Passive smart self-repairing concrete beams by using shape memory alloy wires and fibers containing adhesives

An innovative approach to increase structural survivability of concrete and maintain structural durability of concrete was developed in case of earthquakes and typhoons. This approach takes advantage of the superelastic effect of shape memory alloy(SMA) and the cohering characteristic of repairing adhesive. These SMA wires and brittle fibers containing adhesives were embedded into concrete beams during concrete casting to form smart reinforced concrete beams. The self-repairing capacity of smart concrete beams was investigated by three-point bending tests. The experimental results show that SMA wires add self-restoration capacity,the concrete beams recover almost completely after incurring an extremely large deflection and the cracks are closed almost completely by the recovery forces of SMA wires. The number or areas of SMA wires has no influence on the tendency of deformation during loading and the tendency of reversion by the superelasticity. The adhesives released from the broken-open fibers fill voids and cracks. The repaired damage enables continued function and prevents further degradation.

The Effects of Degradation Phenomena of the Steel-Concrete Interface in Reinforced Concrete Structures

Reinforced concrete (RC) constructions are the innovation of sustainable constructions replacing masonry constructions. Despite this, the use of concrete and steel to improve the performance of structural members in service is a recurring problem due to the immediate or overtime appearance of cracks. The objective of this work was therefore to assess the damage phenomena of the steel-concrete interface in order to assess the performance of an RC structure. Samples of approximately 30 cm of reinforcement attacked by rust were taken from broken reinforced concrete columns and beams in order to determine the impact of corrosion on high adhesion steel (HA) and therefore on its ability to resist. The experimental results have shown that the corrosion degradation rates of reinforcing bars of different diameters increase as the diameter of the reinforcing bars decreases: 5% for HA12;23.75% for HA8 and 50% for HA6. Using the approach proposed by Mangat and Elgalf on the bearing capacity as a function of the progress of the corrosion phenomenon, these rates made it possible to assess the new fracture limits of corroded HA steels. For HA6 respectively HA8 and HA12, their initial limit resistances will decrease by 4/4, 3/4 and 1/4. Based on the results of this study and in order to guarantee their durability, an RC structure can be dimensioned by taking into account the effects of reinforcement corrosion.

Freeze-thaw bond properties of new-old concrete

Using composite cubic specimens of new-old concrete,the bond splitting tensile strength and failure mechanism for the interface of new-old concrete in saturating state were explored when exposed to freeze-thaw cycling. Specimens were experienced for 0,25,50,75,100 and 125 freezing cycles. The roughness and adhesion agent including cement paste,cement mortar and cement paste with 10 percent of UEA expanding agent were also investigated. The test results indicate that the bond splitting tensile strength decreases with increased numbers of freezing-and-thawing cycles. The roughness and adhesion agent have different effects on the bond strength.

Bond Strength of Bamboo Reinforcement in Light Weight Concrete

Bamboo reinforced concrete as a building material is expected to be an alternative to steel reinforced concrete. Due to the fact that steel is not renewable and polluting steel mills are fairly high. The bond strength is a major concern for the natural fiber used as reinforcement in structural composites. This paper reports study on the bond strength of bamboo reinforcement in concrete, to determine the adhesion reinforcement in concrete often do by the pull-out test. The research objective was bond strength of lightweight concrete and bamboo reinforcement. The test used light weight concrete with foam additives klerak. Bamboo slats were coated with paint and sprinkled with sand. The results obtained showed that the bond strength bamboo 60% of the bond strength steel.

An Autonomous Wall-Climbing Robot for Inspection of Reinforced Concrete Structures: SIRCAUR

A wall-climbing inspection robot has been designed to climb on safety-critical concrete structures by adhering to reinforcement steel bars(rebars)using permanent magnets to generate the adhesion forces.Simulation and experimental validation have been performed to determine the optimum flux focusing magnet configurations with the robot operating on 30–35 mm of concrete cover over rebars arranged in different patterns.The goal of adhesion force optimization is to be able to carry a ground-penetrating radar(GPR)sensor which detects rebar corrosion,concrete delamination,and concrete cover deterioration.The autonomous robot uses an ultra-wide band localization system and GPR data to control its motion trajectories to avoid regions where there is an insufficient density of rebars.Nondestructive testing(NDT)inspection data acquired by GPR are transmitted wirelessly to a ground station for processing and monitoring by NDT technicians.

Artificial Neural Network Model for Predicting Ultimate Tensile Capacity of Adhesive Anchors

To predict the tensile capacity of adhesive anchors, a multilayered feed-forward neural network trained with the back-propagation algorithm is constructed. The ANN model have 5 inputs, including the compressive strength of concrete, tensile strength of concrete, anchor diameter, hole diameter, embedment of anchors, and ultimate load. The predictions obtained from the trained ANN show a good agreement with the experiments. Meanwhile, the predicted ultimate tensile capacity of anchors is close to the one calculated from the strength formula of the combined cone-bond failure model.

混凝土外墙面装饰用改性环氧树脂胶粘剂制备及应用

为了提高建筑外墙装饰用混凝土胶粘剂性能。以环氧树脂为原料,以乙酸乙酯为稀释剂,以三苯基膦盐为固化剂制备了建筑外墙装饰用混凝土环氧树脂胶粘剂,并对其性能进行了测试表征。结果表明,冷环境下,随着温度降低混凝土与砖板粘接试件的粘接强度、剥离强度不断下降,冲击强度极速下降,而剪切强度变化并不显著;热环境下,随着温度升高试件的粘接强度、剪切强度、冲击强度并未显著变化,而剥离强度缓慢下降;湿环境下,随着湿度增加试件的粘接强度、剥离强度、剪切强度、剪切强度均明显下降;随着挠度增大,试件的抗压强度呈现为显著变大趋势;环氧树脂胶粘剂表观性能与环保性能表现优异,且整体承载力与抗压强度明显提高。

混凝土加固施工中的环氧树脂胶改性及效果研究

针对传统混凝土施工中环氧树脂胶质脆韧性不足和高温易流挂的问题,提出通过气相白炭黑(MSD)对传统环氧树脂结构胶进行改性。试验结果表明,在酚醛胺固化剂T-31掺量为15%,聚酰胺固化剂PA掺量为40%,硅烷偶联剂KH-792的掺量为3%,超细石英砂掺量为40%,纳米碳酸钙掺量为20%,MSD掺量为3%;短切碳纤维掺量为6%配比下制备的结构胶性能最佳。14 d压缩强度、拉伸强度、正拉粘接强度和拉伸抗拉强度分别为81、34、5.5和18.5 MPa。表现出良好的阻裂粘接性能,可以在桥梁混凝土加固中发挥重要作用。

缓凝粘合剂在建筑结构缓粘结预应力混凝土中的应用

为研究建筑结构缓粘结预应力混凝土中缓凝粘合剂的应用配比,将固化剂与硅胶按照2∶100的比例配制成胶液,浇注后使其固化获得制备好的硅胶模具,应用试验材料制备缓凝粘合剂,设计10种邻苯二甲酸二丁酯与环氧树脂的混合比例,制备10种不同的样品,分2批配制缓凝砂浆,用于包裹预应力筋,当混凝土试块浇筑9 d后,对缓粘结预应力筋实施张拉操作。依照配比的顺序共制备30个缓粘结预应力混凝土试件。结果表明,当邻苯二甲酸二丁酯加入量为25、20 g,环氧树脂加入量为120、125 g时,缓粘结预应力混凝土试件的力学性能与抗震性能均较好。

超高强度混凝土钢纤维黏结性能研究

钢纤维与混凝土基体的黏结性能是应力转换和裂缝控制的关键,能显著影响超高性能混凝土(UHPC)的力学性能。为增强钢纤维黏结性能,提出利用微生物诱导方解石沉淀(MICP)技术,对钢纤维表面进行预处理。研究结果表明,MICP不仅在钢纤维表面生成碳酸钙晶体,导致钢纤维粗糙度增加,还提高了钢纤维的黏结强度和拉拔性能,使水化产物附着在纤维表面。微观结果表明,MICP技术可以增强钢纤维与基体之间的黏合行为。因此,采用MICP技术处理钢纤维可使UHPC的抗压强度和抗折强度分别提高16%和50%。将MICP技术用于超高强度混凝土中有助于提高钢纤维黏结性能。

SBS改性沥青再生废旧聚氨酯混凝土的配制及旧料掺量的影响评价

聚氨酯混凝土是一种新型铺装材料,研究废旧聚氨酯混凝土的再生利用对该材料的推广应用意义重大。首先,通过聚氨酯混凝土室内模拟老化制备了RPC;其次,选用0%、25%、30%、35%、40%、45%和50%7种RPC掺配比例配制了AC-13型SBS改性沥青再生废旧聚氨酯混凝土;再次,对不同RPC掺量下的SBS改性沥青再生RPC进行了路用性能评价;最后,对SBS沥青-石灰岩、SBS沥青-老化聚氨酯和老化聚氨酯-石灰岩3种界面的黏附性能进行了测试,对比分析了RPC对路用性能影响的成因。结果表明,除50%RPC掺量的SBS改性沥青再生RPC外,其余6种RPC掺量的均满足相关技术要求,且随RPC掺量的增加,其高温性能减弱而低温性能和水稳定性增强;SBS沥青-老化聚氨酯和老化聚氨酯-石灰岩的界面黏附性能优于SBS沥青-石灰岩。

水泥改性水性环氧涂料的制备及性能

[目的]聚合物水泥防水涂料在应用于水工混凝土时的粘结强度亟待提高。[方法]将硅酸盐水泥作为第三组分对水性环氧涂料进行改性,研究了水泥掺量(占与石英共同组成的填料质量的10%~50%)对涂料力学性能和防护性能的影响。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和傅里叶变换红外光谱仪(FTIR)分析了水泥对水性环氧乳液的改性机理。[结果]在40%的水泥掺量下,涂层的力学性能和防护性能最优,粘结强度、拉伸强度和断裂伸长率分别为6.14 MPa、2.16MPa和156%,浸水、浸碱和冲蚀后未出现吸水溶胀现象,粘结强度下降和质量损失的程度最小。[结论]水泥的掺入明显改善了涂层的力学性能和防护性能,环氧乳液聚集包裹在石英砂、水泥及其水化产物周围,形成了以环氧乳液为主要成膜物质,石英砂、水泥及其水化产物为次成膜物质的互穿网络结构,CaCO_(3)的存在使网络结构更为致密。

环氧结构胶在混凝土裂缝修复中的影响及应用效果分析

分析了环氧基结构胶中的2种组分A、B的混合比例以及混凝土试件的裂缝宽度对开裂混凝土的抗压强度修复效果的影响。实验结果表明,当环氧基结构胶中的组分A和B的质量比是3:1时,环氧基结构胶在对开裂混凝土抗压修复效果相对显著,而环氧基结构胶在不同裂缝宽度下对开裂混凝土修复后的抗压强度的区别不大。通过有限元软件ABAQUS对开裂混凝土修补中环氧基结构胶的修复效果进行数值建模,发现经过环氧基结构胶修复后的混凝土试件的实际抗压强度与内部的应力分布一致,这也说明在对开裂混凝土的修复中,环氧基结构胶的作用非常重要。

环氧树脂胶粘剂对混凝土裂缝修复性能的影响研究

研究使用环氧树脂胶粘剂修复混凝土裂缝问题,分析环氧树脂胶粘剂对于混凝土结构力学性能的影响,使用丁腈橡胶改性环氧树脂,增加环氧树脂韧性,并与稀释剂、固化剂混合制备修复混凝土的环氧树脂,将该环氧树脂灌注在预制裂缝的混凝土试件中,通过万能试验机等设备测试修复前后试件的抗压、抗折强度变化,并验证丁腈橡胶用量对于修复效果的影响。结果表明,使用改性环氧树脂修复混凝土多种形式的裂缝,能够提升混凝土抗压、抗折强度的恢复率,降低液体向混凝土入渗的速度,提升混凝土的性能,同时在环氧树脂中添加丁腈橡胶8 phr能够提升修复的耐水性。

基于无机胶粘岩土的抗渗性能实验研究

为更好地剖析岩土渗透性能,以无机胶粘岩土为研究对象,提出相应的渗透性评价指标测定方法,测试了9个试样pH值,测定了试样的金属元素含量,开展抗渗实验,分析X射线衍射的成分。实验结果表明,岩土pH值普遍低于7,呈明显酸性,在提升岩土抗渗性能方面具有重要作用;岩土金属元素含量的变化,对岩土抗渗性能影响微乎其微;岩土渗透系数与抗渗标号之间存在负相关关系;氟硅酸钠的改变,会增加对岩土抗渗性能的影响程度。研究结果为相关人员提供有效的借鉴和参考。

一种环氧复合水工修复砂浆粘接固化强度研究

为实现对水工混凝土的有效修复,研究提出了一种基于环氧树脂的环氧砂浆修复材料,该材料主要由环氧树脂、T31固化剂、苄基缩水甘油醚692活性稀释剂等材料复合而成。将环氧砂浆与常规水泥砂浆相连接并养护一段时间,从胶固比、界面剂、养护时间等方面对该材料的修复性能加以验证。经实验研究发现,胶固比为1∶2的环氧砂浆具有最佳的修复性能,平均修复率约为82.06%,并且在酸碱溶液浸泡试验中体现出了较为理想的耐久性,具有一定的应用价值。

氯氧镁水泥结构胶研制及界面高温性能研究

首先对氯氧镁水泥的配比进行优化设计,通过考察改性氯氧镁水泥的力学性能、耐水性能和耐高温性能,辅助微观测试手段进行分析,从而确定氯氧镁水泥的最优配比,结果显示:当采用MgO/MgCl_(2)/H_(2)O摩尔比为9∶1∶10.9,氯氧镁水泥胶的力学性能最优;当羟基乙酸掺量为2%时,软化系数提高到0.88,明显改善氯氧镁水泥的耐水性能,能够满足加固工程需要;加入2%的硼酸镁晶须能够有效降低体积收缩率,提高抗压强度;然后对25~500℃高温处理后的氯氧镁水泥作为胶黏剂的界面黏结性能进行单面剪切试验,结果表明:25℃下氯氧镁水泥胶的界面黏结强度比环氧树脂为胶黏剂低10%,当温度升高至200℃时,界面黏结强度仍为25℃下的84.06%,300℃黏结强度下降为25℃的68.20%。

促进剂改性增强SPU建筑密封胶混凝土的粘接性能研究

为改善建筑密封胶与混凝土材料的粘接效果,采用丙烷二元醇、二月桂酸二丁基锡及无水乙醇等化学材料,制备封端比例分别为0%、30%、60%和100%的促进剂,将其融入至聚氨酯密封胶(SPU)中,制成M1、M2、M3、M4组密封胶试样,通过对表干时间、粘接性能和老化加速测试,测试每组建筑密封胶的应用效果。结果表明,封端比例较小的促进剂增强SPU建筑密封胶表干时间较长,最大拉力延伸率和拉伸模量下降幅度较快;而封端比例为100%密封胶试样的表干时间较短,在拉伸过程中可以保持较高的粘接能力;高温老化加速测试时,可以保持较低的粘接破坏面积,且在90℃老化环境下,M4组试样具有较高的剥离强度。

碳纤维混凝土结构加固补强用环氧胶粘剂改性测试研究

以环氧树脂为基础并在其中加入制备好的氧化石墨烯,实现环氧树脂胶粘剂改性。利用胶粘剂将碳纤维粘接到混凝土结构基体上,得到粘接性能测试用试件。将试件放入不同的测试环境中,进行粘接性能3个描述指标的测试,结果表明,随着测试时间的不断进行,3个粘接性能的测试指标均呈现下降的趋势。在平均剪切强度中,工况2环境下平均剪切强度下降的最快、最多,其次是工况4,然后是工况3,最后是工况1。剥离强度与粘接强度一样,其从低到高排序是工况3、工况2、工况4、工况1,说明高温环境会造成胶粘剂在一定程度上分解,最终导致粘接性下降。

煤化工固废混凝土的制备及力学性能

为解决煤化工固废替代砂石制备混凝土时由于自身孔隙多导致的吸水量大、流动性差及强度低等问题,从固废粗渣表面封堵涂层处理及水泥水化产物形貌调控两个方面提出解决方案。首先制备了一种含有三嗪环、氨基及醛基的固废粗渣表面处理用黏附固化剂(ACA),将其与水泥混合,在固废粗渣表面形成填充封堵涂层,从而解决煤化工固废粗渣制备混凝土时吸水量大及流动性差的问题。其次,制备了氧化石墨烯(GO),并将其与聚羧酸减水剂(PC)混合形成插层复合物(PC-GO),通过掺入PC-GO实现超低掺量GO在水泥基体中的均匀分散及对水泥水化产物形貌结构的调控。在表面封堵涂层及水泥水化产物结构调控的协同作用下制备了高含量煤化工固废混凝土,表征了ACA的结构及其形成封堵涂层的作用原理,提出了超低掺量GO的吸附式分散机理及调控水泥水化产物形貌的晶核效应和模板效应。结果表明:含有60%和80%(质量分数)煤化工固废的混凝土的抗压强度分别大于40 MPa和30 MPa,抗折强度分别大于6 MPa和4.5 MPa,同时高含量煤化工固废混凝土具有良好的抗干缩性能;研究成果对于制备高含量煤化工固废混凝土及煤化工固废的大规模资源化利用具有积极的意义。