碱渣、矿渣、钢渣和脱硫石膏4种固废之间的协同反应机理进行分析,阐述了水化产物的生成过程.对全固废混凝土做耐久性分析发现,混凝土抗冻性及抗碳化性能良好,但干燥收缩性能和抗硫酸盐侵蚀性能不佳.分析了碱渣无熟料混凝土的制备条件、应用方向和应用前景,为固体废弃物的无害化和资源化利用提供科学依据.     

PVA-ECC与混凝土界面钻芯拉拔试验研究

为了研究聚乙烯醇纤维砂浆(PVA-ECC)与混凝土之间的粘结性能,通过钻芯拉拔试验分析了混凝土强度等级、界面剂类型、聚乙烯醇纤维水泥砂浆强度等级3种因素对聚乙烯醇纤维水泥砂浆与混凝土之间粘结性能的影响,最后用Table Curve 3D软件拟合PVA-ECC与混凝土界面的钻芯拉拔强度受3因素影响的回归公式。研究结果表明:混凝土的强度等级对界面粘结性能影响极不显著,而聚乙烯醇纤维水泥砂浆强度等级对界面粘结性能影响显著,界面剂因素影响高度显著。公式计算结果与试验结果吻合良好。     

UHPC梁开裂弯矩和裂缝试验

为研究超高性能混凝土梁的开裂弯矩和裂缝特征及评估现有规范公式计算超高性能混凝土梁开裂弯矩和裂缝宽度的适用性,进行了8根超高性能混凝土T形简支梁的受弯性能试验,观察试验梁的开裂弯矩和裂缝发展．试验结果表明:预应力水平对开裂荷载影响较大;超高性能混凝土梁的弯曲裂缝细而密,加载初期最大裂缝宽度发展较慢,纵筋屈服后最大裂缝宽度发展明显加快;利用现有规范公式计算超高性能混凝土梁开裂弯矩和最大裂缝宽度过于保守．在现行规范公式的基础上引入抗裂影响系数和裂缝修正系数,给出了超高性能混凝土梁开裂弯矩和最大裂缝宽度的建议公式,建议公式的计算值和试验值吻合良好．