外文翻译自密实混凝土的耐久性

1、durability of self-compacting concretegeert de schutter、guang ye、katrien audenaert、dirch bager、frank bellmannabstract：because of the different mix design in comparison with traditional concrete and the absence of vibration, different durability characteristics might be expected for self-compacting c

2、oncrete. the state-of-the-art report, prepared by rilem technical committee tc 205-dsc focuses on the durability of scc, by first gathering the available information concerning pore structure, air-void system and transport mechanisms. the available durability results are studied and summarised keepi

3、ng in mind the fundamental mechanisms and driving forces. all relevant durability issues are considered, like carbonation, chloride penetration, frost resistance, asr, sulphate attack, thaumasite formation, fire resistance, etc. it is not the intention to give a review on these durability aspects fo

4、r concrete in general. the aim however is to point at the specifics related to the use of scc, e.g. due to the addition of a large amount of limestone filler, etc. this paper summarizes the main conclusions of the state-of-the-art report. 1 introduction self-compacting concrete (scc) is an innovativ

5、e concrete that does not require vibration for placing and compaction. it is able to flow under its own weight, completely filling formwork and achieving full compaction, even in the presence of congested reinforcement . self-compacting ability can be, but is not necessary, equivalent to self-levell

6、ing ability . sometimes, the term self-levelling is applied to describe a self-compacting concrete with a perfect levelling after casting. self-compacting concrete (scc) was developed in japan in the 1980s. the aim was to develop concrete that could be placed without vibration. in this way, some hea

7、lth risks as well as environmental problems could be avoided (“white finger syndrome”, noise, vibrations .). 2 scope of the report it is emphasized that this state-of-the-art report is dealing with durability of adequate scc, showing no segregation, bleeding, blocking . the scc should be well design

8、ed, well cured, and the casting should be done in a good way. the contractor should have some experience with scc. no further reference is made to literature in this overview. the references of the scientific sources can be found in the complete report. 3 microstructure of self-compacting concrete c

9、ompared to traditional concrete (tc) and high performance concrete (hpc), the microstructure of self-compacting concrete (scc) is different. the main reasons for the changes of the microstructure in scc are: the modified microstructure of scc is to a great extent the result of changes in the hydrati

10、on process. the hydration of powder type scc is depending on the type of filler added in the system. when limestone filler is applied, three phenomenons can be observed related to the hydration of the cement: the appearance of the extra reaction peak due to the addition of limestone filler is at thi

11、s moment not very well understood, and even leads to some controversy. the first theory starts from the hypothesis that limestone filler is inert and therefore not taking part in the reactions chemically. in this case the third peak is attributed to a catalyst effect, accelerating some reactions rel

12、ated to the c3a present in the cement. the second theory considers the limestone filler as reactive material taking actively part in the reactions, with the formation of monocarboaluminate. from sem images it can be seen that the limestone filler particles remain inert, which would support the first

13、 theory. from a chemical point of view, the formation of the more stable monocarboaluminate in the presence of limestone filler is clear, which would support the second theory. concerning the active role of limestone filler in the formation of carboaluminate, it is to be mentioned that relative to t

14、he cement mass, only a minor amount of limestone filler can react with the portland clinker. compared to traditional vibrated concrete (tc), the microstructure of powder type scc is reported to be denser. the more dense microstructure and decreased porosity can to a great extent be explained by the

15、physical presence of mineral fillers. furthermore, especially the degree of hydration and the w/c ratio in combination with the amount of water strongly influence the pore structure. the hydration products fill up more and more space when the hydration degree increases. the dimensions of the pores d

16、ecrease, inducing a lower connectivity. a lower w/c ratio gives a lower capillary porosity and connectivity. the comparison of properties between scc and tc in general is not easy due to the very different concepts of scc existing worldwide. however, in order to quantify some microstructural propert

17、ies, like gel porosity, capillary porosity, and total porosity, it is shown that powers model is still valid! 4 transport properties for self-compacting concrete (scc), it is still uncertain whether the significant differences in the mix proportions and in placing and compaction processes between sc

18、c and conventional vibrated mix have a considerable effect on the transport properties and their relationships with the microstructural characteristics. work to systematically assess the transport properties of scc, particularly in comparison with conventional vibrated concrete, has been limited. fu

19、rthermore, most of the work carried out in the area has been usually a small part of a project designed for scc mix development or for studying/verifying mechanical or durability properties of a particular scc mix. as a result, there was a lack of suitable reference conventional vibrated mix for com

20、parison with scc in some cases, while in other cases, no detailed test condition was given for the results on transport properties.due to the large number of parameters influencing transport properties and the presence of different transport mechanisms, the comparison of transport properties between

21、 scc and conventional vibrated concrete will depend on the selection of materials, the effective water/cement ratio, powder content and test conditions, etc. this, together with the limited available results, has made it extremely difficult to fully analyse and understand all the results and their d

22、iscrepancies obtained from different sources. however, a few general conclusions can be formulated.5 degradation mechanisms 5.1 carbonation from the available experimental results, self-compacting concrete has sometimes a larger and sometimes a smaller carbonation depth in comparison with traditiona

23、l concrete with the same water and cement content, although the differences are small. such an empirical comparison however is not straightforward. it is very difficult to compare self-compacting concrete with traditional concrete as it is not clear what should be the basis of comparison: the same a

24、mount of water and cement, the same compressive strength,. if self-compacting concrete is cured accurately, the pore structure is denser and less permeable. furthermore, the buffering capacity is very important and normally higher for scc. from the limited experimental work however, it seems that a

25、slightly increased vulnerability is noticed concerning carbonation of scc with limestone filler. in general however, it seems that the carbonation of scc is not significantly deviating from the carbonation of traditionally vibrated concrete. 5.2 sulphate attack physical resistance to sulphate attack

26、 is especially important, as it may be regarded as one of the main factors which differentiate scc from tc. physical resistance and durability properties of scc are influenced by the large amounts of added filler materials, which in turn have an influence on the microstructure and the connectivity/f

27、ineness of the capillary pore system. other factors which influence the nature of sulphate attack are chemical resistance (type of cement), composition of the sulphate solution and addition of pozzolan materials.5.3 alkali-silica reaction little is known about the behaviour of scc in regard to asr.

28、as scc is widely used in concrete structures only since a few years, field reports about damages are nonexistent. the data base of laboratory tests evaluating the potential reactivity of scc is still scarce. at the moment the possible reactivity of scc can only be assessed by transferring experience

29、s and scientific findings obtained from conventionally vibrated concrete on scc. however, this transfer is not straight forward because the peculiar properties of scc have to be taken into account. 5.4 fire resistance fire attack on concrete is more considered as an accidental action, in stead of a

30、degradation process. nevertheless, the microstructure and transport mechanisms of the cementitious material are also very important for the resistance to fire load. as the microstructure of scc is different from traditional concrete, it is worthwhile looking into the fire resistance of scc. referenc

31、es1 the european guidelines for self-compacting concrete specification, production and use (2005) bibm, cembureau, efca, efnarc, ermco, may 20052skarendahl a,petersson o (eds) (2000) self-compacting concrete. state-of-the-art report of rilem technical committee 174-scc. rilem publications3boel v, de

32、 schutter g (2006) porosity of superplasticized cement paste containing limestone filler. adv cem res 18(3):971024boel v, de schutter g (2003) pore structure of scc in comparison with traditional concrete. in: 6th canmet/aci international conference on recent advances in concrete technology, proceed

33、ings, bucharest, 811 june 2003, pp 159173 5skarendahl a, billberg p, beitzel h, dieryck v, ghezal a, khrapko m, leemann a, de schutter g, sonebi m, sterberg t (2006) casting of self-compacting concrete. rilem, isbn 2-35158-001-x, e-isbn 2-912143-98-5, pp 26自密实混凝土的耐久性geert de schutter、guang ye、katrie

34、n audenaert、dirch bager、frank bellmann摘要：相比传统混凝土而言,因为设计的配合比不同，对缺乏振动,不同耐久性特征的混凝土而言，可能被预期为自密实混凝土。最新的报告, rilem 技术委员会 tc 205 dsc 侧重于自密实混凝土的耐久性,且首次收集了关于孔结构，气泡系统和运输机制的可用信息。研究总结出的耐久性结果，被铭记为基本机制和驱动力的变形。所有认为与耐久性相关的问题有,像碳化、氯离子渗透、抗冻性,asr、硫酸盐侵蚀,碳硫硅钙石的形成,耐火性能,等等。大体上，本文不是打算对混凝土耐久性这一方面做的综述。目的不过是指有关自密实混凝土使用的规范,例如增加

35、大量的石灰石填料,等等本文总结了先进报告的重要结论1、引言自密实混凝土(scc)是一家创新型混凝土，不需要放置、振动压实强度。它能够根据自身的重量，完全充填模板，以达致全数压实作用，甚至在拥挤的加固面前流。自密实的能力是可以，但不是必要的，相当于自流平能力。有时,应用自流平来描述自密实混凝土会有一个形变后完美的铸件。自密实混凝土是在20世纪80年代日本所开发的。目的是发展可以替代无振动的混凝土。通过这种方式,一些健康风险以及环境问题就可以避免“白色手指综合症”(“白色、噪声、振动)。2、报告的范围值得强调的是，这个先进的报告一直在处理自密实混凝土的耐久性，处理显示没有分离、 渗色、 阻塞.精心

36、设计出来的自密实混凝土，它的固化和铸造应该是一种很好的方式。承建商应对自密实混凝土有一些体会。没有进一步查阅文献扼要的综述。在完整的报告里可以发现科学的文献来源。3、自密实混凝土的微观组织比起传统的混凝土(tc)和高性能混凝土(hpc)、微观结构的自密实混凝土(scc)是不同的。主要原因是由于其自密实混凝土微观结构中的变化。自密实混凝土修改后的微观结构在很大程度上是水化过程的变化所带来的结果。水化粉型自密实混凝土是依靠添加填料到系统里的类型。当应用的是石灰石填料时,可以观察到三种有关水泥水化的现象。额外的反应峰值的现象是因为添加了石灰石这一填料，在这一刻不太好理解,甚至导致一些争议。其中第一种

37、理论的假设开始于石灰石填料是惰性的,因此它不参与化学反应。在这种情况下,第三高峰是由于催化剂起的作用，因为存在于水泥里的c3a加速了一些反应。第二种理论认为石灰石填料作为反应型材料在反应里起着积极的作用,并伴有monocarboaluminate的形成。从sem分析可以看出,石灰石填料粒子保持着惰性,这将会支持第一种理论。从化学的角度考虑,有石灰石填料在的情况下会形成较稳定的monocarboaluminate，这点是很清楚的,这将会支持第二种说法。关于石灰石填充 carboaluminate 的形成起积极作用，所提到的是相对于水泥质量，只要填充少量的石灰石就可以与水泥孰料反应。比起传统振动混

38、凝土(tc)的微观结构,自密实混凝土的微观结构被报密度更大。更致密的微观结构、降低孔隙率在很大程度上是解释矿物填料的物理存在。此外,特别是水量结合的w/c比值与水化程度强烈影响孔隙结构。水化程度增加时，水化产品填补了越来越多的空间。孔的尺寸减小，导致连通性的降低。更低的 w/c 提供更低的毛细孔隙和连接。传统混凝土和自密实混凝土性能之间的比较,一般来说是不容易的,因为全世界对自密实混凝土有截然不同的概念。然而,为了量化一些微观结构特性,如凝胶孔隙率、毛细孔隙、总孔隙率,结果表明:力量的模型仍然是有效的!4、运输性质对于自密实混凝土 (scc)来说，仍不能确定自密实混凝土和常规振动组合之间的明显

39、区别，混合比例对放置和压实过程中是否有很大的影响，输运性质与显微结构特征的关系。系统地评估表明，与常规振实混凝土相比，尤其是自密实混凝土，输运特性的工作已被限制。此外，大部分地区开展了通常适用于自密实混凝土混合发展或特定的自密实混凝土料研究验证机械或耐久性性能项目的一小部分。因此，在某些情况下，与自密实混凝土相比较，没有足够合适的常规振动组合作为参考对象，而在其他情况下，运输性质上没有给出详细的测试条件作为结果。 由于大量参数影响，输运性质和在场的不同运输机制、常规振动混凝土与自密实混凝土之间的运输性质的比较,将取决于材料选择、有效灰胶比、粉含量和测试条件的选择,等等。这一点,加上可用的有限结

40、果,使它全面分析、理解所有的结果以及它们从不同来源获得的差异变得极其困难。但是,可以制定一些一般性的结论。5、降解机制 5.1、碳化 从有效的实验结果得出,自密实混凝土与传统混凝土相比，有着相同的水和水泥含量，有时会有较大的，有时会有较小的碳化深度，虽然差异性很小。然而这种实验上的比较并不简单。比较自密实混凝土与传统混凝土是非常困难的，什么是比较的基础尚不清楚：相同数量的水和水泥,相同的抗压强度 如果是精确固化的自密实混凝土,其孔隙结构是高密度和低渗透的。此外,其缓冲能力是非常重要的,通常高于自密实混凝土。然而，从有限的实验工作中,关于自密实混凝土石灰石填充碳化这方面似乎注意到略有增加的漏洞。然而,一般看