韧性纤维增强聚合物砂浆的粘结修复与收缩耐久性能

为有效解决严酷环境侵蚀引起的混凝土结构保护层脱落及钢筋锈蚀问题,亟待研制高性能防护砂浆。本研究采用L_9(3~3)的正交实验法来研究聚胶比、砂胶比和PVA纤维掺量3个变量对修补砂浆的抗折强度、抗压强度、粘结强度和收缩率的影响。综合考虑各种因素对修补砂浆粘接强度的影响和实际应用,确定优化配合比:聚胶比为15%,砂胶比为1.5:1,纤维掺量为1.5kg/m~3。     

纳米SiO2-橡胶粉再生混凝土力学性能试验研究及数值模拟

以质量取代法研究纳米SiO2(取代水泥)和橡胶粉(取代河砂)对再生混凝土28 d抗压强度、抗折强度和劈裂抗拉强度的影响,并通过MAT-LAB软件建立了二维随机骨料投放程序,采用ABAQUS软件对再生混凝土单轴受压力学性能进行了数值模拟分析.结果表明:单掺橡胶粉时,随着橡胶粉掺量增加,再生混凝土的抗压强度、劈裂抗拉强度和抗折强度呈先增大后减小的趋势;当橡胶粉掺量恒定时,再生混凝土抗压、劈裂抗拉和抗折强度随着纳米SiO2掺量增加而增大.与未掺SiO2组相比,纳米SiO2掺量为1.5％(质量分数,下同)的再生混凝土28 d抗压强度、劈裂抗拉强度和抗折强度分别提高了13.3％、22.8％、21％.基准组(纳米SiO2和橡胶掺量为0)和试验组(1.5％纳米SiO2和5％橡胶)单轴受压试验模拟结果与真实试验结果的误差较小,表明数值模拟分析所得的计算值与试验值吻合良好.     

复合固化砂土力学及水稳性能试验研究

为探究经水泥、石灰和改性聚丙烯纤维复合固化砂土的力学及水稳性能,进行了系列室内试验,结果表明:随水泥掺量增加,固化砂土无侧限抗压强度和劈裂抗拉强度增大,但增长幅度减小,用一定量石灰取代水泥会降低水泥土强度,纤维可以提高水泥土强度,尤其是抗拉强度;水泥可大幅提高砂土抗剪强度和抗压回弹模量,随着纤维掺量的增加,固化土抗剪强度低于水泥土,黏聚力和回弹模量先增大后又减小,内摩擦角与黏聚力表现出负相关性;0.3%纤维加筋8%水泥固化土可以满足简易机场对基层材料的要求。     

复合固化砂土力学及水稳性能试验研究

为探究经水泥、石灰和改性聚丙烯纤维复合固化砂土的力学及水稳性能,进行了系列室内试验,结果表明:随水泥掺量增加,固化砂土无侧限抗压强度和劈裂抗拉强度增大,但增长幅度减小,用一定量石灰取代水泥会降低水泥土强度,纤维可以提高水泥土强度,尤其是抗拉强度;水泥可大幅提高砂土抗剪强度和抗压回弹模量,随着纤维掺量的增加,固化土抗剪强度低于水泥土,黏聚力和回弹模量先增大后又减小,内摩擦角与黏聚力表现出负相关性;0.3%纤维加筋8%水泥固化土可以满足简易机场对基层材料的要求。     

微胶囊-玄武岩纤维/水泥复合材料的力学性能

以水泥、玄武岩纤维和脲醛/环氧树脂微胶囊为主要材料,制备水泥基复合材料标准试样,研究纤维掺量、纤维长度、微胶囊质量分数、水灰质量比和养护龄期对复合材料抗折强度和抗压强度的影响,利用正交实验确定微胶囊-玄武岩纤维/水泥自修复复合材料力学性能的最优配比。实验结果表明：抗折强度随着纤维掺量的增加而增加,抗压强度随着纤维掺量增加而减小;随着纤维长度的增加,抗折强度略有增加,抗压强度略有降低;抗折强度随着微胶囊质量分数的增加呈现出先增加后减小的趋势,而抗压强度则呈现下降趋势;抗折强度与抗压强度随养护龄期的增加而呈增加的趋势;材料经损伤后修复,抗折强度修复率为117%,恢复率为103%,抗压强度修复率为71%,恢复率为97%。     

PVA纤维改性地坪修补砂浆性能研究

以PVA纤维作为外掺物质,研究了其掺量对水泥砂浆流动度、力学性能以及耐磨性能的影响规律,并对其改性机理进行了分析。结果表明,随着PVA纤维掺量的增加,复合砂浆试样流动度逐渐下降,各龄期复合砂浆试样抗折强度均表现为先增加后降低,PVA纤维复合砂浆试样各龄期单位面积磨损量均表现为先减小后增大。     

PVA及玄武岩纤维对水泥基复合材料力学性能的影响

在水泥基复合材料中掺入适量纤维可显著改善其物理力学性能,但有机-无机混杂纤维对水泥材料性能的影响目前研究不多。进行了单掺PVA纤维、单掺玄武岩纤维以及复掺两种纤维的水泥基复合材料力学性能实验。结果表明,单掺1.6%(体积分数)的短PVA纤维时,水泥基复合材料的抗折强度降低7%、抗压强度提升31%、折压比降低24%;单掺0.3%(体积分数)的短玄武岩纤维时,水泥基复合材料的抗折强度降低8%、抗压强度提升15.7%、折压比降低20%;掺0.3%(体积分数)短玄武岩纤维和0.5%(体积分数)短PVA纤维时,水泥基复合材料的抗折强度几乎无影响,抗压强度显著提升,折压比相对减少,其综合性能最优。     

纤维加筋固化黄土浸水强度试验研究

为探究水泥、石灰以及多种纤维复合固化黄土的水稳定性能,进行了浸水无侧限抗压强度试验和浸水无侧限劈裂抗拉强度试验。试验结果表明:加砂对复合固化黄土的水稳定性能不利;水泥固化效果优于其他固化剂;纤维可以提高浸水水泥固化土的浸水抗压强度和浸水劈裂抗拉强度,其中0.15%和0.30%纤维掺量的水泥固化黄土浸水抗压强度较高,但继续提高纤维掺量会导致抗压强度降低;纤维长度越长则复合固化黄土浸水抗压强度和劈裂抗拉强度越高,两种及两种以上的纤维混杂掺入会导致固化黄土浸水抗压强度和劈裂抗拉强度降低;水泥可以大幅提升固化土浸水劈裂抗拉强度,19mm聚丙烯纤维加筋固化土浸水劈裂抗拉强度较高,提高纤维掺量可以提高浸水劈裂抗拉强度,两种及两种以上的纤维混杂不能提高浸水劈裂抗拉强度。     

养护条件对碱-矿渣-偏高岭土复合胶凝材料强度的影响

研究了偏高岭土对碱矿渣水泥强度的影响规律和不同养护条件下碱-矿渣-偏高岭土复合胶凝材料(M-AAS)的强度发展情况.结果表明:80%湿度和40℃温度下,掺入适量偏高岭土能提高碱矿渣水泥的强度性能,最佳掺量为20%左右;对于掺20%偏高岭土的碱-矿渣-偏高岭土复合胶凝材料,在80%湿度下,养护温度的提高有利于抗压强度的发挥,但对抗折强度的发挥不利;在80%湿度和20℃温度下,复合材料的抗折强度出现倒缩,对80%湿度养护和水中养护两种养护条件进行适当的组合,强度倒缩现象没有发生.     

碳酸钙晶须与硅灰的复合效应对水泥砂浆力学性能的影响

研究了水泥砂浆的抗压强度、抗折强度以及劈裂抗拉强度在固定硅灰掺量的条件下随着碳酸钙晶须掺量的变化关系,并以试验结果和微观形貌观察为基础探讨了碳酸钙晶须对水泥砂浆的增强增韧机理。     

混凝土劈裂抗拉强度和弯曲抗压强度尺寸效应的细观数值分析

混凝土作为非均质材料,其材料性能存在随试件几何尺寸变化的尺寸效应。该文在细观层次上将混凝土看作由粗骨料、砂浆和二者界面过渡区组成的三相复合材料,采用刚体弹簧元数值方法模拟了混凝土的劈裂抗拉强度和弯曲抗压强度的尺寸效应,并与已有的试验结果进行了对比验证。结果表明:劈裂加载的试件破坏形态和劈裂抗拉强度与试验结果均具有良好的一致性,并且小尺寸试件所表现出的尺寸效应要明显于大尺寸试件;对不同尺寸四点弯曲钢筋混凝土梁开展细观数值分析得到跨中截面混凝土的弯曲抗压强度,随着梁有效高度的增加,名义弯曲抗压强度整体上呈现降低的趋势,但当梁有效高度大于240mm时趋于稳定。     

低模量聚酯纤维/水泥基复合材料抗冲击性能及损伤机制

研究聚酯纤维长径比、掺量对混凝土抗压强度、抗折强度、劈裂抗拉强度、断裂韧性及冲击荷载等力学性能的影响;运用复合材料理论和纤维间距理论对聚酯纤维/混凝土增韧阻裂机制进行研究,结合SEM观察微观形貌分析纤维长径比与掺量对增韧阻裂机制的影响;采用正交试验设计方法及激光扫描共聚焦显微镜(LSCM)研究冲击高度、试件厚度、长径比及掺量对纤维/混凝土抗冲击性能的影响。结果表明,长径比为300与600的聚酯纤维会降低混凝土抗压强度,低掺量长径比为150的聚酯纤维通过提高混凝土致密程度使混凝土抗压强度有所提升;在抗拉强度方面长径比为150的聚酯纤维主要以缺陷形式存在,长径比为300的聚酯纤维对改善混凝土内部拉结作用最显著,3%(与胶凝材料体积比)掺量聚酯纤维对提高混凝土抗折强度最显著;对于混凝土断裂韧性,长径比为300与600的聚酯纤维/混凝土断裂韧性提高明显,通过SEM微观形貌发现纤维拉结作用产生的微裂纹会提高混凝土耗能能力,从而提高混凝土极限荷载与破坏时中心挠度,长径比为300的聚酯纤维/混凝土抗拉强度变化规律与复合材料理论和纤维间距理论分析结果较吻合;冲击高度为影响冲击荷载大小的主要因素,纤维长径比较纤维掺量影响较大,通过LSCM三维损伤形貌分析得出长径比为150的聚酯纤维对混凝土材料损伤改善效果较显著,同等掺量下长径比为150的聚酯纤维间距较小导致混凝土局部力学性能提高,从而提高混凝土抗冲击性能。      

磁场诱导定向碳纤维增强水泥砂浆的力学性能

首次利用磁场诱导定向技术,制备了具有明显择优取向的碳纤维增强水泥砂浆,表征与测试了不同水灰比、龄期和纤维掺量的水泥砂浆的碳纤维取向、抗压和劈裂抗拉强度,研究了碳纤维的取向性对力学性能提升效果的影响。结果表明:水灰比、纤维掺量对碳纤维的取向性有显著影响;相较于无择优取向的普通碳纤维增强水泥砂浆,经磁场诱导定向的碳纤维增强水泥砂浆的劈裂抗拉强度有显著增加,而抗压强度无明显变化;相同水灰比下,纤维取向和纤维掺量是影响定向碳纤维增强水泥砂浆劈裂抗拉强度的主要因素。其中,定向碳纤维增强水泥砂浆劈裂抗拉强度增强效率的最佳碳纤维掺量为水泥的0.50%。      

Modelling of slaked lime–metakaolin mortar engineering characteristics in terms of process variables

The purpose of the present study is to determine the effect of factors such as dosage, curing conditions and use of a superplasticiser admixture on the porosity, mechanical strength and composition of slaked lime (SL)–metakaolin (MK) mortars. Statistical correlations have been established to describe the mechanical properties as well as porosity and composition of the slaked lime–metakaolin mortars.The SL/MK ratio has a moderate effect on mortar flexural and compressive strengths. The SL + MK/sand ratio is the factor with the highest impact on all the properties studied: strength, porosity and mortar composition. As this ratio increases, strength, porosity and amount of hydration and carbonation products formed in the samples also rise. The next factor by order of importance is the presence of a superplasticiser admixture, which affects porosity, strength and the amount of calcite in the sample. The presence of this superplasticiser admixture increases strength, raises the percentage of calcite in the mortars and reduces porosity. It is particularly striking that neither curing nor open air carbonation time (in the range studied) has a significant effect on the composition or porosity of the SL–MK mortars studied, although they do have a moderate effect on mechanical strength.     

Influence of clays on the shrinkage and cracking tendency of SCC

The influence of different types of clay on the shrinkage and cracking tendency of fly ash modified self-consolidating concrete (SCCF) for the application of slipform paving were investigated in this study. The mortar phase of each mix was tested for autogenous shrinkage, total free shrinkage under drying and restrained shrinkage cracking. The mechanical properties (flexural strength, compressive strength, and modulus) were studied to supplement the results of the shrinkage and cracking tests. The plain SCCF mix was compared against the clay-modified SCCF mixes, as well as conventional SCC and slipform concrete (SFC) mixes. The results showed that the very early-age autogenous shrinkage of SCCF mortar was increased by the addition of clays due to adsorption effects. The effects of the clays on total shrinkage under long-term drying were found to depend mainly on the pozzolanic reactivity, but these effects were very slight at low dosages of about 1% by mass of binder. The early-age cracking tendency was aggravated by the clays composed of purified magnesium alumino silicate and metakaolin, but little influenced by the clay composed of kaolinite, illite and silica. Overall, the SCC mixture modified with both fly ash and a small amount of clay showed comparable shrinkage and early-age cracking performances as conventional SFC.     

聚丙烯-钢纤维/混凝土柱大偏心受压承载力计算

对270个聚丙烯纤维掺量(体积分数)分别为0vol%、0.1vol%、0.2vol%、0.3vol%、0.4vol%、0.5vol%、钢纤维掺量(体积分数)分别为0vol%、0.5vol%、1vol%、1.5vol%、2vol%的聚丙烯-钢纤维/混凝土试块进行立方体抗压试验、轴心抗压试验和劈裂抗拉试验,基于复合材料力学理论,考虑纤维的取向系数、长度有效系数和界面黏结系数,对其建立强度预测模型并进行机制分析,同时选取掺量分别为0vol%、0.1vol%、0.3vol%的聚丙烯纤维、掺量分别为0vol%、1.5vol%的钢纤维制作6根聚丙烯-钢纤维/混凝土柱,对其进行大偏心受压试验,在强度预测模型的基础上进行承载力计算,提出聚丙烯-钢纤维/混凝土承载力计算方法。结果表明:钢纤维对聚丙烯-钢纤维/混凝土立方体抗压强度、轴心抗压强度和劈裂抗拉强度均有提高;聚丙烯纤维可提高聚丙烯-钢纤维/混凝土的劈裂抗拉强度,但不能提高聚丙烯-钢纤维/混凝土的抗压强度;聚丙烯-钢混杂纤维加入混凝土柱可有效提高其极限承载力。      

Effect of steel fiber on the mechanical properties of oil palm shell lightweight concrete

This paper reports the results of a study conducted to investigate the effect of low volume content of steel fiber on the slump, density, compressive strength under different curing conditions, splitting tensile strength, flexural strength and modulus of elasticity of a grade 35 oil palm shell (OPS) lightweight concrete mixture. The results indicate that an increase in steel fiber decreased the workability and increased the density. All the mechanical properties except the modulus of elasticity (E) improved significantly. The 28 day compressive strength of steel fiber OPS lightweight concrete in continuously moist curing was in the range of 41–45 MPa. The splitting tensile/compressive and the flexural/compressive strength ratio for plain OPS concrete are comparable with artificial lightweight aggregate. The (E) value measured in this study was about 15.5 GPa on average for all mixes, which is higher than previous studies and is in the range of normal weight concrete. Steel fiber can be used as an alternative material to reduce the sensitivity of OPS concrete in poor curing environments.     

Function of styrene-acrylic ester copolymer latex in cement mortar

This paper focuses on the effect of the styrene-acrylic ester copolymer (SAE) latex on the performance of cement mortar, through studying on the water-reduction and water-retention effects of the SAE latex in the mortar, and the influence of the SAE latex on the air-content and the bulk density of the fresh mortar and the bulk density, compressive and flexural strengths, shrinkage rate, water capillary adsorption and anti-penetration capacity of the hardened mortar. The experimental results show that the SAE latex has good water-reduction and water-retention effects in mortar. The SAE latex has also air entrainment effect, increasing the air content and reducing the bulk density of the fresh mortar. The apparent bulk density and dry bulk density of the hardened mortars decrease with the increase of the SAE latex/cement-ratio (m_p/m_c) and the change is in accordance with that for the bulk density of the fresh mortar. The SAE latex influences the development of the compressive strength but slightly on the flexural strength, and improves the toughness, shrinkage property, waterproofing quality and anti-penetration capacity of the mortar significantly.     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO₂的钢纤维混凝土(NSFC)、 钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、 劈裂和抗折强度等力学性能, 对不同温度热处理后的微观结构进行了SEM分析, 对钢纤维与过渡区界面的相结构进行了XRD分析。结果表明: 在测试温度范围内, NSFC的抗压、 劈裂和抗折强度均高于SFRC和NC的强度, 且在400 ℃时达到最大值。在常温下, NSFC的抗压、 劈裂和抗折强度较NC分别提高27.01%、 63.28%和54.12%, 400 ℃高温热处理后比NC分别高35.09%、 84.62%和87.23%; SEM分析表明, 在钢纤维与过渡区的界面处, 致密度提高, 显微硬度提高。由于固相反应, 使界面区结构发生变化, 在钢纤维表层形成扩散渗透层(白亮层), 即化合物层, 呈锯齿状, XRD分析证明, 白亮层主要由FeSi₂和复杂的水化硅酸钙组成, 从而增强了钢纤维与基体的粘结力, 提高了混凝土的高温力学性能。