中英混凝土的壓縮

ShrinkageofConcreteWhenconcretelosesmoisturebyevaporationitshrinks.Shrinkagestrainsaremdependentofthestressconditionsintheconcrete.Ifrestrained,shrinkagestrainscancausecrackingofconcreteandwillgenerallycausethedeflectionofstructuralmemberstoincreasewithtime.ThecalculationofstressanddeformationsduetoshrinkageisdeferreduntilChapter10.AcurveshowingtheincreaseinshrinkagestrainwithtimeappearsinFig.2.21.Theshrinkageoccursatadecreasingratewithtimeappeardinshrinkagestrainsvarygreatly,beinggenerallyintherange0.0002to0.0006butsometimeasmuchas0.0010.Fig.2.21.TypicalshrinkagecurveforconcreteShrinkageistoalargeextentareversiblephenomenon.Iftheconcreteissaturatedwithwaterafterithasshrunk,itwillexpandtoalmostitsoriginalvolume.Thusalternatingdryandwetconditionswillcausealternatingvolumechangesofconcrete.Thisphenomenonispartlyresponsibleforthefluctuatingdeflectionsofstructures(e.g.concretebridges)exposedtoseasonalchangeseachyear.Asarule,concretethatexhibitsahighcreepalsodisplayshighshrinkage.Thusthemagnitudeoftheshrinkagestraindependsonthecompositionoftheconcreteandontheenvironmentinmuchthesamewayasdiscussedpreviouslyforcreep.BoththeACICommittee2092.26andtheCEB-FIP2.27haveproposedempiricalmethodsfortheestimationofshrinkagestrains.Theformerapproachisdescribedblow.AccordingtoACICommittee2092.26fornormalweight,sandlightweightconcrete(usingbothmoistandsteamouringandtypesIandIIIcement),theunrestrainedshrinkagestrainatanytimetisgivenbyWherethecoefficientsaregivenbelow.Ultimateshrinkagestrain,Thevalueofcanvarywidely.InACICommittee209review,wasfoundtobeintherange0.000415to0.00107,withmeanvaluesof0.00080formoist-curedconcreteor0.00073forsteam-curedconcrete.Theseaveragevaluesshouldbeassumedonlyintheabsenceofmoreexactdatefortheconcretetobeused.Timeofshrinkagecoefficient,StAtanytimeafterage7days,formoist-curedconcrete,(2.17a)Wheret=timeindaysfromage7days(St=0.46,0.72,0.84,0.91,and0.98fort=1month,3months,6months,1year,and5years,respectively)or,atanytimeafterage1to3daysforsteam-curedconcrete,(2.17b)咐Whe棵re辰t=煉ti敗me仿in森day肆sf蛛rom采ag青e3腰da異ys續(xù)(妻St=棒0.3虎5,冤0.6粒2,炎0.7統(tǒng)7,腦0.8申7,a艇nd蓬0.9透7f闖or丸t=搬1飽mon戲th,鏈3忘mon咳ths谷,6猛mon核ths私,1當ye磚ar,冶an陶d5獲ye輛ars娃,r覺esp慘ect瞎ive唐ly)剝For緣sh敵rin津kag烈ec萌ons神ide界red赴fr望om巡gre遙ate副ra暫ges盒th型an魄giv駛en慧abo糊ve,戰(zhàn)th玩ed膊iff俊ere辰nce湖ma莖yb拜ed丙ete鍵rmi言ned鼓us虧eE品q.2麥.17贈ao鍵r2姓.17氣bf刷or薯any湯pe叼rio紀da衰fte篩rt蒜han奏ti議me.殼Th陣at饒is梁shr欠ink雙age蛾fo饞rm科ois熟t-c狼ure邊dc度onc扇ret迷eb騾etw窗een睜,s怒ay,劫1渣mon家th揚and趣1菊yea也rw潔oul論db謎ee嚷qua紅lt面ot挪he千7-d商ay瀉to墳1-y梳ear懸pr內oce駝dur短ea竊ssu娃mes鞠th臺at辮the袋mo狀ist稿-cu皺red女co拆nce辭rte臺hs靠be錢en廊cur拴ed謎the外sh紋rin漿kag手en瘋eed借st桿ob食em乳ult黑ipl福ied映by假1.遣2;永al蕉ine俯ar減int描erp達ola裁tio脆nb待etw兔een內1.盤2a電t1球day餃an吉d1址.0場abd創(chuàng)1.姑0a聚t7竊da隆ys偽may汪be襪us帳ed.系Rel壓ati挽ve藝hum立idi倒ty豈coe玩ffi辰cie醬nt,倉S惡h撓S津h烘=1.民4-0植.01房H嗚f指or俗40<賄H<8蟻0%下(償2.1搜8a)熊or,殊陵S基h它=3.汽0-0稱.03那H烏f酸or鼠80<部H<1歸00%騰襲(2.殲18b部)跑Whe針re眠H=行re牛lat瞧ive壞hu憲mid隱ity誼in研pe平rce玩nt滑(揪S軋h損=喊1.0訊0,象0.8嚇0,伏0.6簽0,潑0,f姑or兄40曾,6樸0,陽80,連an跳d1棕00%柳re娘lat盈ive睬hu襲mid曠ity熄)克Min線imu豬mt斷hic重kne鎖ss懶of失mem周ber蟻co欲eff容ici崗ent組,S鬧th不Sth卵=假1.0立0f徐or展6i邪no黃rl姜ess故an千d0肉.84哲fo棵r9查in僚(1宮in近=渴25.毒4mm鼠)始Slu當mp榜of倦con立cre淋te著coe悠ffi餃cie扯nt,測Ss千Ss涌=0仰.97國fo并r2喉in祝,1押.00扭fo旺r2買.7偉in,山1.效01督for頁3i裙n,廢1.0樓5f扎or做4i狹n,絹and益1.翠09嫁for蘆5剩in著(1咐in坊=25修.4m移m)睬Fin策es敲coe敬ffi背cie太nt,著S耽f根S斜f限=0身.86詢fo灰r4碗0%,評1.壘00肅for律50兇%,骨and體1.態(tài)04照for營70遇%f匙ine搬sb彼yw蘋eig筒ht認Air歡co示nte膀nt滋coe弟ffi軌cie侵nt,馬S炭e鴨S毫e產=0.乓98盾for乘4%難,1犯.00愧fo管r6摸%,聞and疫1.保03臘for猾10設%a趁ir媽Cem游ent意co渠nte們nt墊fac屋tor狠,S部c傭S挖c膜=0.越87倦for飽376灘1b隸/yd像3挑,0概.95擔fo容r56魄41申b/閃yd者3食,1蘿.00建fo其r70匯51漢b/y糕d魔3沿a鋒nd1缸.09籌for儉94沸01塑b/y筍d稈3削(癢11蒼b/y竟d糟3間=0.那593宗kg/氣m泊3悄)軌Exa透mpl廳e2桿.2滅Est籍ima酷t(yī)e無the甜fr憐ee潛shr椅ink貨age們st覆rai尺nt壞hat笑ca絹nb妻ee商xpe說cte鳳dt也oo遵ccu損ri紡na專9判in驚(23頃0mm獻)t重hic絕kc嚇onc顧ret企ew休all丟fr仆om異the種ag讀eo損f7圾da想ys串dur罩ing烘a秘5-y柄ear芒pe燙rio猴da屢ta充re是lat輛ive饞hu蘆mid升ity發(fā)of獎60往%.繁The仔co粉ncr艦ete燕ha唐sa屑sl誰ump清of林3雜in框(76猜mm)差,a償fi暑nes帽co些nte軌nt蜓of過34%柜by霉we至igh湯t,對ac更eme窩nt饞con塑ten貨to物f6東00京1b/外yd裕3燙(3勾56k杜g/m逼3學),核an厘air造co摩nte切nt詞of晚5%,突an消di耳sm學ois哈tc原ure摟df叨or竭5da阿ys桑aft觀er姑bei四ng告pla紀ced撒.遣Sol濁uti誰on苦Fro懸mE敬q.0量.16茂we忘ha內ve匪原文翻徐譯韻混凝土娘的收縮樂當混凝燃土由蒸飯發(fā)丟失詳水分時得便產生洲了收縮槳現(xiàn)象世。返致混凝土觸的收縮楚是一種像自發(fā)的雪變形，聞并不依垂靠作用脖在混凝逃土上的滋外力。錘因此當已收縮變胡形不能獄自由進各行時，峽有可能層導致混促凝土產環(huán)生裂縫穴，并且傭裂縫的午數(shù)量隨遮著時間解的增加嶄而增多江。在后斗面的哨第出1趣0恢章具體幟介紹收緞縮產生敢的變形糾和裂縫帝的計算討。良圖養(yǎng)2.2鄰.嫂1悄反應了惰混凝土臂的收縮辨隨時間府發(fā)展的昂規(guī)律，爛早期混漠凝土的示收縮變壺形速率箭隨時間理的增加內變化較顫快，但城是到了片后期混巨凝土的釋收縮變賤形和初灑期相比求有很大貪的不同垮，收縮虛的總量嘩一般為渣（張2圓～頃5倍）較×10壯-4針，有時瘡達甘到誰1×1強0濱-3俱。見圖冶2.2滑1年兩混凝土德收縮隨臂時間發(fā)語展的規(guī)旱律鵲混凝土不的體積初變形，芝包括收迷縮和膨蛙脹兩個巨方面。薦如果混便凝土在殖水中硬炸結時，稿體積就住會增大肢，因此彩分別在蚊干、濕嶄環(huán)境中泉會引起玻體積的凳收縮和軋膨脹。某這種現(xiàn)勇象與結也構的環(huán)扯境變化損有很大咬的關系龍，（如芹：混凝鋪土橋梁睛）很容喇易受到犧每年季薦節(jié)變化什。跑通?；熵S凝土呈暮現(xiàn)收縮印和徐變推兩種情系形。因縱此混凝梢土的收販縮大小橋與混凝造土的構州成及前訓面介紹眠的徐變梁的環(huán)境葉有關。瓣ACI辱209爛2.2假6叨和乏CEB推-FI僅P葬2.2純7號早就提坐出了混燒凝土的湯收縮變涂形的經紛驗公式堵。公式圾如下所浙述。烤根域據(jù)宣ACI渣209路2.2五6英給出的冬重量、解集料級級配及所笛有的混透凝土強大度等級照（使于用久I派到閘II它I財級水泥濤）在假盞設沒有井外力條貞件的混翼凝土收叛縮變形變的時間慌已給出異。先系數(shù)由姥下面給聲出魯最終的愿收縮變敘形主值的變角化范圍捏很大。祝在穩(wěn)ACI泄209傾2.2升6汗提到過秘，韻變化范橡圍爽為降0.0酸004畫1鴨5休～煩0.0物010須7匆，采用蘭濕養(yǎng)護肺方法篩取寫0.0號008朵0掉，采用瓦蒸氣養(yǎng)吳護方法縫取贊0.0之007籍3倡。逢平均值眾常用在著缺乏精監(jiān)確的數(shù)每據(jù)時被稼使用。勝干燥前唇的養(yǎng)護潛時間，氏S拔t或采用濕挖養(yǎng)師護趴7籍天后亡扎青捎雪究捕灑鞋微枯臉(2.堡17a動)希t決=能養(yǎng)院護旅7隙天后的頌時間，胃(St德=0.岔46,載0.妥72,餡0.螺84,妖0.厲91返,殘和蠟0.具98家箭從暴t=扎1土炸個埋月療,邀3京個柄月猜,桂6柳個遇月斯,秤1吼年判,挺棗和他頑5捧年坦,湯壤各自取普值篩)拋或腔者允,脅道采用蒸否汽養(yǎng)治護刊3泛天每后橫,藏焦疫螺細罷鴿評燈輕兵洽(2.憂17b逼)江t優(yōu)=武養(yǎng)脖護毯3臨天后的恨時間，裂(St明=0.切35,讀0.液62,賓0.開77,提0.鄙87帥,點和商0.9僵7父從咐t扁=1飯史個身月獵,3插植個思月噸,冬6良個免月西,1第敵年，滴和盯5武年各自擇取俘值參)呀濕度條報件，翠S巡h辭S桿h厚=1.旦4-0戚.01彈H劍f捎or建40<營H<8延0%哄(山2.1掉8a)藥或者節(jié)，站逼S艷h鐮=3.托0-0扯.03紹H誤f特or永80<增H<1率00%蒙裁(2.恐18b購)濃H=套憤濕度的毛百分比蹈(同S屋h幟=孔1.0凳0,貧0.8茫0,圖0.6富0,茅0泛,狐從葵餅40陰,6譜0,古80圣,捏和煤100表%鄰各自取籌值毀)承試件的究平均厚而度琴，貪S易th蝦Sth煩茶=校小建于斜6悄英尺時滑取釋0.8浩4比，波9