ArchUrban 版 (精华区)

发信人: project (阿蒙), 信区: Architecture
标  题: 冬期大体积混凝土施工
发信站: 紫 丁 香 (Mon Jul 26 15:58:45 1999), 转信


                                               冬期大体积混凝土施工
                                                         王 玲 殷国来
                                     CONSTRUCTION OF MASSIVE CONCRETE IN WIN
TER
                                                    Wang Ling Yin Guolai
                   (Concrete Mixing Plant of No.2 Co.of Beijing Urban Constr
uction Beijing 100039)
 1 工程概况
 　　北京市皂君庙电信大楼工程总高84.9m，地下三层。基础为复合桩基、箱型基础。
底板厚2m，混凝土设计强度等级C35，抗渗等级
 S12，基础底板混凝土总量为1.28万m3 ,混凝土属大体积混凝土。底板在11月26日开始
浇注。根据北京市1995～1996年的气象资料，
 12月中旬为最低温度期间，最低温度夜间为－14℃，将持续5d时间。这时预计混凝土内
部温度达到70℃，而大气温度为－14℃，内外
 温差为84℃。因此必须在降低混凝土内部温度和提高混凝土表层温度上着手解决问题。
据此，施工单位在将供应商品混凝土任务交给
 我搅拌站的同时，提出了以下技术要求：
 　　（1）混凝土满足远距离运输、施工工作面展开的要求，初凝时间要求延缓8h。
 　　（2）解决混凝土核心温度过高及混凝土产生裂缝的问题。
 　　（3）满足混凝土泵送时附加100m排管的输送要求。
 2 材料选用
 　　为了解决内外温差，降低水化热，采用新港水泥厂生产的矿渣425号水泥。
 　　为实现初凝延缓8h，推迟混凝土水化热的峰值，防止混凝土干缩和温度裂缝，选用
北京利力新技术开发公司研制生产的FS－H混凝
 土防水剂。该产品是一种复合型混凝土外加剂，具有微膨胀、减水、缓凝等多功能特点
。其掺量为内掺8％。
 　　为了减少水泥用量，降低水化热，提高混凝土的和易性 ，降低混凝土的粘度，利
于泵送，掺加一定量的粉煤灰（高井电厂生产的
 Ⅱ级粉煤灰）。
 　　采用的砂、石为宝山砂石厂产的中砂和碎卵石，砂子含泥量<2％，石子粒径为5～
25mm，含泥量<1％ 。经试配每m3混凝土用料为
 （kg/m3）：水泥394，水196，砂701，石子1041，粉煤灰53，FS－H防水剂39。试验混
凝土经时坍落度如表1所示。新拌混凝土和易性
 和流动度都很好。
                                                    表1 混凝土经时坍落度
                                                   时间/h
                                                                0
                                                                     1
                                                                           2

                                                                            
    3
                                                                            
          4
                                                                            
                5
                                                 坍落度/mm
                                                               210
                                                                    210
                                                                          20
5
                                                                            
   190
                                                                            
         180
                                                                            
               170
 3 现场混凝土浇注后的情况
 　　混凝土浇注后，表面刷一层混凝土养护剂并覆盖一层塑料薄膜，然后覆盖2层阻燃
稻草被。测温点布置为：每100m2范围内在同面
 层及距面层1m处各设一点。从1997年12月2日开始测温，测得的结果见表2。
                                                    表2 混凝土各测温点温度
                  日期／日
                                 2
                                         3
                                                 4
                                                         5
                                                                 6
                                                                         7
                                                                            
      8
                                                                            
               9
                                                                            
                     10
                                                                            
                            11
                                                                            
                                     12
                                                                            
                                             13
                  表面／℃
                                31
                                        33
                                                 38
                                                         37
                                                                 34
                                                                         31
                                                                            
      28
                                                                            
              27
                                                                            
                     17
                                                                            
                            16
                                                                            
                                     15
                                                                            
                                             15
                  内部／℃
                                36
                                        38
                                                 44
                                                         43
                                                                 43
                                                                         43
                                                                            
      40
                                                                            
              39
                                                                            
                     35
                                                                            
                            32
                                                                            
                                     31
                                                                            
                                             29
 　　从表2可以清楚地看出，选用的混凝土原材料和保湿、保温的养护措施是合理的。
混凝土内部温度最高44℃。混凝土内外温差最大
 的时间为12月10日，差值为18℃，远低于规范要求的差值25℃。由于措施得力，混凝土
降温之后，表面温度也维持在15℃左右，同时
 也给混凝土的强度增长创造了条件。电信大厦底板混凝土强度平均达到44.3 MPa，抗渗
等级达到S12，均满足设计要求。12月底打开保
 温材料，混凝土表面没有裂缝发生。
 4 结 语
 　　（1） 在严冬基础大体积混凝土施工中，不加防冻剂用常温水搅拌的方案是可行的
。
 　　（2） 实践证明，掺入FS－H后不仅使混凝土具有较好的抗裂、抗渗性能，同时能
满足施工中要求的凝结时间，提高了混凝土抗冻
 能力。
 　　（3）必须与施工现场管理人员共同制定切实可行的混凝土表面处理及养护措施，
防止裂缝的产生。

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※ 来源:．紫 丁 香 bbs.hit.edu.cn．[FROM: 202.118.246.62]