【正文】 4 個(gè)月基本穩(wěn)定，半年徐變可完成 70%80%），使徐變變形在吊裝前（或固定前）完成大部分，此時(shí)混凝土具有較長(zhǎng)齡期，強(qiáng)度也較高；預(yù)應(yīng)力混凝土構(gòu)件不要過早放張，以減少收縮徐變變形，提高抗裂能力； 加大端頭支承墊板，改進(jìn)壓力分布層，減少應(yīng)力集中。采用翻轉(zhuǎn)脫模時(shí)應(yīng)平穩(wěn)，防止劇烈沖擊和振動(dòng)，并應(yīng)在平整堅(jiān)實(shí)的鋪砂地面上進(jìn)行；預(yù)應(yīng)力構(gòu)件預(yù)留孔時(shí)管芯要平直，混凝土澆筑后定時(shí)（ 15min 左右）轉(zhuǎn)動(dòng)鋼管，抽管時(shí)間以手壓混凝土表面不顯印痕為宜，抽管時(shí)應(yīng)平穩(wěn)緩慢；胎模應(yīng)選用有效的隔離劑，起模前先用斤頂均勻松動(dòng)，再平緩起吊；構(gòu)件堆放要按支承受力狀態(tài)設(shè)置墊木，重疊堆放時(shí)，支點(diǎn)應(yīng)保持在一條直線上，同時(shí)做好標(biāo)記，避免板、梁、柱構(gòu)件反放；運(yùn)輸中，構(gòu)件之間 設(shè)置墊木并互相綁牢，防止晃動(dòng)碰撞；屋架、柱等大型構(gòu)件吊裝，應(yīng)按規(guī)定設(shè)置吊點(diǎn)；吊裝屋架等側(cè)向剛度差的構(gòu)件時(shí)，應(yīng)用腳手架橫向加固，并設(shè)牽引繩，防止吊裝過程中晃動(dòng)、碰撞；混凝土冬期施工在摻加氯鹽早強(qiáng)劑，同時(shí)也應(yīng)摻加亞硝酸鈉阻銹劑（為水泥質(zhì)量的 1%2%）；滑動(dòng)模板應(yīng)確保安裝尺寸和質(zhì)量，施工中若因某種原因停滑時(shí)間過長(zhǎng)，應(yīng)松開模板后再滑升，以防止拉裂混凝土。 附錄 B 外文文獻(xiàn) On the prevention and treatment of cracks in concrete in the construction works By Asif Hameed Abstract： Concrete cracks a bad phenomenon is mon in construction projects, it directly affects the use of function and durability of concrete structures. Classification of some mon concrete cracks in the building works, and the specific circumstances of prevention and treatment measures. Keywords: concrete。 prevention。 backfill paction in layers in strict accordance with the specification, design requirements paction factor. The second is to do a good job in the pit or foundation around the protective measures to prevent the foundations were immersed in water. Is to ensure that the template of sufficient strength and stiffness. Support additional at the bottom of the plate to ensure a solid support. And the foundation force uniform. The fourth template removed prematurely, and to pay attention to the priorities of form removal. Fifth, it is poured band structure weight or different buildings storey adjacent parts of the set, to be adjacent to the structure of the settlement basically tends to stabilize and then pouring. Temperature cracks and Prevention The trend of temperature crack a certain regularity, usually crisscross, shades. The larger the proportion of long and short sides of the slab structure, cracks parallel to the short side along the long edge segments appear, in the middle more dense and wide. The width of the cracks by temperature changes, winter, wide, narrow summer. The emergence of such cracks will cause reinforcement corrosion and internal concrete carbonation, and seriously affect its function and durability. The main preventive measures: First, try to use low heat or cooked cement, slag cement, fly ash cement. Second, under the premise of ensuring the strength of concrete. Improve the aggregate gradation, fly ash or superplasticizer to reduce the amount of cement. Third, to ensure the workability of concrete and meet the construction needs of the premise, lower watercement ratio. Is to improve the production process of concrete, reduce the temperature of concrete pouring. Is mixed with a certain amount of concrete retarders, delayed the emergence of the thermal peak time. Is to strengthen the concrete temperature monitoring, and to take timely cooling or insulation measures, reducing the temperature difference between inside and outside of the concrete. 7 is to strengthen the concrete curing, pouring concrete, timely cover with wet straw mat, linen piece, and note the sprinkler maintenance, appropriate to extend the curing time. Eight is to configure a small amount of the small size reinforced concrete or mixed fiber material to control the temperature cracks of the concrete within a certain range. Chemical reaction caused by cracks and Prevention Alkali aggregate reaction cracks and steel corrosion cracks in two kinds of cracks caused by the chemical reaction is generally divided into the reinforced concrete structure. Construction works is limited to the position of the concrete, after mixing some alkaline ions, these ions react chemically with some of the reactive aggregate expansion and to absorb the moisture in the surrounding environment, resulting in shortening of concrete, Splitting. Such cracks generally appear in the concrete structure during the event difficult to remedy, and should therefore take effective measures to prevent construction. The main preventive measures are: First, the choice of the alkali reactivity of small gravel aggregate. Second, the selection of lowalkali cement and alkalifree admixture. The third is optional and can inhibit the admixture of alkali aggregate reaction. Adverse phenomenon due to the reinforced protection of reinforced concrete structures during construction caused by bad thin, exposed tendons, cellular, pockmarked face, making the hazardous substances and exposed reinforcement through the concrete and internal reinforcement to react to rust, corrosion of reinforced volume expansion, resulting in concrete spalling, cracks of this type generally along the reinforced positions. The usual precautionary measures。 additional support points on the ponent reinforcement。 rigid sealing material of polymer cement mortar. 5. Crack control measures Contraction (shrinkage) cracks in the control Contraction (shrinkage) cracks in the control is to control the humidity changes, the structure of the ponent has a relatively stable humidity. To strengthen the early curing of concrete, concrete pouring after the exposed surface with straw mats, straw bags or plastic mulch, and wat