高性能环保型尾矿砂水泥基复合材料增韧性能研究

针对项目组研发的高性能环保型建材即替代比率达50%的尾矿砂PVA纤维水泥基复合材料,采用立方体抗压实验、薄板四点弯曲实验和薄板拉伸实验,分别测得了该复合材料的抗压强度、弯曲荷载-挠度位移和拉伸应力-应变等特性曲线,获得了该复合材料的弯曲韧性和弯曲强度以及断裂能和抗拉强度。通过实验,研究PVA纤维掺量和水胶比等因素对尾矿砂PVA纤维水泥基复合材料增强和增韧性能的影响。实验结果表明,配合比对尾矿砂PVA纤维增韧水泥基复合材料的力学性能有显著影响;合适的配合比可使该复合材料获得准应变硬化和多裂缝特征,使其具有良好的弯曲韧性和抗拉延性以及较好的抗压强度、弯曲强度和抗拉强度。综合评价了尾矿砂PVA纤维增强水泥基复合材料的强度、韧性及其适用性,为该环保型复合材料的工程应用提供了依据。     

高韧性水泥基复合材料强度尺寸效应试验研究与正交分析

尺寸效应是水泥基材料的固有特性,它与材料的配合比、强度以及结构组成等因素有关。高韧性水泥基复合材料是一种新型复合材料,具有优异的韧性,但同时其结构组成与普通混凝土相比也具有较大差异。然而,目前针对尺寸效应的研究大多限于普通混凝土和高强混凝土,并且尚无相关标准对高韧性水泥基复合材料尺寸效应的处理作出规范。为了探究该种复合材料的抗压强度尺寸效应,本文采用两种不同尺寸的立方体试件,对16组不同配合比的高韧性水泥基复合材料进行了单轴抗压试验和正交分析,研究了纤维掺量、水胶比、粉煤灰掺量和砂胶比这4个因素对材料强度尺寸效应的影响情况。试验结果表明:与普通混凝土相比,高韧性水泥基复合材料的脆性特征明显减小;诸因素对尺寸效应影响的主次顺序为水胶比纤维掺量粉煤灰掺量砂胶比,其中水胶比和纤维掺量的影响均非常显著,而砂胶比对尺寸效应影响甚微。     

硅灰增强混杂纤维水泥基灌浆料与老混凝土粘结强度研究

通过四因素四水平正交试验进行硅灰增强混杂纤维水泥基灌浆料与老混凝土粘结强度的研究,选取硅灰掺量、钢纤维类型、钢纤维掺量和PVA纤维掺量作为研究因素,设定相应的水平。对粘结试块进行双面剪切试验和劈裂抗拉试验,运用极差分析上述因素和相应水平对粘结强度的影响。结果表明,当硅灰掺量为9%、长度35 mm端钩型钢纤维掺量为1.2%、PVA纤维掺量为0.5%时,粘结强度显著。基于正交试验结果,通过四组对比试验,研究了纤维对水泥基灌浆料与老混凝土粘结的界面剪切特性和劈拉破坏形态的影响。结果表明,当长度35 mm端钩型钢纤维与PVA纤维掺量分别为1.2%和0.5%混杂时,粘结试块的剪切变形性能和劈裂抗拉强度显著提高,表现出较强的粘结性能。     

玄武岩格栅增强水泥基复合材料单轴拉伸力学性能试验及本构关系模型

考虑玄武岩纤维增强树脂合物基复合材料(BFRP)格栅层数和水泥基复合材料(ECC)配比等因素,对BFRP增强大掺量粉煤灰/矿粉ECC棒骨试件进行了静力单轴拉伸试验,研究掺加增强粉煤灰/矿粉ECC的抗拉力学性能。结合试验数据,基于Richard和Abbot的弹塑性应力-应变公式提出掺加增强ECC的应力-应变本构关系模型。试验结果表明:随着掺加层数的增加,格栅增强ECC的极限抗拉强度显著增大。同配合比掺矿粉制成的ECC抗压强度、开裂应变及应力高于掺粉煤灰制成的ECC。掺加增强掺矿粉ECC试件相对掺粉煤灰ECC试件具有较好的抗拉力学性能。计算结果表明,建立的单轴受拉本构关系模型可以有效地预测掺加增强ECC的应力-应变关系和极限抗拉强度。     

高性能PVA 纤维增强水泥基复合材料常规三轴受压本构模型

对PVA 纤维体积率从0%~2%的高性能水泥基复合材料(HPFRCC)圆柱体试件进行了6 种不同围压下的常规三轴受压试验,研究其三轴受压性能,测得了极限抗压强度、峰值应变、极限应变以及应力-应变曲线。根据试验结果得出HPFRCC 的极限抗压强度、峰值应变以及极限应变与侧向围压之间的关系。基于实测圆柱体应力-应变曲线的特点,提出了HPFRCC材料常规三轴受压本构模型。计算结果与试验数据的对比表明,根据该文模型所得的计算曲线与试验曲线吻合较好,研究成果可为HPFRCC结构非线性有限元分析提供依据。     

高延性纤维增强水泥基复合材料的直接拉伸性能

利用国产基体原材料制备了具有较高极限拉伸性能的高延性纤维增强水泥基复合材料(ECC),研究了粉煤灰和胶粉对ECC直接拉伸性能的影响.试验结果表明:采用合理的配合比及测试方法,制备的ECC试件具有应变硬化及多缝开裂特征;粉煤灰掺量为80％时,7d、28 d极限拉应变分别达到3.77％和2.86％,28 d抗压强度为25.4 MPa;掺入10％胶粉,7d、28 d极限拉应变分别达到3.91％和2.37％.在满足强度要求的前提下,适当增大粉煤灰和胶粉掺量有利于提高ECC的延性.     

硅灰掺量对应变硬化水泥基复合材料裂缝控制能力的影响

目前,大跨度、高强度、高质量的建筑物层出不穷,这就要求建筑材料性能在强度和韧度上需同步提升。应变硬化水泥基复合材料(SHCC)具有显著的准应变硬化特性和优异的裂缝无害化分散能力,而硅灰的掺入可以显著提高水泥浆体的强度。通过对三组不同硅灰掺量试件单轴拉伸应变硬化过程及裂缝宽度分布情况的测定,结果表明:硅灰的掺入可以显著提高材料的初裂强度,100kg/m3硅灰掺量对材料初裂强度提高了将近1倍,且三组试件的极限应变均达到了5%以上。但硅灰的掺入对应变硬化水泥基复合材料裂缝控制能力造成了负面影响,100kg/m3硅灰掺量试件的裂缝宽度比0硅灰配比试件裂缝宽度增大了3倍左右。     

高性能PVA纤维增强水泥基材料的制备与性能

为了获得高性能PVA纤维增强水泥基复合材料的制备方法,研究了砂的颗粒级配、水胶比和粉煤灰掺量对高延性纤维增强水泥基复合材料(Engineered Cementitious Composites,ECC)的弯曲性能、抗压、抗折强度及开裂模式的影响。结果表明:随着砂的细度模数降低,ECC的跨中挠度增大,早期强度提高,但后期强度变化不明显。随着水胶比的增大,ECC的初始开裂荷载降低,跨中挠度增大,平均裂缝宽度增加。0.25水胶比的ECC的抗压强度可以满足高强度等级的要求。0.35水胶比的抗压强度可以满足对普通强度等级的要求。随着粉煤灰掺量的增加,ECC的初始开裂荷载降低、抗折和抗压强度逐渐降低,ECC的跨中挠度提高,平均裂缝宽度变小。在水胶比一定的条件下,采用细砂,适当增加粉煤灰掺量有助于提高ECC的韧性和延性。     

ECC单轴受拉损伤本构模型研究EI北大核心CSCD

通过单轴拉伸试验,讨论了PVA纤维体积掺入量和水胶比对工程用水泥基复合材料(ECC)受拉力学性能参数(开裂应变、开裂应力、峰值应变、峰值应力、极限应变以及应力-应变关系曲线)的影响规律。基于此,从损伤力学的角度讨论了ECC在单轴受拉过程的开裂前阶段、应变硬化阶段以及应变软化阶段的损伤演化机制。进而,基于ECC受拉损伤演化机制提出ECC受拉损伤本构模型,并给出模型相关参数的计算方法,分析表明:该文提出损伤模型得到的ECC受拉损伤演化曲线能更为合理的描述ECC的损伤演化全过程。最后,该文损伤模型计算的ECC受拉应力-应变关系曲线和试验曲线对比结果表明,所提出的模型能够合理的描述ECC受拉非线性应力-应变关系特征,且具有良好的精度。     

早龄期复合胶凝材料的裂纹扩展阻力分析

研究了不同组成的复合胶凝材料硬化浆体(硅酸盐水泥,硅酸盐水泥 粉煤灰,硅酸盐水泥 矿渣,硅酸盐水泥 硅灰,硅酸盐水泥 硅灰 粉煤灰)早龄期时裂纹扩展阻力的发展,探讨了粉煤灰掺量对裂纹扩展阻力的影响.结果表明:早龄期时,在相同水胶比条件下,掺加硅灰使胶凝材料体系裂纹扩展阻力明显降低,在低水胶比条件下,掺加一定量的粉煤灰能够明显增加体系的裂纹扩展阻力,掺加20%的粉煤灰能使胶凝材料具有较高的裂纹扩展阻力.     

Rate-dependent tensile behavior of high performance fiber reinforced cementitious composites

High Performance Fiber Reinforced Cementitious Composites (HPFRCC) show strain hardening behavior accompanied with multiple micro-cracks under static tension. The high ductility and load carrying capacity resulting from their strain hardening behavior is expected to increase the resisting capacity of structures subjected to extreme loading situations, e.g., earthquake, impact or blast. However, the promise of HPFRCCs for dynamic loading applications stems from their observed good response under static loading. In fact, very little research has been conducted to investigate if their good static response translates into improved dynamic response and damage tolerance. This experimental study investigates the tensile behavior of HPFRCC using High strength steel fibers (High strength hooked fiber and twisted fiber) under various strain rates ranging from static to seismic rates. The test results indicate that the tensile behavior of HPFRCC using twisted fiber shows rate sensitivity while that using hooked fiber shows no rate sensitivity. The results also show that rate sensitivity in twisted fibers is dependent upon both fiber volume fraction and matrix strength, which influences the interface bond properties.     

Development of recycled strain-hardening cement-based composite (SHCC) for sustainable infrastructures

This paper presents the experimental results of an attempt to develop sustainable strain-hardening cement-based composite (SHCC) using recycled materials. SHCC exhibits desirable mechanical properties, including strain hardening and ductility. However, SHCC is composed of silica sand and a high volume of cement, which makes it more energy intensive than conventional concrete. The aim of this study is to promote SHCC sustainability in infrastructure design through the use of recycled materials. Alternative recycled materials – sand, fly ash, and polyethylene terephthalate (PET) fibers – are used to partially replace silica sand, cement, and polyvinyl alcohol (PVA) fibers, respectively, in SHCC specimens. The effects of the recycled materials on the mechanical behavior of the SHCC specimens are examined by conducting compressive tests, four-point bending (flexural) tests, and uniaxial tensile tests. Fundamental information is then used in the constitutive model to analyze and design infrastructures using SHCC with recycled materials. Test results indicate that fly ash improves both the bending and uniaxial tensile performance of SHCC due to an increase in chemical bond strength at the interface between the PVA fibers and cement matrices. However, SHCC that contains PET fibers does not perform well in the bending and uniaxial tensile tests due to the inferior material properties of the PET fibers, although its compressive behavior is similar to that of the PVA2.0 specimen. Also, it is noted that recycled sand increases the elastic modulus value of SHCC due to its larger grain size compared to that of silica sand. Based on the desire to maintain well-performing SHCC, a replacement ratio below 20% for fly ash or below 50% for recycled sand is deemed appropriate for creating sustainable SHCC, as concluded from this study.     

环境湿度对玻璃纤维增强水泥力学性能的影响

通过开展在不同龄期、不同环境湿度下玻璃纤维增强水泥(GRC)试件的抗折强度、抗压强度试验和基体pH值测定,研究了环境湿度对掺加粉煤灰和硅灰等活性矿物掺合料的GRC试件力学性能的影响。结果表明:环境湿度对GRC试件的抗折强度有重要影响,相对湿度越大,随着龄期增加, GRC试件抗折强度降低越严重;在温度60℃、相对湿度95%条件下,经过56 d龄期后,掺有40%粉煤灰和10%硅灰的GRC试件抗折强度比未掺加粉煤灰和硅灰的GRC试件的抗折强度提高48.5%、抗压强度提高23.6%, GRC基体pH值降低6%。在相同的湿度条件下,掺有粉煤灰和硅灰试件的pH值在各个龄期都低于普通硅酸盐水泥试件,说明粉煤灰和硅灰的掺入能降低水泥水化液相的碱度,进而延缓了纤维受侵蚀的速度,显著改善了GRC试件的力学及耐久性能。通过对试验结果进行分析,利用MATLAB软件建立了GRC试件抗折强度和抗压强度与水泥砂浆基体pH值及时间的关系式。      

Strain rate dependence of HPFRCC cylinders in monotonic tension

High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC) materials exhibit strain hardening in uniaxial, monotonic tension accompanied by multiple cracking. The durability of HPFRCC materials under repeated loading makes them potentially suitable for seismic design applications. In this paper, the strain rate dependence of tensile properties of two HPFRCC materials in cylindrical specimens is reported from a larger study on strain rate effects in tension, compression and cyclic tension–compression loading. The cylindrical specimens were loaded in monotonic tension at strain rates ranging from quasi-static to 0.2 s⁻¹. To evaluate the impact of specimen geometry on tensile response, coupon specimens loaded in monotonic tension under a quasi-static strain rate were compared to corresponding cylindrical specimens made from the same batch of material. Tensile strength and ductility of the HPFRCC materials were significantly reduced with increasing strain rate. Multiple cracking, strain hardening, strain capacity, and the shape of the stress–strain response were found to be dependent on specimen geometry. SEM images taken of the fracture plane of several specimens indicated that pullout and fracture of the fibers occurred for both HPFRCC materials studied here.     

Structure formation of slag ash concrete on the basis of high-calcium fly ash and silica fume

Cementless slag ash concrete may be manufactured using high-calcium fly ash and silica fume as replacements for a binder and a microfiller, and incorporating slag sand from thermal power plants (TPP) as an aggregate. This concrete consists of waste products from TPP (fly ash and slag) and ferro-alloy plants (silica fume) and contains neither natural nor artificial aggregates for lightweight and heavy concretes. Silica fume (10–20% by weight of ash) and hot water together with subsequent heat treatment of concrete products or of castin situ structures binds the excess free calcium oxide present in the ash, and thus prevents deterioration of the concrete. The processes of concrete structure formation were investigated after 24 hours, 28 days, 3 and 6 months and the physico-mechanical, deformation and special properties (frost resistance, heat conductivity, protection of reinforcement from corrosion) were studied. This concrete conforms to the Russian Federation GOST requirement for use in single, two-storey buildings. The cost of the concrete is reduced by a factor of 3 compared with that of ordinary concrete.     

自密实混凝土拉压徐变比较试验研究

对32根梁式自密实混凝土试件进行三点弯曲持续加载,对测得梁体受拉区和受压区应变数据进行累加,得到自密实混凝土受拉徐变的发展特征曲线,并得到自密实混凝土梁拉压徐变比;研究了自密实混凝土养护龄期、水胶比和粉煤灰掺量对拉压徐变度比值的影响。通过试验结果的分析得到:无论是开放状态还是密封状态下,自密实混凝土拉伸徐变都略小于压缩徐变,除拉压基本徐变比随粉煤灰掺量的增大略微增加外,拉伸徐变与压缩徐变的比值随着养护龄期、水胶比和粉煤灰掺量的增大而减小;最后拟合得到拉压徐变比值的计算式,为工程应用提供一定的参考。     

Compressive strength and chloride resistance of self-compacting concrete containing high level fly ash and silica fume

The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength, density, volume of permeable pore space (voids) and water absorption of SCC were investigated. The total charge passed in coulombs was assessed in order to determine chloride resistance of SCC. The results show that binary blended cement with high level fly ash generally reduced the compressive strength of SCC at all test ages (3, 7, 28 and 90 days). However, ternary blended cement with fly ash and silica fume gained higher compressive strength after 7 days when compared to binary blended fly ash cement at the same replacement level. The compressive strength more than 60 MPa (high strength concrete) can be obtained when using high-calcium fly ash and silica fume as ternary blended cement. Fly ash decreased the charge passed of SCC and tends to decrease with increasing fly ash content, although the volume of permeable pore space (voids) and water absorption of SCC were increased. In addition when compared to binary blended cement at the same replacement level, the charge passed of SCC that containing ternary blended cement was lower than binary blended cement with fly ash only. This indicated that fly ash and silica fume can improve chloride resistance of SCC at high volume content of Portland cement replacement.     

PVA短纤维和粉煤灰对地聚合物基复合材料流变学行为和弯曲性能的影响

利用自行研制的活塞式挤压流变仪研究了掺加聚乙烯醇(PVA)短纤维和粉煤灰的地聚合物浆体在挤压过程中的流变学特性,在此基础上通过单轴挤压机成功制备出宽厚比=12.5∶1.0的短纤维增强地聚合物基复合材料。利用MTS电液侍服机系统研究了各种纤维和粉煤灰掺量的地聚合物基复合材料的弯曲行为。采用扫描电镜(SEM)研究了地聚合物基复合材料中纤维的分布、取向、纤维-基体间界面,以及弯曲实验后试样断裂面上的纤维伸出长度、纤维尖端断裂形貌和纤维表面组织,从细观和微观角度探讨各种地聚合物基复合材料微观结构和弯曲破坏机制。结果表明：PVA短纤维的加入改变了地聚合物浆体的破坏模式,由脆性破坏变为延性破坏;对于不掺或掺加少量粉煤灰(≤10%)的地聚合物基复合材料弯曲强度高,但延性小,当粉煤灰的掺加量≥30%时,地聚合物基复合材料的弯曲强度显著下降,但延性增大。