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Quality Control of Mass Concrete Casting

时间:2021-08-14 来源:未知 编辑:梦想论文 阅读:
Absrtact: In recent years, people have higher and higher requirements for the quality of the project, so the quality control and management of the project is particularly important, and the construction technology of mass concrete is one of the most basic and important links in the construction project, so only by controlling the quality of mass concrete pouring in the construction project, can we effectively control all aspects of the project quality. Quantity is effectively controlled and managed. This paper expounds the quality control of mass concrete pouring.
 
 
Key words: mass concrete; pouring; quality control
 
 
Chinese Library Classification Number: TU37 Document Identification Code: A
 
 
Introduction
 
 
Because the construction technology of mass concrete in construction engineering started relatively late in our country, and the construction technology in this area is still in an immature stage, there are still many problems when pouring mass concrete. These problems seriously affect the quality of the whole project. It is very necessary to strengthen the research of quality control of mass concrete pouring. Yes.
 
 
I. Common Quality Problems in Mass Concrete Pouring
 
 
Because of its large construction area and large thickness, large volume concrete is much more difficult to work in the pouring process, and some quality problems are likely to occur, such as construction cracks between upper and lower layers in the case of initial solidification; small holes may be left when scraper is used to treat the concrete surface; uneven thickness during concrete pouring, these problems exist in the process of construction. Mass concrete construction process is difficult, but if we use advanced technical means of scientific construction will greatly reduce the quality problems and achieve the desired results.
 
 
2. Quality Control of Mass Concrete Casting
 
 
1. Control methods of cracks
 
 
1.1 Measures to Control Temperature Cracks
 
 
(1) Rational selection of mix ratio. Strict control of sand, stone gradation and mud content, mixing water reducer and fly ash in concrete, optimizing concrete mix ratio to reduce cement consumption and reduce hydration heat temperature rise, not only to ensure the design strength, but also to make concrete have good workability and pumpability.
 
 
(2) Reduce the temperature of concrete injection. In order to reduce the pouring temperature, low temperature water, stone sprinkler cooling, sand surface covering and other methods are adopted to reduce the mixing temperature, shorten the concrete transportation time as far as possible, add retarder in concrete, prolong the initial setting time to more than 6 hours, slow down the pouring speed, and thin layer pouring, in order to speed up the heat dissipation during pouring, delay the peak of hydration heat and prolong the heating period of concrete. Generally, the temperature of large volume concrete is controlled below 18 C.
 
 
(3) Controlling the demolition time, according to the temperature measurement results, if the difference between the surface temperature or the temperature of the concrete after demolition is less than 25 C, the side mould can be demolished; if the difference between the surface temperature or the temperature of the concrete after demolition is greater than 25 C, not only the side mould can not be demolished, but also the thermal insulation measures covering the thermal insulation material on the template should be adopted to reduce the temperature difference.
 
 
(4) By monitoring, the dynamic change of concrete temperature can be grasped in time. In the process of construction, temperature measuring points should be buried in the places where temperature should be strictly controlled, and records should be made. If the difference between internal and external temperature exceeds the requirements of the code, corresponding measures should be taken to ensure the variation of temperature rise inside concrete members and surface temperature. A. The ultimate purpose of temperature monitoring is to grasp the actual maximum temperature rise inside concrete and the temperature gradient from the center to the surface of concrete. By adopting temperature control measures, the temperature difference between the interior and the surface of mass concrete structure can be guaranteed to meet the requirements of the code; B. Temperature is the key factor directly related to the quality of the whole concrete structure. In order to objectively reflect the temperature condition of concrete, we should strengthen the testing of raw material temperature, outlet temperature, injection temperature, natural temperature, internal temperature of concrete and surface temperature of concrete in order to adjust the temperature control measures in time. Through effective temperature monitoring measures, the temperature difference between the interior and the surface of concrete structure can be guaranteed to be less than the standard requirement of 25 C. It is an effective measure to control the occurrence of concrete surface cracks.
 
 
(5) Strengthen the maintenance and heat preservation of concrete. Early wet curing should be done after concrete pouring to reduce the temperature difference between inside and outside of concrete, so as to improve the early elastic modulus, enhance crack resistance and avoid the combined effect of cooling and drying shrinkage. The concurrent occurrence of cooling and drying shrinkage of mass concrete will lead to stress accumulation, which is one of the main reasons for cracks in later period. Therefore, after the demolition and maintenance of concrete formwork, the backfill soil will be filled immediately, and the whole base slab will be kept in a wet state to prevent excessive dehydration and drying shrinkage and humidity change of concrete during the cooling period.
 
 
1.2 Pouring Scheme of Mass Concrete
 
 
The Pouring Scheme of mass concrete should not only satisfy that every concrete is covered and tampered with a new layer of concrete before its initial setting, but also take into account such factors as the size of structure, the density of reinforcing bars, the retaining of embedded pipes and anchor bolts, the supply of concrete and the heat of hydration.
(1) Overall stratification: that is, after the first layer is fully poured, the second layer is poured back. At this time, the first layer of concrete has not yet been initially solidified, so that it is poured layer by layer continuously until completion. With this scheme, the plane dimension of the structure should not be too large. It is suitable to start from the short side and advance along the long side. When necessary, it can be divided into two sections, from the middle to both ends or from both ends to the middle at the same time.
 
 
(2) Segmental stratification: When concrete is poured, the second layer is poured from the bottom to a certain distance, and then the other layers are poured forward in turn. Since the total number of layers is large, the concrete at the end of the first layer has not yet begun to set after pouring to the top, and can be poured in layers from the second layer in turn. This scheme is suitable for less concrete required per unit time and is not as centralized as the first one. This scheme is suitable for projects with less thickness and larger area or length of structures.
 
 
(3) Slope stratification: Slope gradient is not more than 1/3, which is suitable for the case where the length of the structure is more than three times the thickness. The concrete starts from the lower end of the pouring layer and gradually moves upward.
 
 
1.3 Concrete Maintenance Technology
 
 
(1) Thermal insulation and maintenance measures. Temperature difference between inside and outside of concrete pouring block and cooling speed should meet the requirements of temperature control index.
 
 
(2) The duration of heat preservation and maintenance should be controlled and determined according to the temperature stress (including the stress caused by shrinkage of concrete), but not less than 15 days. The removal of thermal insulation cover should be carried out step by step.
 
 
(3) During the process of heat preservation and maintenance, the surface of concrete should be kept wet. Thermal insulation maintenance is the key link of mass concrete construction. The main purpose of heat preservation and maintenance is to reduce the temperature difference between inside and outside of mass concrete blocks to reduce the win-win stress of thermosetting soil blocks. The second is to reduce the cooling speed of mass concrete blocks and make full use of the tensile strength of concrete to improve the crack resistance of concrete blocks under temperature stress until the purpose of preventing or controlling temperature cracks is achieved. At the same time, keep good humidity and windproof conditions in the maintenance process, so that concrete can be maintained in a good environment. The constructor should determine the maintenance measures after pouring the volume concrete according to the requirements of the temperature control index determined beforehand.
 
 
(4) Plastic cracks may appear on the surface within 1 to 16 hours after concrete pouring, and can be treated by secondary calendering or secondary pouring layer.
 
 
(5) Plastic film and straw bag sawdust can be used as insulation material to cover concrete and formwork. Wind shielding and insulation shed can be built in cold season. The thickness of covering layer should be calculated according to the requirements of temperature control index. Materials with good thermal insulation performance can be used in thermal insulation maintenance of dry concrete. In mass concrete construction, materials with good thermal insulation performance and low cost can be used according to local conditions. The material is used for thermal insulation maintenance of large volume coagulation.
 
 
2. Control Method of Flatness
 
 
For the scraping technology of mass concrete, we adopt a scraping bracket system, which is composed of channel steel, bolt and square steel with a length and width of 65. The bracket of scraping technology of mass concrete is formed by welding channel steel and bolt together to form a bracket, then tightening the bracket with the welded nut and placing square steel above as the trajectory of scraping board. Before pouring mass concrete, some marking steel bars should be placed to control the thickness and smoothness of mass concrete. The thickness of concrete pouring should be slightly thicker than the thickness of the floor, and then vibrating the concrete and rough scraping to ensure that the support is removed before the initial setting of the concrete.
 
 
The scraping of large volume concrete is usually completed in two parts: before initial setting and immediately when it is dry and hard, before initial setting, we can use mechanical polishing machine to roughen the surface once, which can not only ensure the smoothness but also achieve the effect of vibration and compaction. When it is dry and hard immediately, it is important to grind it carefully once more. Mass concrete of plate and column shape is usually coated with artificial grouting.
 
 
In the whole concrete scraping work, it is necessary to ensure that enough concrete surface paste is poured, and that no small holes can appear on the surface. When scraping is finished, concrete curing is carried out to improve the quality of the structure.
 
 
Concluding remarks
 
 
The quality of mass concrete pouring determines the quality of the whole building, so we should strictly standardize the pouring technology and not cut down materials in order to catch up with the progress. Construction enterprises must strengthen the quality management of mass concrete pouring, be good at controlling the pouring technology of concrete, and promote the quality of concrete pouring in our country.
 
 
Reference
 
 
[1] Yang Tieyu. Construction Technology of Mass Concrete Pouring in Construction Engineering [J]. Style of Architectural Science and Technology - New Science and Technology and New Technology (Electronic Edition), 2012.
 
 
[2] Wang Fan. On the Construction Management of Mass Concrete in Construction Engineering [J]. Private Science and Technology-Management Vertical and Transverse (Electronic Edition), 2011.
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