1. Vibration mode

在施工过程中应对混凝土进行充分振捣，做到不漏振，不过振。对混凝土过振造成分层离析、表面浮浆，致使混凝土产生不均匀沉降收缩，在结构厚薄交界处出现裂缝。漏振不利于混凝土密实，造成混凝土蜂窝、麻面等缺陷。混凝土振捣应根据混凝土工作性，确定振捣时间。混凝土应充分振捣，其标志是：混凝土表面出现浆体，没有气泡溢出，混凝土充满试模，不在显著下沉。

In the construction process, the concrete should be fully vibrated to ensure that there is no missing vibration but no vibration. The excessive vibration of concrete results in layered segregation and floating slurry on the surface, resulting in uneven settlement and shrinkage of concrete and cracks at the junction of thickness and thickness of the structure. Leakage vibration is not conducive to concrete compaction, resulting in concrete honeycomb, pitted surface and other defects. The concrete vibration time shall be determined according to the workability of concrete. The concrete should be fully vibrated, and its signs are: the slurry appears on the surface of the concrete, there is no bubble overflow, the concrete is full of the test mold, and there is no significant subsidence.

2、二次振捣和多次抹面

2. Secondary vibration and multiple plastering

施工人员应根据商品混凝土的特点，商品混凝土坍落度比较大，凝结时间比较长（一般8～12h），应做好二次振捣和抹压，使塑性收缩裂缝及时充分愈合。采用二次振捣可以消除因塑性沉降而引起的内分层，阻断因泌水而留下的连贯通道，改善骨料界面结构，提高混凝土强度和抗渗透能力。

According to the characteristics of commercial concrete, the slump of commercial concrete is relatively large, and the setting time is relatively long (generally 8-12h). The secondary vibration and plastering pressure should be done well to make the plastic shrinkage cracks fully heal in time. The secondary vibration can eliminate the internal delamination caused by plastic settlement, block the continuous channel left by bleeding, improve the interface structure of aggregate, and improve the strength and permeability of concrete.

在干燥的春季，混凝土掺了缓凝减水剂后，表面被风干，水分蒸发很快，表面形成一层“硬壳”。当气温较高并蒸发量大时，应采用边喷水雾的方法，可以解决混凝土“结壳”的现象。

In the dry spring, the surface of concrete is dried by air after adding high efficiency retarding and water reducing agent, and the water evaporates quickly, forming a layer of "hard shell" on the surface. When the air temperature is high and the evaporation is large, the method of spraying water at the same time should be adopted to solve the problem of concrete "crusting".

3、现场养护

3. On site maintenance

混凝土浇筑后，若表面不及时覆盖、浇水养护，表面水分迅速蒸发，很容易产生收缩裂缝。特别在相对湿度低、风速大的情况下，干缩更容易发生。有资料表明，当风速为16m/s时，混凝土中的水分蒸发速度为无风时的四倍。

After the concrete pouring, if the surface is not covered and watered in time, the surface moisture will evaporate rapidly, which is easy to produce shrinkage cracks. Especially in the case of low relative humidity and high wind speed, drying shrinkage is more likely to occur. Some data show that when the wind speed is 16m / s, the evaporation rate of water in concrete is four times of that in the absence of wind.

目前，有些施工工地在浇筑混凝土时，不能做到及时覆盖保温养护。一般总要等到一遍抹光结束后才覆盖，还有好多工地根本不覆盖，或只是派人隔几小时去浇一次水。在次抹平后，立即用塑料薄膜覆盖，不让水分蒸发掉，依靠混凝土自身的水分进行保湿养护。需进行第二次抹光时，揭开薄膜，抹完了仍要覆盖好。保湿养护不得少于7d，抗渗等有特殊要求的工程养护时间不少于14d。
 

At present, some construction sites are unable to cover and maintain insulation in time when pouring concrete. Generally, it is necessary to wait until the last finishing time before covering. There are many construction sites that are not covered at all, or only send people to water every few hours. After the first troweling, the concrete shall be covered with plastic film immediately to prevent water from evaporating, and the concrete shall be kept moist by its own moisture. When the second troweling is needed, the film shall be uncovered and covered after finishing. The moisturizing curing time shall not be less than 7d, and the curing time of impermeability and other special requirements shall not be less than 14d.

4、拆模的时间

4. Time of formwork removal

混凝土拆模时，要注意拆模的时间及顺序。对于梁、墙板等结构应适当延长拆模时间，拆模后应继续采取措施进行养护。且不易在楼板上进行施工作业或堆放重物，以减少或避免钢筋混凝土结构产生收缩变形裂缝。

When removing concrete form, attention should be paid to the time and sequence of formwork removal. For beams, wallboards and other structures, the formwork removal time should be appropriately extended, and measures should be taken to maintain after the formwork removal. And it is not easy to carry out construction work or stack heavy objects on the floor, so as to reduce or avoid the shrinkage deformation cracks of reinforced concrete structure.

5、关于凝结的时间

5. On the time of condensation

春季气温多变，昼夜温差大，晚上气温较低，易使凝结时间延长，应注意做好保温养护工作。商品混凝土公司也采取措施，严格控制坍落度及外加剂用量，特别是使用缓凝型减水剂时，更要注意温度对混凝土凝结时间的影响。如果混凝土坍落度损失大，工作性不能满足施工要求，请及时通知商品混凝土公司，进行调整。工地不要随意加水或添加外加剂调整混凝土坍落度，以免出现混凝土质量问题。

In spring, the temperature is changeable, the temperature difference between day and night is large, and the temperature at night is low, which is easy to prolong the setting time. Commercial concrete companies also take measures to strictly control the slump and the amount of additives, especially when using retarded superplasticizer, more attention should be paid to the influence of temperature on the setting time of concrete. If the concrete slump loss is large and the workability can not meet the construction requirements, please timely inform the commercial concrete company for adjustment. Do not add water or additives at will to adjust the slump of concrete, so as to avoid concrete quality problems.