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.     

Potential use of strain hardening ECC in permanent formwork with small scale flexural beams

Utilizing pre-cast ECC panels as participating permanent formwork of concrete members, and the validity of using ECC to disperse the single crack in concrete into multiple ones in ECC were studied. In the process, totally two kinds of ECC with different tensile properties, 7 series of flat panels with different top surface figures and 3 U-shape panels with different inner surface forms were investigated. To evaluate the performance of the permanent formworks, small ECC-concrete composite beams were cast and tested mechanically. The 4-point bending test results show that the use of pre-cast ECC panels as permanent formwork can significantly improve the load capacity and toughness of a concrete member, effectively dispersing single widely opened crack in concrete into multiple ones in ECC. Most permanent formworks show perfect bond with the concrete cast on them, while the ones with partially debonded zone achieve the best mechanical performance. The U-shape permanent formworks show better performances than the flat ones, achieving much better improvements in both the load capacity and toughness, together with better crack width control. Funded by the Hong Kong Research Grant Council(No. CERG UST6138/04E), the Key Program of National Natural Science Foundation of China (No. 50438010), and the Research & Application of Key Technology for the South-North Water Transfer Project Construction in China (No. JGZXJJ2006-13)     

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.     

超高韧性水泥基复合材料的波传播试验研究

为了研究超高韧性水泥基复合材料（UHTCC）中应力波的传播特性,采用Hopkinson杆加载UHTCC试件,测得UHTCC在0.2、0.3、0.4、0.5 MPa冲击气压下的应力波信号. 通过对比入射杆波形,验证相同加载条件下加载波形的一致性. 分别采用两点法和峰值法计算每种冲击气压下UHTCC中应力波的波速,结果显示,两点法适用性较广,计算结果较稳定,利用峰值法测波速则需要入射杆和试件波阻抗相近. 计算结果显示,UHTCC中应力波波速、衰减系数随冲击气压均无明显变化,平均波速为3.060 km/s,平均衰减系数为2.777 m^?1. 可以利用朱-王-唐本构模型参数表达材料中应力波的波速和衰减,也可以利用实测的波速和衰减系数将UHTCC的朱-王-唐冲击本构模型表示为只含单个准静态参数的方程,从而提供通过试验直接确定UHTCC动态本构的方法.     

新型组合梁板连接中板的抗弯性能

在高层建筑结构设计中,由于上部荷载较大或梁的跨度较大,使得梁的截面高度较高,通常会影响建筑的有效层高和建筑的总体高度。为了减小各层梁板结构高度,有效增大各层净高,提出了一种钢箱梁嵌入现浇板的新型组合梁板连接方式。针对这种新型连接方式,对6个钢箱梁混凝土板组合连接区域进行了板承受支座负弯矩的单调加载试验,对比分析了采用钢箱梁嵌入混凝土板组合楼盖与传统栓钉连接组合楼盖中板抵抗支座负弯矩的性能差异;并利用ABAQUS对试件进行了有限元分析。试验与有限元分析结果表明：采用钢箱梁嵌入板连接组合方式,其混凝土板抵抗支座负弯矩的能力与传统连接方式板抵抗支座负弯矩能力没有明显差异。     

掺轻质砂超高性能混凝土的轴拉力学性能

为研究轻质砂对不同试件尺寸下超高性能混凝土（ultra high performance concrete,UHPC）拉伸应变强化性能的影响,采用轻质砂对原黄砂进行等体积替代,完成9组不同轻质砂体积率（0~35%）和不同试件厚度（30~100 mm）的单轴拉伸试验,并同步进行声发射实时探伤测试。结果表明:轻质砂体积率对UHPC弹性极限点对应应力和对应应变的影响较小,但轻质砂体积率由0增加到35%时,UHPC的极限抗拉强度和极限拉应变分别由10.6 MPa和2.35×10^-3提高到了19.4 MPa和4.3×10^-3;轻质砂体积率大于15%时,UHPC的应变强化程度得到显著提升,试件内部产生的损伤点数更多且分布更均匀,展现出良好的裂缝控制能力;在相同轻质砂体积率下,UHPC的应变强化程度随试件厚度的增加而降低,且试件内部的损伤点趋于集中,表现出明显的尺寸效应。     

Numerical study on flexural behaviors of steel reinforced engineered cementitious composite (ECC) and ECC/concrete composite beams

Engineered cementitious composite(ECC)is a class of high performance cementitious composites with pseudo strain-hardening behavior and excellent crack control capacity.Substitution of concrete with ECC can largely reduce the cracking and durability problems associated with brittleness of concrete.In this paper,a simplified constitutive model of the ECC material was applied to simulate the flexural behaviors of the steel reinforced ECC and ECC/concrete composite beams with finite element method.The simulation results are found to be in good agreement with test results,indicating that the finite element model is reasonably accurate in simulating the flexural behaviors of the steel reinforced ECC flexural members.The effects of the ECC modulus,ECC tensile ductility,ECC thickness and ECC position on flexural behaviors in terms of ultimate moment,deflection and the maximum crack width of the steel reinforced ECC or ECC/concrete composite beam are hence evaluated.     

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and ...     

预应力RPC-NC叠合梁抗弯延性试验分析

为有效推动高性能材料在现代桥梁结构中的应用以满足快速发展的高速铁路技术,本文设计并制作了10根预应力活性粉末混凝土(RPC)-普通混凝土(NC)叠合梁和1根预应力纯NC梁,通过试验方法研究了高性能材料RPC在梁结构中应用后叠合梁的抗弯延性性能,并以叠合梁跨中位移延性系数进行描述.试验主要考虑了RPC高度、预应力比率、NC等级等因素对叠合梁抗弯延性的影响.研究结果表明:随着RPC高度的增加,叠合梁截面配筋指数降低,抗弯位移延性系数增大;随着钢绞线根数的增多,预应力比率增大,位移延性系数相应增大;叠合梁上部NC等级提高后,脆性破坏特征并不明显,抗弯位移延性系数增大.由于RPC材料优异的力学性能以及钢纤维的作用提高了叠合梁在出现峰值荷载后的变形能力,使得其抗弯位移延性要明显优于纯NC梁,可见RPC材料在拥有高强度的同时具有良好的延性特征.同时以试验数据为基础,拟合出适用于预应力RPC-NC叠合梁抗弯位移延性系数的计算公式.     

超轻质水泥基复合材料基本力学性能

为探究超轻质水泥基复合材料(ultra lightweight cement composite,ULCC)的基本力学性能及应力-应变曲线本构关系.以粉煤灰空心微珠为唯一轻质微集料,以水泥和硅灰为胶凝材料,以高效减水剂和减缩剂为外加剂,配制了钢纤维体积掺量为1%,表观密度介于1 250~1 550 kg/m3,轴心抗压强度介于47.9~70.0 MPa的4种不同密度等级的ULCC.对其分别进行单轴抗压和单轴抗拉试验,分别研究了ULCC的轴心抗压和轴心抗拉力学性能,测得了ULCC材料轴心抗压强度、轴心抗拉强度、弹性模量、泊松比及单轴抗压和单轴抗拉应力-应变曲线.结果表明:ULCC的抗压强度、抗拉强度和弹性模量均随密度的增加而增加; ULCC的轴心抗压强度和弹性模量与密度呈较强线性相关性.轴心抗拉试验结果表明ULCC抗拉应力-应变曲线关系呈现明显的峰后平台段,ULCC材料具有良好的拉伸变形能力.根据试验测得的ULCC单轴抗压和单轴抗拉应力-应变全曲线,建立了ULCC单轴抗压和单轴抗拉的分段式应力-应变本构方程.研究成果可为ULCC结构的设计和非线性有限元计算提供理论依据.     

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。     

膏体充填材料力学性能的初步实验

介绍了一种适合于煤矿膏体充填的专用膏体胶结料，它可以在50kg／m^3左右的极少用量条件下，保证膏体快速凝结固化，达到膏体充填不迁村采煤工程需要的强度性能，该膏体充填材料具有典型的塑性特征，弹性模量大，在低围压下就转变为应变强化特征，是一种比较理想的充填胶结材料。     

纤维素纤维增强高韧性水泥基复合材料的拉伸力学性能

研究了3种纤维掺量UF纤维素纤维增强水泥基复合材料(UF-ECC)的单轴拉伸性能及纤维掺量对ECC力学性能的影响规律,探讨了裂缝扩展宽度与轴拉应力的关系,分析了ECC的拉伸断裂能与特征长度.结果表明:当纤维体积掺量由0.3%提高到0.6%时,UF-ECC的最大拉应变提高183%,断裂能提高419%,特征长度提高281%.ECC复合材料的最大拉应变是聚丙烯纤维混凝土的8~20倍.UF纤维素纤维具有良好的阻裂增韧效用,显著提高了ECC的变形能力,ECC在单轴拉伸荷载下能实现应变硬化和多重裂纹初裂.     

高韧性纤维增强水泥基复合材料的单轴拉伸力学性能

试验研究了3种纤维掺量聚乙烯醇纤维增强水泥基复合材料(PVA-ECC)的单轴拉伸力学性能及纤维掺量对ECC力学性能的影响规律,探讨了裂缝扩展宽度与轴拉应力的关系,分析了ECC拉伸断裂能与特征长度.结果表明:当纤维掺量由0.308%提高到0.462%时,PVA-ECC的断裂能提高128%,特征长度提高146%,最大拉应变提高128%.PVA-ECC的断裂能和最大拉应变比聚丙烯纤维混凝土分别提高209%和3 614%.表明PVA纤维具有良好的阻裂增韧效用,显著提高了ECC的抗裂性能和变形能力,ECC在单轴拉伸荷载下能实现应变硬化和多重裂纹开裂.     

Mechanics behavior of ultra high toughness cementitious composites after freezing and thawing

Mechanical behaviors of UHTCC after freezing and thawing were investigated, and compared with those of steel fiber reinforced concrete (SFRC), air-entrained concrete (AEC) and ordinary concrete (OC). Four point bending tests had been applied after different freezing-thawing cycles (0, 50, 100, 150, 200 and 300 cycles, respectively). The results showed that residual flexural strength of UHTCC after 300 freezing-thawing cycles was 10.62 MPa (70% of no freezing thawing ones), while 1.58 MPa (17% of no freezing thawing ones) for SFRC. Flexural toughness of UHTCC decreased by 17%, while 70% for SFRC comparatively. It has been demonstrated experimentally that UHTCC without any air-entraining agent could resist freezing-thawing and retain its high toughness characteristic in cold environment. Consequently, UHTCC could be put into practice for new-built or retrofit of infrastructures in cold regions.     

超高性能水泥基材料的力学行为及机理分析

研究安防系统对超高性能水泥基复合材料工作性及超高力学性能的特殊要求,以大掺量超细工业废渣取代水泥,掺加超高硬度细集料,采用高温干热养护制度,成功制备出一种超高性能水泥基复合材料.对其工作性及不同养护温度和养护时间下的力学性能进行测试,结果表明,制备的材料具有较好的工作特性及超高力学性能,可满足安保产品要求,其抗压强度最高可达240 MPa.采用X射线衍射技术、差热-热重分析方法及扫描电镜对其微观结构形成进行分析,结果显示,超高硬度细集料与胶凝材料的强物理结合使其在复合材料中起增强相的作用,高温养护加速了水泥的水化及矿物惨合料的火山灰反应,降低了材料中Ca(OH)2的含量,增加了C-S-H凝胶的含量,提高了材料的密实度,改善了界面微观结构,提高了超高性能水泥基复合材料的宏观力学性能.     

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.     

预制钢-混凝土组合楼梯抗弯性能与舒适度分析

为推进组合材料在建筑结构中的应用,对预制钢-混凝土组合楼梯踏步的抗弯性能和楼梯整体的舒适度进行研究。进行6个楼梯踏步试件的四点弯曲试验,主要探究抗剪件形式和踏步与梯梁的连接方式对楼梯踏步承载性能的影响。试验结果表明,相对于角钢和栓钉抗剪件,槽钢抗剪件对楼梯踏步的承载力提升更为显著。此外,焊接试件的承载力受抗剪件的影响较小,并且高于简支试件的承载力,在今后的工程应用中,焊接可以作为钢-混凝土组合楼梯踏步与梯梁连接的主要方式。为了更准确地研究楼梯踏步的力学行为,使用ABAQUS有限元软件对其进行建模,该有限元模型能够准确模拟楼梯踏步的力学行为。在验证模型准确性的基础上,对整体楼梯进行舒适度分析。结果表明,在规范限值范围内,楼梯的自振频率和人致激励下的加速度响应均满足行走的舒适度要求,使用过程中不会引起明显不适,符合人体工程学的要求。试验和建模分析证明,槽钢抗剪件对楼梯踏步的承载力提升效果更好,焊接可以作为楼梯踏步与梯梁的连接方式,并且楼梯的舒适度满足规范要求。     

肋筋模板钢-混凝土组合板力学性能的试验研究

针对一种新型的组合板－肋筋模板钢－混凝土组合板（以下简称肋筋模 板组合板），进行了43块板的试验研究。分析了这种组合板在施工阶段的承载能力、稳定性及破坏形式，以及在使用阶段考虑底模作用时的荷载－变形关系、钢材和混凝土的应变和裂缝的发展等。试验结果表明：肋筋模板组合板在施工阶段具有良好的稳定性，在使用阶段具有较高的承载力和良好的延性。优化结果表明这种板具有较好的经济性。     

阶梯形修理复合材料层合板拉伸性能研究

为获得不同参数对阶梯形修理结构拉伸力学性能的影响,本文开展了试验研究.针对铺层数目为8层的复合材料层合板,分别研究了阶梯数目为2个、4个和8个的无附加层的情况.另外针对4个阶梯的情况,研究了附加层数目的影响.作为对比,对相同修理区大小情况下的斜切形挖补修理结构也进行了测试.结果显示,对阶梯形修理结构,拉伸强度随阶梯数目的增加而增加,当阶梯数目由2个增加到8个时,修理接头的强度恢复率由36%增加到67%.通过引入附加层能够有效的提高修理结构的强度,但随着附加层的引入以及附加层数目的增加,修理结构强度的分散性变大.阶梯形修理和斜切形挖补修理的对比显示,相同修理面积的情况下,由于斜切形挖补修理能够提供更加均匀的胶膜应力分布,斜切形挖补的修理效率要高于阶梯形修理,相比4个阶梯的阶梯形修理,斜切形挖补修理强度能够提高25%.最后,根据修理接头表面各点的应力/应变分布规律,获得了拉伸载荷作用下修理接头的失效机理和失效过程.