建筑结构无损检测方法简介

在建筑结构检测中 ,采用的无损检测技术越来越多。如超声法检测[1,2 ] 、高应变动力[3 ] 和低应变动力检测[4 ] 、探地雷达检测[5] 及ＦＣＴ10 1测试仪检测[6 ] 等。超声波无损检测技术多年来在非金属材料的力学性能测试、混凝土结构物建筑质量的检验以及岩土工程勘测方面获得了广泛应用。1　混凝土结构缺陷检测超声法是国内目前普遍采用的现场混凝土结构质量检测方法 ,并已制订了相应的技术规程[1] ,包括对裂缝深度、灌注桩和钢管混凝土缺陷、混凝土密实情况及空洞以及混凝土表面损伤层的检测[711] 。浅裂缝检测方法是指适用于结构混凝土开…     

浅谈钢筋混凝土结构裂缝的开展机理

在许多工程中,经常会遇到混凝土结构出现裂缝的问题.综合分析其原因,笔者指出,裂缝的出现与混凝土抗拉强度有关;裂缝的分布又与混凝土和钢筋间的粘结强度及混凝土的保护层厚度有关;裂缝的宽度则与裂缝间距、混凝土和钢筋间的滑移量、钢筋应力大小,以及荷载的长期作用因素有关.     

浅谈混凝土裂缝原因及预防措施

混凝土在现代工程建设中占有重要地位。而在今天，混凝土的裂缝较为普遍，在混凝土结构施工中裂缝几乎无所不在。尽管我们在施工中采取各种措施，小心谨慎，但裂缝仍然时有出现。     

浅议混凝土裂缝产生的原因及预防措施

混凝土结构裂缝是建筑工程中常见的现象,当前已提出了多种预防混凝土开裂的方法及相应处理措施。本文对工程中常见的混凝土裂缝作了简要分类,并针对不同类型裂缝出现的原因及其相关处理措施进行简要讨论。     

浅谈建筑施工中的混凝土裂缝控制

随着建筑工程中混凝土结构应用越来越普遍,在施工中出现了大量的混凝土裂缝,严重影响了建筑物的使用安全。本文对建筑工程混凝土裂缝产生的原因进行分析,探讨了防治的措施。     

浅谈现浇混凝土裂缝产生原因及预防措施

论述现浇混凝土施工过程中混凝土出现的质量问题,分析混凝土裂缝产生的原因,从而提出防治措施,为大体积混凝土的施工过程提出质量控制要求。     

油田地面建筑工程混凝土裂缝的原因分析

最近的几年中我国的经济发展速度越来越快,油气资源的需求量也越来越大,油气资源的开采离不开地面建筑工程,油田地面建筑工程质量又和混凝土质量有着直接的影响。本文主要阐述了油田地面建筑工程混凝土裂缝产生的原因,以及油田地面建筑工程混凝土裂缝的预防措施及处理措施分析,促进我国油田地面建筑工程的可持续发展。     

石材质量的超声波检测技术

岩石和混凝土的超声无损检测原理是相同的。将成熟的超声波无损检测混凝土缺陷的方法移植于石材质量的判定检测。试验表明,针对混凝土非均质材料的超声检测技术,完全适用于在石材上的无损试验。研究结果对于均质石材内部质量的判据,采用统计方法检测石碑的均匀性,判断石碑的缺陷,所取异常数据判断值应比混凝土更严格些,建议提高至声速平均值减一倍标准差的临界值来评判,能避免缺陷的漏判。对石碑的裂缝检测时,结合超声首波相位反转的现象计算裂缝深度,可提高检测裂缝的精度。     

浅谈大体积混凝土施工的裂缝控制措施

随着建筑施工技术的飞速发展，特别是泵送混凝土的大量使用，使混凝土浇筑的体积由几百立方米逐渐增大到几万立方米。由于其体积大，表面积小，产生较大的温度应力和收缩应力，导致大体积混凝土产生温度裂缝，影响结构安全和正常使用。因此对大体积混凝土施工的裂缝控制措施提出了更高的要求。为有效克服大体积混凝土裂缝，确保工程质量，本文从裂缝产生的原因入手，从选料、配合比设计、施工方法、温度控制、养护等方面采取综合性控制措施。阐述一些看法。     

高层砼施工易出现的质量问题与防治

高层建筑工程中全剪力墙体系混凝土工程量大,砼施工中常会遇见如下质量问题:筏板基础砼裂缝;剪力墙砼漏振,胀模,露筋;现浇板砼出现裂缝。现就我接触过的高层建筑为例,谈谈针对以上易出现的质量问题的原因及防治。     

3D Numerical modelling of steel corrosion in concrete structures

The paper deals with a 3D numerical model for transient analysis of processes after depassivation of reinforcement in concrete, which are relevant for calculation of corrosion rate. The aim of the study is to investigate the influence of the concrete quality, cracking and water saturation in concrete on the current density. The results show that the corrosion rate is higher in poor quality concrete than in good quality concrete. The model predicts that cracks do not influence corrosion rate for the case where the only influence of the crack is on the rate at which oxygen can reach the steel.     

Gerissener Stahlbeton: Wie korrosionsgefährdet ist die Bewehrung?

Cracked reinforced concrete: What about corrosion risk? The formation of cracks within the tension zone of the concrete is part of the design principle of reinforced concrete structures. The width of these cracks can be limited by means of crack limiting reinforcement. Already by the end of the fifties first examinations have been carried out to determine the influence of cracks and their width on the corrosion risk. Compared to uncracked concrete CO₂ and chlorides as corrosion promoting substances are able to move faster towards the reinforcement within a crack, leading to an earlier depassivation of the reinforcement within the cracks. Before Schießl published his results, from experiments and literature research, it had been assumed that the corrosion rate of reinforcement within cracks increases with increasing crack width. Hence a differentiated maximum crack width linked to exposure classes had to be complied according to the DIN 1045 until the version of 1988. For the first time the DIN 1045 version 1988 did not enclose this differentiation, for durability reasons a maximum crack width of 0.25 mm has been fixed for reinforced concrete. In the version of 2001 the calculated crack width has been raised from 0.25 mm to 0.30 mm. Therewith the findings of Schießl (published in book no. 370 by the Deutscher Ausschuss für Stahlbeton) have been implemented by now. The main contributing factors influencing the corrosion rate of cracked concrete are the concrete quality and the concrete cover and not the crack width, whereas horizontal structural parts exposed to chlorides have to protected generally by additional measures.     

Einfluß einer Feuerverzinkung und PVC-Beschichtung von Bewehrungsstählen und von Inhibitoren auf die Korrosion von Stahl in gerissenem Beton

Influence of galvanizing and PVC-coating of reinforcing steels and of inhibitors on steel corrosion in cracked concrete Cracked concrete beams of concrete quality B15 and B35 with carbonized cracks were exposed in artificial seawater, under frost and deicing salt conditions and in industrial climate. The reinforcement was composed of black steel, galvanized and PVC-coated steel. For the purpose of additional protection the concrete was partly mixed with an inhibitor Ca(NO₂)₂. The concrete cover was 1,5 till 5,0 cm. It was found that the inhibitor protects satisfactorily only in the case of the higher concrete quality, cover 1,5 cm and not to high crack width. A protective effect of galvanizing is given by not to high chloride contents (< 1,5% relative to cement) and crack widths. The chosen PVC-coating failed because of chemical instability in the alcaline medium concrete.     

Crack shape and rust distribution in corrosion-induced cracking concrete

This study investigated a reinforced concrete specimen that had deteriorated in an artificial environment for 2 years. The crack width and the rust distribution were observed by digital microscopy. The variation of the total circumferential crack width along the radial direction is presented using a linear function. Observation reveals that rust does not penetrate into the corrosion-induced cracks before concrete surface cracking. After concrete surface cracking, rust fills the cracks, lining the edges of the cracks due to the circulation of the outer solution. A schematic diagram is proposed to describe crack propagation and rust development.     

Distribution of millscale on corroded steel bars and penetration of steel corrosion products in concrete

This study investigated a reinforced concrete specimen that had deteriorated in an artificial environment for 2 years. The steel/concrete interface and corrosion-induced cracks were observed by SEM to investigate the millscale on the rebar surface and the distribution of rust. The millscale was not further oxidised before the surface cracking of the concrete cover. The penetration of corrosion products into concrete and the formation of a corrosion layer proceeded simultaneously. The rust did not fill the corrosion-induced cracks in concrete. Instead of the three-stage model, a two-stage model is proposed to describe the concrete cracking process induced by steel corrosion.     

Korrosionverhalten von schlaffer und vorgespannter Bewehrung in Betonbauteilen

Corrosion behaviour of stressed and prestressed reinforcement in concrete structural elements In steel reinforced or prestressed concrete structures corrosion protection of the reinforcement is resulting from the high alkalinity of the concrete environment which guarantees passivity of the steel surface. The long time efficiency of the corrosion protection is a function of the design of the structure and influence from the properties of the used concrete materials as well as the environmental conditions of the structure. Essential factors preventing corrosion are given by a good quality and thickness of the concrete covering, a proper curing of the concrete and position of the reinforcement which avoids cracks and defects in the concrete covering. Passivity of the reinforcement can be destroyed by carbonisation of the concrete or a sufficiently high amount of chlorides in the concrete. Under such conditions in prestressing steels hydrogen induced stress corrosion occurs while in normal steel reinforcement the corrosion products due to their increasing volume lead to cracking and spalling of the concrete and a decreasing cross section of the reinforcement. In this report typical failures are demonstrated and discussed.     

混凝土裂缝的成因及其预防控制处理

阐述了混凝土裂缝的类型及其各类裂缝产生的原因。并对工程中常见的裂缝,如温度裂缝、收缩裂缝等,提出了相应的预防控制方法及处理措施。     

The influence of cracks on chloride-induced corrosion of steel in ordinary Portland cement and high performance concretes subjected to different loading conditions

Many reinforced concrete structures are subjected to variable loads, but little information is available on the effect of such loading, and the accompanying opening and closing of cracks, on the initiation and propagation of chloride-induced rebar corrosion. The purpose of this paper is to provide that information for reinforced ordinary Portland cement concrete and high performance concrete exposed to static or cyclic three-point bending and exposed to salt solution.It was observed that: (i) corrosion occurred only at intersections of the rebar with cracks in the concrete; (ii) high performance concrete was more protective than ordinary Portland cement concrete and (iii) the type of loading had less impact on corrosion than the type of concrete and exposure conditions.     

Feasibility of detecting embedded cracks in concrete structures by reflection seismology

Reflection seismology has been widely used in the petroleum exploration industry for decades. To improve the capabilities of detecting the depths and lengths of cracks inside a concrete element, an ultrasonic common depth point (CDP) reflection technique was employed in this study. The effectiveness and accuracy of applying the reflection seismology method to detect cracks embedded in concrete structures are discussed. Test results show that simulated blind cracks with certain lengths, dip angles and depths inside concrete specimen can be successfully imaged and identified. This study shows that when the signals reflected from the crack are obscure, the CDP signal stacking method is very useful and provides an opportunity to look into the object, which is not possible with traditional ultrasonic methods.