6.2. 1 vibration
1. Considering the stability of formwork support system, concrete pouring should be carried out in layers, and the thickness of each layer is 400~500mm. Concrete pouring shall be carried out continuously, and the intermittent time shall not exceed 2.5h
2. When pouring concrete, 3~4 vibrators shall be arranged at the ash outlet of each pump truck. When pouring concrete in the bottom slab, the slump of concrete is relatively large, so it can flow obliquely in the bottom slab with the thickness of 1 .65m, and the distance is about1m.. Two vibrators are mainly responsible for vibrating the lower slope, and the other vibrator 1~2 is mainly responsible for vibrating the top concrete.
3. Due to the large slump of concrete, water will be generated at the lower part of the surface reinforcement, or tiny cracks will be generated in the concrete at the upper part of the surface reinforcement. In order to prevent such cracks, secondary plastering and compaction measures are taken before the initial setting of concrete and after the pre-settlement of concrete.
surface treatment
The surface cement slurry of pumped concrete is thick. After pouring, use a long ruler to make preliminary leveling according to the elevation before initial setting, and then rub it repeatedly with a wooden washboard for several times to make its surface dense. Before the final set, an iron washboard should be used for calendering.
6.2.3 Precautions for concrete pouring:
1. Before pouring, water, iron wires, nails and other sundries in the formwork shall be removed, and the formwork shall be wetted with water. When using steel formwork, its surface should be kept clean and free of laitance. Before pouring, check whether the formwork and scaffolding, steel bars and embedded parts meet the requirements.
2. The moving distance of the internal vibrator for tamping concrete should not be greater than 1.5 times of its action radius, and the distance between the vibrator and the template should not be greater than1/2 of its action radius; And should try to avoid collision with steel bars, templates, embedded pipes, etc. The vibrator shall be inserted into the lower concrete by 5cm.
3, pouring concrete should be continuous.
6.3 Matters needing attention after concrete pouring
6.3. 1 Temperature control measures
In order to effectively control the adiabatic heating and cooling measures of foundation concrete and avoid the occurrence of temperature stress cracks, our company entrusts the quality inspection center of No.1 Metallurgical Company to carry out temperature detection on the concrete construction of the pool and pump house floor to understand the temperature field distribution of concrete, so as to adjust the thermal insulation and maintenance measures in time.
See the special construction scheme for specific temperature monitoring methods.
6.3.2 Specific heat preservation measures
According to the actual situation on site, our unit takes measures to reduce the temperature difference between the inside and outside of concrete. Specific measures include:
? 0? 5 pouring time should be arranged on cloudy days as far as possible;
? 0? 5. Sprinkle water on the coarse aggregate yard to cool down;
? 0? 5. Sprinkle the mixer with water frequently;
? 0? 5 concrete into the mold temperature control at 25℃;
? 0? 5 In order to avoid the structural temperature stress caused by the change of environmental temperature difference, two layers of plastic film and three layers of straw bags are covered on the surface of the concrete floor to keep warm and moist. Straw bags are staggered up and down, overlapped and compacted, and wrapped at the junction to form a good insulation layer, which keeps the concrete surface at a high temperature. Covering several layers of straw bags around the pool wall formwork for thermal insulation can reduce the temperature difference between the concrete surface and the air temperature to within 10℃, at the same time, it can reduce the thermal diffusion on the concrete surface, give full play to the potential of concrete strength and the relaxation characteristics of materials, and make the stress less than the tensile strength.
? 0? 5 In order to avoid the influence of the weather and prevent the straw bag from losing its thermal insulation ability due to rain, rain-proof measures must be taken for the foundation pit: after concrete pouring, scaffolding should be erected in the foundation pit (scaffolding can be supported by the middle pool wall), scaffolding in the middle of the pool must be erected above the elevation of the top surface of the pool, and the whole foundation pit should be covered with colored strips.
6.4 concrete form removal:
Attention should be paid not to damage the formwork concrete structure when removing formwork. It should be pointed out that:
Side formwork should be removed when the strength of concrete can ensure that its surface and edges and corners are not damaged by formwork removal;
In the process of form removal, if the concrete is found to have problems affecting the safety and quality of the structure, the construction should be stopped and reported to the technical director for research and treatment before it can be removed;
The structure of the dismantled formwork and its support should bear all the calculated loads only after the concrete reaches the design strength. When the construction load is greater than the design load, temporary support should be added.
Seven, quality control points
7. 1 material control
A. raw materials must be inspected, and if there is any change, the reinspection should be conducted, and the concrete mixture ratio should be adjusted in time;
B. Check and weigh raw materials at least twice per shift;
C. At the mixing and pouring site, measure the concrete slump at least twice per shift;
D. concrete test block:
Strength test block: The compressive strength of concrete shall be measured with a cubic test block with a side length of 150cm in a humid environment with a temperature of 20℃ 3℃ and a relative humidity of more than 90% or under the standard conditions of water, and the pressure test shall be conducted after 28 days of curing.
Test blocks must be made at the casting site, and a set of test blocks shall be made every 200m3. The lien of test block shall comply with the provisions of Code for Construction and Acceptance of Concrete Structure Engineering.
Temperature control during curing of mass concrete
The curing of mass concrete should not only meet the needs of strength growth, but also prevent structural cracking caused by temperature through artificial temperature control.
The purpose of temperature control is to artificially control the initial temperature (pouring temperature) of concrete and the highest temperature inside concrete.
Temperature control in concrete curing stage should follow the following points:
1. The difference between the central temperature of concrete and the surface temperature, and the difference between the surface temperature of concrete and the outdoor minimum temperature shall be less than 20℃; When it is determined by calculation that the structural concrete has sufficient crack resistance, it is allowed not to exceed 25~30℃.
2. The temperature environment should be taken into account in the concrete form removal time. , it must be conducive to the normal growth of strength, that is, the temperature difference during concrete formwork removal should not exceed 20℃, and its temperature difference should include the temperature difference between surface temperature, central temperature and external temperature, and the sum of shrinkage equivalent temperature difference.
3. After mass concrete pouring, it should be watered and cured as soon as possible, and the concrete surface should be covered with straw bags to keep the concrete surface moist. The template should also be watered frequently. The curing time of concrete shall not be less than 21d; ; In dry and hot climate, the curing time should be no less than 28d；; When there are strict requirements for cracks, they should be extended appropriately.
The temperature control methods in concrete curing can be divided into cooling method and heat preservation method.
The cooling method is to pre-arrange water pipes inside the concrete and introduce cooling water to reduce the maximum temperature inside the concrete. Cooling down immediately after concrete pouring can effectively control the structural cracking caused by the temperature difference between the inside and outside of concrete. The cooling water pipes can be made of steel pipes or aluminum pipes with a diameter of 25mm or 19mm, which are arranged in a snake shape. The horizontal pipe spacing is 1.5 ~ 3.0m, and the vertical pipe spacing is 1.5 ~ 3.0m, which are connected by risers. General water flow is 14 ~ 20L/min. In order to ensure the cooling effect of the water pipe, the diameter of the inlet and outlet water pipes can be increased to 50 mm. ..
Thermal insulation method is to cover the exposed concrete surface of the structure and the outside of the formwork with thermal insulation materials (such as straw bags, sawdust, wet sand, etc.). ), and using the initial temperature of concrete and the temperature rise of cement hydration heat to make concrete obtain the necessary strength in the process of slow heat dissipation to control the temperature difference between inside and outside of concrete to be less than 20℃.
In addition to the above cooling method and heat preservation method to control the temperature of concrete, water storage method and water bath method can also be used.
Water storage method is to store a certain height of water on the surface of concrete after its final setting, which has a certain thermal insulation effect and can delay the rapid separation of hydration heat temperature in concrete. Therefore, it is expected to control the difference between the surface temperature of concrete and the internal central temperature within a specified date, so that concrete has a high ability to resist temperature deformation.
The water bath method is to install two annular spray pipes by using the inner and outer hangers of the structural sliding platform, and send cold water into the annular spray pipes with a high-pressure pump and spray it on the inner and outer walls of the top concrete. From top to bottom, the water not only wets the concrete surface, but also takes away a lot of heat, which makes the temperature of the concrete surface heated by the sun drop. When spraying water is suspended, the residual water attached to the concrete surface takes away some heat due to moisture evaporation. Because the water sprayed by the annular sprinkler pipe is basically uniform, it can not only maintain the concrete, but also reduce the temperature difference between the inside and outside of the concrete and the sunshine temperature difference at each position.
First, the basic requirements of concrete curing
Concrete can gradually set and harden after being cast, mainly because of the effect of shotcrete, and hydration needs suitable temperature and humidity conditions. Therefore, in order to ensure that concrete has suitable hardening conditions and its strength continues to grow, concrete must be cured. The purpose of curing concrete (concrete) is to create various conditions to fully hydrate cement and accelerate the hardening of concrete; And to prevent the abnormal shrinkage, cracks and other damage phenomena caused by sun, wind, cold and other conditions after concrete molding.
There are two kinds of concrete curing methods: natural curing and heating floating. Cast-in-place concrete usually adopts natural curing under normal conditions. Basic requirements for nature protection: 1. After pouring is completed, it shall be cured within 12h; Before the concrete strength reaches C 12, it is forbidden for anyone to walk on it, install formwork supports, and do not hit or chop on it.
Second, the maintenance process
Covering curing is the most commonly used method of heat preservation and moisture retention. The main measures are:
1. After the initial setting, start covering and curing, and after the final setting (12 hours later), start watering, covering, straw, rotten straw mats, bamboo curtains, sacks, weaving, etc.
Watering tools can be water pipes, buckets and other tools to ensure the wettability of concrete.
The curing time is related to the sub-projects, cement varieties and foreign aid, and should be no less than 7 days under the normal temperature conditions of five kinds of commonly used cement; The project with admixture or with impermeability and frost resistance requirements shall be no less than 14 days and 1. After concrete pouring, it should be covered and watered within 12 hours. First plastic, then sacks, then watering. 12 hour is the theoretical time and room temperature, and someone covers it in 6 hours.
2, do not water in winter, because the plastic film can keep moisture and make it less volatile, but also for antifreeze consideration. Theoretically speaking, when the average temperature of the day is lower than 5℃, it is not allowed to water conservation, and it is appropriate to cover the insulation with plastic film or sacks and straw bags.
3. In summer, the temperature is high, the humidity is low, and it dries quickly. The water and soil conservation method is the first choice for sustainable maintenance. One or two days before concrete pouring, the concrete should be kept fully wet. For large-scale flat slab projects, curing with curing liquid is more practical and convenient. To put it bluntly, it is water storage. Thermal insulation and heat storage in winter.
The reason of honeycomb pitting is that the concrete at the bottom of the column bears the greatest pressure when pouring concrete. If the bottom of the formwork is not tight enough, mortar will slip away along the gap of the formwork, so only the aggregate in concrete is left at the bottom after the formwork is removed. This is the phenomenon of honeycomb pitting.
When pouring columns and other structures, a layer of 50- 100mm cement mortar (the mixture ratio is the same as that in concrete) is poured at the bottom to supplement the mortar at the bottom, which can avoid the phenomenon of honeycomb pits.