【正文】 n , increasing and apt , improvement plasticity, the experiment that we should carry on in this respect more in the project practice is pared with and studied, than lean against not improving terms more simple,may getting simple and more direct, economy. Early maintenance of 4 concrete Practice has proved , the mon crack of concrete , most is the surface crack of different depth, main reason its whether temperature gradient cause cold temperature of area lower too easy to form crack suddenly. So say the warm keeping of the concrete is especially important to preventing the early crack of surface. From the viewpoint of temperature stress, should reach and require to keep warm followingly: 1)Prevent concrete internal and external temperature poor and concrete surface gradient from , prevent the surface crack. 2)Prevent concrete from to be ultra and cold , should is it is it make the minimum temperature is not lower than the steady temperature of concrete service 17 time construction time in concrete to try to try one39。 (2)Add water or the water to cool the broken stone in order to reduce the temperature of building of the concrete while mixing and shutting the concrete。Temperature stress。防水混凝土養(yǎng)護(hù)應(yīng)不少于 14 d防水混凝土拆模要求也比較高，拆模時(shí)間不宜過(guò)早 ，拆模時(shí) 應(yīng)精心操作，防止用鐵棍撬，大錘猛敲硬撬 ，使混凝土遭到破壞。同時(shí)，隨著澆筑高度的 逐步提高，應(yīng)逐步減少用水量，減小坍落度防止?jié)仓缴喜砍霈F(xiàn) 骨料偏 少而水泥漿偏多現(xiàn)象。 2)嚴(yán)格做到定點(diǎn)定量下料 。若采用鋼筋鐵馬架固定鋼筋時(shí)，也應(yīng)加焊止水鐵板或固 定在墊塊上，以增強(qiáng)防水效果 ,本工程用新型材料尼龍固定片有效 的防止了鋼筋保護(hù)層偏差過(guò)大的質(zhì)量通病。 影響防水混凝土的質(zhì)量因素很多。 混凝土的早期養(yǎng)護(hù)，主要目的在于保持適宜的溫濕條件，以達(dá)到兩個(gè)方面的效果，一方面使混凝土免受不利溫、濕度變形的侵襲，防止有害的冷縮和干縮。 （ 7）摻加外加劑可使混凝土密實(shí)性好，可有效地提高混凝土的抗碳化性，減少碳化收縮。增大毛細(xì)孔徑可降低毛細(xì)管表面張力，但會(huì)使混凝土強(qiáng)度降低。鋼的線脹系數(shù)與混凝土線脹系數(shù)相差很小，在溫度變化時(shí)兩者間只 發(fā)生很小的內(nèi)應(yīng)力。 3 控制溫度的措施如下： （ 1）采用改善骨料級(jí)配，用干硬性混凝土，摻混 合料，加引氣劑或塑化劑等措施以減少混凝土中的水泥用量； （ 2）拌合混凝土?xí)r加水或用水將碎石冷卻以降低混凝土的澆筑溫度； （ 3）熱天澆筑混凝土?xí)r減少澆筑厚度，利用澆筑層面散熱； （ 4）在混凝土中埋設(shè)水管，通入冷水降溫； （ 5）規(guī)定合理的拆模時(shí)間，氣溫驟降時(shí)進(jìn)行表面保溫，以免混凝土表面發(fā)生急劇的溫度梯度； （ 6）施工中長(zhǎng)期暴露的混凝土澆筑塊表面或薄壁結(jié)構(gòu)，在寒冷季節(jié)采取保溫措施； 改善約束條件的措施是： （ 1）合理地分縫分塊； （ 2）避免基礎(chǔ)過(guò)大起伏； （ 3）合理的安排施工工序，避免過(guò)大的高差和側(cè)面長(zhǎng)期暴露； 此外，改善混凝土的性能，提高抗裂能力，加強(qiáng)養(yǎng)護(hù)，防止表面干縮，特別是保證混凝土的質(zhì)量對(duì)防止裂縫是十分重要，應(yīng)特別注意避免產(chǎn)生貫穿裂縫，出現(xiàn)后要恢復(fù)其結(jié)構(gòu)的整體性是十分困難的，因此施工中應(yīng)以預(yù)防貫穿性裂縫的發(fā)生為主。例如，橋梁墩身，結(jié)構(gòu)尺寸相對(duì)較大，混凝土冷卻時(shí)表面溫度低，內(nèi)部溫度高，在表面出現(xiàn)拉應(yīng)力，在中間出現(xiàn)壓應(yīng)力。有時(shí)溫度應(yīng)力可超過(guò)其它外荷載所引起的應(yīng)力，因此掌握溫度應(yīng)力的變化規(guī)律對(duì)于進(jìn)行合理的結(jié)構(gòu)設(shè)計(jì)和施工極為重要。當(dāng)這些拉應(yīng)力超出混凝土的抗裂能力時(shí)，即會(huì)出現(xiàn)裂縫。這主要是由于兩方面的原因。 1 混凝土的施工過(guò)程中溫度與裂縫控制 By G. K. Kululanga, W. Kuotcha, R. McCaffer, Member, ASCE, and F. EdumFotw 美國(guó)土木工程師學(xué)會(huì) 。首先，在施工中混凝土常常出現(xiàn)溫度裂縫，影響到結(jié)構(gòu)的整體性和耐久性。許多混凝土的內(nèi)部濕度變化很小或變化較慢，但表面濕度可能變化較大或發(fā)生劇烈變化。 溫度應(yīng)力的分析 根據(jù)溫度應(yīng)力的形成過(guò)程可分為以下三個(gè)階段： （ 1）早期：自澆筑混凝土開(kāi)始至水泥放熱基本結(jié)束，一般約 30 天。 （ 2）約束應(yīng)力：結(jié)構(gòu)的全部或部分邊界受到 外界的約束，不能自由變形而引起的應(yīng)力。 在混凝土的施工中，為了提高模板的周轉(zhuǎn)率，往往要求新澆筑的混凝土盡早拆模。由于鋼的彈性模量為混凝土彈性模量的 7~15倍，當(dāng)內(nèi)混凝土應(yīng)力達(dá)到抗拉強(qiáng)度而開(kāi)裂時(shí)，鋼筋的應(yīng)力將不超過(guò) 100~200kg／ cm2..因此，在混凝土中想要利用鋼筋來(lái)防止細(xì)小裂縫的出現(xiàn)很困難。這個(gè)表面張力理論早在六十年代就已被國(guó)際上所確認(rèn)。 （ 8）摻減水防裂劑后混凝土緩凝時(shí)間適當(dāng)，在有效防止水泥迅速水化放熱基礎(chǔ)上，避免因水泥長(zhǎng)期不凝而帶來(lái)的塑性收縮增加。一方面使水泥水化作用順利進(jìn)行，以期達(dá)到設(shè)計(jì)的強(qiáng)度和抗裂能力。任何一個(gè)環(huán)節(jié)不注意均會(huì)不同程度地?fù)p失防水混凝土阻 水功能，在地下室工程施工中，采取了從模板制作與安裝、鋼筋制作與綁扎、混凝土的拌制和運(yùn)輸、混凝土的澆筑和振搗、施工縫作法、混凝土的養(yǎng)護(hù)與拆模以 及做好回填土等方面嚴(yán)把質(zhì)量關(guān) 方法確保防水混凝土自防水，并通過(guò)實(shí)踐獲得成功。 由于防水混凝土要求較高的密實(shí)性，所以拌制也要有較好的均勻性，為此應(yīng)做好如下幾點(diǎn)： 1)確保攪拌時(shí)間，每次攪拌從投料到出料一般不少于 2 min。根據(jù)分層澆筑高度和運(yùn)輸工具的車(chē)容量，嚴(yán)格進(jìn)行定點(diǎn)定量方可下料，這是提高防水混凝土澆 筑質(zhì)量的重要一環(huán)。 施工縫作法 8 施工縫是防水結(jié)構(gòu)的薄弱環(huán)節(jié)之一。 做好回填土 地下防水結(jié)構(gòu)的回填土是 最后一道工序，它往往被忽視，這實(shí)在是一個(gè)很大的失誤。Crack 。 (3)Reduce the thickness of building while building the concrete on hot day, utilize and build the aspect to dispel the heat。s best. 3)Prevent the old concrete subcooling , in order to reduce the restraint among the old and new concrete. The early maintenance of the concrete, the main purpose lies in keeping the suitable warm and humid condition , in order to get the result of two respects, on the other hand make the concrete avoid the invasion and attack of the unfavorable and warm , humidity out of shape, the ones that prevent from harmfully are cold to contract and do to contract. On one hand make cement water function go on smoothly , is in the hope of reaching the intensity designed and resisting the ability of splitting. The suitable warm damp condition is interrelated. Mix warm keeping measure paid to congeal often protect wet results too. Analyse , water concrete include moisture can meet demand , cement of water have enough and to spare newly theoretically. But because the reason of evaporating etc. often causes losses of the moisture, thus postpone or hinder water of the cement from, the surface concrete receives this kind of adverse effect easiestly and directly. Key period when maintained in initial a few days after so the concrete is built, should pay attention to conscientiously in constructing. Conclusions Construction temperature and relation of crack in concrete the above carry on preliminary discussion of theory and practice, though the academia has different theories to origin cause of formation and puting technology of the concrete crack, but to concrete prevention and improving the measure suggestion to relatively unify , application in practice result fine too at the same time, concrete to is it observe , pare more more by us to want in constructing, analyse more , summarize more after going wrong , bine many kinds of prevention and deal with the measure, 18 the crack of the concrete can be avoided. control of waterproof concrete construction Combined with experience, from formwork design, fabrication and installation, assembing reinforoement, pouring and curing of concrete and other aspects construction technology of fairfaced concrete is introduced as well as quality control measures and standards in order to reduce engineering cost to acquire satisfied economic and social benefits. The factors of influening waterproof concrete quality are very many Any links does not pay attention to the waterproof concrete of field loss hinders the water function without exception jointly with construction in the basement adopts secondary form board fabrication and installa