Dynamic Mechanical Behaviour of Ultra-high Performance Fiber Reinforced Concretes

Ultra-high performance fiber reinforced concretes （UHPFRC） were prepared by replacing 60% of cement with ultra-fine industrial waste powder. The dynamic mechanical behaviour of UHPFRC with different fiber volume fraction was researched on repeated compressive impact in four kinds of impact modes through split Hopkinson pressure bar （SHPB）. The experimental results show that the peak stress and elastic modulus decrease and the strain rate and peak strain increase gradually with the increasing of impact times. The initial material damage increases and the peak stress of the specimen decreases from the second impact with the increasing of the initial incident wave. Standard strength on repeated impact is defined to compare the ability of resistance against repeated impact among different materials. The rate of reduction of standard strength is decreased by fiber reinforcement under repeated impact. The material damage is reduced and the ability of repeated impact resistance of UHPFRC is improved with the increasing of fiber volume fraction.

Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete

Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.

Improved Mechanical Properties of Textile Reinforced Concrete Thin Plate

Textile reinforced concrete （TRC） is especially suitable for the thin-walled and light-weight structural elements with a high load-bearing capacity. For this thin element, the concrete cover thickness is an important factor in affecting the mechanical and anti-crack performance. Therefore, the influences of the surface treatment of the textile and mixing polypropylene fiber into the concrete on the properties of the components with different cover thickness were experimentally studied with four-point bending tests. The experimental results show that for the components with the same cover thickness, sticking sand on epoxy resin-impregnated textile and adding short fiber into the concrete are helpful to improve their mechanical performance. The 2-3 mm cover thickness is enough to meet the anchorage requirements of the reinforcement fiber and the component has good crack pattern and mechanical behavior at this condition. Comparison between the calculated and the experimental Values of flexural capacity reveals satisfactory agreement. Finally, based on the calculation model of the crack spacing of reinforced concrete structures, the crack extension of this thin-wall component was qualitatively analyzed and the same results with the experimental were obtained.

Analysis and Prediction Model Reinforced UHPC Shrinkage Property

This paper explores the shrinkage of reinforced UHPC under high-temperature steam curing and natural curing conditions.The results are compared with the existing shrinkage prediction models.The results show that the maximum shrinkage strain of reinforced UHPC after steam curing is 164μεand gradually becomes zero.As for natural curing,the maximum shrinkage strain is 173μεand the value stabilizes on the 10th day after pouring.This indicated that steam curing can significantly reduce shrinkage time.Compared with the plain UHPC tested in the previous literature,the structural reinforcement can significantly inhibit the UHPC shrinkage and greatly reduce the risk of cracking due to shrinkage.By comparing the results in this paper with the existing models for predicting the shrinkage strain development,it is found that the formula recommended in the French UHPC structural and technical specification is suitable for the shrinkage curve in the present paper.

Experimental testing of RC shear wall seismic retrofit using selective weakening,self-centering and Ultra High performance concrete

Traditional retrofit methods often focus on increasing the structure’s strength,stiffness,or both.This may in-crease seismic demand on the structure and could lead to irreparable damage during a seismic event.This paper presents a retrofit method,integrating concepts of selective weakening and self-centering(rocking)to achieve low seismic damage for non-code compliant reinforced concrete shear walls.The proposed method involves con-verting traditional cast-in-place concrete shear walls into rocking walls,which helps to lower the shear demand,while allowing re-centering.Two large-scale lateral load tests were performed to validate the retrofit concept on a concrete shear wall designed according to pre-1970s standards.The design parameters investigated were amount of energy dissipating reinforcements and confinement enhancement.Two different methods using Ultra High Performance Concrete(UHPC)were investigated to provide additional confinement to boundary elements of older shear walls.Observations from the tests showed minimized damage and enhanced recentering in the retrofitted wall specimens.Use of UHPC in the boundary elements of the retrofitted walls provided additional confinement and reduced damage in the rocking corners.

Bending performance of TRC-strengthened RC beams with secondary load under chloride erosion

Textile reinforced concrete(TRC)has good bearing capacity,crack resistance and corrosion resistance and it is suitable for repairing and reinforcing concrete structures in harsh marine environments.The four-point bending method was used to analyze the influence of the salt concentration,the damage degree and the coupled effect of the environment and load on the bending performance of TRC-strengthened beams with a secondary load.The results showed that as the salt concentration increased,the crack width and mid-span deflection of the beam quickly increased,and its bearing capacity decreased.As the damage degree increased,the early-stage crack development and mid-span deflection of the beam were less affected and the ultimate bearing capacity significantly decreased.In addition,the coupled effect of the environment and load on the beams with a secondary load was significant.As the sustained load increased,the ultimate bearing capacity of the strengthened beam decreased,and cracks developed faster in the later stage.In addition,the mid-span deflection of the beam decreased at the same load level because of the influence of the initial deflection due to the sustained load corrosion.

纤维编织网增强混凝土(TRC)加固锈蚀RC柱研究进展

钢筋混凝土柱是混凝土结构中最重要的承重构件及抗侧力构件,尤其是滨海环境的混凝土结构,长期处于氯盐环境中的钢筋混凝土柱很容易出现外部混凝土性能劣化、内部钢筋锈蚀等问题。如不进行加固修复处理,将危及整个结构的安全。纤维网增强混凝土(TRC)作为一种新型纤维增强复合材料,应用于锈蚀钢筋混凝土柱的加固,不仅能够提高锈蚀钢筋混凝土柱的力学性能,而且能够有效阻止氯离子对构件的进一步侵蚀。对现阶段TRC加固锈蚀钢筋混凝土柱研究现状进行梳理,介绍了TRC加固锈蚀钢筋混凝土柱的受压性能和低周反复加载下的抗震性能,并提出了后续研究亟待解决的问题。

纤维编织网增强混凝土的研究进展及应用

纤维编织网增强混凝土(TRC)是一种新型的纤维增强水泥基复合材料,它是纤维编织网与精细混凝土的结合。系统介绍纤维编织网与精细混凝土的界面性能、TRC基本力学性能和耐久性能、TRC用于结构加固修复的特点和TRC加固板、梁、柱等构件的力学性能、纤维编织网联合钢筋增强混凝土的抗弯性能及TRC在工程实际中的应用。最后,结合国内外的研究现状提出该研究领域中有待进一步研究的问题。

纤维编织网增强混凝土(TRC)研究进展

纤维编织网增强混凝土(Textile Reinforced Concrete)克服了普通钢筋混凝土耐久性差、抗裂性差、自重大等致命缺点,成为最有潜力的混凝土拓展应用替代材料.详细阐述了纤维编织网增强混凝土基体混合料的开发、纤维编织网与基体混凝土间的粘结,重点介绍了纤维编织网增强混凝土的力学性能及其影响因素、纤维编织网增强混凝土的耐久性、纤维编织网增强混凝土工程应用的最新进展,并在此基础上评价和展望了TRC的发展前景.

玻璃纤维编织网增强混凝土薄板力学性能研究

通过对纤维编织网增强混凝土薄板的拉伸试验和四点弯曲试验,探讨不同水泥基体对薄板的抗拉性能的影响和纤维编织网表面不同粘砂粒径、不同掺量的PVA短纤维对薄板的弯曲性能的影响.结果表明:以快硬硫铝酸盐水泥(低碱度硫铝酸盐水泥)为基体的TRC薄板的拉力-位移曲线为多折线型的,在拉伸过程中出现多重裂缝,内部纤维起到了增强的作用;而以普通硅酸盐水泥为基体的TRC薄板则是一斜线型的,在拉伸过程中只出现一条裂缝,脆性破坏明显.从耐久性的角度考虑,普通硅酸盐水泥、快硬硫铝酸盐水泥和低碱度硫铝酸盐水泥中,低碱度硫铝酸盐是最适合作为纤维编织网增强混凝土基体的.对普通硅酸盐水泥基的薄板进行四点弯曲试验,当基体混凝土中掺加体积率为2%的PVA短纤维、纤维编织网经环氧树脂浸渍且表面粘有粒径0.6~1.2 mm的细砂时,纤维编织网增强混凝土薄板的弯曲力学性能最佳.

地震作用下纤维编织网增强钢筋混凝土柱的抗震性能分析

为了解地震作用下纤维编织网增强钢筋混凝土柱的抗震性能,采用钢筋、混凝土、纤维编织网浇筑纤维编织网增强钢筋混凝土柱,编织网主材为碳、玻璃纤维束;利用电液伺服加载系统为试件加载地震作用,监测相关数据,部分试件置入氯化钠溶液进行多次干湿循环。不同环境下的实验结果显示:纤维编织网层数越多,纤维编织网增强钢筋混凝土柱承载能力越强,抗震性能越好;配箍间距较大时,纤维编织网增强钢筋混凝土柱的抗震性能仅在地震作用的后期呈现较差状态;干湿循环次数越多,纤维编织网增强钢筋混凝土柱承载力越弱,抗震性能越差。对于氯盐环境而言,可增加纤维编织网增强钢筋混凝土柱的抗腐蚀措施改善抗震性能。适当增加纤维编织网的数量、降低配箍间距有利于提升纤维编织网增强钢筋混凝土柱的抗震性能。

力与氯盐侵蚀耦合作用下TRC叠合梁的力学性能退化研究

使用预制织物增强混凝土(TRC)永久性模板制作叠合梁构件,并采用电化学侵蚀方法,加速侵蚀,继而开展抗弯试验,分析了2根对比梁和5根TRC叠合梁在氯盐侵蚀作用下溶液浓度、持荷状态、锈蚀率的不同对TRC叠合梁受弯性能的影响.结果表明:锈蚀状态下TRC叠合梁的力学性能退化情况优于普通梁;U型TRC梁模可以阻碍氯离子的渗入,延缓梁内钢筋锈蚀;溶液浓度的提高、钢筋锈蚀率的增大是影响TRC叠合梁承载力下降的直接因素;在较小的锈蚀率下,TRC叠合梁的屈服荷载和极限荷载略有提升.在试验分析的基础上,给出了TRC叠合梁在锈蚀状态下的承载力计算公式,理论计算结果与试验结果较为吻合.

基于数字图像技术的TRC加固砌体裂缝发展研究

采用纤维编织网增强混凝土进行砌体墙的加固,并利用数字图像相关技术(DIC)可以全场测量的特点,在全场范围内对加固砌体墙在承受荷载时所产生的裂纹扩展情况进行探测.探测结果表明:随着荷载的增加,砌体墙加固层持续开裂,由微裂纹逐渐形成肉眼可见的裂缝,裂缝的形态和扩展路径与应变场的变化相对应.

树脂涂层及海水浸泡对玄武岩纤维织物增强海水海砂混凝土力学性能的影响

为了研究不同树脂(环氧树脂、呋喃树脂、乙烯基树脂)涂层及海水浸泡对玄武岩纤维织物增强海水海砂混凝土(BTR-SSC)力学性能的影响,采用万能试验机对各树脂涂层纤维束和海水浸泡不同时间下BTR-SSC试件进行静态拉伸试验,并通过拔出试验评估纤维-基体界面粘结性能。结合数字图像相关分析得到裂纹与应变分布,并采用扫描电镜分析损伤机制。通过界面粘结强度计算公式实现以裂纹分布和基体强度评估界面长期性能。结果表明:3种树脂对纤维束的增强效果显著且相近(32%左右),均可显著提升BTR-SSC力学性能,乙烯基树脂涂层表现最佳,抗拉性能和界面粘结性能分别提升77%和180%。海水浸泡下BTR-SSC试件力学性能明显劣化,未处理试件仅高温浸泡14天后便脆断,环氧树脂、呋喃树脂和乙烯基树脂涂层试件浸泡7天时相对未处理试件抗拉强度分别提升81%、48%和94%,浸泡28天时仍呈多裂缝开展,界面粘结性能分别损失64%、57%和55%。该成果将有助于提升BTR-SSC在海洋环境中长期性能并促进其在海工结构中的应用。

氯盐干湿循环次数对TRC加固RC柱抗震性能影响

为了研究在侵蚀环境下纤维编织网增强混凝土(textile reinforced concrete,TRC)加固RC柱的抗震性能,设计制作了9根钢筋混凝土方柱,其中,3根为对比柱,其余6根为TRC加固柱。采用时控开关控制的水泵定时抽水的方式对水槽内的全部试件进行氯盐干湿循环试验。氯盐干湿循环完成后,对9根试件进行了低周往复加载试验,分析了不同氯盐干湿循环次数对TRC加固柱抗震性能的影响。结果表明:在氯盐干湿循环下,TRC加固能够限制裂缝的发展,提高试件的开裂荷载、屈服荷载和峰值荷载,增大加固试件屈服前的刚度,延缓屈服后的刚度退化,提高加固试件的变形能力和耗能能力;氯盐干湿循环会降低TRC的力学性能;氯盐干湿循环对加固试件的开裂荷载影响不大,但随着氯盐干湿循环次数的增加,加固试件的屈服荷载和峰值荷载减小,耗能能力降低,位移延性系数先增大后减小再增大,在试件屈服前后,刚度退化速率变化规律与位移延性系数相同,但到了位移加载后期,氯盐干湿循环次数对试件刚度退化无明显影响。因此,随着氯盐干湿循环次数的增加,TRC加固RC柱的整体抗震性能有一定程度降低。

纤维网增强水泥基复合材料加固低延性RC柱抗震性能研究

为明确纤维网增强水泥基(TRC)复合材料加固对低延性钢筋混凝土(RC)柱抗震性能的提升作用,对6根TRC加固RC柱和2根未加固柱分别进行低周反复加载试验,研究TRC加固层纤维织物网层数、剪跨比、轴压比及配箍率对RC柱地震破坏模式的影响,分析TRC加固对低延性RC柱承载能力、变形性能、荷载-位移曲线及耗能能力的影响规律,并给出TRC加固柱等效阻尼比计算方法。结果表明:TRC加固可以明显改善RC柱的低延性地震破坏特性;与未加固柱相比,TRC加固柱的屈服荷载、侧向承载力、延性及耗能能力均有不同程度的提高,且提高幅度随加固层中纤维网布设层数的增加而增大,当采用4层纤维网加固时,柱屈服荷载、承载力、延性提高程度分别可达31.3%、37.8%、109.2%,且总滞回耗能是未加固柱的11倍;所建立的RC柱等效黏滞阻尼比计算模型,可用于地震作用下TRC加固弯剪破坏型RC柱耗能能力评估。

纤维网增强混凝土复合材料约束混凝土应力-应变关系研究

为研究纤维网增强混凝土(TRC)加固层对混凝土柱的约束性能,对13根混凝土柱试件(包括10根TRC加固柱和3根对比柱)进行了轴心受压试验,分析了纤维网层数、短切纤维及混凝土强度对TRC加固效果的影响,基于试验结果提出了TRC约束混凝土应力-应变关系简化计算模型。研究结果表明:TRC加固可改善混凝土柱的轴压破坏形态;与未加固柱相比,TRC加固柱的承载能力和变形能力有不同程度提高,且提高幅度与纤维网层数、混凝土强度以及短切纤维掺入相关,纤维网层数越多、混凝土强度越低时,加固柱的承载力和延性提高幅度越大,最高可分别达67.3%和65.2%;TRC基体中掺入短切纤维有利于加固柱的承载力和延性提高;提出的TRC约束混凝土应力-应变关系计算模型与试验结果吻合较好,可用于描述TRC约束混凝土应力-应变关系曲线。

FRP和TRC加固砌体墙受剪性能试验研究

砌体结构的抗震性能较差,且砌体墙作为主要承载构件易在地震中受到面内剪切作用。而加固是提高砌体墙面内受剪性能的有效方法。FRP (fiber-reinforced polymer)和TRC(textile-reinforced concrete)两种材料具有轻质、高强、耐腐蚀等优势,在应用于砌体结构加固时增强效果显著。为了比较这两种材料加固砌体墙的受剪性能,采用砂浆、FRP和TRC对砌体墙进行加固,进行了加固砌体墙试件的面内受剪试验,分析不同加固方式的破坏模式、承载力、延性和耗能能力。研究表明,未加固和砂浆加固的砌体墙在破坏时有不同程度的脆性特征,采用FRP和TRC加固均可改善这一现象。在本研究试验条件下,FRP和TRC在提升峰值剪应力方面增强效果相似,但TRC加固试件在延性和耗能方面效果更好。最后,结合现有规范中的相关计算方法,计算FRP和TRC加固层的受剪承载力,并且将计算值与试验值进行对比以评估相关计算方法的合理性,结果表明相关计算方法较为保守。

TRC单面加固受损砖砌体墙抗震性能研究与受剪承载力分析

无筋砌体墙具有很强的脆弱性,在地震作用下容易发生破坏,但部分墙体在震后经过修复加固仍能继续承载。为研究纤维编织网增强混凝土(TRC)单面加固受损砖砌体墙的抗震性能,对3片TRC加固砌体墙和1片未加固砌体墙进行了低周往复试验,分析TRC单面加固砖砌体墙的破坏机制、滞回特性、位移延性和能量耗散。试验结果表明:TRC单面加固能够较好的约束受损墙体,改善墙体的脆性破坏特征,墙体裂缝宽度明显减小。TRC加固墙体的抗震性能得到不同程度的提高,相较于未加固墙体,未损伤单面TRC加固墙体、中度损伤单面TRC加固墙体和严重损伤单面TRC加固墙体的受剪承载力分别提高了23.4%、22.3%和13.5%;位移延性系数分别提高27%、7.5%和1.3%;耗散能量提高了78.2%、43.2%和7.1%。TRC单面加固对中度损伤墙体具有良好的加固效果,而对严重损伤墙体的加固效果有限。提出TRC加固构造柱约束砖砌体墙受剪承载力计算方法,计算值接近且低于试验值,未加固墙体、未损伤单面TRC加固墙体、中度损伤单面TRC加固墙体和严重损伤单面TRC加固墙体的受剪承载力计算值与试验值分别相差-0.1%、-4.7%、-12.0%和-14.0%。

预加载水平对TRC加固RC柱轴压性能影响

为研究纤维编织网增强混凝土(textile-reinforced concrete,TRC)对损伤钢筋混凝土(reinforced concrete,RC)柱力学性能的提升效果,对6根RC柱进行了轴心受压试验,分析了不同预加载水平对TRC加固柱受力性能的影响规律。研究结果表明:预加载水平对TRC加固柱的破坏形态影响较小;与未加固损伤RC柱相比,加固3层的损伤RC柱承载能力和变形能力最大增幅可分别达24.32%和16.90%;与未损伤未加固柱相比,当预加载水平不超过RC柱的峰值荷载时,加固3层能够恢复并提高损伤RC柱的承载能力,但随着预加载水平的提高,加固柱承载能力增幅降低。提出了考虑箍筋和TRC的约束以及纵筋作用的加固损伤RC柱轴向承载力计算公式,TRC加固损伤RC柱承载力公式预测值与试验值吻合较好。