外文翻譯--高性能混凝土的耐久性特點一綜述

1、<p><b>　　本科畢業(yè)設計</b></p><p><b>　　英 文 翻 譯</b></p><p>　　院（系部） 土木工程學院 </p><p>　　專業(yè)名稱 土木工程專業(yè) </p><p>　　年級班級　 道橋07-4班 </p><p&

2、gt;　　學生姓名　 周 鵬 </p><p>　　指導老師 程 朝 霞 </p><p>　　河南理工大學土木工程學院</p><p><b>　　二○一一年六月十日</b></p><p>　　The durability characteristics of high perfor

3、mance concrete: a review</p><p><b>　　Abstract</b></p><p>　　Durability problems of ordinary concrete can be associated with the severity of the environment and the use of inappropriat

4、e high water/binder ratios. High-performance concrete that have a water/binder ratio between 0.30 and 0.40 are usually more durable than ordinary concrete not only because they are less porous, but also because their cap

5、illary and pore networks are somewhat disconnected due to the development of self-desiccation. In high-performance concrete (HPC), the penetration of aggress</p><p>　　Author Keywords: Curing; Durability

6、; Fire-resistance; Freezing and thawing; High performance concrete </p><p>　　Article Outline</p><p>　　1. Introduction</p><p>　　2. Volumetric changes</p><p>　　3. Curing

7、concrete</p><p>　　4. Durability</p><p>　　4.1. General matters</p><p>　　4.2. Durability in a marine environment</p><p>　　4.2.1. Nature of the aggressive action</p>

8、<p>　　4.2.2. Chemical attack on concrete</p><p>　　4.2.3. Abrasion resistance</p><p>　　4.3. Freeze–thaw resistance</p><p>　　5. Fire resistance of HPC</p><p>　　5.1

9、. The channel tunnel fire</p><p>　　5.2. The Düsseldorf airport fire</p><p>　　5.3. Spalling of concrete under fire conditions</p><p>　　5.4. The Brite–Euram HITECO BE-1158 resear

10、ch project</p><p>　　6. Concluding remarks</p><p>　　References</p><p>　　1. Introduction</p><p>　　The recent developments in the field of high-performance concrete (HPC)

11、represent a giant step toward making concrete a high-tech material with enhanced characteristics and durability. These developments have even led to it being a more ecological material in the sense that the components––a

12、dmixtures, aggregates, and water––are used to their full potential to produce a material with a longer life cycle. Be that as it may, we know that concrete will never be an eternal material when measured agai</p>

13、<p>　　The concrete that was known as high-strength concrete in the late 1970s is now referred to as HPC because it has been found to be much more than just stronger: it displays enhanced performances in such areas a

14、s durability and abrasion resistance. Although widely used, the expression “HPC” is very often criticized as being too vague, even as having no meaning at all. Since there is no single best definition for the material kn

15、own as HPC, it is preferable to define it as a low water/binder concret</p><p>　　HPC can be made with cement alone or any combination of cement and mineral components, such as, blast furnace slag, fly ash, s

16、ilica fume, metakaolin, rice husk ash, and fillers, such as limestone powder. Ternary systems are increasingly used to take advantage of the synergy of some mineral components to improve concrete properties in the fresh

17、and hardened states, and to make high performance concrete more economical and ecological.</p><p>　　Fig. 1 represents schematically the fundamental microstructural difference between cement pastes havin

18、g a 0.65 and 0.25 water/cement ratio. In a 0.25 W/Cratio cement paste, there are more cement grains and consequently less water per unit volume so that cement grains are much closer to each other than in a 0.65 

19、;W/C cement paste. This major difference results in a completely different type of hydrated cement paste. A 0.65 W/C ratio cement paste is very porous and rich in crystallized outer hydrat</p><p

20、>　　Fig. 1. Schematical representation of the microstructure of two cement pastes having W/C ratios of 0.65 and 0.25.</p><p>　　Fig. 2. Microstructure of high water/cement ratio concrete: (a) high

21、 porosity and heterogeneity of the matrix, (b) orientated crystal of Ca(OH)2 on aggregate (AG), (c) CH crystals.</p><p>　　Fig. 3. Microstructure of a HPC: low porosity and homogeneity of the matrix: (a)

22、 absence of transition zone between the aggregate and cement paste; (b) dense cement paste in an air entrained high performance concrete.</p><p>　　In particular, in HPC, the coarse aggregate can be the weake

23、st link in concrete when the strength of the hydrated cement paste is drastically increased by lowering its water/binder ratio. In such cases, concrete failure can start to develop within the coarse aggregate. As a conse

24、quence, there can be exceptions to the water/binder ratio law when dealing with HPC. In some areas, decreasing the water/binder ratio below a certain level is not practical from a mechanical point of view because the str

25、</p><p>　　2. Volumetric changes</p><p>　　As with any other material, the volume of concrete changes as its temperature changes. Like any other material concrete creeps. But it is not the only vo

26、lumetric variations exerting itself on concrete. Depending on its curing condition, concrete presents volumetric variations, it usually shrinks but sometimes it swells. In this paper, swelling of chemical origin, such as

27、 sulfate or thaumasite attack or alkali aggregate reaction will not be considered, the only volumetric variation taken into acc</p><p>　　In all cases that will be considered in this paper, the origin of the

28、volumetric variation is the same, the appearance of tensile stresses in the menisci created in the fresh concrete as it is drying (plastic shrinkage) or in the hardened concrete due to self-desiccation (autogenous shrink

29、age) and due to dying (drying shrinkage).</p><p>　　Autogenous shrinkage is a consequence of the chemical contraction occurring in the cement paste when water hydrates cement particles. In fact, the absolute

30、volume of the hydrates formed is smaller than the sum of the absolute volume of the cement particles and the water that have reacted. Hydration creates some 8% voids, as found by Le Chatelier and Powers [3]. This very fi

31、ne porosity drains water from the coarser capillaries where water is not as strongly bonded. Consequently, as hydration prog</p><p>　　Drying shrinkage occurs when concrete dries in dry air, as concrete loose

32、s some of its internal water; menisci appear within the coarse superficial capillaries. In the case of drying shrinkage there is a mass loss.</p><p>　　In ordinary concrete with W/C ratio greater th

33、an 0.50, for example, there is more water than required to fully hydrate the cement particles and a large amount of this water is contained in well connected large capillaries so that the menisci created by self-desiccat

34、ion appear in large capillaries where they generate only very low tensile stresses. Therefore, the hydrated cement paste barely shrinks when self-desiccation develops (40–60 microstrains) [4].</p><p>　　In th

35、e case of HPC with a W/B ratio of 0.35 or less, significantly more cement and less mixing water have been used, so that the initial pore network is essentially composed of very fine capillaries. When self-desic

36、cation starts to develop, as soon as hydration begins, menisci rapidly develop into small capillaries if no external water is added. Since many cement grains start to hydrate simultaneously in HPC, the drying of the very

37、 fine capillaries can generate high tensile stresses that shrink </p><p>　　But, when there is an external supply of water, the capillaries do not dry out as long as they are connected to this external source

38、 of water [5]. The result is that no menisci, no tensile stress, and no autogenous shrinkage develop within a HPC thin element having a W/C ratio of 0.35 that is constantly water cured from the moment of its se

39、tting. But when the W/C ratio is lower than 0.35 or at the center of a large concrete element made with a 0.35 W/C ratio HPC, concrete microstructure can be s</p><p>　　Thus, the essential

40、 difference between ordinary concrete and HPC is that ordinary concrete exhibits practically no autogenous shrinkage, whether it is water cured or not, whereas HPC can experience significant autogenous shrinkage if it is

41、 not water cured during the hydration process. Autogenous shrinkage does not develop in HPC as long as the pores and capillaries are interconnected and have access to external water, but, when the continuity of the pore

42、and capillary systems is broken, then, an</p><p>　　Fig. 4. Influence of curing conditions on the occurence of autogenous shrinkage.</p><p>　　Drying shrinkage of the hydrated cement paste begins

43、at the surface of the concrete and progresses more or less rapidly through the concrete, depending on the relative humidity of the ambient air and the size of capillaries. Drying shrinkage of ordinary concrete is therefo

44、re rapid because the capillary network is well connected and contains open capillaries at the surface of the concrete. Drying shrinkage in HPC is slow because capillaries are very fine and soon get disconnected.</p>

45、;<p>　　Another major difference between drying shrinkage and autogenous shrinkage is that drying shrinkage develops from the surface inwards, while autogenous shrinkage is homogeneous and isotropic, insofar as the

46、 cement particles and water are well dispersed within the concrete.</p><p>　　Thus, there are considerable differences between ordinary concrete and HPC with respect to their shrinkage behavior. The cement pa

47、ste of an ordinary concrete exhibits rapid drying shrinkage progressing from the surface inwards, whereas HPC cement paste can develop a significant isotropic autogenous shrinkage when not water cured. This difference in

48、 the shrinkage behavior of the cement paste has very important consequences for concrete curing and concrete durability.</p><p>　　Although the shrinkage of a hydrated cement paste is a very important paramet

49、er with respect to concrete volumetric stability, it is not the only one. A key parameter is the amount of aggregate, and, more specifically, the quantity of coarse aggregate. Too often it is forgotten that aggregates do

50、 more than simply act as fillers in concrete. In fact, they actively participate in the volumetric stability of concrete when they restrain the shrinkage of the hydrated cement paste: concrete shrinkage </p><p

51、>　　3. Curing concrete</p><p>　　HPC must be cured quite differently from ordinary concrete because of the difference in shrinkage behavior described above, as emphasized in Fig. 5. If HPC is not water

52、 cured immediately following placement or finishing, it is prone to develop severe plastic shrinkage because it is not protected by bleed water, and later on develops severe autogenous shrinkage due to its rapid hydratio

53、n. While curing membranes provide adequate protection to ordinary concrete (which is insensitive to autogenous s</p><p>　　Fig. 5. The most appropriate curing regimes during the course of the hydration reacti

54、on.</p><p>　　The critical curing period for any HPC runs from placement or finishing, up to 2 or 3 days later, and the most critical period is usually between 12 and 36 h. In fact, the short time during whic

55、h efficient water curing must be applied to HPC can be considered a significant advantage over ordinary concrete.</p><p>　　Those who specify and use HPC must be aware of the dramatic consequences of missing

56、early water curing. Initiating water curing after 24 h is too late, because most of the time, a great deal of plastic and autogenous shrinkage have already occurred and, by this time, the capillary and pore network are d

57、isconnected in many places and the microstructure is already so compact that external water has little chance of penetrating very deep into the concrete.</p><p>　　Water ponding or fogging is the best way to

58、cure HPC; one of these two methods must be applied as soon as possible, immediately following placement or finishing. An evaporation retarder can be applied temporarily to prevent the development of plastic shrinkage. If

59、, for any reason, water ponding or fogging cannot be implemented for 7 days, then the concrete surface should be covered with wet burlap (hessian) or preferably a prewetted geotextile. The burlap or the geotextile must b

60、e kept constantl</p><p>　　Moreover, it is observed that when any concrete is water cured during setting it does not shrink but rather swell. Fig. 6 illustrates the effect of early water curing on t

61、he volumetric change of concrete.</p><p>　　Fig. 6. Length changes according to different curing regimes for the 0.35 W/C ratio concrete.</p><p>　　Water curing can be stopped after 7 da

62、ys because most of the cement at the surface of concrete has hydrated and any further water curing has little effect on the development of shrinkage. After 7 days of water curing, HPC experiences slow drying shrinkage du

63、e to the compactness of its microstructure, and that autogenous shrinkage has already dried out the coarse capillaries pores. Even then, theoretically the best thing to do is to paint HPC or to use a sealing agent so tha

64、t the last water that </p><p>　　Partial replacement of coarse aggregate by an equivalent volume of saturated lightweight aggregate has been used to counteract autogenous shrinkage internally [7]. The saturat

65、ed lightweight aggregate particles act as small water reservoirs throughout the mass of concrete; they can fill the very fine pores created by hydration reactions. Therefore, the water of the lightweight aggregate partic

66、les is drained along with that contained in the fine capillaries of the HPC. The menisci within the cemen</p><p>　　It is well known that concrete is never cured properly in the field, despite the fact that i

67、t is always written in the specifications that contractors have to cure concrete. Contractors are not curing concrete for a very simple reason: they are not specifically paid for it, therefore, concrete curing is always

68、perceived by them as an unprofitable activity or even a source of expense and therefore a waste of time. But, when contractors are specifically paid to water cure concrete they do it as th</p><p>　　Therefore

69、, the best way to be sure that HPCs are properly and efficiently cured in the field is to specifically pay contractors to cure concrete [6].</p><p>　　This very long introductory remarks were made to emphasiz

70、e that two important key parameters control the penetration of any aggressive agents in concrete: the water/cement or the water/binder ratio, and the curing of concrete. Specifying a low water/binder ratio concrete is a

71、necessary condition, but not a sufficient one..</p><p>　　高性能混凝土的耐久性特點：一綜述</p><p><b>　　摘要</b></p><p>　　普通混凝土的耐久性問題，與環(huán)境的嚴重程度和不適當?shù)母咚冶认嗦?lián)系。具有水灰比在0.30和0.40之間的高性能混凝土通常比普通混凝土更耐

72、用，不僅因為他們氣孔少，而且還因為他們的毛細管和毛孔網(wǎng)狀物有點不連通而導致自我干燥的發(fā)展。在高性能混凝土（HPC），入侵性因子的滲透是相當困難的，只有表面的滲透。然而，自干燥非常有害，如果它不是在水化反應的早期發(fā)展階段的控制，因此，高性能混凝土的養(yǎng)護必須完全不同于普通混凝土。遠在北海和加拿大的經(jīng)驗表明，當混凝土得到適當設計和養(yǎng)護，即使在非常惡劣的環(huán)境中也令人滿意。然而，高性能的耐火不如普通混凝土，但有時并不像一些悲觀的報告中那樣寫的不好

73、。混凝土，無論其類型，相對于其他建筑材料而言，仍然是一個安全的材料。</p><p>　　作者關(guān)鍵詞：固化；耐久性；耐火性 ；冷凍和解凍；高性能混凝土</p><p><b>　　文章概要</b></p><p><b>　　1．介紹</b></p><p><b>　　2．體積變化<

74、;/b></p><p><b>　　3．混凝土養(yǎng)護</b></p><p><b>　　4．耐久性</b></p><p><b>　　4.1．一般內(nèi)容</b></p><p>　　4.2．在海洋環(huán)境中的耐久性</p><p>　　4.2.1．更

75、強硬措施的性質(zhì)</p><p>　　4.2.2．化學對混凝土侵蝕</p><p><b>　　4.2.3．耐磨性</b></p><p><b>　　4.3．耐凍融性</b></p><p>　　5．高性能混凝土的耐火性</p><p>　　5.1．英吉利海峽隧道內(nèi)火災<

76、;/p><p>　　5.2．杜塞爾多夫機場的火災</p><p>　　5.3．火災條件下的混凝土剝落</p><p>　　5.4．Brite-Euram HITECO BE-1158的研究項目</p><p><b>　　6．結(jié)束語</b></p><p><b>　　參考文獻</b&

77、gt;</p><p><b>　　1、簡介</b></p><p>　　在高性能混凝土領(lǐng)域的最新發(fā)展（HPC）代表一個巨大的進步，并增加其耐久性與特性，使混凝土成為高科技材料。這些事態(tài)發(fā)展，甚至導致它是一個在意義上更加生態(tài)材料的組件 ——外加劑，骨料，水 ——是用來實現(xiàn)其全部潛力，生產(chǎn)具有較長的生命周期材料。雖然如此，可我們知道，從對地質(zhì)測量時間來說，混凝土絕不會是

78、一個永恒的材料。如果我們放眼未來足夠遠，任何混凝土，將結(jié)束其生命周期，像石灰石，粘土和石英砂，這是鈣，硅，鐵，和鋁在地球環(huán)境中最穩(wěn)定的礦物形式。因此，作為工程師或科學家，我們所能做的就是將盡可能多的延續(xù)這些人工巖石的生命周期。</p><p>　　在70年代末被認為是高強度混凝土現(xiàn)在被稱為高性能混凝土，因為它被發(fā)現(xiàn)不僅僅是強度大：它顯示為增強耐久性和耐磨性等方面性能。 雖然廣泛使用，但是“高性能混凝土”

79、還是很經(jīng)常被過于模糊的批評，甚至有沒有意義。 由于高性能混凝土沒有一個最佳的材料定義，更適合將其定義為一低水灰比并接收充足的水分固化的混凝土。</p><p>　　高性能混凝土，可單獨與水泥或與水泥和任何礦物成分結(jié)合，如高爐礦渣，粉煤灰，硅粉，偏高嶺土，稻殼灰，石灰石粉填料。三元系統(tǒng)越來越多地用于采取一些礦物成分的協(xié)同作用，以改善混凝土在新鮮和硬化方面的性能，使高性能混凝土更經(jīng)濟和生態(tài)。</p&g

80、t;<p>　　圖1代表最根本的微觀結(jié)構(gòu)，在水灰比為0.65和0.25的水泥漿體之間的區(qū)別。在水灰比為0.25的水泥漿中的單位體積內(nèi)有更多的水泥顆粒和較少的水，使其水泥顆粒比水灰比為0.65水泥漿中的更緊密。這個主要的不同結(jié)果在于水泥漿水化的類型完全不同。水灰比為0.65的水泥漿會有很多孔和通過降解水的過程形成富含結(jié)晶的外部水化產(chǎn)物，而一個水灰比為0.25的水泥漿非常緊湊，在本質(zhì)上水泥水化產(chǎn)物組成的是一種凝膠中發(fā)展類似的擴

81、散過程。圖2和圖3說明了在高和低水灰比的水泥漿之間的主要顯微結(jié)構(gòu)的差異。在這個根本的微觀結(jié)構(gòu)差異的一個主要差異是水泥漿和過渡區(qū)的糊狀物和骨料的機械和耐久性。</p><p>　　圖1 .表示的是水灰比為0.25和0.65的水泥漿體的顯微結(jié)構(gòu)。</p><p>　　圖2 微觀結(jié)構(gòu)的高水灰比的混凝土:(a)高孔隙度和儲層非均質(zhì)性的基質(zhì)(b)朝向晶體的Ca(OH)2的骨料(AG),(c)CH晶體

82、。</p><p>　　圖3 高性能混凝土的微觀結(jié)構(gòu)和孔隙度低均勻的基質(zhì):(a)在水泥漿和骨料之間缺乏的過渡區(qū);(b)濃厚的水泥漿在一個空氣中產(chǎn)生高性能混凝土。</p><p>　　在高性能混凝土中，特別是粗骨料在混凝土中最薄弱的環(huán)節(jié)時，通過降低其水灰比，使水泥漿的強度大幅增加。在這種情況下，混凝土破壞就可以開始在粗骨料發(fā)展。因此，在高性能混凝土處理的時候，可以有例外水灰比。在一些地區(qū)，

83、減少了水灰比且低于一定水平的比例，實際上并不是從機械角度，因為高性能混凝土的強度不會明顯超過了混凝土骨料的抗壓強度。當其抗壓強度被粗骨料限制，唯一的方法只有增加骨料的強度，才能獲得較高的強度。不過，減少水灰比時雖然沒有增加抗壓強度，但基質(zhì)密壓實度的增大，也提高高性能混凝土的耐久性。</p><p><b>　　2、體積變化</b></p><p>　　與任何其他材料一

84、樣，混凝土體積隨溫度變化而變化。像任何其他材料一樣具體的蠕動。但它不是混凝土本身發(fā)生變化的唯一體積。根據(jù)其固化條件，混凝土出現(xiàn)體積變化，它通常會縮小，但有時它膨脹。在本文中，化學制品膨脹的來源，如硫酸鹽或碳硫硅鈣石攻擊或堿骨料反應等引起的膨脹將不予考慮，只有考慮塑性收縮，自體或等溫收縮，干燥收縮等引起的體積變化。碳化收縮將不會被考慮，因為這是一個非常緩慢的過程，發(fā)生的晚得多。</p><p>　　在所有被本文所考

85、慮的情況下，體積變化的來源是相同的，拉應力出現(xiàn)在新拌混凝土制造中，因為它是干燥（塑料收縮）或在硬化混凝土中因為自干燥（自收縮）和死亡（干燥收縮）而引起的。</p><p>　　自收縮是一種發(fā)生在水泥水化物水泥顆?；瘜W收縮的結(jié)果。事實上，固化劑的絕對體積小于水泥顆粒和參加反應的水總和絕對體積。水化能產(chǎn)生8％空隙，被Le Chatelier和Powers發(fā)現(xiàn)。這很細的孔隙從較粗的毛細管那里吸水。因此，水化的進展已觀察

86、到，粗毛細管的水被掏空（如在干燥收縮的情況），但沒有任何質(zhì)量損失。這種現(xiàn)象被稱為自干燥。自干燥是由于水的運動正在從既存的粗毛細血管向很細的孔隙度由水泥水化。</p><p>　　當混凝土干燥收縮在干燥空氣中，混凝土會輸送一些內(nèi)部水，半月板在粗糙毛細管表面出現(xiàn)。在干燥收縮的情況是有質(zhì)量的損失。</p><p>　　在普通混凝土中水灰比比值大于0.50，例如，有更多的水要被水泥顆粒充分水化，大

87、量的水都包含在與其保持良好關(guān)系,以便狀大微血管由自干燥出現(xiàn)于大毛細管的地方,他們只生成非常低的拉應力。因此，水泥的水化時幾乎縮自干燥的發(fā)展。</p><p>　　在高性能混凝土中水灰比為0.35或低于的情況下，顯然更多的水泥和少量水已被使用，因此，初始孔隙網(wǎng)絡基本上是由很細的毛細血管組成。當自我干燥開始發(fā)展，一旦水化開始，如果沒有外部加水則將迅速發(fā)展成為小毛細管。由于許多水泥顆粒開始在高性能混凝土中與水化合，非常

88、細的干燥毛細管可以產(chǎn)生高拉應力。這種早期收縮被稱為自收縮。當然，這兩種類型的干燥發(fā)展在相同直徑的毛細管中，在普通混凝土中可以看到自收縮和干燥收縮的收縮率是一樣大的。</p><p>　　但是，當有外部提供的水，只要它們連接到這個水源，毛細管就不會干燥。結(jié)果是，沒有半月板就無拉應力，并且沒有自收縮發(fā)展在一個水灰比為0.35且有不斷的水來養(yǎng)護的高性能混凝土中。但是，當水灰比低于0.35或在該中心有一些大的混凝土構(gòu)件水

89、灰比為0.35的高性能混凝土時，混凝土微觀結(jié)構(gòu)是如此密集，可以阻止水的滲透，和在混凝土自我干燥。事實上，當水泥顆粒和有外加水源的水水化，水泥絕對體積的增加，導致了充填的一些小孔和毛細管。在這種情況下，有個更為合適說法那是等溫收縮而不是自體收縮，因為自收縮是指一個封閉系統(tǒng)的收縮。</p><p>　　因此，高性能混凝土和普通混凝土的本質(zhì)區(qū)別是，無論是水養(yǎng)護與否，普通混凝土是幾乎沒有自收縮，而高性能混凝土如果不是水化

90、過程中水的養(yǎng)護，可以看到到顯著的自收縮。只要毛孔和毛細管是相互關(guān)聯(lián)的并已獲得外部的水，在高性能混凝土之內(nèi)，自收縮不會發(fā)展。但是，當連續(xù)性的孔隙毛細管系統(tǒng)被打破，那么在高性能混凝土的水化水泥中自收縮內(nèi)開始發(fā)展，如圖所示，如圖4。</p><p>　　圖4 養(yǎng)護條件的影響發(fā)生在自收縮上。</p><p>　　水泥漿體的干燥收縮開始在混凝土表面，并且迅速或多或少向混凝土內(nèi)部進展，根據(jù)周圍空氣相對

91、濕度和毛細管的大小而定。普通混凝土的干燥收縮是快速的，因為毛細管網(wǎng)良好的聯(lián)系，并包含在混凝土表面開放的毛細管。高性能混凝土干燥收縮是緩慢的，因為毛細管非常細，并很快得到斷開。</p><p>　　干燥收縮和自收縮另一個主要區(qū)別是，干燥收縮的發(fā)展由表及里,而自收縮均勻和各向同性,因此在水泥顆粒與水是分散在混凝土內(nèi)。</p><p>　　因此，普通混凝土和高性能混凝土在收縮行為上有著巨大的差異

92、。一個普通水泥混凝土展品的干燥收縮快速從表面進入臟腑，而高性能混凝土水泥漿沒有水養(yǎng)護，能顯著的各向同性自收縮。水泥混凝土收縮行為的差異性，對混凝土的養(yǎng)護和耐久性非常重要。</p><p>　　雖然水化水泥的收縮是一種非常重要的因數(shù)，對混凝土體積的穩(wěn)定性,它不是唯一的一個。關(guān)鍵參數(shù)是一定量的骨料,更確切的說,粗集料的數(shù)量。常常忘記，在混凝土中骨料不僅僅是作為填料。事實上，當他們抑制水泥水化收縮時，他們積極參與混凝土

93、體積穩(wěn)定性：混凝土的收縮率總是遠遠低于同一水灰比的水泥漿。眾所周知，通過增加粗集料的含量，可以很容易地減少混凝土的收縮，但它絕不能忘記的是，水泥的水化收縮保持不變，它簡直更容易受約束的,并且有更少的水泥,使得該混凝土的體積穩(wěn)定性增加?？梢酝ㄟ^修改粗骨料骨架來抑制水化水泥的收縮，可能或不可能產(chǎn)生一個有裂紋的網(wǎng)絡，根據(jù)過程中拉應力的強度的發(fā)展，考慮水化水泥拉伸的強度。</p><p><b>　　3、混凝土

94、養(yǎng)護</b></p><p>　　高性能混凝土的養(yǎng)護不同于普通混凝土，因為以上所述普通混凝土的收縮行為上的差異，在圖5被強調(diào)。如果HPC不是水養(yǎng)護好后立即寄養(yǎng)或整理，因為它不放水保護，很容易出現(xiàn)嚴重的塑性收縮的發(fā)展，以及后面的嚴重的自收縮是由于快速水化的發(fā)展。雖然養(yǎng)護膜對普通混凝土提供足夠的保障（這是不敏感的自收縮），但它們只能幫助在高性能混凝土中防止塑性收縮，但沒有抑制自體收縮。</p>

95、<p>　　圖5 水化反應過程中最合適的養(yǎng)護制度。</p><p>　　任何高性能混凝土的養(yǎng)護時間從寄養(yǎng)或完成，最多2到3天之后，而最關(guān)鍵的時期通常是12至36小時。事實上，在很短的時間，高效水固化必須運用在高性能混凝土中，才可以被認為是超過普通混凝土的一個重要優(yōu)勢。</p><p>　　指定并使用高性能混凝土的人必須意識到這種失去早期水養(yǎng)護巨大的影響。24小時后啟動水養(yǎng)護為

96、時已晚，因為大多數(shù)時候，大量的塑料和自收縮已經(jīng)發(fā)生了改變，這時候，在許多地方毛細血管和毛孔網(wǎng)絡斷開，并且圍觀結(jié)構(gòu)已經(jīng)很緊湊，外部水滲透到混凝土非常深的機會很小。</p><p>　　積水或霧化是養(yǎng)護高性能混凝土最好的方法來;這兩種方法之一，必須盡快應用后，立即寄養(yǎng)或完成。蒸發(fā)緩速器可用于暫時以防止塑性收縮。出于任何原因，如果積水或霧化不能實施7天，然后用濕麻袋（麻袋）在混凝土表面覆蓋或最好是用一種專用土工布。土工

97、布或粗麻布必須經(jīng)常用透雨軟管保持濕潤了，并且采用聚乙烯板保護其免受干燥,以確保養(yǎng)護期間的任何時期都是混凝土允許干燥上和經(jīng)歷任何自收縮的時間。</p><p>　　而且，觀察到任何混凝土在設定的水養(yǎng)護中不是收縮而膨脹。圖6在混凝土的體積變化說明早期水養(yǎng)護的影響。</p><p>　　圖6長度的變化取決于水灰比為0.35的混凝土的養(yǎng)護制度。</p><p>　　水養(yǎng)護在

98、7天后可停了，因為在混凝土表面的水泥已經(jīng)水化，任何進一步的水養(yǎng)護對收縮的影響不大。經(jīng)過7天的水養(yǎng)護，高性能混凝土的經(jīng)驗干燥收縮緩慢，是由于其微觀結(jié)構(gòu)緊湊，而且自收縮已經(jīng)干涸了毛細血管粗大毛孔的水。即使這樣，理論上最好的辦法是噴涂油漆或使用高性能密封劑，使最后在混凝土中的水仍然可以保留為水化作出貢獻。沒有實際的優(yōu)勢，噴涂或密封多孔混凝土，因為它是不可能獲得絕對防水涂料、噴涂或高性能混凝土密封，但是，可以很容易和有效的。</p>

99、<p>　　采用等效容量的飽和輕質(zhì)骨材來更換局部粗集料已被用來抵消內(nèi)部的收縮。飽和輕集料顆粒作為小規(guī)模水庫貫穿整個混凝土的質(zhì)量，他們能夠填滿該極細毛孔由水化反應。因此,水輕骨料顆粒中的水沿著在高性能混凝土優(yōu)良的毛細管排出。在水泥漿在小毛細血管發(fā)展，這意味著更低的拉應力和較低的自收縮。輕集料還降低了抗壓強度和彈性模量。減縮外加劑也可以用。</p><p>　　眾所周知，在場地混凝土是不可能被適當?shù)酿B(yǎng)護

100、，但是事實上它總是在說明書上被承建商寫出。 承包商不養(yǎng)護混凝土的原因很簡單：因為他們沒有明確的為養(yǎng)護混凝土付費用，因此，混凝土養(yǎng)護總是被他們視為一個無利可圖的活動甚至是花費的來源和浪費時間。 但是，當承包商明確的支付養(yǎng)護混凝土的費用時，他們才這樣做，因為他們的任何其他項目是一樣支付。 三年來，蒙特利爾市和魁北克省的運輸要求直接給出早期水養(yǎng)護每個項目的單位價格。 由于這項新對早期混凝土養(yǎng)護水政策的引

101、發(fā)，讓人吃驚的是，看到多么的熱心的承建商成為水養(yǎng)護的問題?，F(xiàn)在對他們來說水養(yǎng)護是被視為利潤來源。 從第一次在這個問題上的經(jīng)驗已經(jīng)發(fā)現(xiàn)，早期水養(yǎng)護成本大約是1％，是非常溫和的價格時，考慮到這種方式是建立完善混凝土結(jié)構(gòu)耐久性的十分之一。</p><p>　　因此，最好的辦法，以確保在場地能適當和有效的養(yǎng)護高性能混凝土，是明確具體支付承包商養(yǎng)護混凝土的費用。</p><p>　　這很長