氯盐干湿环境下TRC与老混凝土的界面特性研究

采用双面剪切的加载方式研究了氯盐干湿循环对纤维编织网增强混凝土(Textile reinforced concrete,TRC)与普通硅酸盐混凝土界面性能的影响,并通过SEM(Scanning electron microscope)技术探究了氯盐干湿循环作用下界面的微观结构。研究发现:氯盐干湿循环下,TRC与老混凝土界面微观结构会损伤劣化;与连续氯盐浸泡相比,氯盐干湿循环对界面粘结性能的影响较大;相同干湿循环次数下,加固界面的粘结强度随着氯盐溶液浓度的增加而降低;相同氯盐溶液浓度下,加固界面的粘结强度随着循环次数的增加而降低。     

氯盐环境下纤维编织网增强混凝土拉伸性能

通过拉伸试验研究了氯盐干湿、氯盐冻融循环和常规环境下纤维编织网层数、种类以及氯盐浓度和循环次数等因素对纤维编织网增强混凝土（纤维/混凝土）拉伸性能的影响。结果表明：三种环境下,增加纤维编织网层数均可提高纤维/混凝土的拉伸性能,且碳纤维编织网较玄武岩纤维编织网的增强作用更明显;氯盐浓度、干湿或冻融循环次数对纤维/混凝土拉伸极限荷载影响不明显;常规环境和氯盐干湿循环下,掺入短切聚乙烯醇（PVA）纤维和耐碱玻璃（AR-glass）纤维均可以提高纤维/混凝土的拉伸极限荷载;氯盐冻融循环下,掺入短切PVA纤维的纤维/混凝土的拉伸极限荷载未有提高,而掺入短切AR-glass纤维的纤维/混凝土的拉伸极限荷载增大。     

硫酸环境作用下粉煤灰混凝土性能劣化时变规律

为了评价硫酸腐蚀对粉煤灰混凝土的性能劣化程度,研究了粉煤灰掺量(0%、20%、30%、40%)、酸液pH值(2、4)与干湿循环腐蚀对混凝土质量损失、抗压强度以及酸性化腐蚀深度的影响。通过回归分析,建立了质量损失与强度变化规律演化方程,基于Fick第一定律,求解了酸性化速度系数。结果表明:掺入20%粉煤灰的混凝土抗硫酸腐蚀性能最佳;混凝土性能的劣化随着腐蚀龄期的延长、pH值的降低而增大,硫酸—干湿循环耦合腐蚀对混凝土性能的劣化程度高于硫酸溶液浸泡腐蚀;硫酸环境下混凝土质量损失与强度变化规律的时变方程可用一元三次方程Δy=A0+A1t+A2t2+A3t3进行表征;酸性化速度系数K与粉煤灰掺量、硫酸pH值呈指数关系。     

玄武岩-聚乙烯醇混杂纤维水泥基材料的耐久性研究

确定了玄武岩-聚乙烯醇混杂纤维水泥基材料的最优配合比,将玄武岩-聚乙烯醇混杂纤维水泥基材料与普通C40混凝土在相同条件下进行耐久性对比实验。结果表明,玄武岩-聚乙烯醇混杂纤维水泥基材料在300次冻融循环后,质量损失不到1.5%,而在不到150次冻融循环中,普通C40混凝土的质量损失已接近5%;混杂纤维水泥基材料28和56 d的渗透系数为普通C40混凝土的53%和26%,混杂纤维水泥基材料具有较强的抗渗透能力,抗渗性随着龄期增长逐渐增强;碳化时间<28 d时,混杂纤维水泥基材料的碳化深度大于普通C40混凝土,但碳化时间56 d时,混杂纤维水泥基材料的碳化深度为普通C40混凝土的90%;混杂纤维水泥基材料28和56 d的电通量分别为普通C40混凝土的65%和49%,混杂纤维水泥基材料的抗氯离子性能明显高于普通C40混凝土。玄武岩-聚乙烯醇混杂纤维水泥基材料的各项耐久性指标均优于普通C40混凝土。     

硫酸盐干湿交替对碳纤维增强环氧树脂-混凝土界面粘结性能的影响

为了研究硫酸盐腐蚀对碳纤维增强环氧树脂复合材料（CF/EP）-混凝土界面性能退化的影响。通过硫酸盐干湿交替加速腐蚀试验模拟硫酸盐环境,对硫酸盐腐蚀下CF/EP-混凝土界面粘结性能退化规律进行了研究。结果表明：硫酸盐干湿交替作用对CF/EP-混凝土界面的破坏形态影响较大;界面粘结性能（峰值剪应力、极限承载力和初始剪切刚度）随腐蚀时间呈先小幅增加后加速下降的趋势。在试验和已有界面理论的基础上,提出了考虑腐蚀时间的界面粘结-滑移模型,通过模型预测数据与试验数据的对比分析,该模型能够很好反映硫酸盐干湿交替作用下界面粘结性能退化规律。     

钢纤维对玄武岩纤维编织网增强混凝土板双向弯曲性能的影响

为了研究钢纤维对玄武岩纤维网格布增强混凝土方板双向受弯性能的影响,借鉴欧洲EFNARC标准,利用四边简支方板试验,分别对素混凝土方板、玄武岩纤维网格布增强混凝土方板、钢纤维增强混凝土方板及钢纤维与玄武岩纤维网格布混杂增强混凝土方板的弯曲性能进行研究,同时与传统钢筋网混凝土方板的弯曲性能进行对比,分析了网格布对混凝土方板的双向增强效果,探讨了钢纤维与玄武岩纤维网格布混杂使用代替传统钢筋网的可行性。结果表明:玄武岩纤维网格布可以改善方板的内力重分布,显著提高其承载力,但是破坏时脆性特征明显;钢纤维与玄武岩纤维网格布混杂使用表现出显著的正混杂效应,方板的韧性明显提高;在正常使用极限状态下,30 kg/m3的钢纤维与玄武岩纤维网格布混杂方板的弯曲性能高于传统钢筋网混凝土方板,说明钢纤维与玄武岩纤维编织网混杂使用可以代替传统钢筋网。      

混杂FRP加固腐蚀混凝土柱恢复力模型研究

研究外贴纤维增强聚合物（Fiber Reinforced PolymerFRP）、钢筋腐蚀对混凝土柱恢复力特性的影响,是研究服役混凝土结构抗震性能的重要内容。该文根据混杂FRP加固腐蚀混凝土柱抗震性能试验结果,在完好钢筋混凝土构件的截面分析和Clough滞回规则的基础上,提出了混杂FRP加固腐蚀混凝土柱恢复力模型及其骨...     

盐渍土腐蚀环境下微胶囊自修复混凝土抗腐蚀性能研究

为保证盐渍土地区混凝土服役寿命,区别于以往自修复材料,合成一种可以感知外界腐蚀离子并释放内部修复剂的微胶囊,以合成温度为变量控制引发剂分解速率得到了具有不同包裹率的微胶囊。选取其中包裹率、腐蚀离子响应能力较好的微胶囊,将其掺入混凝土中得到具有自修复功能的混凝土。改变微胶囊掺量测试混凝土动弹性模量及抗腐蚀能力。研究结果表明：在合成温度为75℃环境条件下的微胶囊包裹率优于65和85℃环境条件下。盐渍土-硫酸盐干湿循环腐蚀下混凝土构件动弹性模量均呈现先上升后下降的趋势,在20次干湿循环后未掺微胶囊的混凝土动弹性模量急速下降,在40次干湿循环后为掺微胶囊的混凝土内部侵入了更多的硫酸盐,试验拌制的自修复混凝土具有良好的抗硫酸盐侵蚀能力,对实际工程中建筑结构应对硫酸盐腐蚀具有十分重要的借鉴意义。     

干湿循环作用对混凝土抗氯离子渗透侵蚀性能的影响

为了加速模拟海洋潮差区环境对混凝土耐久性能的影响,掺入矿粉和纳米改性矿物掺合料,研究了氯盐干湿循环作用对混凝土抗氯离子侵蚀性能及微观结构的影响,并将干湿循环试验与常规浸泡试验进行了对比。结果发现,干湿循环作用粗化了混凝土试件表层孔结构,增大了孔径>50 nm的孔隙含量,显著提高了自由及总氯离子浓度;掺入纳米改性矿物掺合料能降低混凝土内部孔隙率,减少有害孔含量,提高混凝土内部氯离子结合能力;干湿循环60天后混凝土表层Ca（OH）₂逐渐被消耗,生成了Friedel盐和CaCO₃。      

纤维混杂效应对混凝土复合材料的力学及耐久性能的影响

以研究混杂纤维增强混凝土复合材料的力学性能及耐久性能为出发点,利用碳纤维(CF)、钢纤维(UR)和玻璃纤维(SGF)3种纤维按照不同比例掺入混凝土中,制作了对比试件CF-1和混杂纤维混凝土试件CF-2、CF-3及CF-4.通过弯拉强度试验和弯曲韧性试验,分析了混杂纤维混凝土试件的抗折性能和抗弯性能;通过抗冻试验和抗渗试...     

The co-existence of thaumasite and ettringite in concrete exposed to magnesium sulfate at room temperature and the influence of blast-furnace slag substitution on sulfate resistance

The effects of Type I Portland cement replacement by 45% or 72% blast-furnace slag on the sulfate resistance of laboratory concretes were analyzed by microstructural investigation. The concretes investigated were stored in water or in magnesium sulfate solutions for 23 years under laboratory conditions. For those stored in water only surface layers of carbonation and decalcification were observed. Concretes exposed to sulfate solutions formed brucite, ettringite and thaumasite. Thus, thaumasite was observed to form in concretes stored under laboratory conditions. In all cases both ettringite and thaumasite were found to co-exist in the damaged zones. However, the thaumasite appears to be moving in from the exterior after initial formation of ettringite, and has not resulted in the massive destruction of the hydrated matrix as has been found elsewhere at lower temperature exposures. Slag replacement was observed to be an effective means of conferring resistance to sulfate attack. Although the concretes studied were prepared at a W/cm (water-to-cementitious materials) ratio of 0.50, the depths of attack observed were comparable to those observed in concrete prepared at w/c=0.45 using ASTM Type V (SRPC) cement alone.     

高温作用后聚丙烯纤维混凝土的抗冻性

本文开展了高温作用后的聚丙烯纤维混凝土冻融循环试验,研究分析了高温与冻融循环耦合作用下聚丙烯纤维混凝土抗冻性能的退化规律,采用扫描电子显微镜(SEM)研究分析了聚丙烯纤维混凝土细微观结构损伤特征。研究表明,高温对混凝土的抗冻性有显著影响,经历温度越高,混凝土抗冻性越差。高温和冻融循环的耦合作用加速了混凝土动弹性模量和抗压强度的衰减,掺入适量的聚丙烯纤维能够改善和提高混凝土高温损伤后的抗冻性能。     

Increased sulfate resistance of ggbs concrete in the presence of carbonate

Significant occurrence of the thaumasite form of sulfate attack (TSA) has only been identified in concrete containing carbonate aggregate, leading to a perception that the presence of calcium carbonate is undesirable in concrete exposed to sulfate attack. This paper reports on how the addition of a small percentage of calcium carbonate or calcium sulfate, affects the sulfate resistance of concrete containing ground granulated blastfurnace slag (ggbs). Three test methods were employed to assess sulfate resistance (all at 20 °C):

• Cubes were immersed in magnesium and sodium sulfate solutions and monitored for corner-loss and strength-loss, over six years.

• Mortar was sieved from fresh concrete and used to make prisms. These prisms were immersed in magnesium and sodium sulfate solutions and their expansions monitored for up to six years.

• In accordance with a draft of a European Standard for sulfate resistance, mortar prisms were prepared and monitored for expansion for one year.

• It was found that both calcium carbonate and calcium sulfate additions, had a consistent beneficial effect on the resistance of ggbs concrete to conventional sulfate attack, both in respect to expansion and in respect of disintegration. The paper discusses possible mechanisms for the improved resistance.

     

Sulfate attack and role of silica fume in resisting strength loss

This paper presents a detailed experimental study on the sulfate attack of Portland cement mortars, and the effectiveness of silica fume in controlling the damage arising from such attack. The test solutions used to supply the sulfate ions and cations were 5% sodium sulfate solution and 5% magnesium sulfate solution. Tap water was used as the reference solution. The main variables investigated in the study were the water/cementitious materials ratio, and the level of cement replacement. Compressive strength measured on 50 mm cubes was used to assess the changes in the mechanical properties of mortar specimens exposed to sulfate attack for 510 days. X-ray diffraction and differential scanning calorimetry were used to evaluate the microstructural nature of the sulfate attack. The test results showed that the presence of silica fume had a beneficial effect on the strength loss due to sodium sulfate attack. The best resistance to sodium sulfate attack was obtained with a SF replacement of 5–10%, but even then, a strength loss of 15–20% can be expected. On the other hand, mortars with silica fume were severely damaged in the magnesium sulfate environment. Further, the compressive strength loss actually increased with increasing SF content. The test results thus showed clearly that the use of SF in concrete exposed to magnesium sulfate solution is not recommended. The test results also showed that the w/cm ratio is the most critical parameter influencing the resistance of concrete to sulfate attack. All the tests reported in the study were carried out at 20 ± 1 °C.     

考虑氯离子侵蚀与混凝土碳化的公路桥梁时变可靠度分析

基于国内外对氯离子侵蚀和混凝土碳化环境下钢筋锈蚀速率的最新研究成果,建立了混凝土构件在氯离子侵蚀下考虑坑蚀和在混凝土碳化下考虑平均锈蚀的弯曲抗力退化模型,用Monte Carlo方法和统计回归法编制了退化钢筋混凝土构件及系统的时变可靠度计算程序。以北京地区一座公路桥为算例,结果表明:在氯离子侵蚀下考虑坑蚀的桥梁承载能力时变可靠度在30年左右即下降到设计目标可靠度,在混凝土碳化下考虑平均锈蚀的桥梁承载能力时变可靠度在50年左右即下降到设计目标可靠度,从而需要补强,这表明考虑主筋锈蚀后我国钢筋混凝土公路桥一般达不到100年设计使用期;对因主筋锈蚀导致混凝土保护层胀裂而言,构件达到抗裂正常使用极限状态远远早于达到承载能力极限状态,建议将混凝土保护层开裂时间作为桥梁检查/维修参考点。     

纤维/高强混凝土抗冻性能试验

通过纤维/高强混凝土快速冻融循环试验,从试件外观损伤形态、相对动弹性模量、抗冻等级、抗冻耐久性指数角度,研究了不同纤维体积分数的玄武岩纤维、纤维素纤维和不同纤维长度的玄武岩纤维对C60高强混凝土抗冻性能的影响。结果表明,加入玄武岩或纤维素纤维可改善C60高强混凝土的外观剥落损伤程度。C60高强混凝土的抗冻性均随玄武岩纤维（长度为18 mm）和纤维素纤维体积分数的增大而提高,在体积分数0.10vol%~0.20vol%内,前者的提高程度远大于后者,玄武岩纤维/高强混凝土能在更严酷的寒冷环境中满足更久的使用时间。玄武岩纤维长度的改变对C60高强混凝土的抗冻性影响较大,相对于18 mm长度,6 mm和30 mm长度的玄武岩纤维对C60高强混凝土抗冻性能改善作用很有限。      

Model for practical prediction of natural carbonation in reinforced concrete: Part 1-formulation

A model is proposed for prediction of natural carbonation in reinforced concrete (RC) structures, and is potentially applicable to existing and new RC structures. The major components of the model comprise mathematical functions applied to predict the influence of concrete composition, and environmental factors on natural carbonation.This paper introduces the model concept and explains its structure including derivation, optimization and calibration. Over 163 data sets taken from a 10-year carbonation study were used in the model development and calibration. Only the experimental data that were based on outdoor natural exposure environment were employed in this research. Also in this study, the proposed model is compared with fib-Model Code 2010 using carbonation predictions generated from 346 data sets involving real world, highway structures. It is shown that the proposed model is comparably accurate and involves mainly basic tests with no major anticipated costs.     

Freezing and de-icing salt resistance of blast furnace slag concretes

This paper presents the results on investigations made into a concrete containing cement rich in granulated blast furnace slag (57%). Whereas slag cement concretes have proved successful in structures subjected to chemical attack, their use in structures subjected to freezing and de-icing salt attack is a problem of numerous investigations. The results concerning water/cement ratio and air content in concrete mixtures are presented in this paper. The effect of polypropylene microfibre addition to the concrete was also analysed. The research shows that air entraining the concrete mix up to the level of 5–6% guarantees obtaining high resistance to the action of de-icing agents, even at relatively high values of water/cement ratio. Apart the air content, the addition of microfibre to the concrete mixture was highly effective. For these samples scaling was the lowest. Phase composition investigations confirm that calcite and aragonite (as the carbonation products) were present on the surface of concrete.     

Chemical and mineralogical alterations of concrete subjected to chemical attacks in complex underground tunnel environments during 20–36 years

This paper investigates the chemical and mineralogical alterations of concrete in underground tunnel structures built from 1980 to 1996, located on the China's east seashore. The underground water around the tunnels had once been treated to be not or little aggressive. However, the complex environments in the tunnels had increased the aggressiveness of certain ingredients, thus causing chemical attacks. The chlorides in the leakage underground water cause chloride attack, and the NaCl crystallizations on the surface of the C50 pre-cast concrete segments induce a deeper chloride contamination. When the concrete suffers flowing leakage water, calcium leaching also occurs, leading to decalcification and magnesium incorporation. Under this circumstance, C50 pre-cast concrete shows a higher resistance compared with C30 cast-in-place concrete, mainly due to the low water to binder ratio. Within the C30 cast-in-place concrete facing concentrated leakage water and NaCl crystallizations, a strong magnesium chloride attack is observed. Besides the materials factors, the environmental factors, including the high concentrations of both chloride and magnesium ions, the removal timing of calcium ion, and the water saturation, are believed to take responsibility for the magnesium chloride attack.