【正文】 ether is it reduce water is it split pharmaceutical to defend , I summarize his main function in practice to use. (1)There is pore Dao of a large number of mao in the concrete , produce capillary tension in the capillary after water is evaporated, make concrete is it contract out of shape to do. Increasing the thin aperture of hair can reduce the capillary surface tension , but will make the intensity of concrete reduce . This surface tension theory has already been confirmed in the world as far back as the sixties. (2)Water dust than influence important factor that concrete shrink, is it reduce water is it split pharmaceutical can make concrete water consumption reduce by 25% to defend to use. (3)Cement consumption important factor, concrete of person who shrink too, is it add and subtract water is it split concrete reducible 15% of the cement consumption on terms that keep the intensity of concrete of pharmaceutical to defend to mix, its volume is supplemented by increasing aggregate consumption. (4)Reduce water is it split pharmaceutical can improve consistency of grout , reduce concrete secrete ink to defend, reduce and sink and draw back deforming. (5)Improve glueing the strength of forming of the grout and aggregate, the concrete improved resists the performance of splitting. (6)Concrete is it produce stress of drawing to restrain from while shrinking, crack when drawing the stress and is greater than concrete tensile strength can produce. Reduce water is it split pharmaceutical effective concrete tensile strength of improvement very to defend , improve resisting the performance of splitting of concrete by a wide margin. (7)It can make the concrete density good to add the admixture to mix , can improve resisting carbonization of concrete effectively , reduce carbonization to shrink. (8)Is it reduce water is it split slow coagulation time proper concrete under pharmaceutical to defend , on the basis of preventing the fast water of cement from sending out heat effectively to mix, prevent the plasticity shrink that brings because the cement is not congealed for a long time from increasing. (9)Mix admixture concrete and getting easy and kind , surface easy to feel flat , form little membrane, reduce the moisture to evaporate, reduce drily and shrink. A lot of admixture all have the functions of slow coagulation , increasing and apt , improvement plasticity, the experiment 土木建筑 學院 0504 班學生 高尚立 畢業(yè)設計 第 11 頁 共 14頁 濟南大學畢業(yè)設計用紙 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 time construction time in concrete to try to try one39。 (6)The concrete with medium and longterm and exposed construction builds a piece of surface or thin wall structure, take the measure of keeping warm in cold season。 (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。t deformation doing, often cause the crack too. The concrete is a kind of fragility material , tensile strength is about 1/10 of the pression strength, is it carry on one39。在澆筑豎壁時應在接縫處先澆一層 5cm～ 10 cm 厚的同標號水 泥砂漿銜接層，以保證接縫處振搗密實。 為防止水泥漿與 骨料分離，防水混凝土下料時自由高度應不超過防水結 構鋼筋密集，當澆筑高度較高時 ，應按規(guī)定在模板上開門子下料或用串桶 (溜槽 )下料，防止水泥漿與骨料分離，同時也避免水泥 漿或混凝土松散地堆積于鋼筋交叉處和水泥漿濺粘于模板表面，既造成后面下料困難 ，又影響結構表面光滑，成為日后滲漏隱 患。防水混凝土澆筑應嚴格分層進行 ，并一次連續(xù)施工完成土木建筑 學院 0504 班學生 高尚立 畢業(yè)設計 第 6 頁 共 14頁 濟南大學畢業(yè)設計用紙 前后及上下層之間接頭應嚴格控制在 水泥的初凝時間內為此 ，可將操 作工人分成幾個作業(yè)組同時相 向或相背而行。 3)施工過程中應定期抽查測定混凝土坍落度，施工中如遇下 雨或其他原因，砂石含水量發(fā)生變化時，應及時測定其含水率，并 調整施工配合比。 防水混凝土鋼筋保護層最小厚度不小于 25 mm，特別是迎水面的保護層不允許有負誤差，用砂漿墊塊作保護層時，應用預埋在砂漿塊內的鐵絲與 鋼筋綁扎 牢固。嚴格控制模板間的縫隙大小 ，超過 2 mm 的必須用海綿條塞縫 ，對于板面多孔的模板一律不用，土木建筑 學院 0504 班學生 高尚立 畢業(yè)設計 第 5 頁 共 14頁 濟南大學畢業(yè)設計用紙 同時做好墻柱爛根防治工作，采取根部貼海綿條，底部抹水泥砂漿 ，澆筑混凝土前，先注入同標號的水 泥砂漿 由于防水混凝土結構壁厚大多較薄，為保證構件的幾何尺寸，常采用內外螺栓拉接的措施，需要注意的是 ，應在拉接螺栓中間設置止水鐵板 ，以防止水沿著螺栓滲漏，形成引水通路。 結合 經驗 ，對模板的設計、制作安裝、鋼筋綁扎、混凝土澆筑及養(yǎng)護等關鍵工序的操作要點進行了闡述，并介紹了成型后混凝土的質量控制標準，以降低工程造價，具有很好的經濟和社會效益?；炷系谋卮胧┏３Ｒ灿斜竦男Ч?。 3）防止老混凝土過冷，以減少新老混凝土間的約束。 混凝土的早期養(yǎng)護 實踐證明，混凝土常見的裂縫，大多數(shù)是不同深度的表面裂縫，其主要原因是溫度梯度造成寒冷地區(qū)的溫度驟降也容易形成裂縫。減水防裂劑可有效的提高的混凝土抗拉強度，大幅提高混凝土的抗裂性能。 （ 3）水泥用量也是混凝土收縮率的重要因素，摻加減水防裂劑的混凝土在保持混 凝土強度的條件下可減少 15％的水泥用量，其體積用增加骨料用量來補充。例如使用減水防裂劑，筆者在實踐中總結出其主要作用為： （ 1）混凝土中存在大量毛細孔道，水蒸發(fā)后毛細管中產生毛細管張力，使混凝土干縮變形。而且如果鋼筋的直徑細而間距密時，對提高混凝土抗裂性的效果較好。在溫度不太高及應力低于屈服極限的條件下，鋼的各項性能是穩(wěn)定的，而與應力狀態(tài)、時間及溫度 無關。新澆筑早期拆模，在表面引起很大的拉應力，出現(xiàn)“溫度沖擊”現(xiàn)象。 溫度的控制和防止裂縫的措施 為了防止裂縫，減輕溫度應力可以從控制溫度和改善約束條件兩個方面著手。 這兩種溫度應力往往和混凝土的干縮所引起的應力共同作用。 根據(jù)溫度應力引起的原因可分為兩類： （ 1）自生應力：邊界上沒有任何約束或完全靜止的結構，如果內部溫度是非線性分布的，由于結構本身互相約束而出現(xiàn)的溫度應力。由于彈性模量的變化，這一時期在混凝土內形成殘余應力。但是在施工中混凝土由最高溫度冷卻到運轉時期的穩(wěn)定溫度，往往在混凝土內部引起相當大的拉應力。混凝土是一種脆性材料，抗拉強度是抗壓強度的 1／ 10 左右，短期加荷時的極限拉伸變形只有（ ～ ） 104， 長期加荷時的極限位伸變形也只有（ ～ ） 于原材料不均勻，水灰比不穩(wěn)定，及運輸和澆筑過程中的離析現(xiàn)象，在同一塊混凝土中其抗拉強度又是不均勻的，存在著許多抗拉能力很低，易于出現(xiàn)裂縫的薄弱部位。氣溫的降低也會在混凝土表面引起很大的拉應力。我們遇到的主要是施工中的溫度裂縫，因此本文僅對施工中混凝土裂縫的成因和處理措施做一探討。 在大體積混凝土中，溫度應力及溫度控制具有重要意義。 關鍵詞 ： 混凝土 ； 溫度應力 ； 裂縫 ； 控制 混凝土在現(xiàn)代工程建設中占有重要地位。本文 通過多年的現(xiàn)場觀察，通過查閱有關混凝土內部應力方面的專著，對混凝土溫度裂縫產生的原因、現(xiàn)場混凝土溫度的