This study developed a thermal-alkaline activation method to enhance the activity of recycled concrete powder (RCP). The physical and chemical properties of RCP were characterized using X-ray Fluorescence, X-ray Diffraction, scanning electron microscope (SEM), and thermogravimetric-differential scanning calorimetry tests, which determined the calcination temperature range for RCP and compared the microstructural morphology and phase changes of RCP before and after calcination. The unconfined compressive strength (UCS) tests were conducted to evaluate the effect of calcination conditions (i.e., conditioning temperature range: 650-800 degrees C, conditioning time: 15-45 min, preblending NaOH percentage: 0-8 %) on the geopolymer strength. Finally, the strength growth mechanism of RCP-derived geopolymer was investigated through SEM and energy dispersive spectroscopy tests. The results indicated that preblending 6 % sodium hydroxide with RCP and calcinating them at 750 degrees C for 45-minute yielded the highest USC growth rate of geopolymer. Under this calcination condition, the 28-day UCS of the RCP-derived geopolymer achieved 20.9 MPa, which was almost five times greater than that of the uncalcined geopolymer. To balance the UCS growth and energy consumption, a calcination scheme with 750 degrees C calcination temperature and 15-minute calcination duration was recommended for precursor treatment. After calcination with preloaded NaOH, the amount of amorphous material in the RCP significantly increased, which resulted in an increasing amount of gels produced after the geopolymerization reaction.

This paper proposes a modified testing method for the determination of chloride ion concentration of concrete, which is a significant parameter for the durability design and service life prediction of concrete structures in marine environment. The existence of sulphate ions and allied cations in the seawater not only alter the diffusion and distribution of chloride ions in the concrete, but also effect the accuracy of chloride ion concentration measured by silver nitrate titrate method. In the modified testing method, barium nitrate was used to eliminate the adverse effects of sulphate ions. Besides, the influences of barium nitrate addition and allied cations on both free and total chloride ion concentration test results were investigated respectively. The results demonstrate that the sulphate ion released from ettringite in dilute nitric acid, leading to a larger tested chloride ion concentration, and the error became larger with increasing sulphate ion concentrations. The addition of barium nitrate in immersion process reduced the error in the measurement of total chloride ion concentration. However, for determination of free chloride ion concentration, the addition of barium nitrate resulted in a lower test result since part of free chloride ions were replaced with sulphate ions in ettringite. Thus, addition of barium nitrate is only suitable for the determination of total chloride ion concentration, and traditional water -soluble method is more accurate for free chloride ion concentration measurement.

服役于海洋环境中的混凝土常受到氯盐-硫酸盐共同侵蚀,结构表面也常处于干湿交替环境中.以24h为一个循环,研究不同干湿交替条件下受氯盐-硫酸盐侵蚀的混凝土中结合氯离子含量及结合特性,通过X射线衍射(XRD)、热重分析(TG-DTG)揭示结合机理.结果表明:同一腐蚀方式下,结合氯离子含量随着腐蚀时间的延长而增加.相同时间内,在腐蚀早期干湿比≤1的试件中结合氯离子浓度要大于干湿比＞1的试件,腐蚀后期则相反.经过30d干湿循环后,试件中结合氯离子低于长期浸泡状态.复合溶液同时侵蚀时,采用Freundlich等温吸附曲线来描述自由氯离子与结合氯离子间的关系更合适.

为探究刚性道面动态弹性模量的变化规律,使用有限元软件建立某机场道面实体模型,以HWD的4种落锤荷载(200 kN、250 kN、300 kN和350 kN)对静态弹性模量分别为35 GPa、40 GPa、45 GPa时的刚性道面进行冲击模拟,取荷载中心弯沉值对动态弹性模量进行换算.通过分析,得到4种落锤荷载对应动态弹性模量值与静态弹性模量的关系曲线,分析刚性道面动、静模量相同时所需HWD落锤动荷载随混凝土板的静态弹性模量变化规律;拟合得到不同静态模量下刚性道面动、静模量关系函数;结合模拟规律和现场实测结果,当板体静态模量为40 GPa时,将HWD落锤荷载设置为335 kN可使刚性道面动态弹性模量与静态弹性模量大小基本一致,此时该机场刚性道面静态弹性模量可通过HWD无损检测获取.

为研究机场土面区在主起落架作用下的承载力,根据规范制备以黏性土为主的填料.使用便携式落锤弯沉仪经实验得出填料在不同密实度下与动态弹性模量之间的关系,根据函数曲线关系及相关研究结果,建模计算当填料处于3种不同密实度时,B737-800飞机在滑行和着陆两个阶段冲出跑道时的作用结果.计算表明:随着填料密实度值的增加,土面区的承载力也在增加;当密实度不足87％ 时,填料在荷载作用下易出现剪切破坏,导致主起落架陷入土面区;当密实度达到87％ 时,荷载作用产生的竖向变形最小,承载能力最大,土面区可承担主起落架作用.

This study investigated the stability of bound chloride ions in the cement mortars incorporating supplementary cementitious materials (SCM) during the electrochemical chloride extraction (ECE) process. The effect of the replacing ratio of fly ash (FA) and silica fume (SF) and sulfate concentration on the chloride binding and distribution after ECE treatment was studied using water and acid-soluble methods, X-ray diffraction (XRD) analysis and thermogravimetric analysis (TGA). The results showed that the concentration of the bound chlorides in the SCM incorporated cement mortars depended heavily on the content of Al2O3 and the pH of the pore solution. Without ECE treatment, an increase in the FA content increased the concentration of bound chlorides while the addition of SF significantly decreased the chloride binding capacity. During ECE treatment, however, the stability of bound chlorides declined with increasing the FA content but increased with increasing the SF content under an electric field. It was also found that the presence of sulfate ions reduced the content of the chemically bound chlorides residing in Friedel's salts (FS) but had a negligible influence on the physically bound chlorides absorbed by calcium silicate hydrate (C-S-H gel). (C) 2020 Elsevier Ltd. All rights reserved.

钢筋锈蚀是造成混凝土结构耐久性下降的首要因素.介绍了钢筋锈蚀破坏原理、钢筋钝化膜的形成及其破坏机理.分析了近些年国内外对钢筋腐蚀的研究现状.

混凝土中氯离子的结合会影响其侵蚀进程.且结合氯离子并不稳定,在酸化、碳化、化学侵蚀与通电作用等情况下会失稳释放,从水泥结合氯离子的机理、结合能力及结合氯离子稳定性等方面对中外研究现状进行综述.提出了对于某些因素需要建立更合理的评价标准,需要深入研究多因素耦合作用及降低失稳氯离子对钢筋腐蚀危害的研究建议.

钢箱梁正交异性板在桥梁建设中应用广泛,对此类结构疲劳损伤进行无损检测并发现病害特征,有利于及时的进行现场维修加固.该文使用高倍数显微相机进行疲劳微裂纹的检测,提出基于条件随机场(CRFs)的金属疲劳微裂纹检测算法,该方法使用单个像素的表观特征来进行裂纹判别,同时也考虑其他像素标注值间的影响,从而很好地抑制离散噪音点.通过多种表观特征和机器学习方式自动识别出区分性最强的特征从而加以选择使用.实验结果表明,基于CRFs模型的裂纹检测方法对于试件6～16万次的图像裂纹宽度测量与人工测量值非常接近,这为钢箱梁正交异性板疲劳损伤快速检测提供可靠的分析手段.

跨座式单轨列车在重庆推广运营过程中出现了严重的偏磨损现象并引发一系列安全、环境、运行成本等问题.为探索其偏磨机理及控制方法,采用ABAQUS软件建立了走行轮轮胎的有限元模型,通过轮胎模态试验验证了其建模方法的有效性,并基于行波理论,利用有限元方法计算了考虑走行轮轮胎滚动效应的工作模态,同时探索了走行轮轮胎工作模态与偏磨的关联关系.并根据轮胎结构与模态的内在关系,提出了通过改变轮胎结构参数来控制走行轮轮胎偏磨的控制方法.分析结果表明:通过合理改变0°带束层弹性模量可以降低走行轮一阶扭转前后行波差,有效降低跨座式单轨走行轮的偏磨.

超高层三塔连体建筑的主塔由于两子塔和裙楼的干扰效应,其风荷载的确定相比单个超高层建筑更加复杂.本文主要基于CFD方法,采用了标准k-ε、RNG k-ε、SST k-ω、大涡模拟(LES)四种不同的湍流模型对某超高层三塔连体建筑进行了不同风向角下的数值模拟计算,并与风洞试验数据作对比,验证了数值模拟的有效性.结果表明:不同湍流模型对该三塔连体建筑上游影响并不明显,k-ε和SST k-ω模型计算结果较为接近,尾流呈现对称分布,而RNG k-ε和LES结果较为接近,尾流呈现非对称涡状分布;不同湍流模型计算得到的迎风面风压值大致相同,背风面和侧风面风压系数值有一定波动;主塔迎风面风压极大值出现在塔高2/3高度左右,两侧同一高度处出现极大值,且与风洞实验规律一致,屋顶棱角尖锐部位压力线较密集;整体体型系数的取值需要考虑主塔两侧的子塔遮挡效应.

For the anti fatigue performance of reinforced steel orthotropic plate test ,two methods of hybrid glassy car-bon fiber (C/GFRP) and crack welding are used .The results show that hybrid glassy carbon fiber cloth and crack welding test piece show the same fatigue failure form of steel structure as the test piece without reinforcing reinforcement .The structure steel degree degradation can be divided into three stages ,and the two reinforcement methods can effectively im-prove the structure life .

混凝土配合比设计方法并不统一,我国的配合比设计认为骨料是干燥状态,美国的配合比设计认为骨料是饱和面干状态.因此,在实际的计算过程中,骨料含水率和吸水率对于混凝土配合比设计产生了不同的作用,按照骨料的两种含水状态分别进行不同强度等级的混凝土配合比设计,通过强度、抗碳化结果,分析骨料含水状态对混凝土配合比的影响.结果显示,饱和面干状态相当于增加了混凝土单位体积用水量,对保证混凝土强度及耐久性不利.

The paper aimed at certain three -span variable section cross -section twin pylons and single cable plane pres-tressed concrete low -pylon cable -stayed bridge to conduct study,considering under different closure height difference, the influence of forced closure on entire deflection and internal force after the bridge completed,the difference of bridge en-tire alignment and internal force under every closure height difference were analyzed,which can provide reference for the similar bridge construction.

中国大陆与台湾地区的普通混凝土配合比设计方法有差异,通过步骤分解和实例演算,将当中的差别更清晰的呈现出来,因所处环境及原材料不同,两种方法不能比较优劣.但如含气量等细节差异还希望引起从业者关注.

文章针对运营阶段钢箱梁的结构特点,提出一种根据实测数据拟合温度梯度公式的方法,以此弥补仅按照规范计算温度梯度效应的不足,结果证明,此方法获得的温度梯度模式,在计算运营阶段刚箱梁的温度梯度作用时更为精准.

混凝土配合比设计方法并不统一，我国的配合比设计认为新拌普通混凝土中空气含量的值是固定的，美国的配合比设计认为这一值与粗骨料的最大粒径相关。含气量的不同将直接影响混凝土配合比的确定，因此，采用两种方法计算配合比，并分别测定空气含量及28 d强度，结果表明，新拌混凝土中空气含量随着粗骨料最大粒径的增加而减小，这一变化较明显，不能被忽略。

通过改变矿渣和硅灰的掺量,制备4个系列、10组不同配合比,进行抗压强度实验,得到不同配合比的混凝土强度值.结果发现:单掺矿渣或单掺硅灰时,混凝土的强度值随着掺量的增加出现先增加后降低的趋势;相同掺量时,单掺硅灰对混凝土的强度提高效果好于单掺矿渣;复掺两种矿物掺合料,不能提高混凝土的强度.若需要通过掺入矿物掺合料提高混凝土强度,建议掺加掺量为10％的硅灰.

混凝土养护剂在国内应用还不广泛,但随着水资源日趋匮乏以及对环境保护和人力资源价值重视程度的日益提高,未来有广阔的应用空间.试验以水玻璃和氢氧化钙为基础材料配置6组养护剂,并将试块在浸泡养护、覆膜养护、自然养护、标准养护和喷洒养护五种养护条件下进行养护.通过测试试块的抗压强度、抗碳化能力和保水率来检验养护效果.结果表明A2型、A5型养护效果良好,可以应用到非承重的混凝土结构养护中.

通过控制掺入硅灰和矿粉的量,制备了3个系类10种不同配比的混凝土.测试混凝土在循环制度一(干燥6h,浸泡18h)和循环制度二(干燥24h,浸泡48h)的抗氯离子渗透性能.实验结果显示:干湿循环频率越慢,混凝土内部的氯离子浓度越低;混凝土的抗氯离子渗透能力随着单掺矿物掺合料掺量的增加而增加,掺硅粉混凝土的抗氯离子能力更好,当硅粉的量为20％时,混凝土内部的氯离子浓度最低;双掺硅灰和矿粉不能提高混凝土的抗氯离子渗透能力;混凝土内部的氯离子浓度随着深度的增加而降低.