Estimates of self-compacting concrete ‘potential’ durability

The building industry is progressively trying to use self-compacting concrete (SCC) in order to improve many aspects of construction, principally reinforced concrete. However, the problem of its durability still exists, particularly in terms of physicochemical properties which are essential to avoid corrosion of rebars. The purpose of this project was to qualify the ‘potential’ durability of self-compacting concrete and reference vibrated concrete (VC) with similar compressive strength according to French recommendations. To do this, general indicators of durability (water porosity, chloride diffusion, oxygen permeability) and additional properties necessary for a better understanding (mercury porosity, water absorption by capillarity, carbonation and ammonium nitrate leaching) were examined. Various mixes of SCC and VC were therefore made with the same raw materials in identical proportions (except for the high-performance concrete). The tests conducted on the concretes studied revealed that the durability of both concretes could be regarded as equivalent. So, at the same level of compressive strength, self-compacting concrete can be considered to be as durable as vibrated concrete.     

对混凝土耐久性模型的思考——兼与《评价高性能混凝土耐久性综合指标》作者商榷和讨论

论述了混凝土渗透性与耐久性的关系.混凝土渗透性与Cl-侵入、碳化、硫酸盐化学侵蚀有一定相关性.渗透性与其他一些耐久性如抗冻性、硫酸盐结晶破坏、碱集料反应等关系不大.指出混凝土的渗透性不能作为综合指标评价混凝土的耐久性,并建立了新的混凝土耐久性模型.     

拉会大桥高性能硅粉混凝土试验研究

对拉会大桥预应力混凝土连续刚构桥采用的C50高性能硅粉混凝土进行了试验研究,主要研究硅粉掺量对C50高性能混凝土的工作和易性、抗氯离子渗透和抗碳化的影响。试验结果表明:掺入适量硅粉有助于提高高性能混凝土和易性,同时对改善混凝土抗氯离子渗透和抗碳化等耐久性有显著作用。根据试验确定拉会大桥C50高性能混凝土硅粉掺量为5.66%,据此制备的混凝土各方面性能较优,能满足规范和设计要求。     

活性掺合料超代技术对混凝土耐久性能影响研究

研究了活性掺合料超量替代水泥对混凝土氯离子渗透性能、气体渗透性能、抗碳化性能、抗冻融循环性能和干缩性能的影响。研究结果表明,矿渣等量替代水泥40％,再采用矿渣、粉煤灰、钢渣超代能有效提高混凝土抗渗透能力、抗碳化性能、抗冻性能和降低混凝土干燥收缩率。最佳超代系数为1．3。矿渣钢渣复合超代技术可以使混凝土在其他耐久性指标大致相当的前提下,大幅度降低混凝土收缩值。可以使混凝土早期裂缝减少,提高混凝土耐久性能。     

荷载作用下混凝土的耐久性研究

混凝土结构的使用荷载与使用环境是共存的,从渗透性、抗碳化性能、抗冻融性能、抗氯离子和硫酸根离子侵蚀等方面阐述了荷载对混凝土耐久性的影响,得出一致结论:施加荷载的混凝土构件要比无荷载作用的混凝土构件耐久性水平低,荷载是耐久性研究中不可忽视的因素之一.     

铁路隧道衬砌机制砂混凝土耐久性能试验研究

目前天然河砂资源紧缺,基于叙毕铁路川滇段某标段隧道工程大量采用机制砂施作隧道衬砌混凝土的现状,为揭示铁路隧道衬砌机制砂与河砂混凝土耐久性能方面的差异,考虑细骨料、混凝土强度等级、养护条件等因素的影响,进行电通量与碳化试验,研究不同因素对混凝土抗氯离子渗透性能和抗碳化性能的影响。试验结果表明:相同强度等级的机制砂混凝土耐久性能指标高于河砂混凝土约6%~10%,且混凝土耐久性能随强度等级的提高得到不同程度的提升;标准养护条件下混凝土耐久性能明显优于隧道内自然养护条件下混凝土,其抗氯离子渗透性能和抗碳化性能分别提升约43%、37%。根据试验结果,在隧道施工过程中需加强衬砌混凝土养护以增强其耐久性能。     

Durability of concrete pipes subjected to combined steam and carbonation curing

A beneficial use of carbonation as an auxiliary curing regime for concrete pipes was studied in an attempt to reduce steam curing time, improve durability performance and explore the possibility of using concrete pipe to sequester carbon dioxide. Durability performance of the carbonated concretes was characterized by carbon uptake, strength gain, pH, calcium hydroxide content, permeability, sorptivity and sulfate and acid resistance. It was found that initial curing using steam is necessary to facilitate carbonation. Although the contribution of early carbonation to strength gain is not noticeable after initial steam curing, the process is unique in promoting enhanced durability performance of concrete. The early carbonation leads to a reduction in calcium hydroxide near the surface while maintaining a pH above the corrosion threshold value at the core. Carbonated concretes also exhibit improved resistance to sulfate attack, water absorption, and chloride ion penetration. A carbon uptake of 9% by cement mass makes concrete pipe an ideal candidate for carbon dioxide capture and storage.     

荷载与环境因素耦合作用下结构耐久性研究进展

为了说明荷载对结构耐久性的影响作用,本文分别介绍了荷载与碳化、化学物质侵蚀、水渗透性、冻融循环耦合作用的研究成果.结果发现,与无荷载作用相比,荷载作用下的混凝土结构耐久性能均有不同程度的降低,得出了荷载是耐久性研究中重要影响因素的结论,同时指出需要对不同荷载类型作用下的混凝土碳化深度、硫酸盐侵蚀、水渗透性能、冻融循环性...     

多因素作用下建筑物耐久性检测与研究

以南方沿海某建筑物为研究对象,探讨建筑物在多因素腐蚀作用下的耐久性问题。重点研究了导致该情况发生的耐久性影响因素,检测了该建筑物混凝土保护层的碳化深度、游离氯离子浓度及浓度-深度的变化梯度。在检测中发现其碳化深度均已经超过了混凝土保护层厚度,而不同构件的氯离子含量却相差很大。对该情况出现的原因及产生的后果进行了讨论,断定为是在南方沿海的气候环境下,混凝土保护层的碳化、氯离子侵蚀等多因素的共同作用,最终导致了该建筑物的迅速劣化。     

Strength properties and durability aspects of high strength concrete using Korean metakaolin

Metakaolin is a cementitious material used as admixture to produce high strength concrete. In Korea, the utilization of this material remained mainly limited to fireproof walls but began recently to find applications as a replacement for silica fume in the manufacture of high performance concrete.In order to evaluate and compare the mechanical properties and durability of concrete using metakaolin, the following tests were conducted on concrete specimens using various replacements of silica fume and metakaolin; mechanical tests such as compressive, tensile and flexural strength tests, durability tests like rapid chloride permeability test, immersion test in acid solution, repeated freezing and thawing test and accelerated carbonation test.Strength tests revealed that the most appropriate strength was obtained for a substitution rate of metakaolin to binder ranging between 10% and 15%. It was observed that the resistance to chloride ion penetration reduced significantly as the proportion of silica fume and metakaolin binders increased. The filler effect resulting from the fine powder of both binders was seen to ameliorate substantially the resistance to chemical attacks in comparison with ordinary concrete. Durability tests also verified that concrete using metakaolin bore most of the mechanical and durability characteristics exhibited by concrete using silica fume. The tests implemented in this study confirmed that metakaolin constitutes a promising material as a substitute for the cost prohibitive silica fume.     

引气混凝土的抗碳化性能研究

分别研究了不同浆骨比、含气量和水胶比情况下,掺入粉煤灰后高耐久性混凝土的抗碳化性能和抗氯离子渗透性能。研究结果表明:碳化深度随粉煤灰掺量的增加而增大;氯离子扩散系数随粉煤灰掺量的增加而减小,当粉煤灰掺量超过一定掺量时氯离子扩散系数又随粉煤灰掺量的增加而增加。碳化深度、氯离子扩散系数随含气量增加而减小,而当含气量大于4%时,碳化深度、氯离子扩散系数又随含气量的增加而增大;碳化深度、氯离子扩散系数随浆骨比(32.5/67.5至37.5/62.5)的增大而增大;水胶比越小的抗碳化性能越好、氯离子扩散系数越小。     

预应力空心板的混凝土耐久性检测诊断

文章结合某已基本使用10年的旧桥预应力混凝土空心板，对影响混凝土耐久性的各项指标如混凝土碳化、预应力钢丝腐蚀电位、混凝土电阻率以及氯离子含量等进行了系统的检测诊断分析，并于相关破坏荷载试验完成后凿取结构钢丝对检测结果进行验证，为同类混凝土结构的耐久性检测提供了试验依据。     

钢筋混凝土桥梁防腐蚀技术措施研究

对上海地区五座被腐蚀的桥梁混凝土的现场取样测试结果显示 ,原设计强度为C30混凝土强度和耐久性均严重降低。近年来上海建成了大量桥梁、高架和轨道交通工程 ,钢筋混凝土防腐技术措施研究无疑将成为一个紧迫的课题。通过对涂有 (纯丙乳液、苯丙乳液、叔碳酸盐和有机硅 )涂层的混凝土的氯离子渗透性、气体渗透性以及碳化性能进行了研究 ,发现除有机硅外 ,其他几种涂层对混凝土防腐效果显著 ,其中苯丙乳液效果最佳。     

沿海桥梁混凝土结构腐蚀调查及分析

针对日照沿海桥梁的耐久性现状进行调研,通过对桥梁墩身、边梁和栏杆混凝土的保护层厚度、碳化深度以及桥梁不同部位的游离氯离子浓度的检测表明:桥梁混凝土结构保护层厚度偏小、车辆超载、结构设计不合理、施工管理不当、缺乏维护管理是导致沿海桥梁混凝土结构损伤劣化的主要原因。此外,海洋环境中的氯离子和空气中的二氧化碳将导致桥梁混凝土中钢筋腐蚀,海水中的盐在混凝土中结晶将导致桥梁墩身腐蚀破坏。     

Study of the hydration process of quaternary blended cements and durability of the produced mortars and concretes

This study aims to clarify the effect that blended cements with four components have on the hydration process and durability of concrete. Therefore, blended cements with two different proportions of high calcium fly ash, natural pozzolan and limestone have been produced and have been compared with CEM I. Compressive strength was measured at different ages and the hydration kinetics was studied by means of proton nuclear magnetic resonance (NMR-H). Furthermore, the above mentioned cements have been used to produce mortars and concretes and their durability have been determined. The aspects of durability that has been determined are: pore size distribution by means of NMR-H and mercury intrusion porosimetry, penetration of chlorides, carbonation and resistance to sulfates attack. The conclusion of the present study is that quaternary blended cements can perform as well as CEM I cement as far as compressive strength are concerned and they produce durable mortars and concretes.     

火灾后混凝土结构耐久性的若干研究

火灾对混凝土结构的安全性和适用性带来了严重的危害,而对其耐久性造成的危害同样不可忽视。由于火灾的高温和含氯烟雾作用,混凝土结构存在严重氯离子侵蚀问题。火灾的高温导致混凝土结构碳化,同时,火灾后的混凝土结构也存在着硫酸盐侵蚀等其他一些比较常见的耐久性问题。火灾对混凝土结构耐久性诸多影响的作用机理有别于通常状况,在深入研究火灾影响混凝土结构耐久性各种因素的作用机制的基础上,提出利用特殊的氯离子扩散模型来评估火灾后混凝土结构抵抗氯离子侵蚀耐久性能;引入混凝土结构内部温度场分布理论来评估火灾后混凝土结构碳化剩余寿命。     

In-situ condition monitoring of reinforced concrete structures

Performance of concrete structures is significantly influenced and governed by its durability and resistance to environmental or exposure conditions, apart from its physical strength. It can be monitored, evaluated and predicted through modeling of physical deterioration mechanisms, performance characteristics and parameters and condition monitoring of in situ concrete structures. One such study has been conducted using Non-destructive testing equipment in the city of Bhopal and around located in India. Some selected parameters influencing durability of reinforced concrete (RC) structures such as concrete cover, carbonation depth, chloride concentration, half cell potential and compressive strength have been measured, for establishing correlation among various parameters and age of structures. Effects of concrete cover and compressive strength over the variation of chloride content with time are also investigated.     

防辐射混凝土的耐久性能研究

该文系统研究了利用铁矿石和重晶石配制的不同强度等级防辐射混凝土的抗水渗透性能、抗氯离子渗透性能、抗碳化性能、抗冻性能和早期收缩性能。相同水胶比参数条件下不同骨料防辐射混凝土的对比结果表明,抗渗等级、电通量和氯离子渗透系数、抗冻等级和早期收缩结果受骨料影响的规律一致,铁矿石组的最大,重晶石的最小;不同骨料对28 d碳化试验结果影响并不明显。     

暴露21年后混凝土的碳化及氯离子侵入研究

对暴露21年的挡浪坝和预制混凝土扭工字块钻取了一批直径100 mm的混凝土芯样。在实验室测定了芯样中的碳酸钙含量和氯离子分布;通过压汞试验测定了混凝土表层和内部的孔结构;分析材料因素和环境因素对碳化及氯离子分布的影响。结果表明,在相对湿度较高时,混凝土碳化十分有限,且以未完全碳化区为主导;实际暴露混凝土中氯离子侵入深度...