CN113668928A

CN113668928A - Method for controlling construction cracks of ultra-large-volume concrete water pool

Info

Publication number: CN113668928A
Application number: CN202110676430.5A
Authority: CN
Inventors: 王建芳; 谢志娟; 吴建云; 杨智勇; 张伟
Original assignee: China National Chemical Engineering No14 Construction Co ltd
Current assignee: China National Chemical Engineering No14 Construction Co ltd
Priority date: 2021-06-18
Filing date: 2021-06-18
Publication date: 2021-11-19
Anticipated expiration: 2041-06-18
Also published as: CN113668928B

Abstract

A method for controlling the crack generated by the construction of super-long large-volume concrete pool includes such steps as analyzing the crack generated by concrete pool, designing the raft foundation and shear wall of frame, and cooling. By the improvement of the method, cracks generated in the construction of the large-volume concrete pool are fewer or even eliminated, and the construction quality and the working efficiency are ensured.

Description

Method for controlling construction cracks of ultra-large-volume concrete water pool

Technical Field

The invention belongs to the technical field of engineering construction, and particularly relates to a method for controlling construction cracks of an ultra-long large-volume concrete water pool.

Background

At present, reinforced concrete water tanks such as fire-fighting water tanks, water storage tanks, sedimentation tanks, filter tanks and the like are found everywhere in the building industry. In order to meet the requirement of industrial development, the design size and the section size of the pool are gradually increased, so that the concrete pouring amount is increased, the hydration heat released by cement is larger, the anti-seepage requirement is stricter, and the construction difficulty is greatly increased. The method is particularly important for controlling cracks, once cracks appear, not only is the integral rigidity and stability damaged, but also the corrosion of internal reinforcing steel bars can be caused, and the seepage prevention and the durability of the water supply pool are greatly influenced. Therefore, the occurrence of cracks in the reinforced concrete water pool is strictly controlled in the construction process.

In the prior art, the strength grade of mass concrete is gradually increased, the design strength is overhigh, the cement consumption is overlarge, the hydration heat of the concrete is inevitably overhigh, the internal temperature of a concrete block is high, the temperature difference inside and outside the concrete exceeds more than 30 ℃, the temperature stress easily exceeds the tensile strength of the concrete, and the cracking is generated.

Along with the industrial development, the construction technology and the process of the reinforced concrete pool structure are greatly improved, but a quite common quality problem exists all the time, namely the crack problem of the reinforced concrete pool structure, which affects the safety and the normal use of the pool structure, the crack not only affects the beauty, but also brings about the damages of leakage, strength reduction and reinforcing steel bar corrosion when the size of the crack exceeds a certain limit, and further weakens the durability to cause the damages of a structure, collapse and the like.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention provides a method for controlling the construction cracks of an ultra-long large-volume concrete pool, which comprises the following steps:

first, material requirements

1.1 cement: ordinary portland cement (e.g., p.o42.5) is used;

1.2 coarse aggregate: adopting broken stone with the particle size of 5-25mm and the mud content of not more than 1%;

1.3 Fine aggregate: medium sand is adopted, the average grain diameter is more than 0.5mm, and the mud content is not more than 5.0 percent;

1.4 additive I: selecting a pumping agent; additive II: selecting an expanding agent;

second, pouring method

2.1 Raft foundation construction

The raft foundation adopts an inclined plane layering method and push type continuous pouring: the pushing type continuous casting direction is casting from the central point of the raft foundation to the periphery in an annular divergence manner; the inclined plane layered pouring is to gradually move upwards from the lower end of a pouring layer and pour layer by layer; the layering thickness of the inclined plane is 250-300 mm;

the concrete is doped with the retarder, so that the initial setting time of the concrete reaches 8-10 hours, the slump constant of the concrete is not lower than 160mm, and the natural flowing of the concrete is not more than 7: 1;

during pouring, the moving distance of the vibrating rods is less than 50cm, and the duration time of each vibrating point is determined by the degree that floating slurry appears on the surface and does not sink any more; the vibrator is inserted into the lower layer for coagulation for 5 cm; re-vibrating every 20-30 min;

when the concrete is poured to the position 5m away from the side formwork, the concrete distributing pipe is transferred to the side formwork, so that the concrete is poured from the edge to the middle;

after each section of the poured concrete is vibrated, a flat vibrator is used for pressing and vibrating once, and the concrete is scraped and pressed and rubbed flat according to the elevation;

a post-cast strip is reserved on the whole raft foundation along the length direction of the raft foundation, and the post-cast strip is divided into a plurality of casting areas for respective construction;

when the foundation bottom plate and the concrete at the haunching position are poured for the second time, pouring the concrete of the foundation bottom plate firstly, and pouring the concrete at the haunching position before the concrete is initially set; and when vibrating, the vibrating rod is inserted into the lower layer concrete by 50 mm;

2.2 frame shear wall construction

When the shear wall concrete is poured, an integral layered continuous pouring method is adopted for construction, and when one layer of concrete is poured, the next layer of concrete is poured;

before pouring, 50-100mm of mortar with the same mixture ratio of cement and sand in the concrete of the wall body is poured at the bottom; continuously pouring concrete, wherein the pouring thickness of each layer of concrete is controlled within 50 cm;

selecting a vibrating rod: adopting two vibrating rods of phi 50mm and phi 30 mm; the moving distance of the vibrating rod is as follows: the diameter of the vibrating rod is 50mm and is 40-50 cm; the diameter of the vibrating rod is 30 cm; vibrating concrete at the dense part of the reinforcing steel bars by a vibrating rod with the diameter of phi 30mm, and vibrating other positions by a vibrating rod with the diameter of phi 50 mm;

the vibration requirement is as follows: vibrating twice by using an inserted vibrating rod, wherein the first vibrating time is 15-30 seconds, and the second re-vibrating time is 15-30 seconds after 20-30 seconds;

inserting a vibrating rod into the lower-layer concrete by 50mmm before the initial setting of the lower-layer concrete;

concrete pouring is continuously carried out, and the interval time is not more than 3 hours;

after concrete pouring, before initial setting, leveling according to the elevation, and before final setting, plastering and pressing for multiple times;

concrete temperature measuring method

Monitoring the temperature of the poured concrete, and mastering the dynamic change of the internal temperature of the concrete at any time so as to guide the maintenance work of the concrete; simultaneously controlling the temperature difference between the inside and the outside of the concrete not to exceed 25 ℃;

arranging temperature measuring points:

the plane arrangement point is arranged at the center of the plane pouring area, and the side edge and the corner corresponding to the center;

the side arrangement points are arranged at the positions 50mm away from the bottom of the raft foundation, in the middle of the raft and at the positions 50mm away from the surface of the raft;

embedding a temperature sensor of a thermodetector at a temperature measuring point;

fourthly, concrete curing

After the concrete is poured, adopting a heat storage method for maintenance:

after the concrete is vibrated and scraped, leveling and galling before final setting for two hours, and sealing and covering by using a plastic film;

then covering a heat insulation material to control the temperature difference between the interior and the surface of the concrete and the temperature difference between the surface of the concrete and the atmosphere within 25 ℃, and keeping the concrete to be wet and cured for not less than 14 days;

the dismantling time of the heat insulation material is subject to the condition that the temperature difference between the interior and the surface of the concrete and the temperature difference between the surface of the concrete and the atmosphere are less than 25 ℃; the removal of the insulation was 15 days later.

By the method, starting from the aspects of materials, construction process, temperature control and the like, the occurrence of cracks is reduced or even eliminated, and the engineering quality is guaranteed.

Drawings

Fig. 1 is a schematic view of cast-in-place around a central point in a circular divergence in raft foundation layering casting;

FIG. 2 is a schematic view of concrete slab top and haunching and concrete upper and lower layer pouring vibration;

FIG. 3 is a schematic illustration of frame shear wall concrete placement;

FIG. 4 is a schematic view of a concrete cooling circulation water pipe;

in the figure: the concrete vibrating device comprises upper-layer concrete 1, lower-layer concrete 2, a vibrating rod 3, a temperature measuring sensor 4, a water pipe 5, a water inlet 6 and a water outlet 7.

Detailed Description

The method will be described below by taking the example of producing fire pool 05Z2501a/b by using the auxiliary facility device of the PVC continued construction project of the chlor-alkali industry division of the electric metallurgy group of electric power metallurgy Co., Ltd.

The pool is 67.6m long, 24.6m wide and 5.75m high, and multiple layered continuous pouring is adopted in the construction process due to the fact that the pool is large, so that cracks can be effectively reduced, construction quality is improved, and construction cost is saved.

First, the cause of crack generation was technically analyzed:

according to data, the crack cause of the structure in engineering practice is more than 80% caused by deformation change (temperature, humidity and foundation deformation) and about 20% caused by load. In the construction of mass concrete engineering, the concrete cracks due to the drastic changes of the internal temperature and temperature stress of the concrete casting caused by the hydration heat of cement.

Next, a general technical idea for solving the problem is proposed:

the temperature rise of the concrete pouring block body caused by the hydration heat, the temperature difference between the inside and the outside of the concrete pouring block body and the cooling speed are controlled, and the concrete is prevented from generating temperature cracks. For the fire-fighting water pool with longer length in the construction process, a reasonable construction scheme is adopted according to the structural form of the construction; the crack is avoided in the construction process, and multiple times of layered continuous pouring are carried out in the concrete pouring process of the pool.

During specific construction:

1. material selection

1.1 cement: considering that the common cement has high hydration heat, particularly when applied to large-volume concrete, a large amount of cement hydration heat is not easy to dissipate, the temperature in the concrete is too high, and a large temperature difference is generated between the cement hydration heat and the surface of the concrete, so that the pressure stress is generated in the concrete, and the tensile stress is generated on the surface. When the surface tensile stress exceeds the tensile strength of early concrete, temperature cracks are generated, so that P.O42.5 ordinary portland cement with stable performance is selected to reduce the hydration heat.

1.2 coarse aggregate: the concrete is prepared from broken stones with the particle size of 5-25mm and the mud content of not more than 1, and the stones with larger particle size and good gradation are selected, so that the concrete has better workability and higher compressive strength.

1.3 Fine aggregate: the medium sand is adopted, the average grain diameter is more than 0.5mm, and the mud content is not more than 5.0.

1.4 the additive I selects high-efficiency pumping agent; the admixture II is YP-SFA high-efficiency expanding agent.

2. Pouring method

Description of terms: the concrete is the concrete.

2.1 Raft foundation construction

The raft thickness of the constructed production fire pool 05Z2501a/b is 1300mm, the raft foundation needs to be poured in layers, namely, circularly pushed, and an inclined surface layering and pushing continuous pouring method is adopted, namely, the raft foundation is implemented according to a method of 'one gradient, layering pouring and tamping, and progressive', the method not only can facilitate vibrating, but also can utilize the concrete layer surface for heat dissipation, and is beneficial to reducing the temperature rise of mass concrete. In order to prevent the concrete from flowing too much naturally and the concrete from being supplied slowly to form a condensation seam in the pouring process, the retarder is added into the concrete, so that the initial setting time of the concrete reaches 8-10 hours; the slump of the concrete is not lower than 160mm, so that the natural flowing of the concrete is not more than 7:1, the layering thickness of the inclined plane is controlled to be 250-300 mm, the concrete is covered by upper concrete before initial setting, and the concrete is vibrated to be repelled along the flowing direction of the concrete.

During pouring, the moving distance of the vibrating rods is less than 50cm, and the duration of each vibrating point is determined by the degree that floating slurry appears on the surface and does not sink any more. Meanwhile, the vibrator is inserted into the lower layer for 5cm of concrete, and the whole vibrating operation is not required to vibrate the die vibration ribs and collide various embedded parts, iron parts and the like. And the repeated vibration is carried out at intervals of about 20-30 min, so that the compactness and uniformity of the concrete are improved. In order to ensure the compactness of concrete, the operation of the vibrating rod should be realized in a manner of fast insertion and slow pulling, and the vibration is not leaked or avoided. When the concrete is poured to the position which is about 5m away from the side template, the distributing pipe is transferred to the side template, so that the concrete is poured from the edge to the middle, and the slurry is prevented from being gathered at the side template. And (3) pressing and vibrating once by using a flat vibrator after each section of the poured concrete is vibrated, scraping the concrete by using a long scraping ruler according to the elevation, beating and pressing by using an iron trowel, and rubbing the concrete by using a wood trowel.

Two post-cast strips with the width of 1000mm are arranged in the east-west direction of the whole basic raft plate, and the specific positions are located at 3-4 shafts and 6-7 positions. The large-volume concrete of the basic raft is divided into pouring areas 1#, 2# and 3# from left to right according to the axis of the concrete.

The raft foundation is poured in layers, and the schematic diagram that pouring is performed from the central point to the periphery in an annular divergence mode is shown in figure 1.

When the foundation slab and the concrete at the haunching position are poured for the second time, the concrete at the foundation slab is poured firstly, and the concrete at the haunching position is poured before the strength of the concrete is initially set. And the vibrating spear needs to be inserted into the lower layer by 50mm, so that the vibrating time is required to be paid attention to, and the over-vibration is strictly prohibited, so that the concrete is prevented from flowing out from the foundation slab.

The concrete bottom plate top layer and the haunching position and the concrete upper and lower layer pouring vibration schematic diagram are shown in figure 2.

2.2 frame shear wall construction

The shear wall concrete is cast by adopting an integral layered continuous casting method, mortar with the same mixture ratio of cement and sand in the wall concrete is cast at the bottom of the shear wall before casting by 50-100mm, the concrete casting is continuously carried out, the casting thickness of each layer of concrete is controlled within 50cm, the concrete is checked by a flashlight, and the blanking thickness is controlled by a layered ruler rod.

The concrete pouring schematic diagram of the frame shear wall is shown in figure 3.

Selecting a vibrating rod: two types of phi 50 vibrating rods and phi 30 vibrating rods are adopted, and the moving distance of the vibrating rods is as follows: the phi 50 vibrating rod is 40-50 cm; the phi 30 vibrating rod is 30 cm. The phi 30 vibrating spear is mainly used for vibrating concrete at the dense positions of reinforcing steel bars such as columns, connecting beams and the like, and the phi 50 vibrating spears are adopted for the rest. The vibrating distance of the vibrating rod is controlled by brushing red paint marks on the wall formwork at intervals of 50cm, and blue paint marks are brushed at the dense positions of the reinforcing steel bars such as columns, connecting beams and the like at intervals of 30 cm. The vibrating depth is controlled by a method of winding adhesive tape marks on a vibrating rod at intervals of 50 cm.

The vibration requirement is as follows: the adoption of the inserted vibrating rod needs to carry out vibration twice, the first vibration time is 15-30 seconds, the surface is required to present floating slurry and not sink any more, and secondary re-vibration is carried out after 20-30 seconds to be beneficial to improving the compactness of concrete and eliminating water bubbles and shrinkage cracks around the structural member.

In order to integrate the upper and lower concrete layers, a vibrating rod must be inserted into the lower concrete layer by 50mmm before the lower concrete layer is initially set, and the lower concrete layer must be vibrated in place. In the positions where the steel bars such as the hidden columns, the connecting beams and the like are dense, the lower bar points are checked and determined in advance, the concrete is guaranteed to be vibrated compactly, and vibration leakage and mold sticking bubbles are prevented. Concrete pouring needs to be carried out continuously, and the interval time is not longer than 3 hours.

After concrete pouring, before initial setting, the concrete is scraped by a long scraping rod according to the elevation, and before final setting, manual multiple-time plastering and pressing are applied, so that the shrinkage and cracking of the concrete surface are reduced.

When the concrete in the whole pool is poured, a water pump is reserved, and bleeding caused by vibration is timely pumped out to prevent concrete segregation. A small amount of bleeding which cannot be discharged in time is pushed forward along with the pouring direction and is driven to the side mold, and a broom is used for sweeping the side mold.

3. Concrete temperature measuring method

3.1 the thickness of the engineering bottom plate concrete (namely concrete) is 1300mm, the one-time pouring area is large, the hydration heat released by the concrete hardening can generate higher heat, and because of the difference of the hardening speed and the heat dissipation condition of the concrete in a larger section range, a certain temperature difference can be generated inside the concrete, so that the bottom plate concrete can generate temperature cracks, particularly deep and through cracks. The temperature of the poured concrete is monitored, the internal temperature change dynamics of the concrete is mastered at any time, so as to guide the maintenance work of the concrete, the concrete covering and maintenance work is done in time, and the temperature difference of the inner surface of the concrete is controlled not to exceed 25 ℃.

The raft foundation adopts the mode that sets up the circulation downcomer in the concrete, through the circulation operation of intraductal rivers, reduces the inside hydration heat temperature of concrete, ensures that the difference in temperature is in standard allowed range inside and outside the concrete to with the stress value control of concrete within allowed range. Because the concrete center hydration heat is larger, the generated heat is the highest, the middle part of the bottom plate foundation is planned to be arranged by adopting a 25mm curved corrugated pipe for cooling water pipes, the water pipes are pre-arranged above the bottom reinforcing steel bar layer and are arranged in a manner of diverging towards the four-circumference back-shaped mode from the center of the foundation, the pipe spacing is about 2m, and after the concrete is poured, a matched circulating water pump is adopted for carrying out uninterrupted circulating water cooling.

Drawing a temperature measuring point plane layout engineering drawing in advance, and arranging the temperature measuring pipes in place;

the concrete cooling circulation water pipe is schematically shown in figure 4, wherein the unit is mm.

3.2 the bottom plate concrete temperature measurement adopts JDC-II type portable building electronic temperature measuring instrument, and is matched with a temperature measuring lead and a temperature measuring probe for use. When the temperature measuring device is embedded, a steel bar can be used as a bearing carrier, a temperature measuring line is firstly tied on the steel bar, a temperature sensor of the temperature measuring line is positioned at the position of the temperature measuring point and cannot be in direct contact with the bottom plate and the supporting steel bar, when concrete is poured, the steel bar tied with the temperature measuring line is implanted into the concrete, and the plug is left outside and covered by a plastic bag, so that the moisture is avoided, and the cleanness is kept. Each group of test points comprises three temperature measurement induction points, and each temperature measurement point is inserted before bottom plate concrete pouring

The thread reinforcing steel bar support is pre-embedded, and each sensor is respectively attached to

And the steel bar support. When the temperature is measured, the power switch of the host computer is pressed, the plugs of the temperature measuring points are sequentially inserted into the socket of the host computer, and the temperature of the corresponding temperature measuring points can be displayed on the screen of the host computer.

Arranging temperature measuring points:

plane arrangement: (1) dividing the center of the plane pouring area; (2) the side edge and the corner corresponding to the center;

side arrangement: (1) is positioned 50mm away from the base of the raft foundation; (2) the middle of the raft plate; (3) 50mm away from the surface of the raft.

4. Concrete curing

And after the concrete is poured, maintaining by adopting a heat storage method. After the concrete is vibrated and scraped, the concrete is sealed and covered by a plastic film about two hours after the concrete is leveled and napped before final setting to prevent the concrete from dehydrating and cracking, then cotton felt or geotextile is added to effectively control the temperature difference between the inside and the surface of the concrete and the temperature difference between the surface of the concrete and the atmosphere, the temperature difference between the inside and the outside is controlled within 25 ℃, and the concrete is maintained to be not less than 14 days for moist maintenance to prevent the concrete from generating cracks due to temperature difference stress. The time for removing the heat insulating material is subject to the temperature difference between the interior and the surface of the concrete and the temperature difference between the surface and the atmosphere being far less than 25 ℃. After the concrete is poured, the temperature rises in the third and fourth days, the temperature is gradually reduced, the removal of the heat insulation material is generally 15 days later, and the temperature measurement result and the pressure test result of the test block cured under the same conditions are still used as the standard. The cooling speed should not be too fast to prevent the temperature difference stress from generating cracks.

5. Major management measures

5.1 the raw materials for mixing the concrete need to be inspected, and can be used after being qualified. Meanwhile, the temperature of each raw material is required to be paid attention to so as to ensure that the mold-entering temperature of the concrete is basically similar to the theoretical calculation.

5.2 the concrete mixing plant is provided with a specially-assigned person to mix the admixture, and the mixing amount is accurate.

5.3 the commercial concrete station is required to be provided with enough transport vehicles and the quantity of concrete, so that the commercial concrete can be supplied without breaking at a constant speed, and the requirement of continuous pouring of the concrete can be met. And simultaneously preparing a slump cone and a test mould, carrying out pre-control work and other approach inspections on the concrete of each truck, measuring the slump during unloading, making detailed construction records, and strictly forbidding the concrete mixer truck to temporarily add water on a construction site.

5.4 concrete pouring should be carried out continuously, and the intermittent time should not exceed 3 h.

And 5.5, before concrete is poured, sundries in the foundation trench and the template need to be cleaned.

Claims

1. A method for controlling construction cracks of an ultra-long large-volume concrete pool is characterized by comprising the following steps:

one) material requirements

1.1) cement: ordinary portland cement (p.o42.5) is adopted;

1.2) coarse aggregate: adopting broken stone with the particle size of 5-25mm and the mud content of not more than 1%;

1.3) fine aggregate: medium sand is adopted, the average grain diameter is more than 0.5mm, and the mud content is not more than 5.0 percent;

1.4) additive I: selecting a pumping agent; additive II: selecting an expanding agent;

second) pouring method

2.1) Raft foundation construction

2.2) construction of frame shear wall

third) concrete temperature measuring method

arranging temperature measuring points:

IV) curing of concrete

After the concrete is poured, adopting a heat storage method for maintenance:

2. The method as claimed in claim 1, wherein the bleeding water generated by the vibration is discharged in time when the concrete is poured in the whole pool.

3. The method for controlling the construction cracks of the ultra-long large-volume concrete pool as claimed in claim 1, wherein the method for controlling the temperature difference between the inside and the outside of the concrete not to exceed 25 ℃ comprises the following steps: the raft foundation adopts a mode of arranging a circulating downcomer in concrete, and the hydration heat temperature in the concrete is reduced through the circulating operation of water flow in the downcomer, so that the temperature difference inside and outside the concrete is ensured to be within a standard allowable range, and the stress value of the concrete is further controlled to be within the allowable range;

arranging cooling water pipes in the middle of the raft foundation by adopting 25mm curved corrugated pipes, wherein the water pipes are pre-fixed above the bottom reinforcing steel bar layer and are divergently arranged in a shape of a Chinese character hui from the center of the raft foundation to the four sides;

and (4) after the concrete is poured, adopting a matched circulating water pump to perform uninterrupted circulating water cooling.

4. The method for controlling the cracks in the construction of the ultra-long large-volume concrete pool as claimed in claim 1, wherein in the concrete temperature measurement, a building electronic temperature measuring instrument is adopted; when the temperature sensor is pre-embedded, a steel bar is used as a bearing carrier, a temperature measuring line of a temperature measuring instrument is bound on the steel bar, and the temperature sensor connected with the temperature measuring line is positioned at the position of the temperature measuring point and is not in direct contact with the bottom plate and the supporting steel bar;

when concrete is poured, the steel bar bound with the temperature measuring line is implanted into the concrete, and the plug of the temperature measuring line is left outside the concrete and covered by a plastic bag;

each group of temperature measuring points comprises three temperature measuring induction points, namely three temperature sensors; and each temperature measuring point is embedded by inserting a steel bar support before the bottom plate concrete is poured, and each temperature sensor is attached to the steel bar support.