CN116180746A - Large-volume concrete construction process capable of effectively preventing concrete from shrinking in temperature - Google Patents

Abstract

The invention discloses a large-volume concrete construction process for effectively preventing concrete shrinkage cracks, which comprises the following steps of: before the concrete of the table body is poured, arranging cooling pipes in the table body, welding the cooling pipes at the turning positions by using elbows, arranging 2 layers of vertical cooling pipes of the table body and 3 layers of vertical cooling pipes of the table body, transversely arranging one row every 5 meters, arranging a water inlet and a water outlet on each layer of cooling pipes, and arranging one water inlet and one water outlet on the table body; the water inlet and the water outlet between the layers are independent, a valve is arranged at the water inlet to control the flow of cooling water, so that the circulation speed and the water inlet temperature of each layer are correspondingly adjusted according to temperature measurement data, the cooling pipe is erected in the table body by adopting a steel bar frame and is tied firmly by iron wires, and bleeding test is carried out on the cooling pipe after the cooling pipe is installed, so that no blockage and no water leakage are ensured. The invention can effectively solve the problem of cracks.

Description

Mass Concrete Construction Technology Effectively Preventing Concrete Thermal Shrinkage Cracks

technical field

The invention relates to the field of mass concrete construction. More specifically, the present invention relates to a large-volume concrete construction technique for effectively preventing thermal shrinkage cracks of concrete.

Background technique

For various reasons, concrete structures will be subjected to different temperature effects from the beginning of construction to normal use. The most adverse effect is the temperature cracks in the concrete structure. According to incomplete statistics, the cracks in the concrete structure are mainly caused by deformation. About 80% of cracks are caused by load, and about 20% are caused by load. In cracks caused by deformation changes, temperature deformation is the main cause of cracks. Therefore, for large-volume concrete, it is even more cautious. In recent years, with the development of the national economy and industrial and civil buildings, there are more and more large-volume concrete construction projects, and the problem of cracks in construction also occurs from time to time. There are many reasons for cracks. In essence, the temperature difference between inside and outside of concrete and shrinkage are one of the main reasons for cracks. Cement releases heat during the hydration process, and each gram of cement can generate about 500J of heat, and if 1kg of cement is added to each square of concrete, the heat of hydration will increase by about 0.1°C. Concrete itself has poor thermal conductivity, and the adiabatic temperature rise of large-volume concrete can reach more than 70°C due to heat accumulation. When the temperature stress and shrinkage stress generated by the internal and external temperature difference exceed the tensile strength of the concrete itself, cracks will occur and affect the service life of the structure. Cracks are the subject and difficult problem of concrete quality control.

Contents of the invention

The purpose of the present invention is to provide a large-volume concrete construction technology that can effectively prevent concrete temperature shrinkage cracks, and can effectively solve the problem of cracks.

The technical solution adopted by the present invention to solve this technical problem is: a large-volume concrete construction process that effectively prevents concrete temperature shrinkage cracks, including:

Before the concrete pouring of the table body, cooling pipes are arranged inside it. The cooling pipes at the corners are welded with elbows. There are 2 layers of vertical cooling pipes in the table body, and 3 layers in some parts. A row is arranged every 5 meters in the horizontal direction, and each layer is cooled. The pipe is provided with a water inlet and a water outlet, both of which are located on the platform; the water inlet and water outlet between the layers are independent, and valves are set at the water inlet to control the flow of cooling water, so that the water circulation of each layer can be adjusted accordingly according to the temperature measurement data. Speed and water inlet temperature, the cooling pipe is erected in the table body with steel bars and tied firmly with iron wires. After installation, it must be tested for bleeding to ensure that it does not block or leak;

The raft slab concrete pouring adopts a continuous pouring method of horizontal layering and layer by layer to the top. The long direction is the pouring direction and the short direction is the pouring surface. The thickness of each layer is controlled at 25-30cm. Tamping process, the time is controlled within 2-3 hours after pouring, and when vibrating, it should be inserted into the lower layer 5-15cm to ensure that the concrete is dense inside and outside.

Preferably, the poured concrete is high-performance concrete, which includes by parts by weight:

160-190 parts of water, 350-400 parts of cement, 400-500 parts of coarse aggregate, 350-450 parts of fine aggregate, 75-85 parts of slag powder, 65-75 parts of fly ash, 5-13 parts of water reducing agent, 3 to 5 parts of retarder;

The retarder is composed of modified bagasse and esterified modified hemicellulose with a mass ratio of 8 to 10:1;

The coarse aggregate is shell powder with a particle size greater than 5mm, and the fine aggregate is machine-made sand with a fineness modulus of 2.5-3.5

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly.

Preferably, when pumping concrete is used for pouring, the laitance and bleeding produced on the surface should be removed in time; During the time between initial setting and final setting of concrete, carry out secondary compaction and plastering.

Preferably, 3 sections are set up, each section has 3 measurement areas, and each measurement area is divided into upper, middle and lower places to bury temperature sensors, and the upper and lower parts should be 50mm away from the concrete surface; Use wires to distinguish them, and then tie them to the upper, middle and lower places of the Φ10 steel bars respectively. Finally, put the steel bars bound with the temperature sensor along the thickness direction of the concrete, and spot weld or tie them at the places close to the cloth bars. When measuring the temperature, directly Lead out a joint from the thermometer, and connect the temperature sensors of each measuring area in turn.

Preferably, the cooling pipe starts to flow water after it is covered with a layer of concrete, and stops water flow when the cement hydration heat temperature reaches its peak value and begins to drop to a temperature difference between inside and outside ≤ 25°C, during which the water inlet temperature and water flow are adjusted according to the detected temperature Speed and duration of water flow. The flow of circulating cold water in the cooling pipe is used to take away the heat of hydration generated inside the concrete and reduce the appearance of temperature cracks.

Preferably, before the initial setting of the large-volume concrete is poured, the spray curing is carried out immediately; and then plastic film, geotextile or sacks are used for covering and curing.

The present invention at least includes the following beneficial effects:

1. Safety: It enhances the impermeability, effectively reduces the occurrence of large-volume concrete cracks, improves the quality of the project, and at the same time prolongs the service life of the structure, thereby reducing the construction and maintenance costs of highway bridges.

2. Quality: By reducing the heat of hydration of concrete, the amount of cement is reduced, non-renewable material resources are saved, and engineering costs are saved.

3. Cost and construction period: The use of slag powder, fly ash, retarder and other external materials can delay the concentration of concrete hydration heat on the one hand, improve the performance of concrete, enhance pumpability and impermeability, and more effectively The construction quality is guaranteed. On the other hand, shell waste residue is effectively used, waste is utilized, waste is turned into wealth, environmental pollution is reduced, and project cost is reduced, so it has significant economic and social benefits.

Other advantages, objectives and features of the present invention will partly be embodied through the following descriptions, and partly will be understood by those skilled in the art through the research and practice of the present invention.

Description of drawings

Fig. 1 is the concrete structure schematic diagram of platform body of the present invention;

Figure 2 shows the test results of concrete adiabatic temperature rise.

Explanation of reference numerals: 1 concrete body, 2 cooling pipes.

Detailed ways

The present invention will be described in detail and completely below in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it needs to be particularly pointed out that: the technical solutions and technical features provided in each part of the present invention, including the following description, in the case of no conflict, these technical solutions and Technical features can be combined with each other.

In addition, the embodiments of the present invention referred to in the following description are generally only some embodiments of the present invention, not all of them. Therefore, based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The invention provides a large-volume concrete construction technique for effectively preventing concrete temperature shrinkage cracks, including:

Before pouring the platform concrete 1, as shown in Figure 1, a cooling pipe 2 is arranged inside it. The cooling pipe is a steel pipe with an outer diameter of 50 mm and a wall thickness of 2 mm. The cooling pipe at the corner is welded with an elbow, and the joint position must be welded and sealed tightly To ensure the welding quality, there are 2 layers of vertical cooling pipes in the table body, 3 layers in some parts, and a row every 5 meters in the horizontal direction. Each layer of cooling pipes has a water inlet and a water outlet, all of which are located on the table body; The water inlet and water outlet are independent, and valves are set at the water inlet to control the cooling water flow, so that the water circulation speed and water inlet temperature of each layer can be adjusted accordingly according to the temperature measurement data. The backing is firm, and after the installation is completed, a bleeding test should be carried out to ensure that it is not blocked or leaked;

The raft slab concrete pouring adopts a continuous pouring method of horizontal layering and layer by layer to the top. The long direction is the pouring direction and the short direction is the pouring surface. The thickness of each layer is controlled at 25-30cm, which not only prolongs the cement hydration heat release time, It also slows down the concrete cooling rate and reduces the temperature stress, which is beneficial to control the shrinkage cracks inside the concrete. During the construction process, the position of the concrete pump truck should be considered to ensure a balanced distribution and to ensure that a layer of concrete is poured before the initial setting. The inter-layer concrete vibration adopts the secondary vibration process, and the time is controlled within 2-3 hours after pouring. When vibrating, it should be inserted into the lower layer 5-15cm to ensure that the concrete is dense inside and outside.

In the above embodiment, when pouring concrete, the mold entry temperature should be strictly controlled within 30°C. Coarse aggregates should be sprayed with water or covered to cool down during construction in summer, and ice water can be added to the water in high temperature seasons to reduce the mixing water temperature. Set up sunshade facilities on the construction site and set up colorful strip sheds to avoid direct sunlight. For structures with large-volume concrete and dense steel bars, in order to facilitate construction and ensure that the concrete is compacted by vibration, operators go to the bottom layer to pour and vibrate.

The technical solution may also include the following technical details to better achieve the technical effect: the poured concrete is high-performance concrete, and it is calculated in parts by weight, including:

160-190 parts of water, 350-400 parts of cement, 400-500 parts of coarse aggregate, 350-450 parts of fine aggregate, 75-85 parts of slag powder, 65-75 parts of fly ash, 5-13 parts of water reducing agent, 3 to 5 parts of retarder;

The retarder is composed of modified bagasse and esterified modified hemicellulose with a mass ratio of 8 to 10:1;

The coarse aggregate is shell powder with a particle size greater than 5mm, and the fine aggregate is machine-made sand with a fineness modulus of 2.5-3.5

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly.

This technical solution may also include the following technical details to better achieve the technical effect: when pumping concrete is used for pouring, the laitance and bleeding generated on the surface should be removed in time; Vibrate to achieve the best compactness and improve the strength of the structure. Due to the relatively large slump of the pumped concrete, moisture will be generated in the lower part of the surface reinforcement during pouring, resulting in small cracks in the concrete above the reinforcement. In order to overcome the occurrence of cracks, after the pouring is completed, before the initial setting of the concrete, carry out slurry extraction, compaction, and plastering on the concrete surface, and perform secondary compaction and plastering during the time between the initial setting and final setting of the concrete. Minimize shrinkage on concrete surfaces.

This technical solution may also include the following technical details to better achieve technical effects: According to the principle of plane layout of the survey area and combined with the actual situation on site, a total of 3 sections are set up this time, each section has 3 survey areas, and each survey area is Bury temperature sensors in three places, upper, middle and lower, among which the upper and lower parts should be 50mm away from the concrete surface; when laying out on site, each part should be distinguished by lines, and then tied to the upper, middle and lower places of the Φ10 steel bar respectively, and finally the tied The steel bars with temperature sensors are put in along the direction of concrete thickness, and are fixed by spot welding or binding at the place close to the fabric bars. When measuring temperature, directly lead out a joint from the thermometer, and connect the temperature sensors in each measuring area in turn.

This technical solution can also include the following technical details to better achieve the technical effect: the cooling pipe starts to pass water after covering a layer of concrete, and stops when the cement hydration heat temperature reaches the peak value and begins to drop to a temperature difference between the inside and outside of ≤ 25°C During the water flow, the inlet water temperature, water flow speed and water flow duration are adjusted according to the detected temperature. The flow of circulating cold water in the cooling pipe is used to take away the heat of hydration generated inside the concrete and reduce the appearance of temperature cracks.

The technical solution may also include the following technical details to better achieve the technical effect: before the initial setting of the large-volume concrete is poured, the spray curing is carried out immediately; Take temperature control measures such as watering and curing according to the climatic conditions, measure the surface and internal temperature of the concrete, and control the temperature difference within the range required by the design. If necessary, a wind-shielding and heat-insulating shed or a sunshade and cooling shed can be erected. In hot weather, early curing should be carried out after 30 minutes after the concrete bristles are finished. When the internal temperature of the structure rises, it is strictly forbidden to directly use cold water for curing.

In this application, by adding external materials such as slag powder, fly ash, high-efficiency water reducer and retarder to the mix ratio, the prepared high-performance concrete can effectively reduce the heat of hydration, delay the appearance of temperature peaks, and reduce concrete shrinkage , improve the volume stability of concrete, and significantly increase the concrete strength, impermeability and other indicators.

The above scheme is applied to the large-volume concrete for the design of the raft cap of the coal shed. There are 102 pieces ^{in total, and the quantity of each raft is 1300m 3 .} The unit price of the high-performance concrete mix is 330 yuan/m ³ , with a difference of 26 yuan per square meter, which will directly save 3.4476 million yuan in costs.

The application of mass concrete construction technology can effectively reduce the occurrence of structural cracks, improve project quality, and prolong the service life of structures, which has good economic and social benefits.

Example 1

The poured concrete is high-performance concrete, which is calculated in parts by weight, including:

160 parts of water, 380 parts of cement, 420 parts of coarse aggregate, 400 parts of fine aggregate, 80 parts of slag powder, 70 parts of fly ash, 6 parts of water reducing agent, and 5 parts of retarder;

The water reducer is a polycarboxylate water reducer; the retarder is composed of modified bagasse and esterified modified hemicellulose with a mass ratio of 8:1; the coarse aggregate has a particle size greater than 5mm shell powder, the fine aggregate is machine-made sand with a fineness modulus of 2.5-3.5; the cement is ordinary Portland cement;

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm It was mixed evenly at a stirring speed of 1 min. After testing, the impermeability performance of the specimen prepared in Example 1 was W10.

Comparative example 1

The poured concrete is high-performance concrete, which is calculated in parts by weight, including:

160 parts of water, 380 parts of cement, 420 parts of coarse aggregate, 400 parts of fine aggregate, 80 parts of slag powder, 70 parts of fly ash, 6 parts of water reducer;

The water reducer is a polycarboxylate water reducer; the retarder is composed of modified bagasse and esterified modified hemicellulose with a mass ratio of 8:1; the coarse aggregate has a particle size greater than 5mm shell powder, the fine aggregate is machine-made sand with a fineness modulus of 2.5-3.5; the cement is ordinary Portland cement;

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly. After testing, the impermeability performance of the specimen prepared in Comparative Example 1 was W6.

Comparative example 2

The poured concrete is high-performance concrete, which is calculated in parts by weight, including:

160 parts of water, 380 parts of cement, 420 parts of coarse aggregate, 400 parts of fine aggregate, 80 parts of slag powder, 70 parts of fly ash, 6 parts of water reducing agent, and 5 parts of retarder;

The water reducer is a polycarboxylate water reducer; the retarder is composed of modified bagasse; the coarse aggregate is shell powder with a particle size greater than 5mm, and the fine aggregate is a fineness modulus of 2.5-3.5 machine-made sand; the cement is ordinary Portland cement;

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly. After testing, the impermeability performance of the specimen prepared in Comparative Example 2 was W8.

Comparative example 3

The poured concrete is high-performance concrete, which is calculated in parts by weight, including:

160 parts of water, 380 parts of cement, 420 parts of coarse aggregate, 400 parts of fine aggregate, 80 parts of slag powder, 70 parts of fly ash, 6 parts of water reducing agent, and 5 parts of retarder;

The water reducer is a polycarboxylate water reducer; the retarder is composed of esterified modified hemicellulose; the coarse aggregate is shell powder with a particle size greater than 5mm, and the fine aggregate is fineness modulus 2.5-3.5 machine-made sand; the cement is ordinary Portland cement;

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly. After testing, the impermeability performance of the specimen prepared in Comparative Example 3 was W6.

Comparative example 4

The poured concrete is high-performance concrete, which is calculated in parts by weight, including:

160 parts of water, 380 parts of cement, 420 parts of coarse aggregate, 400 parts of fine aggregate, 80 parts of slag powder, 70 parts of fly ash, 6 parts of water reducing agent, and 5 parts of retarder;

The water reducer is a polycarboxylate water reducer; the retarder is composed of modified bagasse and esterified modified hemicellulose with a mass ratio of 4:1; the coarse aggregate has a particle size greater than 5mm shell powder, the fine aggregate is machine-made sand with a fineness modulus of 2.5-3.5; the cement is ordinary Portland cement;

The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly. After testing, the impermeability performance of the specimen prepared in Comparative Example 4 was W8 grade.

The concrete prepared in Example 1 and Comparative Examples 1-4 were subjected to adiabatic temperature rise test according to DL/T 5150-2001 Hydraulic Concrete Test Regulation, and the results are shown in Fig. 2 . When the modified bagasse and esterified modified hemicellulose in the retarder are combined in a specific ratio, the adiabatic temperature rise of concrete can be significantly reduced, because the modified bagasse can absorb gel substances and slow down the occurrence of cement coagulation reaction At the same time, the esterified modified hemicellulose fills the pores in the hydration product, which reduces the early hydration heat of concrete, and at the same time, the overall structural impermeability is better, reducing the risk of cracking in large-volume concrete. When modified bagasse and esterified modified When the proportion of permanent hemicellulose is less than a specific range, the concrete adiabatic temperature rise is not much different from that of Example 1, but the impermeability of concrete decreases.

Although the embodiment of the present invention has been disclosed as above, it is not limited to the use listed in the specification and implementation, it can be applied to various fields suitable for the present invention, and it can be easily understood by those skilled in the art Therefore, the invention is not limited to the specific details and embodiments shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims (6)

1. A mass concrete construction technique for effectively preventing concrete thermal shrinkage cracks, characterized in that it comprises: Before the concrete pouring of the table body, cooling pipes are arranged inside it. The cooling pipes at the corners are welded with elbows. There are 2 layers of vertical cooling pipes in the table body, and 3 layers in some parts. A row is arranged every 5 meters in the horizontal direction, and each layer is cooled. The pipe is provided with a water inlet and a water outlet, both of which are located on the platform; the water inlet and water outlet between the layers are independent, and valves are set at the water inlet to control the flow of cooling water, so that the water circulation of each layer can be adjusted accordingly according to the temperature measurement data. Speed and water inlet temperature, the cooling pipe is erected in the table body with steel bars and tied firmly with iron wires. After installation, it must be tested for bleeding to ensure that it does not block or leak; The raft slab concrete pouring adopts a continuous pouring method of horizontal layering and layer by layer to the top. The long direction is the pouring direction and the short direction is the pouring surface. The thickness of each layer is controlled at 25-30cm. Tamping process, the time is controlled within 2-3 hours after pouring, and when vibrating, it should be inserted into the lower layer 5-15cm to ensure that the concrete is dense inside and outside. 2. the mass concrete construction technique of effectively preventing concrete temperature shrinkage cracks as claimed in claim 1, is characterized in that, the concrete of pouring is high-performance concrete, and it is counted in parts by weight, comprising: 160-190 parts of water, 350-400 parts of cement, 400-500 parts of coarse aggregate, 350-450 parts of fine aggregate, 75-85 parts of slag powder, 65-75 parts of fly ash, 5-13 parts of water reducing agent, 3 to 5 parts of retarder; The retarder is composed of modified bagasse and esterified modified hemicellulose with a mass ratio of 8 to 10:1; The coarse aggregate is shell powder with a particle size greater than 5mm, and the fine aggregate is machine-made sand with a fineness modulus of 2.5-3.5 The preparation method of the concrete is to mix and stir the weighed coarse aggregate, fine aggregate, slag powder, and fly ash for 5-6 minutes, and then add cement, water, water reducer and retarder at 100 rpm min stirring speed to mix it evenly. 3. The mass concrete construction technique for effectively preventing concrete temperature shrinkage cracks as claimed in claim 1, wherein, when using pumped concrete pouring, the laitance and bleeding that are poured to the surface layer should be removed in time; pouring After the completion, before the initial setting of the concrete, carry out the slurry extraction, compaction, and plastering work on the concrete surface, and perform secondary compaction and plastering during the time between the initial setting and final setting of the concrete. 4. The mass concrete construction technique for effectively preventing concrete temperature shrinkage cracks as claimed in claim 2, characterized in that, 3 sections are established altogether, and each section has 3 measurement areas, and each measurement area is divided into upper, middle, lower, and lower sections. Buried temperature sensors at the top and bottom of the concrete surface, the upper and lower parts should be 50mm away from the concrete surface; when the site is arranged, each part should be distinguished with a line, and then tied to the upper, middle and lower three places of the Φ10 steel bar respectively, and finally the steel bar tied with the temperature sensor Put it in along the thickness direction of the concrete, spot weld or bind it against the reinforcement, and directly lead out a joint from the thermometer when measuring the temperature, and connect the temperature sensors in each measurement area in turn. 5. The mass concrete construction technique for effectively preventing concrete temperature shrinkage cracks as claimed in claim 1, wherein the cooling pipe starts to pass water after covering one deck of concrete, and when the cement hydration heat temperature reaches a peak value and starts When the temperature difference between inside and outside is ≤25℃, the water flow is stopped, and the water inlet temperature, water flow speed and water flow duration are adjusted according to the detected temperature. The flow of circulating cold water in the cooling pipe is used to take away the heat of hydration generated inside the concrete and reduce the appearance of temperature cracks. 6. The mass concrete construction technique of effectively preventing concrete temperature shrinkage cracks as claimed in claim 1, wherein, before the mass concrete is poured and initially set, the spray curing work is carried out immediately; then plastic film, geotextile or Items such as sacks are covered for health preservation.

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