外文翻譯---商品混凝土早期裂縫的成因及防治措施

1、<p>　　Ready Mixed Concrete early Crack and prevention measures</p><p>　　商品混凝土早期裂縫的成因</p><p><b>　　及防治措施</b></p><p>　　學(xué) 生 姓 名： 王 昀 </p><p&g

2、t;　　學(xué) 生 班 級(jí)： 土木0648班 </p><p>　　所 在 學(xué) 院： 土 木 學(xué) 院 </p><p>　　所 學(xué) 專 業(yè)： 土 木 工 程 </p><p>　　專 業(yè) 方 向： 建 筑 工 程 </p><p>　　指 導(dǎo) 教 師： 袁志仁老師

3、 </p><p>　　教 師 職 稱： 講 師 </p><p>　　土 木 學(xué) 院</p><p>　　2010年 4月15日</p><p>　　Ready Mixed Concrete Crack and early</p><p>　　prevention measu

4、res</p><p>　　Abstract: This paper on the engineering practice prone to early fracture analysis and description, but also introduced a number of targeted prevention and control measures</p><p>　　

5、With the continuous expansion of the scale of construction and quality of construction works to raise awareness of the importance of commodities for its concrete technical and economic advantages, in particular, is stabl

6、e, reliable, good quality favored by construction units. However, the use of commercial concrete construction quality of works is also a lot of accidents, the most common problem when the number of cracks, in particular

7、the coefficient of the surface plate, mass concrete walls, a</p><p>　　Concrete is a solid, liquid, gas, a combination of non-homogeneous composite material, after forming as the temperature, humidity and oth

8、er environmental conditions will be formed under the influence of the naked eye can not see the micro-cracks in the concrete composition of materials and micro - different structures as well as the environmental impact o

9、f different causes of the cracks in the concrete have a very complicated and only works in this article the author encountered in the actual si</p><p>　　1, aggregate concrete cracks caused by plastic setting

10、</p><p>　　When in the pouring of concrete, due to vibration and gravity the role of rods, sinking aggregate, cement increased, until this fall when the side to stop the concrete to harden, when such a fall b

11、y the plastic template, steel and embedded parts of inhibition ( subsidence or a template, move) the cracks will appear, which cracks appear in most of half an hour after pouring concrete to 3 hours, still in the plastic

12、 state of concrete, concrete surface when the immediate disappearance of Shuiguang </p><p>　　Prevention measures to meet the pumping and construction under the premise of minimizing the collapse of concrete,

13、 the construction process should be kept under observation in the displacement of the template and trace the dense poured concrete, the vibration can not leak, over-vibration, and in the first Vibration 20 ~ 30mm after t

14、he interval after the resumption of the second vibration. If such cracks in the concrete before the final setting of concrete trowel surface to re-use of wood rubbed </p><p>　　2, plastic shrinkage cracks<

15、/p><p>　　After pouring the concrete is still in plastic state, as a result of surface evaporation caused by excessive cracks, this kind of crack on the surface appear more seamless, shape irregular, varying the

16、 length of width, was cracked like a depth less than 50mm, but sheet if the concrete in the structure of clay mixed with large quantities of silt are likely to be penetrated. The main causes of concrete after pouring abo

17、ut 3 ~ 4 hours is not covered by the surface, especially the flat structure in </p><p>　　Prevention approach is the construction units in a timely manner after the pouring of concrete covering the conservati

18、on and increase environmental humidity, concrete products can be pumped in to meet, and easy under the premise of the machine to minimize the collapse, the lower the rate of sand, and strictly control bone the volume of

19、material containing clay, mixed materials, such as mixing fly ash, such as cracks in the concrete before the end of the second condensate clean light, then a time</p><p>　　Cracks in the general setting of pl

20、astic and plastic shrinkage cracks are non-structural cracks in the structural properties of no significant impact. Plastic sink and sometimes there is no significant difference between contraction, intertwined with, the

21、 quality of concrete used in raw materials have a certain influence, but not decisive role. We have encountered a work sheet in the process of pouring, when the hot season in August, the morning of pouring concrete into

22、the cracks began to appea</p><p>　　3, the temperature of mass concrete cracks</p><p>　　Hydration process of cement hydration have some heat, and most of its heat is released within three days, c

23、oncrete is a poor conductor of heat, especially the large volume of concrete, resulting in a large number of hydration heat is not easy to distribute, the internal temperature rising , and the concrete surface heat faste

24、r, so have a temperature gradient inside and outside the cross-section, especially when the temperature difference between day and night, the temperature difference between </p><p>　　Prevention is the mass c

25、oncrete should be prepared with low heat of hydration of cement, such as slag cement, mixing expansion agent and, more importantly, the construction units to set up temperature measurement devices, thermal insulation at

26、the same time take measures, such as the use of plastic film and bags coverage to to ensure that the temperature difference between inside and outside is less than 25 ℃</p><p>　　4, the construction caused cr

27、acks</p><p>　　To drive the progress of construction, pouring concrete does not meet the design strength, even in the casting that is less than 24 hours after the beginning of Master, piling up loads, often r

28、esulting in cracking plate. Consequently, only the supply of units and construction units work closely with the two sides and concrete products in strict accordance with the relevant standards, norms for the management o

29、f production and construction in order to effectively guarantee the quality of concrete</p><p>　　From 《Construction & Engineering Industry Profile》 United Kingdom</p><p>　　商品混凝土早期裂縫的成因及防治

30、措施</p><p>　　摘要：本文就工程實(shí)際中容易出現(xiàn)的早期裂縫進(jìn)行了分析和說(shuō)明，同時(shí)也有針對(duì)性的介紹了一些防治措施。 </p><p>　　隨著建設(shè)規(guī)模的不斷擴(kuò)大及人們對(duì)建筑工程質(zhì)量重要性認(rèn)識(shí)的提高，商品混凝土以其技術(shù)、經(jīng)濟(jì)上的優(yōu)越性，尤其是穩(wěn)定、可靠、優(yōu)良的質(zhì)量深受建設(shè)單位的青睞。但是，目前使用商品混凝土施工的工程出現(xiàn)質(zhì)量事故的現(xiàn)象也很多，其中最常見(jiàn)的當(dāng)數(shù)裂縫問(wèn)題，尤其是表面系數(shù)大的

31、板、墻以及大體積混凝土施工工藝不良等原因造成混凝土出現(xiàn)裂縫的問(wèn)題，引起了很多不必要的糾紛，有些早期裂縫如果早發(fā)現(xiàn)早處理的話是不會(huì)影響結(jié)構(gòu)物的外觀及使用的。 </p><p>　　混凝土是由固、液、氣組合而成的非均質(zhì)復(fù)合材料，在成型后隨著溫度、濕度等環(huán)境條件的影響下會(huì)形成肉眼看不到的微裂縫，由于混凝土的組成材料和微觀構(gòu)造不同以及受環(huán)境影響的不同，混凝土產(chǎn)生裂縫的原因很復(fù)雜，本文中筆者僅就工程實(shí)際中遇到的情況對(duì)早期裂

32、縫的成因及預(yù)防略加說(shuō)明。 </p><p>　　1、混凝土骨料塑性沉落引起的裂縫</p><p>　　混凝土在澆注時(shí)，由于振動(dòng)棒和重力的作用，骨料下沉、水泥漿上升，這種沉落直到混凝土硬化時(shí)方停止，當(dāng)這種塑性沉落受到模板、鋼筋及預(yù)埋件的抑制(或者模板沉陷、移動(dòng)時(shí))就會(huì)出現(xiàn)裂縫，這種裂縫大多出現(xiàn)在混凝土澆注后半小時(shí)至3小時(shí)之間，混凝土尚處在塑性狀態(tài)，混凝土表面消失水光時(shí)立即產(chǎn)生，沿著梁及板上面

33、鋼筋的走向出現(xiàn)，主要是混凝土塌落度大、沉陷過(guò)高所致。另外在施工過(guò)程中如果模板綁扎的不好、模板沉陷、移動(dòng)時(shí)也會(huì)出現(xiàn)此類裂縫。 </p><p>　　預(yù)防的措施是在滿足泵送和施工的前提下盡可能減小混凝土塌落度，施工過(guò)程中應(yīng)經(jīng)常觀察模板的位移和混凝土澆搗的密實(shí)情況，不能漏振、過(guò)振，且在第一次振搗后間隔20～30mm后，進(jìn)行第二次復(fù)振。如果產(chǎn)生這種裂縫，在混凝土終凝前將混凝土裂面用木抹子重新抹平搓毛，可使裂縫愈合。 &l

34、t;/p><p><b>　　2、塑性收縮裂縫</b></p><p>　　混凝土澆注后仍處于塑性狀態(tài)時(shí)，由于表面水分蒸發(fā)過(guò)快而產(chǎn)生的裂縫，這類裂縫隙多在表面出現(xiàn)，形狀不規(guī)則、長(zhǎng)短寬窄不一、呈龜裂狀，深度一般不超過(guò)50mm，但薄板結(jié)構(gòu)如果混凝土中摻有含泥量大的粉砂則可能被穿透。產(chǎn)生的原因主要是混凝土澆注后3～4小時(shí)左右表面沒(méi)有被覆蓋，特別是平板結(jié)構(gòu)在炎熱或大風(fēng)天氣混凝土表

35、面水分蒸發(fā)過(guò)快，或者是被基礎(chǔ)、模板吸水過(guò)快，以及混凝土本身的水化熱高等原因造成混凝土產(chǎn)生急劇收縮，到此時(shí)混凝土強(qiáng)度趨近于零，不能抵抗這種變形應(yīng)力而導(dǎo)致開(kāi)裂，從混凝土中蒸發(fā)和吸收水分的速度越快，塑性收縮裂縫越易產(chǎn)生，而商品混凝土由于為了滿足可泵性、流動(dòng)性、出機(jī)時(shí)混凝土的塌落度和砂率比普通混凝土大很多，再加上夏季施工中及大體積混凝土中摻加緩凝劑，早期強(qiáng)度低所以其水分特別容易散失，表面容易形成裂縫。</p><p>　

36、　預(yù)防的辦法是施工單位在澆注混凝土后要及時(shí)覆蓋養(yǎng)護(hù)，增加環(huán)境濕度，商品混凝土公司在滿足可泵性、和易性的前提下盡量減小出機(jī)塌落度、降低砂率、嚴(yán)格控制骨料的含泥量、摻加粉煤灰等混合材，如出現(xiàn)裂縫在混凝土終凝前進(jìn)行二次抹光，然后及時(shí)灑水或覆蓋。</p><p>　　一般的塑性沉落裂縫和塑性收縮裂縫都屬于非結(jié)構(gòu)性裂縫，對(duì)結(jié)構(gòu)性能無(wú)大影響，塑性沉落和收縮有時(shí)沒(méi)有明顯區(qū)別，交織在一起，混凝土所用原材料質(zhì)量有一定影響，但不起決

37、定作用。我們?cè)龅揭还こ淘跐舶暹^(guò)程中，正值8月份炎熱季節(jié)，上午澆注的混凝土到中午就開(kāi)始出現(xiàn)裂縫，至下午我們建議未終凝的部分進(jìn)行二次抹光，裂縫消失(注：二次抹光的時(shí)機(jī)要掌握好，因初凝前作用很小，終凝后抹不動(dòng))但是已終凝的部分裂縫大部分已穿透板面，并呈龜裂狀，傍晚澆注的混凝土通過(guò)調(diào)整配比，去掉其中摻用的細(xì)砂，未再發(fā)現(xiàn)裂縫。但是之后此工地使用相同配合比及相同原材料又澆注了兩次板，上午澆注還是有裂縫出現(xiàn)而午后澆注的基本上未發(fā)現(xiàn)。且相同的混凝土不

38、同的施工隊(duì)伍裂縫程度不同，此說(shuō)明施工工藝與環(huán)境條件對(duì)混凝土非結(jié)構(gòu)性裂縫起決定性作用。</p><p>　　3、大體積混凝土的溫度裂縫</p><p>　　水泥水化過(guò)程產(chǎn)生一定的水化熱，并且其大部分熱量是在3天以內(nèi)放出，混凝土是熱的不良導(dǎo)體，特別是大體積混凝土，產(chǎn)生的大量水化熱不容易散發(fā)，內(nèi)部溫度不斷上升，而混凝土表面散熱較快，使內(nèi)外截面產(chǎn)生溫度梯度，特別是晝夜溫差大時(shí)，內(nèi)外溫度差別更大，內(nèi)

39、部混凝土熱脹變形產(chǎn)生壓力，外部混凝土冷縮變形，產(chǎn)生拉應(yīng)力，由于混凝土此時(shí)抗拉強(qiáng)度較低，當(dāng)混凝土內(nèi)部拉應(yīng)力超過(guò)混凝土抗拉強(qiáng)度時(shí)，混凝土便產(chǎn)生裂縫，這種裂縫隙一般較深，有時(shí)是貫穿性的，有一工程地下室為有肋梁筏片基礎(chǔ)，肋梁截面900×1600mm表面系數(shù)小，而每方混凝土水泥用量為425#R普硅水泥522kg，水泥水化熱高，澆注后3天拆模，在13.5℃的大氣溫度下，表面降溫快，形成溫度梯度，混凝土抗拉強(qiáng)度低，因而引起梁裂縫。</

40、p><p>　　預(yù)防措施是配制大體積混凝土宜使用低水化熱水泥如礦渣水泥、摻加膨脹劑，更重要的是施工單位要設(shè)置測(cè)溫裝置，同時(shí)采取保溫措施，如采用塑料薄膜和草袋履蓋以確保內(nèi)外溫差小于25℃。</p><p>　　4、施工方面原因造成裂縫</p><p>　　施工單位為趕進(jìn)度，澆注混凝土未達(dá)到設(shè)計(jì)強(qiáng)度，甚至在澆注后不到24小時(shí)即開(kāi)始上人，堆放荷載，經(jīng)常導(dǎo)致板開(kāi)裂。 因此只有供