摘要：混凝土工程中裂縫問題的預防與處理措施
混凝土是一種由砂石骨料、水泥、水及其他外加材料混合而成的非均質脆性材料。由於混凝土施工和本身變形、約束等一係列問題，硬化成型的混凝土中存在著眾多的微孔隙、氣穴和微裂縫。裂縫的存在通常會使內部的鋼筋等材料產生腐蝕，降低鋼筋混凝土材料的承載能力、耐久性及抗滲能力，影響建築物的外觀及使用壽命，嚴重者將會威脅到人身安全。混凝土裂縫產生的原因很多，有溫度變化、收縮、膨脹、不(bu)均(jun)勻(yun)沉(chen)陷(xian)等(deng)原(yuan)因(yin)引(yin)起(qi)的(de)裂(lie)縫(feng)，有(you)外(wai)載(zai)作(zuo)用(yong)引(yin)起(qi)的(de)裂(lie)縫(feng)，有(you)養(yang)護(hu)不(bu)當(dang)和(he)化(hua)學(xue)作(zuo)用(yong)引(yin)起(qi)的(de)裂(lie)縫(feng)等(deng)。不(bu)同(tong)原(yuan)因(yin)產(chan)生(sheng)的(de)裂(lie)縫(feng)在(zai)實(shi)際(ji)操(cao)作(zuo)中(zhong)要(yao)區(qu)別(bie)對(dui)待(dai)，根(gen)據(ju)實(shi)際(ji)情(qing)況(kuang)解(jie)決(jue)問(wen)題(ti)。
下麵是混凝土工程中常見的幾種裂縫及預防措施
幹縮裂縫及預防
gansuoliefengduochuxianzaihunningtuyanghujieshuhoudeyiduanshijianhuohunningtujiaozhuwanbihoudeyizhouzuoyou。shuinijiangzhongshuifendezhengfahuizaochenggansuo，bingqiezhezhongshousuoshibukenide。gansuoliefenghaiyinhunningtuneiwaishuifenzhengfachengdubutongerbutong：混hun凝ning土tu受shou外wai部bu條tiao件jian的de影ying響xiang，表biao麵mian水shui分fen損sun失shi過guo快kuai，變bian形xing較jiao大da，內nei部bu濕shi度du變bian化hua較jiao小xiao變bian形xing較jiao小xiao，較jiao大da的de表biao麵mian幹gan縮suo變bian形xing受shou到dao約yue束shu，產chan生sheng較jiao大da拉la應ying力li而er產chan生sheng裂lie縫feng。相xiang對dui濕shi度du越yue低di，水shui泥ni漿jiang體ti幹gan縮suo越yue大da，幹gan縮suo裂lie縫feng越yue易yi產chan生sheng。幹gan縮suo裂lie縫feng多duo為wei表biao麵mian性xing的de平ping行xing線xian狀zhuang或huo網wang狀zhuang淺qian細xi裂lie縫feng，寬kuan度du多duo在zai0.05毫米~0.2毫hao米mi，大da體ti積ji混hun凝ning土tu中zhong平ping麵mian部bu位wei多duo見jian，較jiao薄bo的de梁liang板ban中zhong多duo沿yan其qi短duan向xiang分fen布bu。幹gan縮suo裂lie縫feng通tong常chang會hui影ying響xiang混hun凝ning土tu的de抗kang滲shen性xing，引yin起qi鋼gang筋jin的de鏽xiu蝕shi，影ying響xiang混hun凝ning土tu的de耐nai久jiu性xing，在zai水shui壓ya力li的de作zuo用yong下xia會hui產chan生sheng水shui力li劈pi裂lie現xian象xiang影ying響xiang混hun凝ning土tu的de承cheng載zai力li。混hun凝ning土tu幹gan縮suo主zhu要yao和he混hun凝ning土tu的de水shui灰hui比bi、水泥的成分、水泥的用量、集料的性質和用量、外加劑的用量等有關。
主要預防措施：一yi是shi選xuan用yong收shou縮suo量liang較jiao小xiao的de水shui泥ni，一yi般ban采cai用yong中zhong低di熱re水shui泥ni和he粉fen煤mei灰hui水shui泥ni，降jiang低di水shui泥ni的de用yong量liang。二er是shi混hun凝ning土tu的de幹gan縮suo受shou水shui灰hui比bi的de影ying響xiang較jiao大da，水shui灰hui比bi越yue大da，幹gan縮suo越yue大da，因yin此ci在zai混hun凝ning土tu配pei合he比bi設she計ji中zhong應ying盡jin量liang控kong製zhi好hao水shui灰hui比bi的de選xuan用yong，用yong時shi摻chan入ru合he適shi的de減jian水shui劑ji。三san是shi嚴yan格ge控kong製zhi混hun凝ning土tu攪jiao拌ban和he施shi工gong中zhong的de配pei合he比bi，混hun凝ning土tu的de用yong水shui量liang絕jue對dui不bu能neng大da於yu配pei合he比bi設she計ji所suo給gei定ding的de用yong水shui量liang，必bi要yao時shi請qing有you資zi質zhi的de技ji術shu人ren員yuan進jin行xing現xian場chang配pei比bi。四si是shi加jia強qiang混hun凝ning土tu的de早zao期qi養yang護hu，並bing適shi當dang延yan長chang混hun凝ning土tu的de養yang護hu時shi間jian。冬dong季ji施shi工gong時shi要yao適shi當dang延yan長chang混hun凝ning土tu保bao溫wen覆fu蓋gai時shi間jian，並bing塗tu刷shua養yang護hu劑ji養yang護hu。五wu是shi在zai混hun凝ning土tu結jie構gou中zhong設she置zhi合he適shi的de收shou縮suo縫feng。
塑性收縮裂縫及預防
塑性收縮是指混凝土在凝結之前，表麵因失水較快而產生的收縮。塑性收縮裂縫一般在幹熱或大風天氣出現，裂縫多呈中間寬、兩端細且長短不一，互不連貫狀態。其產生的主要原因為：混(hun)凝(ning)土(tu)在(zai)終(zhong)凝(ning)前(qian)幾(ji)乎(hu)沒(mei)有(you)強(qiang)度(du)或(huo)強(qiang)度(du)很(hen)小(xiao)，或(huo)者(zhe)混(hun)凝(ning)土(tu)剛(gang)剛(gang)終(zhong)凝(ning)而(er)強(qiang)度(du)很(hen)小(xiao)時(shi)，受(shou)高(gao)溫(wen)或(huo)較(jiao)大(da)風(feng)力(li)的(de)影(ying)響(xiang)，混(hun)凝(ning)土(tu)表(biao)麵(mian)失(shi)水(shui)過(guo)快(kuai)，造(zao)成(cheng)毛(mao)細(xi)管(guan)中(zhong)產(chan)生(sheng)較(jiao)大(da)的(de)負(fu)壓(ya)而(er)使(shi)混(hun)凝(ning)土(tu)體(ti)積(ji)急(ji)劇(ju)收(shou)縮(suo)，而(er)此(ci)時(shi)混(hun)凝(ning)土(tu)的(de)強(qiang)度(du)又(you)無(wu)法(fa)抵(di)抗(kang)其(qi)本(ben)身(shen)收(shou)縮(suo)，因(yin)此(ci)產(chan)生(sheng)龜(gui)裂(lie)。影(ying)響(xiang)混(hun)凝(ning)土(tu)塑(su)性(xing)收(shou)縮(suo)開(kai)裂(lie)的(de)主(zhu)要(yao)因(yin)素(su)有(you)水(shui)灰(hui)比(bi)、混凝土的凝結時間、環境溫度、風速、相對濕度等。
主要預防措施：一是選用幹縮值較小、早(zao)期(qi)強(qiang)度(du)較(jiao)高(gao)的(de)矽(gui)酸(suan)鹽(yan)或(huo)普(pu)通(tong)矽(gui)酸(suan)鹽(yan)水(shui)泥(ni)。二(er)是(shi)嚴(yan)格(ge)控(kong)製(zhi)水(shui)灰(hui)比(bi)，摻(chan)入(ru)高(gao)效(xiao)減(jian)水(shui)劑(ji)來(lai)增(zeng)加(jia)混(hun)凝(ning)土(tu)的(de)坍(tan)落(luo)度(du)和(he)和(he)易(yi)性(xing)，減(jian)少(shao)水(shui)泥(ni)和(he)水(shui)的(de)用(yong)量(liang)。三(san)是(shi)澆(jiao)築(zhu)混(hun)凝(ning)土(tu)之(zhi)前(qian)，將(jiang)基(ji)層(ceng)和(he)模(mo)板(ban)澆(jiao)水(shui)至(zhi)濕(shi)透(tou)。四(si)是(shi)及(ji)時(shi)覆(fu)蓋(gai)塑(su)料(liao)薄(bo)膜(mo)或(huo)者(zhe)潮(chao)濕(shi)的(de)草(cao)墊(dian)、麻(ma)片(pian)等(deng)，保(bao)持(chi)混(hun)凝(ning)土(tu)終(zhong)凝(ning)前(qian)表(biao)麵(mian)濕(shi)潤(run)，或(huo)者(zhe)在(zai)混(hun)凝(ning)土(tu)表(biao)麵(mian)噴(pen)灑(sa)養(yang)護(hu)劑(ji)等(deng)進(jin)行(xing)養(yang)護(hu)。五(wu)是(shi)在(zai)出(chu)現(xian)高(gao)溫(wen)和(he)大(da)風(feng)天(tian)氣(qi)時(shi)設(she)置(zhi)遮(zhe)陽(yang)和(he)擋(dang)風(feng)設(she)施(shi)，及(ji)時(shi)養(yang)護(hu)。
沉陷裂縫及預防
沉(chen)陷(xian)裂(lie)縫(feng)的(de)產(chan)生(sheng)是(shi)由(you)於(yu)結(jie)構(gou)地(di)基(ji)土(tu)質(zhi)不(bu)勻(yun)，回(hui)填(tian)土(tu)不(bu)實(shi)，或(huo)浸(jin)水(shui)而(er)造(zao)成(cheng)不(bu)均(jun)勻(yun)沉(chen)降(jiang)所(suo)致(zhi)。有(you)時(shi)也(ye)因(yin)為(wei)模(mo)板(ban)剛(gang)度(du)不(bu)足(zu)，模(mo)板(ban)支(zhi)撐(cheng)間(jian)距(ju)過(guo)大(da)，或(huo)支(zhi)撐(cheng)底(di)部(bu)鬆(song)動(dong)等(deng)而(er)形(xing)成(cheng)，特(te)別(bie)是(shi)在(zai)冬(dong)季(ji)，模(mo)板(ban)支(zhi)撐(cheng)在(zai)凍(dong)土(tu)上(shang)，凍(dong)土(tu)化(hua)凍(dong)後(hou)產(chan)生(sheng)不(bu)均(jun)勻(yun)沉(chen)降(jiang)，致(zhi)使(shi)混(hun)凝(ning)土(tu)結(jie)構(gou)產(chan)生(sheng)裂(lie)縫(feng)。此(ci)類(lei)裂(lie)縫(feng)多(duo)為(wei)深(shen)進(jin)或(huo)貫(guan)穿(chuan)性(xing)裂(lie)縫(feng)，其(qi)走(zou)向(xiang)與(yu)沉(chen)陷(xian)情(qing)況(kuang)有(you)關(guan)，一(yi)般(ban)沿(yan)與(yu)地(di)麵(mian)垂(chui)直(zhi)或(huo)沿(yan)30度角至45dujiaofangxiangfazhan。jiaodadechenxianliefengwangwangyouyidingdecuowei，liefengkuanduwangwangyuchenjiangliangchengzhengbiguanxi。liefengkuandushouwendubianhuadeyingxiangjiaoxiao。dijibianxingwendingzhihou，chenxianliefengyejibenquyuwending。
主要預防措施：一是對鬆軟土、填tian土tu地di基ji在zai上shang部bu結jie構gou施shi工gong前qian進jin行xing必bi要yao的de夯hang實shi和he加jia固gu。二er是shi保bao證zheng模mo板ban有you足zu夠gou的de強qiang度du和he剛gang度du，且qie支zhi撐cheng牢lao固gu，並bing使shi地di基ji受shou力li均jun勻yun。三san是shi防fang止zhi混hun凝ning土tu澆jiao灌guan過guo程cheng中zhong地di基ji被bei水shui浸jin泡pao。四si是shi模mo板ban拆chai除chu的de時shi間jian不bu能neng太tai早zao，且qie要yao注zhu意yi拆chai模mo的de先xian後hou順shun序xu。五wu是shi在zai凍dong土tu上shang搭da設she模mo板ban時shi要yao注zhu意yi采cai取qu一yi定ding的de預yu防fang措cuo施shi。
溫度裂縫及預防
溫(wen)度(du)裂(lie)縫(feng)多(duo)發(fa)生(sheng)在(zai)大(da)體(ti)積(ji)混(hun)凝(ning)土(tu)表(biao)麵(mian)或(huo)溫(wen)差(cha)變(bian)化(hua)較(jiao)大(da)地(di)區(qu)的(de)混(hun)凝(ning)土(tu)結(jie)構(gou)中(zhong)。混(hun)凝(ning)土(tu)澆(jiao)築(zhu)後(hou)，在(zai)硬(ying)化(hua)過(guo)程(cheng)中(zhong)，水(shui)泥(ni)水(shui)化(hua)產(chan)生(sheng)大(da)量(liang)的(de)水(shui)化(hua)熱(re)。由(you)於(yu)混(hun)凝(ning)土(tu)的(de)體(ti)積(ji)較(jiao)大(da)，大(da)量(liang)的(de)水(shui)化(hua)熱(re)聚(ju)集(ji)在(zai)混(hun)凝(ning)土(tu)內(nei)部(bu)而(er)不(bu)易(yi)散(san)發(fa)，導(dao)致(zhi)內(nei)部(bu)溫(wen)度(du)急(ji)劇(ju)上(shang)升(sheng)，而(er)混(hun)凝(ning)土(tu)表(biao)麵(mian)散(san)熱(re)較(jiao)快(kuai)，這(zhe)樣(yang)就(jiu)形(xing)成(cheng)內(nei)外(wai)的(de)較(jiao)大(da)溫(wen)差(cha)，較(jiao)大(da)的(de)溫(wen)差(cha)造(zao)成(cheng)內(nei)部(bu)與(yu)外(wai)部(bu)熱(re)脹(zhang)冷(leng)縮(suo)的(de)程(cheng)度(du)不(bu)同(tong)，使(shi)混(hun)凝(ning)土(tu)表(biao)麵(mian)產(chan)生(sheng)一(yi)定(ding)的(de)拉(la)應(ying)力(li)。當(dang)拉(la)應(ying)力(li)超(chao)過(guo)混(hun)凝(ning)土(tu)的(de)抗(kang)拉(la)強(qiang)度(du)時(shi)，混(hun)凝(ning)土(tu)表(biao)麵(mian)就(jiu)會(hui)產(chan)生(sheng)裂(lie)縫(feng)，這(zhe)種(zhong)裂(lie)縫(feng)多(duo)發(fa)生(sheng)在(zai)混(hun)凝(ning)土(tu)施(shi)工(gong)中(zhong)後(hou)期(qi)。在(zai)混(hun)凝(ning)土(tu)的(de)施(shi)工(gong)中(zhong)當(dang)溫(wen)差(cha)變(bian)化(hua)較(jiao)大(da)，或(huo)者(zhe)混(hun)凝(ning)土(tu)受(shou)到(dao)寒(han)潮(chao)的(de)襲(xi)擊(ji)時(shi)往(wang)往(wang)會(hui)產(chan)生(sheng)裂(lie)縫(feng)，這(zhe)種(zhong)裂(lie)縫(feng)通(tong)常(chang)隻(zhi)在(zai)混(hun)凝(ning)土(tu)表(biao)麵(mian)較(jiao)淺(qian)的(de)範(fan)圍(wei)內(nei)產(chan)生(sheng)。
溫wen度du裂lie縫feng的de走zou向xiang通tong常chang無wu一yi定ding規gui律lv，大da麵mian積ji結jie構gou裂lie縫feng常chang縱zong橫heng交jiao錯cuo。梁liang板ban類lei長chang度du尺chi寸cun較jiao大da的de結jie構gou，裂lie縫feng多duo平ping行xing於yu短duan邊bian。深shen入ru和he貫guan穿chuan性xing的de溫wen度du裂lie縫feng一yi般ban與yu短duan力li方fang向xiang平ping行xing或huo接jie近jin平ping行xing，裂lie縫feng沿yan著zhe長chang邊bian分fen段duan出chu現xian，中zhong間jian較jiao密mi。裂lie縫feng寬kuan度du大da小xiao不bu一yi，受shou溫wen度du變bian化hua影ying響xiang較jiao為wei明ming顯xian，冬dong季ji較jiao寬kuan，夏xia季ji較jiao窄zhai。高gao溫wen膨peng脹zhang引yin起qi的de混hun凝ning土tu溫wen度du裂lie縫feng是shi通tong常chang中zhong間jian粗cu兩liang端duan細xi，而er冷leng縮suo裂lie縫feng的de粗cu細xi變bian化hua不bu太tai明ming顯xian。此ci種zhong裂lie縫feng的de出chu現xian會hui引yin起qi鋼gang筋jin的de鏽xiu蝕shi、混凝土的碳化，降低混凝土的抗凍融、抗疲勞及抗滲能力等。
主要預防措施：一是盡量選用低熱或中熱水泥，如礦渣水泥、粉fen煤mei灰hui水shui泥ni等deng。二er是shi減jian少shao水shui泥ni用yong量liang。三san是shi降jiang低di水shui灰hui比bi。四si是shi改gai善shan骨gu料liao級ji配pei，摻chan入ru粉fen煤mei灰hui或huo高gao效xiao減jian水shui劑ji等deng來lai減jian少shao水shui泥ni用yong量liang，降jiang低di水shui化hua熱re。五wu是shi改gai善shan混hun凝ning土tu的de攪jiao拌ban加jia工gong工gong藝yi，在zai傳chuan統tong的de三san冷leng技ji術shu的de基ji礎chu上shang采cai用yong二er次ci風feng冷leng新xin工gong藝yi，降jiang低di混hun凝ning土tu的de澆jiao築zhu溫wen度du。六liu是shi在zai混hun凝ning土tu中zhong摻chan入ru一yi定ding量liang的de具ju有you減jian水shui、增塑、緩凝等作用的外加劑，改善混凝土拌和物的流動性、保(bao)水(shui)性(xing)，降(jiang)低(di)水(shui)化(hua)熱(re)，推(tui)遲(chi)熱(re)峰(feng)的(de)出(chu)現(xian)時(shi)間(jian)。七(qi)是(shi)高(gao)溫(wen)季(ji)節(jie)澆(jiao)築(zhu)時(shi)可(ke)以(yi)采(cai)用(yong)搭(da)設(she)遮(zhe)陽(yang)板(ban)等(deng)輔(fu)助(zhu)措(cuo)施(shi)降(jiang)低(di)澆(jiao)築(zhu)混(hun)凝(ning)土(tu)的(de)溫(wen)度(du)。八(ba)是(shi)大(da)體(ti)積(ji)混(hun)凝(ning)土(tu)的(de)溫(wen)度(du)應(ying)力(li)與(yu)結(jie)構(gou)尺(chi)寸(cun)相(xiang)關(guan)，混(hun)凝(ning)土(tu)結(jie)構(gou)尺(chi)寸(cun)越(yue)大(da)，溫(wen)度(du)應(ying)力(li)越(yue)大(da)，因(yin)此(ci)要(yao)合(he)理(li)安(an)排(pai)施(shi)工(gong)工(gong)序(xu)，分(fen)層(ceng)、分fen塊kuai澆jiao築zhu，以yi利li於yu散san熱re。九jiu是shi在zai大da體ti積ji混hun凝ning土tu內nei部bu設she置zhi冷leng卻que管guan道dao，通tong冷leng水shui或huo冷leng氣qi冷leng卻que，減jian小xiao混hun凝ning土tu的de內nei外wai溫wen差cha。十shi是shi加jia強qiang混hun凝ning土tu溫wen度du的de監jian控kong，及ji時shi采cai取qu冷leng卻que、保護措施。十一是預留溫度收縮縫。十二是澆築混凝土前宜在基岩和老混凝土上鋪設5毫米左右的砂墊層或使用瀝青等材料塗刷。十三是加強混凝土養護，混凝土澆築後，及時用濕潤的草簾、麻ma片pian等deng覆fu蓋gai，並bing注zhu意yi灑sa水shui養yang護hu，適shi當dang延yan長chang養yang護hu時shi間jian，保bao證zheng混hun凝ning土tu表biao麵mian緩huan慢man冷leng卻que。在zai寒han冷leng季ji節jie，混hun凝ning土tu表biao麵mian應ying設she置zhi保bao溫wen措cuo施shi，以yi防fang止zhi寒han潮chao襲xi擊ji。十shi四si是shi混hun凝ning土tu中zhong配pei置zhi少shao量liang的de鋼gang筋jin或huo者zhe摻chan入ru纖xian維wei材cai料liao將jiang混hun凝ning土tu的de溫wen度du裂lie縫feng控kong製zhi在zai一yi定ding的de範fan圍wei之zhi內nei。