外文翻譯自密實混凝土的耐久性

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自密實混凝土的耐久性geert de schutter、guang ye、katrie

34、n audenaert、dirch bager、frank bellmann摘要：相比傳統(tǒng)混凝土而言,因為設計的配合比不同，對缺乏振動,不同耐久性特征的混凝土而言，可能被預期為自密實混凝土。最新的報告, rilem 技術委員會 tc 205 dsc 側重于自密實混凝土的耐久性,且首次收集了關于孔結構，氣泡系統(tǒng)和運輸機制的可用信息。研究總結出的耐久性結果，被銘記為基本機制和驅動力的變形。所有認為與耐久性相關的問題有,像碳化、氯離子滲透、抗凍性,asr、硫酸鹽侵蝕,碳硫硅鈣石的形成,耐火性能,等等。大體上，本文不是打算對混凝土耐久性這一方面做的綜述。目的不過是指有關自密實混凝土使用的規(guī)范,例如增加

35、大量的石灰石填料,等等本文總結了先進報告的重要結論1、引言自密實混凝土(scc)是一家創(chuàng)新型混凝土，不需要放置、振動壓實強度。它能夠根據(jù)自身的重量，完全充填模板，以達致全數(shù)壓實作用，甚至在擁擠的加固面前流。自密實的能力是可以，但不是必要的，相當于自流平能力。有時,應用自流平來描述自密實混凝土會有一個形變后完美的鑄件。自密實混凝土是在20世紀80年代日本所開發(fā)的。目的是發(fā)展可以替代無振動的混凝土。通過這種方式,一些健康風險以及環(huán)境問題就可以避免“白色手指綜合癥”(“白色、噪聲、振動)。2、報告的范圍值得強調的是，這個先進的報告一直在處理自密實混凝土的耐久性，處理顯示沒有分離、 滲色、 阻塞.精心

36、設計出來的自密實混凝土，它的固化和鑄造應該是一種很好的方式。承建商應對自密實混凝土有一些體會。沒有進一步查閱文獻扼要的綜述。在完整的報告里可以發(fā)現(xiàn)科學的文獻來源。3、自密實混凝土的微觀組織比起傳統(tǒng)的混凝土(tc)和高性能混凝土(hpc)、微觀結構的自密實混凝土(scc)是不同的。主要原因是由于其自密實混凝土微觀結構中的變化。自密實混凝土修改后的微觀結構在很大程度上是水化過程的變化所帶來的結果。水化粉型自密實混凝土是依靠添加填料到系統(tǒng)里的類型。當應用的是石灰石填料時,可以觀察到三種有關水泥水化的現(xiàn)象。額外的反應峰值的現(xiàn)象是因為添加了石灰石這一填料，在這一刻不太好理解,甚至導致一些爭議。其中第一種

37、理論的假設開始于石灰石填料是惰性的,因此它不參與化學反應。在這種情況下,第三高峰是由于催化劑起的作用，因為存在于水泥里的c3a加速了一些反應。第二種理論認為石灰石填料作為反應型材料在反應里起著積極的作用,并伴有monocarboaluminate的形成。從sem分析可以看出,石灰石填料粒子保持著惰性,這將會支持第一種理論。從化學的角度考慮,有石灰石填料在的情況下會形成較穩(wěn)定的monocarboaluminate，這點是很清楚的,這將會支持第二種說法。關于石灰石填充 carboaluminate 的形成起積極作用，所提到的是相對于水泥質量，只要填充少量的石灰石就可以與水泥孰料反應。比起傳統(tǒng)振動混

38、凝土(tc)的微觀結構,自密實混凝土的微觀結構被報密度更大。更致密的微觀結構、降低孔隙率在很大程度上是解釋礦物填料的物理存在。此外,特別是水量結合的w/c比值與水化程度強烈影響孔隙結構。水化程度增加時，水化產(chǎn)品填補了越來越多的空間?？椎某叽鐪p小，導致連通性的降低。更低的 w/c 提供更低的毛細孔隙和連接。傳統(tǒng)混凝土和自密實混凝土性能之間的比較,一般來說是不容易的,因為全世界對自密實混凝土有截然不同的概念。然而,為了量化一些微觀結構特性,如凝膠孔隙率、毛細孔隙、總孔隙率,結果表明:力量的模型仍然是有效的!4、運輸性質對于自密實混凝土 (scc)來說，仍不能確定自密實混凝土和常規(guī)振動組合之間的明顯

39、區(qū)別，混合比例對放置和壓實過程中是否有很大的影響，輸運性質與顯微結構特征的關系。系統(tǒng)地評估表明，與常規(guī)振實混凝土相比，尤其是自密實混凝土，輸運特性的工作已被限制。此外，大部分地區(qū)開展了通常適用于自密實混凝土混合發(fā)展或特定的自密實混凝土料研究驗證機械或耐久性性能項目的一小部分。因此，在某些情況下，與自密實混凝土相比較，沒有足夠合適的常規(guī)振動組合作為參考對象，而在其他情況下，運輸性質上沒有給出詳細的測試條件作為結果。 由于大量參數(shù)影響，輸運性質和在場的不同運輸機制、常規(guī)振動混凝土與自密實混凝土之間的運輸性質的比較,將取決于材料選擇、有效灰膠比、粉含量和測試條件的選擇,等等。這一點,加上可用的有限結

40、果,使它全面分析、理解所有的結果以及它們從不同來源獲得的差異變得極其困難。但是,可以制定一些一般性的結論。5、降解機制 5.1、碳化 從有效的實驗結果得出,自密實混凝土與傳統(tǒng)混凝土相比，有著相同的水和水泥含量，有時會有較大的，有時會有較小的碳化深度，雖然差異性很小。然而這種實驗上的比較并不簡單。比較自密實混凝土與傳統(tǒng)混凝土是非常困難的，什么是比較的基礎尚不清楚：相同數(shù)量的水和水泥,相同的抗壓強度 如果是精確固化的自密實混凝土,其孔隙結構是高密度和低滲透的。此外,其緩沖能力是非常重要的,通常高于自密實混凝土。然而，從有限的實驗工作中,關于自密實混凝土石灰石填充碳化這方面似乎注意到略有增加的漏洞。然而,一般看