FB/PP混杂纤维对混凝土性能的影响

为提高混凝土的韧性,添加水镁石纤维(FB)与聚丙烯纤维(PP)的混杂纤维制成纤维混凝土材料.进行了混凝土的工作性和力学性能试验,研究了纤维对塌落度、抗压强度、弯拉强度及劈裂抗拉强度的影响.实验结果表明:FB/PP混杂纤维可以明显提高混凝土的弯拉强度及劈裂抗拉强度,且优于单一纤维增强的效果.在总纤维用量为0.5%的情况下,随PP纤维比例的增加,混凝土的塌落度及抗压强度减少,但劈裂抗拉强度上升.混凝土的弯拉强度先上升,后下降.弯拉强度最大值出现在PP∶FB=0.2%∶0.3%左右.随水灰比的降低,单一FB纤维对混凝土强度的增强效果一般呈加强趋势,而FB/PP混杂纤维对混凝土弯拉强度增强效果降低,对混凝土的劈裂抗拉强度的增强效果加强.     

有机纤维对“客运专线”用C40高性能混凝土性能的影响

目的为增强混凝土早期抗塑性开裂性能及耐久性,研究了有机纤维种类、长度及掺量对混凝土工作性能、力学性能及抗碳化性能的影响．方法采用坍落度试验、抗压与抗折强度试验、混凝土碳化试验及平板约束法测试进行研究．结果聚丙烯腈（PAN）纤维对混凝土工作性能影响最大,坍落度降幅达86％;掺入19mm聚丙烯（PP）单丝纤维,坍落度下降25％;加入0．15％PP纤维,坍落度降幅达28．7％,含气量增加25．9％;掺入聚乙烯醇（PVA）纤维后,混凝土7d、28d抗压强度降幅最大,分别达30．4％、23．5％;12mmPP单丝纤维体积掺量为0．15％时混凝土的抗裂效果明显好于0．05％掺量,而碳化深度较基准低30％．结论混凝土中掺入有机纤维后,早期抗塑性开裂性能明显增强;混凝土的抗裂效果随纤维长度和掺量增加,效果越来越明显;有机纤维的加入明显提高混凝土的抗碳化力,力学性能有所降低,但降幅不大．     

添加不同纤维的高性能混凝土力学性能试验

通过试验研究了弹性模量具有明显差异的3种纤维对于混凝土的力学性能改善所起的作用,以及钢纤维、碳纤维和聚丙烯纤维单掺或复掺对于混凝土的抗压强度、劈裂抗拉强度和弹性模量的影响。结果表明：添加0．5％高弹性模量的钢纤维对于混凝土的强度和弹性模量均有提高作用,复掺0．3％钢纤维和0．2％碳纤维的混凝土抗拉强度的提高大于抗压强度;添加0．5％钢纤维的混凝土HPC-2的弹性模量最大,比基准混凝土提高6．5％;添加0．2％聚丙烯纤维的混凝土HPC-3的弹性模量最小,且小于基准混凝土;此外,混凝土抗压强度的影响程度与纤维的弹性模量的关系更为直接,混凝土劈裂抗拉强度的改善与纤维的抗拉强度的关系更为直接,纤维的弹性模量与基体弹性模量的比值,对复合材料的弹性模量有直接的影响。     

钢纤维再生混凝土劈拉强度试验研究

通过钢纤维再生混凝土立方体试件的劈拉强度试验,研究了钢纤维体积分数(0.0%～2.0%)、3种钢纤维类型(MF,SF,BF)、再生粗骨料处理方式以及试件尺寸变化对再生混凝土劈拉性能的影响.结果表明:钢纤维的加入显著提高了再生混凝土的劈拉强度,当纤维体积分数超过1.5%后,钢纤维再生混凝土的劈拉强度接近甚至超过天然钢纤维混凝土;钢纤维类型对再生骨料钢纤维混凝土影响显著,钢纤维对再生混凝土和天然混凝土的增强效果比较接近,其中BF钢纤维增强效果最好;尺寸效应对钢纤维再生混凝土的影响比天然钢纤维混凝土显著;再生骨料处理方法对钢纤维再生混凝土的劈拉强度也有一定的影响;现行钢纤维混凝土劈拉强度计算公式仍适用于钢纤维再生混凝土.     

混杂纤维对高性能混凝土拉压比的影响

为研究低掺量钢-聚丙烯混杂纤维对高性能混凝土拉压比的影响,采用正交试验法设计了18组混杂纤维高性能混凝土试件及1组普通高性能混凝土对比试件,通过标准试验方法进行立方体抗压强度和劈裂抗拉强度试验,试验中考虑的因素主要是钢纤维的特征参数(类型、体积率、长径比)和聚丙烯纤维体积率.分析各因素对高性能混凝土拉压比的影响,结果表明:混杂纤维高性能混凝土具有明显延性破坏特征,而普通高性能混凝土表现为脆性破坏,混杂纤维的掺入使高性能混凝土的拉压比最大提高了26.2%,平均提高了9.9%.在影响高性能混凝土拉压比的四个因素中,钢纤维类型的影响最大,其次是聚丙烯纤维的体积率,影响最小的是钢纤维长径比.高性能混凝土中掺入适量钢-聚丙烯混杂纤维后,拉压比显著提高,韧性得到明显改善.     

剑麻-耐碱玻璃纤维混凝土基本强度研究

为研究剑麻-耐碱玻璃纤维混凝土基本强度,设计了30组不同纤维掺量的混凝土试件,测试并分析其抗压强度、劈裂抗拉强度和抗折强度。试验结果表明:剑麻纤维和耐碱玻璃纤维单掺和双掺均能大幅提高普通混凝土基本强度,试验中纤维体积掺量为1.5 kg/m³时,单掺剑麻纤维,混凝土基本强度提升5.65%~15.74%;单掺耐碱玻璃纤维,混凝土基本强度提升3.03%~9.14%;混掺剑麻纤维和耐碱玻璃纤维,混凝土基本强度提升8.33%~21.31%,且试件强度提升效果表现出劈裂抗拉强度>抗压强度>抗折强度。研究成果对剑麻-耐碱玻璃纤维混凝土的制备以及植物纤维在混凝土中的应用提供了参考。     

溶蚀混凝土力学性能退化的试验研究

通过实验室试验研究了不同配合比混凝土力学性能随溶蚀时间的演化规律.试验设计变量主要为水灰比和骨料体积率,采用硝酸铵溶液加速混凝土溶蚀过程.试验结果表明：酚酞指示剂法能够较准确地表征混凝土的溶蚀深度,溶蚀深度近似与溶蚀时间的平方根成线性关系.混凝土弹性模量、抗压强度和劈拉强度均随着溶蚀时间的增长而减小,水灰比和骨料体积率对它们的减小速率有较大影响.与弹性模量相比,溶蚀对抗压强度和劈拉强度影响更大.当溶蚀损伤变量小于0.6时,溶蚀混凝土抗压强度模型与试验结果良好吻合.     

废弃纤维再生混凝土的劈裂抗拉强度试验

目的 为提高废弃混凝土利用率,研究再生骨料掺入量、纤维长度、水灰质量比等因素对再生混凝土劈裂抗拉强度的影响.方法 采用干拌法掺入不同掺量纤维,制作150 mm×150 mm× 150 mm标准立方体试块,标准养护28 d后进行劈裂抗拉试验.结果随着废弃纤维掺入量的增加,废弃纤维再生混凝土的劈裂抗拉强度增加,当掺入量达到0.12％时,劈裂抗拉强度有所下降或者增加趋势有所减弱.掺入纤维长度增加,纤维体积掺入量增加,劈裂抗拉强度下降或者增长趋势有所减弱;再生骨料掺入量的增加、水灰质量比增加使劈裂抗拉强度有所降低.结论试验证明废弃纤维再生混凝土的劈裂抗拉强度比普通混凝土的劈裂抗拉强度有所提高.     

混杂纤维增强高性能混凝土拉压比试验研究

研究了揭示钢纤维和聚丙烯纤维混杂后对高性能混凝土强度和拉压比的影响.参照国家标准和试验方法,按不同的纤维掺量设计了9组混杂纤维增强高性能混凝土试件以及3组钢纤维增强高性能混凝土对比试件和1组普通高性能混凝土对比试件,进行了大量立方体抗压强度试验和劈裂抗拉强度试验研究,并对拉压比进行回归分析.结果在高性能混凝土中掺加适量的钢纤维和聚丙烯纤维后:对抗压强度影响不明显,但可使抗拉强度提高10%~30%,使拉压比增大到0.06~0.068;钢纤维体积掺量为0.8%、聚丙烯纤维体积掺量为0.11%时,混杂纤维增强高性能混凝土拉压比为0.068;混杂纤维增强高性能混凝土的劈裂抗拉试验为近似于延性断裂破坏.结论掺加适量钢纤维和聚丙烯纤维后,高性能混凝土的抗拉强度和拉压比均有不同程度的提高,这有利于提高高性能混凝土的抗裂性能和抗震性能.     

Charactersitics of Stress-strain Curve of High Strength Steel Fiber Reinforced Concrete under Uniaxial Tension

A whole of 110 specimens divided into 22 groups were tested with varying the volume fraction of steel fibers and the matrix strength of these specimens. The stress-strain behaviors of four types of steel fiber reinforced concrete （SFRC） under uniaxial tension were studied experimentally. When the matrix strength and the fiber content increase, the tensile stress and tensile strain vary differently according to the fiber type. The mechanisms of reinforcing effect for different types of fiber were analyzed and the stress-strain curves of the specimens were plotted. Some experimental factors for stress or strain of SFRC were given. A tensile toughness modulus Re0.5 was introduced to evaluate the toughness characters of SFRC under uniaxial tension. Moreover, the formula of the tensile stress-strain curve of SFRC was regressed. The theoretical curve and the experimental ones fit well, which can be used for references in construction.     

温度对C50纤维混凝土力学性能的影响

结合武汉市某工程大体积混凝土实测温度,试验研究了高温高碱环境对纤维自身力学性能的影响,及不同养护温度下混凝土的力学性能发展趋势.试验结果表明:聚丙烯纤维在10%浓度的NaOH溶液中浸泡24 h且经历室温—65℃—室温循环,纤维自身力学性能下降约10%;处理后的纤维掺入混凝土中对标准养护的试块强度无不良影响;不同养护温度下纤维混凝土力学性能发展趋势差异明显,65℃养护1 d龄期的轴心抗压强度、弹性模量、劈裂抗拉强度可达标准养护28 d龄期相应参数的97%,74%,74%,4 d龄期轴心抗压强度、劈裂抗拉强度有一定增长趋势.因此,大体积混凝土实体结构强度评定需考虑水化温度作用的影响.     

反分析法确定钢纤维水泥砂浆的拉伸残余强度

根据三点弯曲缺口梁的荷载与裂缝张开位移曲线,用反分析法确定了钢纤维水泥砂浆的拉伸残余强度。试验制作了5种不同体积含量的钢纤维水泥砂浆试件。采用虚拟裂缝模型用有限元法数值模拟了三点弯曲缺口梁的荷载与裂缝张开位移,用反分析法确定了钢纤维水泥砂浆的弹性模量和拉伸残余强度。研究结果表明,数值模拟得到的钢纤维水泥砂浆弹性模量以及三点弯曲缺口梁荷载与裂缝张开位移曲线均与试验结果吻合较好,且在常用的钢纤维含量范围内,钢纤维水泥砂浆的残余强度与钢纤维含量基本上成正比。     

混凝土与钢纤维混凝土双轴拉伸与拉压作用的试验研究

对素混凝土与钢纤维混凝土在双轴拉伸与拉压应力作用下的性能进行了试验研究。试验结果表明：混凝土双轴拉拉伸强度低于单轴拉伸强度，在双轴拉压区段抗压强度随拉应力的增加而降低，钢纤维的掺入（掺量不太高）对混凝土的破坏形态影响不很明显，但使混凝土限拉应变有所增加，同时给出了混凝土在双轴拉伸与拉压区段实用的极限强度准则。     

Effects of fibers on mechanical properties of high-performance concrete subjected to elevated temperatures

The compressive strength and ilexural toughness as well as fracture energy of fiber reinforced highperformance concrete （FRHPC） subjected to different high temperatures were studied. The results showed that after exposure at 300,600 and 900℃, the concrete mixes retained 88.1% , 41.3% and 10.2% of the original compressive strength on average, respectively. Steel fiber and polypropylene （PP） fiber were both effective in minimizing the damage effect of high temperatures on the compressive strength. The HPC reinforced with steel fibers showed higher flexural toughness and fracture energy before and after the high-temperature exposures. In comparison, PP fibers had minor beneficial effects on the flexural toughness and fracture energy. The mechanical properties of HPC reinforced with hybrid fibers （steel fiber ＋ PP fiber） were equivalent to or better than those of HPC reinforced with steel fibers alone. In addition, the failure pattern of FRHPC beams changed from pull-out of steel fibers at lower temperatures （20, 300 and 600℃） to tensile failure of steel fibers at higher temperature （900 ℃）.     

钢纤维超高强混凝土的力学性能试验

为了配制出强度高、韧性好、抗冲击性能良好的超高强混凝土,对钢纤维掺入体积率(Vf)为0~3%、基体强度为110 MPa以上的钢纤维超高强混凝土(SFRVHSC)进行立方体抗压、轴向抗压、劈裂抗拉、抗折强度和弹性模量等性能的测试,并对钢纤维超高强混凝土弯曲韧性进行了试验研究.结果表明,SFRVHSC抗压强度随Vf(0~3%)的增加有一定的增长,弹性模量随着材料抗压强度的提高略有增加;钢纤维对SFRVHSC的劈裂抗拉、抗折强度有显著的增强作用.SFRVHSC表现出优异的韧性,弯曲韧性指数I5、I10、I20分别达基体混凝土的4.71~5.15、9.47~11.23、19.02~24.06倍.SFRVHSC梁的荷载-位移曲线与坐标轴包含的面积也明显增加.     

Mechanical Properties of Phenolic-Resin Composites Reinforced with CF/BF Interlayer Hybrid Fibers

Phenolic-resin composites reinforced with carbon fiber (CF) and basalt fiber (BF) interlayer hybrid fibers plain fabric were fabricated. The tensile strength, compressive strength and interlaminar shear strength of the prepared composites were studied. The results indicated that hybrid fibers reinforced composites possessed the advantages of both CF and BF. When resin content was 35% by volume fraction, the comprehensive mechanical performance of BF/CF reinforced phenolic resin composites reached the optimal values with the warp and weft direction tensile strength, compressive strength and interlayer shear strength being 252 MPa and 487 MPa, 105 MPa and 129 MPa, 21 MPa and 20 MPa, respectively. The scanning electron microscope (SEM) observations showed that the BF/CF hybrid fibers reinforced composites had better interfacial adhesion.     

纤维高强粉煤灰混凝土劈拉强度试验研究

针对掺加纤维可改善高强混凝土的受拉性能特点,进行纤维粉煤灰高强混凝土的立方体劈拉试验研究。试验参数主要有纤维类型、纤维形状、纤维含量。试验结果表明：随纤维掺量的增大,纤维高强混凝土劈拉强度总体上呈增大趋势;扁头型和弓型钢纤维对混凝土劈拉强度的增强作用最明显,而合成纤维对混凝土劈拉强度的增加作用很小;掺入钢纤维对高强混凝土劈拉强度与抗压强度的比值明显提高。     

Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.     

大掺量粉煤灰超高性能钢纤维混凝土的静动态力学行为

研究了4种不同钢纤维掺量(体积掺量分别为0%,1.0%,1.5%,2.0%)的大掺量粉煤灰超高性能混凝土的单轴压缩强度、弹性模量、单轴抗拉强度、弯曲韧性、断裂韧性、断裂能等静态力学行为,以及高速冲击、压缩作用下的应力波传播规律、应力–应变曲线和破坏特征等动态力学行为.结果表明:掺加钢纤维的大掺量粉煤灰超高性能混凝土的轴心抗压强度、弹性模量和抗拉强度略有增大,韧性指数、残余强度、断裂韧度和断裂能成倍提高;未能增加冲击、压缩作用下的应变率效应程度,但却增大动态应力–应变曲线下的面积,提高试件破坏的应变率阈值,使混凝土存在裂而不散的破坏现象.     

Influence of the aggregate volume on the electrical resistivity and properties of portland cement concretes

The electrical resistivity of concretes with various aggregate volume fractions (V _a) of 0%–70% at water/cement (W/C) ratios of 0.4 and 0.5 during 1 day was monitored. It is found that the addition of normal aggregate to cement paste leads to a regular increase in concrete resistivity at each hydration stage and the electrical resistivity has a deeper increase for the lower W/C at a fixed aggregate volume fraction. The number of normalized resistivity (NR) of concrete to its paste matrix was introduced, which is only a function of aggregate volume fraction (V _a). The quantitative relationships give an alternative method for the prediction of aggregate volume in the concrete. A logarithmic relation is established between the elastic modulus of concrete at 7 days or 28 days and the electrical resistivity of concrete at 1 day. The equations are obtained, the compressive strength of concrete at 7 days or 28 days can be determined by the electrical resistivity of concrete at 1 day and the used aggregate content in the concrete. The quantitative relationships give a non-destructive test (NDT) method for prediction of concrete elastic modulus and compressive strength.