冻融条件下新老混凝土粘结后抗折性能

对经历0、10、20、30、40和50次冻融循环的混凝土试块进行抗折强度试验,分析新老混凝土外观特征、动弹性模量、质量损失率和抗折强度等参数与冻融循环次数之间的变化规律.结果表明:每间隔10次冻融循环后,新老混凝土试样的表观剥蚀逐渐加重,质量损失率初期略有降低、后期快速增长,试件的抗折强度和动弹性模量衰减较快;Ⅰ型和Ⅱ型粘结面试件抗折破坏主要集中粘结面处;Ⅲ型和Ⅳ型粘结面试件的破坏面从粘结面处逐渐向试件强度低的一侧转移.增加黏结面粗糙度,可以有效提高冻融环境下新老混凝土的抗折强度.     

高温后新旧混凝土粘结的剪切性能研究

对先粘结后高温与先高温后粘结两种类型的129块Z形新旧混凝土粘结试件进行了直剪试验,主要考察了温度(常温到900℃)、冷却方式、界面粗糙度和界面剂对粘结面剪切性能的影响。在此基础上,得到了粘结面的剪切滑移曲线,给出了相应的统一计算公式,并建立了先高温后粘结类型的神经网络预测模型,较为系统地对高温后新旧混凝土粘结面的剪切性能进行了研究,以供工程参考。     

粘结混凝土结构超声波时域和频域特性研究

装配式建筑在后浇混凝土过程中存在不同混凝土相互结合的问题,混凝土结合面粘结质量对粘结混凝土结构的受力性能具有重要影响。为研究粘结混凝土结构在不同粘结质量情况下的声波特性,运用有限元方法建立六类粘结混凝土结构在不同粘结质量情况下的物理模型,模拟了超声波在粘结混凝土结构模型中的传播过程。通过提取时域信号峰值,对频域数据进行积分处理,对比分析了各类粘结混凝土结构在不同粘结质量情况下的时域特征和频域特征。结果表明：不同混凝土强度等级相结合的粘结混凝土结构,界面反射较强,且强度等级差别越大,界面反射越强;时域信号峰值与频域积分随着粘结界面质量的提高而增大。根据这一特征,通过试验制作了三种不同粗糙度的粘结混凝土结构样本,采用斜测法对样本进行超声测试,结果表明界面粗糙度越高,超声波透射粘结界面区域内的时域信号峰值和频域积分越大。研究结果可为粘结混凝土结构质量检测提供参考和依据。     

混凝土粘结面粗糙的分维评价方法

粘结面粗糙度是影响新老混凝土粘结性能的一个重要因素。定量评价粗糙度对控制与预测粘结面强度具有重要作用。本文采用分形理论对粘结面度进行了高差分维研究,经和灌砂法对比分析认为,此法可以较好地定量评价粘结面的粗糙度。     

高温后型钢混凝土粘结滑移性能研究

高温后型钢与混凝土之间的粘结滑移对型钢混凝土结构的高温后力学性能具有重要影响,为了研究高温后型钢混凝土的粘结强度与滑移特性,进行18个高温后型钢混凝土短柱推出试验及3个常温下的对比试验。试验结果表明:高温后型钢混凝土短柱试件的荷载-滑移曲线与常温下大体相似,但随着曾经经历最高温度的提高及最高温度持续时间的增大,型钢与混凝土之间的极限粘结强度和残余粘结强度降低,与极限粘结强度相对应的滑移减小,与残余粘结强度相对应的滑移增大。在试验结果基础上,构建了高温后型钢混凝土粘结滑移本构模型,提出了本构模型中极限粘结强度、残余粘结强度及相应滑移的计算方法,计算结果与试验结果总体相符,研究成果为高温后型钢混凝土构件考虑粘结滑移影响的数值模拟分析提供了条件。     

超高性能RPC钢筋网加固混凝土界面粘结性能试验研究

针对现有混凝土加固技术导致的耐久性弱、承载力低的问题,该文基于活性粉末混凝土钢筋网加固混凝土技术(Technical for strengthening concrete structures with reactive powder concrete and bar mesh, RPCBM),展开了双面剪切试验。该文评估了各试件的抗剪强度、破坏形态与荷载位移曲线,系统性地探讨了粗糙度、植筋率、钢筋网规格对RPCBM加固旧混凝土结构界面剪切性能的影响。结果表明：RPCBM加固混凝土结构的界面抗剪强度和延性提升幅度较大,具有良好的粘结性能。在一定范围内,随着粗糙度增大,粘结界面抗剪强度提高;植筋率增高,抗剪强度与延性增强;钢筋网规格是改善界面延性的重要因素。在此基础上,为了更好地计算RPCBM加固混凝土的界面粘结强度,该文基于以上数据建立了粘结界面抗剪强度的模型,提出了综合计算RPCBM加固普通混凝土(Ordinary Concrete, OC)界面抗剪强度的公式,试验结果与理论分析吻合较好,为工程实践中加固材料的选择和改进施工方法提供了理论依据。     

高温后型钢混凝土粘结滑移性能研究EI北大核心CSCD

高温后型钢与混凝土之间的粘结滑移对型钢混凝土结构的高温后力学性能具有重要影响,为了研究高温后型钢混凝土的粘结强度与滑移特性,进行18个高温后型钢混凝土短柱推出试验及3个常温下的对比试验。试验结果表明:高温后型钢混凝土短柱试件的荷载-滑移曲线与常温下大体相似,但随着曾经经历最高温度的提高及最高温度持续时间的增大,型钢与混凝土之间的极限粘结强度和残余粘结强度降低,与极限粘结强度相对应的滑移减小,与残余粘结强度相对应的滑移增大。在试验结果基础上,构建了高温后型钢混凝土粘结滑移本构模型,提出了本构模型中极限粘结强度、残余粘结强度及相应滑移的计算方法,计算结果与试验结果总体相符,研究成果为高温后型钢混凝土构件考虑粘结滑移影响的数值模拟分析提供了条件。     

高温作用后GFRP筋与海水珊瑚混凝土粘结性能试验研究

为了研究高温后玻璃纤维增强树脂复合材料(GFRP)筋与海水珊瑚混凝土的残余粘结性能,对54个GFRP筋珊瑚混凝土试件及钢筋珊瑚混凝土对比试件进行了高温作用后的中心拔出试验,最高温度为350℃,混凝土强度等级考虑C20～C30。观察了高温后试件的表观变化及粘结破坏形态,获取了各试件的粘结-滑移曲线、粘结强度、粘结刚度和峰值滑移量,分析了不同温度、GFRP筋直径、海水珊瑚混凝土强度等因素对高温后GFRP筋与海水珊瑚混凝土粘结性能的影响。基于烧失率和XRD分析,剖析了GFRP筋海水珊瑚混凝土的高温劣化机制。最后,提出高温后GFRP筋与珊瑚混凝土的剩余粘结强度计算式和粘结-滑移本构模型。研究结果表明：高温作用后,尽管GFRP筋与珊瑚混凝土的粘结破坏形态与常温相似,GFRP筋的碳化和珊瑚混凝土的分解使得二者界面发生显著劣化;随着温度的提高,GFRP筋与珊瑚混凝土的粘结强度逐渐降低,峰值滑移量增大;GFRP筋直径越小,高温后的剩余粘结强度和剩余粘结刚度越小;珊瑚混凝土强度等级越高,剩余粘结刚度越大,峰值滑移量越小。所提出的高温后GFRP筋与珊瑚混凝土剩余粘结强度和粘结-滑移本构关系计算结果与试验结...     

组合混凝土界面粘结性能多因素正交试验分析

组合混凝土叠合构件通过在预制陶粒混凝土部件上现浇普通混凝土而制成,兼具预制结构的施工方便和工期较短、现浇结构的整体性能和抗震性能良好等优点;同时,可充分发挥两种不同混凝土材料各自的性能优势.为分析叠合浇筑间隔时间、混凝土强度等级匹配、浇筑结合面处理方式、钢纤维掺入及附加法向约束力等因素对组合混凝土叠合界面粘结性能的显著影响,本工作设计制作了40组双面直剪组合混凝土试块进行正交试验分析.试验结果表明:附加法向约束力的施加对叠合界面粘结剪切强度的影响高度显著,法向力的增加可明显提高粘结剪切强度;次之,影响程度相接近的为混凝土强度等级匹配及结合面处理方式,在试验所考虑变化范围内,混凝土强度等级的提高可有效改善叠合界面粘结剪切强度,露骨料剂处理方式相比较人工凿毛、粉煤灰砂浆涂刷及自然浇筑面等具有更好的粘结剪切性能;而混凝土内钢纤维的掺入对叠合界面粘结剪切性能的影响不显著.不同浇筑界面处理方式下,随着浇筑间隔时间的延长,界面粘结剪切强度均发生较明显的、规律近似相同的降低变化;当叠合浇筑间隔时间从10 h变化到28 d,在粉煤灰砂浆涂刷、人工凿毛与露骨料剂不同处理方式下,界面粘结剪切强度分别降低为原强度的43.4％、48.1％和46.2％.在不同浇筑间隔时间情况下,露骨料剂处理方式可获得比人工凿毛处理和自然浇筑状态方式下相对较好的界面粘结剪切性能.     

超高性能混凝土-既有普通混凝土界面粘结性能研究综述

超高性能混凝土(Ultra-high performance concrete, UHPC)具有优异的力学性能和耐久性，被广泛应用于组合构件及结构加固中，其中，UHPC与既有普通混凝土(Existing normal concrete, NC)之间的界面粘结性能至关重要。本文综述了国内外UHPC-NC的界面粘结性能的试验方法及界面抗剪强度计算公式、影响因素与界面耐久性能的研究进展，指出了测试方法存在的不足，探究了不同规范的界面抗剪强度计算式对UHPC-NC的适用性，总结了不同因素对UHPC-NC界面粘结性能的影响，包括纤维、界面粗糙度、界面含水率、界面剂、既有混凝土强度、胶凝材料和养护制度等，阐述了其界面特性的增强机理，探讨了耐久性的现阶段研究。UHPC-NC具有优异的界面粘结强度，其中，合适的养护制度与纤维能够减少UHPC的收缩，增强材料之间相容性；界面粗糙度与既有混凝土强度的增加可以有效避免界面破坏；界面剂、胶凝材料及适当的界面含水率可以改善过渡区；UHPC-NC界面具有较好的抗渗透性能和抗冻融性能。     

部分预制装配型钢混凝土柱火灾后偏压试验研究

通过6个试件的火灾后偏压试验以及1个试件的常温下偏压试验,对配置活性粉末混凝土外壳的部分预制装配型钢混凝土（Partially Precast Steel Reinforced Concrete,PPSRC）柱和空心预制装配型钢混凝土（HollowPrecast Steel Reinforced Concrete,HPSRC）柱的火灾及火灾后偏压性能进行了对比分析。研究了受火时间、偏心率和核心混凝土强度对PPSRC柱及HPSRC柱的火灾下内部温度分布及火灾后剩余承载力、变形能力等方面的影响,并基于试验结构,对火灾下试件截面温度场进行了数值模拟分析。试验结果表明:火灾升温过程中试件截面测点温度存在明显的温度平台,火灾后试件的活性粉末混凝土外壳未发生爆裂现象,混凝土对型钢具有较好保护作用;模拟结果表明,截面温度及温度变化幅度由表及里逐渐降低,核心混凝土受到良好保护作用,温度相对较低;在偏压荷载下,火灾后试件的偏心受压破坏过程以及破坏形态和常温下类似,剩余承载力随火灾升温时间的增长和偏心率的增大而降低,随核心混凝土强度的增大而升高,试件的延性随核心混凝土的强度增大而增大。     

高强钢筋混凝土预制弧板井壁力学特性分析

对高强钢筋混凝土预制弧板井壁结构的研究表明,实验结果与数值计算结果基本一致.高强钢筋混凝土预制弧板井壁结构具有很高的承载能力,影响其承载能力的主要因素依次为混凝土的强度等级、厚径比和配筋率.在均布荷载作用下,混凝土的强度等级提高10 MPa,极限承载力提高1.26 MPa.厚径比每增加1%,极限承载力增加0.85 MPa.增大配筋率对提高其极限承载力作用不大,配筋率增大3倍,极限承载力只增加了0.1 MPa.     

The resistance of compressed spun concrete members reinforced by high-strength steel bars

The expediency of using precast spun concrete columns and other members of annular cross sections reinforced by high-strength steel bars is discussed. Test material properties and production, curing and testing procedures, response factors and ultimate compressive stresses of plain and reinforced spun concrete specimens are presented. The strength and strain features of compressed tubular reinforced concrete members are considered. Modeling of a bearing capacity of eccentrically loaded members of annular cross sections is based on the concepts of bending with an concentrical force and compression with a bending moment. The comparison of modeling and test data of concentrically and eccentrically loaded members is analysed.     

Fracturing behaviors of FRP-strengthened concrete structures

In this paper, we focus on the study of concrete cracking behavior and interfacial debonding fracture in fiber reinforced polymer (FRP)-strengthened concrete beams. An experimental program is systematically reviewed according to the observed failure modes, in which it is found that the interfacial debonding may propagate either within the adhesive layer or through concrete layer in the vicinity of bond interface. A finite element analysis is performed to investigate the different types of debonding propagation along FRP-concrete interface and crack distribution in concrete. For the numerical fracture models, interfacial debonding that initiates and propagates in adhesive layer is modeled by fictitious interfacial crack model. And concrete cracking, including the debonding fracture through interfacial concrete, is modeled by smeared crack model. Properties of the interfacial adhesive layer and concrete are considered to significantly influence the debonding propagation types and crack distribution. The interactions between interfacial bond strength, interfacial fracture energy of bond adhesive layer and tensile strength, fracture energy of concrete are discussed in detail through a parametric study. According to the results, the effects of these properties on different types of interfacial debonding, concrete cracking behavior and structural load-carrying capacity are clearly understood.     

Prediction of Interfacial Cracking due to Differential Drying Shrinkage of Concrete in Precast Shell Pier Cap

In a precast shell pier cap, cracking at the interface between the precast shell and the cast-in-place concrete may happen due to differences between the drying shrinkage of the inner and the outer concrete. The objective of this study is to establish a prediction method for interfacial cracking that will consider the real mechanism of differential drying shrinkage and creep. The main parameters used in the analysis were determined from experiments for a concrete mix that is applied to the manufacturing of pier caps. The variation of internal relative humidity over time was first calculated based on the nonlinear moisture diffusion; cracking analysis then followed. Prediction of the initiation of interface cracks and the increase of their width over time was performed. It was found that additional reinforcement across the interface is very effective at reducing crack width.     

FRP加固混凝土构件中裂纹扩展规律的数值模拟

用材料破坏过程分析系统MFPA(MaterialFailureProcessAnalysis)对FRP(FiberReinforcedPolymer)加固混凝土梁在外荷载作用下沿FRP板和混凝土之间界面剥落的不同破坏模式以及混凝土中的裂纹分布进行了数值模拟。通过分析,发现剥落破坏可能产生在FRP板与混凝土之间的粘结层内或其上方附近的混凝土中。模拟结果与实验结果较吻合。粘结层和混凝土的特性对于剥落传播的类型及裂纹的分布有很大的影响。着重探讨了混凝土的强度参数以及粘结层的强度参数对于整个构件承载能力及最终破坏模式的影响。     

Influence of Aggregate Structure on Mode-III Interfacial Fracture between Concrete and CFRP

One of the crucial issues in the use of fiber reinforced polymers for civil engineering applications is the interfacial bonding between the different materials used. As a load transfer from the concrete to the composite components occurs via shear stresses in the interfacial region, studies of the interfacial bond quality should concentrate on load situations in which primarily shear stresses are induced. In this study, a 3-Point Bending Test was modified to initiate shear failure under Mode-III conditions in the interface between a composite and a concrete component. In particular it was the objective to study the interfacial shear strength between three different concretes and an unidirectional carbon fiber reinforced epoxy matrix system. The three concretes had the same compressive strength (B35 KP, German Standard), but differed in the type of filler material: (a) heavy concrete, filled with granite (Diorit) particles, (b) normal concrete, filled with gravel grains (Pyrite), and (c) light weight concrete, filled with vopourtone (Liapur). The mechanical test results showed that both the type of filler exposed to the joint surface as well as the type of adhesive used clearly influence the interfacial shear strength. Best values were achieved with Diorit-fillers, and the Sikadur-adhesive was in all cases superior to the Dywipox-adhesive. Reasons for these differences were demonstrated by light optical and scanning electron micrographs of the fractured surfaces.     

Effects of Fibre Geometry and Volume Fraction on the Flexural Behaviour of Steel‐Fibre Reinforced Concrete

Abstract: This work aims in studying the mechanical behaviour of concrete, reinforced with steel fibres of different geometry and volume fraction. Experiments include compression tests and four‐point bending tests. Slump and air content tests were performed on fresh concrete. The flexural toughness, flexural strength and residual strength factors of the beam specimens were evaluated in accordance with ASTM C1609/C1609M‐05 standard. Improvement in the mechanical properties, in particular the toughness, was observed with the increase of the volume fraction of steel‐fibres in the concrete. The fibre geometry was found to be a key factor affecting the mechanical performance of the material.