Analysis of intelligent curing system for precast concrete girders and slabs?

A large number of engineering practice shows that there are many factors that cause concrete disease, and maintenance is an important part of it. First of all, the precast concrete girder intelligent curing system in the construction of the application of research. Then from the precast concrete girder intelligent curing system characteristics, process principles and operation points are analyzed. Finally, relevant quality control measures and safety measures are proposed in combination with example projects.

1 Project Overview

Guizhou Province Dejiang to Muchuan Expressway No. DWTJ-1 contract section starts from Dejiang County Qianjia Tujia Township, the starting point pile number K0+000, connecting with the Yanhe to Dejiang Expressway, through the setting of Qianjia junction interchanges to realize the traffic conversion, the interchanges landing for the service of the Dejiang County Town, the end of the pile number for the YK6+755, the total length of 6.739km. road base Width 24.5m, two-way 4 lanes, design traffic speed 80km / h. The main works: earth and stone 2.046 million m3, tunnel 3358m / 2, bridge 2655m / 6. The project*** has prefabricated T-beams*** counting 645 pieces (including 560 pieces of 30mT-beams and 85 pieces of 40mT-beams). To ensure the quality of prefabricated T-beams, which is an important link to guarantee the quality of the project, an intelligent curing system of prefabricated concrete girder slabs is adopted to ensure the quality of the girder slabs' curing.

2Features

(1) After the arrangement of the curing pipeline is completed, one key starts the intelligent curing system, then the full-cycle curing construction is automatically completed. (2) At the right time for the concrete surrounding the whole cover, shade and moisturizing, the whole process of monitoring the environment around the beam and surface temperature, humidity and automatically make a judgment to control the maintenance of highway to complete the maintenance, in order to guide the release of hydration heat at the right time, to prevent the emergence of early maintenance cracks. (3) with the use of winter maintenance with self-control hot water boiler, can be in the winter at a lower temperature for concrete construction, accelerate the construction progress, shorten the construction period.

3 Process principle

3.1 Process principle of intelligent curing system Cement concrete intelligent curing system mainly consists of wireless temperature and humidity measurement terminals, the system host, curing terminals (scaffolding, piping, sprinkler) three parts. The system host consists of controller, speed inverter, power distribution system, multi-stage vertical pump, temperature and humidity sensors, pressure sensors and other components to ensure that any nozzle to maintain 0.20MPa spray pressure.

3.2 Wireless temperature and humidity measurement terminal Wireless temperature and humidity measurement terminal is arranged on the surface of the concrete structure to be cured, it should monitor the surface temperature and humidity of the beam at any time, and control the curing system to start the spraying curing when the temperature and humidity exceed the set value. The wireless transmission distance of the terminal is more than 300m, transmits data once every 30s, comes with wireless battery and can be used continuously for 3 years.

3.3 system host composition ① controller: the component according to the detected temperature and humidity conditions, hydration heat release rate control frequency converter frequency adjustment multi-stage vertical pump speed to adjust the water supply pressure to ensure that the spray head spray effect. ② speed inverter: the component is used to control the vertical multi-level water pump speed to adjust the pressure and flow, adjust the outlet pressure, while realizing the effect of frequency conversion and energy saving. ③ Power distribution system: used to supply power to each electrical component. ④ Vertical multi-stage water pump: used for water supply pressurization. ⑤ Temperature and humidity sensor: used to check the environment temperature and humidity. (6) Pressure sensor: used to check the water supply pressure. 3.4 Composition of maintenance terminal (1) The spraying pipeline adopts PP-R water supply pipe with a strength of 1.6MPa and diameters of φ25 and φ32. (2) The spraying nozzle adopts the double-type spraying nozzle made of plastic material, which is divided into two kinds of fixed angle and 360°adjustable angle. (3) Maintenance trellis: φ32, φ40, wall thickness of 2.5mm galvanized pipe, according to the type of beam design and processing.

4 Construction Operation Points

4.1 On-site Water Collection Point Setting Intelligent maintenance construction site water collection point water supply main diameter is not less than φ50mm, to ensure that the water supply is sufficient during the maintenance construction period, the distance from the water collection point to the intelligent maintenance instrument should be within 5 m, not more than 8 m. The water collection point should be appropriately distributed based on the site components, structural location to meet the requirements of the distance of the water collection. The girder yard should arrange water catchment canal according to the terrain, and the water left after maintenance should be collected to catchment pool for recycling after precipitation.4.2 Establishment of intelligent maintenance host placement location Intelligent maintenance instrument should be placed in the center of each member and structure to be maintained to reduce the loss of water in the process of conveying water for maintenance, such as the use of prefabricated girder yard, it is appropriate to plan and centralize the prefabrication in batches to reduce the moving of maintenance host. Intelligent maintenance instrument should be placed on a flat ground, the use of the process should be done to cover the sun, rain cover, the ground shall not have water.

4.3 maintenance pipeline, maintenance scaffolding production ① maintenance pipeline production: according to the components to be maintained, the structure of the appearance of the dimensions, the design of the maintenance pipeline layout form and nozzle layout spacing, to ensure that the spray curing area to be covered by the surface of the concrete to be cured, the spray head using a double-head high atomization nozzles, curing radius of more than 1.0 m. ② maintenance scaffolding production: according to the appearance of the different components, the structure of the size, the design of maintenance covering scaffolding, the design of the maintenance covering the surface of the concrete to be maintained. Size, design maintenance covering trellis, covering trellis using φ32, φ40 steel pipe production (wall thickness of 2.5 ~ 3mm).4.4 connecting pipeline, power connection between the maintenance instrument host and to be maintained between the components or structure of the pipeline; connecting the water point and the intelligent maintenance instrument between the pipeline.4.5 set up wireless temperature and humidity terminals in the girder plate in the girder plate adhesive or to prevent the wireless temperature and humidity terminals are used for the testing of the girder surface temperature and humidity. surface temperature and humidity.

4.6 start the maintenance host, set maintenance parameters system start, open the distribution box door, touch screen open, set maintenance parameters. Pressure target value: the water pressure value of the water outlet, according to the calculation of head loss to ensure that the last nozzle with 0.2MPa pressure value. Minimum temperature: 5 ℃ according to the code requirements, winter program below 5 ℃ system automatically spray hot water, summer program below 5 ℃ system does not start. The control program needs to be updated when connecting or disconnecting the boiler. Maximum temperature: usually set at 40 to 45°C. Maximum humidity: usually set to 90% or more. Clock control spray time: that is, each time the start of the spray conservation time, according to the number of spray nozzles set to 2 ~ 4min; clock control conservation stage settings: divided into three stages, the first stage for the first day; the second stage for the second to third days, the third stage for the fourth day to the end of the conservation. Can be set for different stages of the clock spraying frequency, such as the first stage of the day 30min / times, 60min / times at night. Press the channel button corresponding to a certain piece of beam curing pipeline on the control panel, and immediately start to implement the full cycle of curing construction.4.7 End of curingTo be cured concrete beams and slabs to reach the age of curing, press the control button corresponding to the channel on the control panel of the curing mainframe, and the indicator light goes out, and curing ends instantly. The scaffolding and piping move to other beam slabs to be cured.

5 Quality Control

(1) Establish quality assurance system and implement quality responsibility system to ensure the quality of project construction. (2) precast concrete girder slab pouring initial condensation, mold removal immediately after the installation of maintenance pipeline to start spraying maintenance. When it is necessary to take mold maintenance, the maintenance scaffolding should be installed to cover, and the spraying maintenance should start immediately after the slurry collection. (3) Spray curing pipeline nozzle spacing 1.0 ~ 1.5m set up a, to ensure that the spray range covers all areas of the surface of the concrete, can be appropriate to manually adjust the angle of each nozzle. (4) After the concrete is demolded in winter, cover it immediately to ensure that the temperature difference between the concrete surface and the surrounding environment does not exceed 20℃. (5) When the ambient temperature is lower than 5℃ in winter, the host of the curing system should be used together with the self-controlled hot water boiler to spray hot water for heat preservation and moisturizing curing. (6) The curing cycle shall not be less than 7d in general, and the concrete with special needs shall be extended according to the ambient temperature and humidity, cement varieties and admixtures, etc. as appropriate. (7) The whole process of curing should keep the water and electricity unimpeded, should be regularly cleaned curing host filter and test curing nozzle.

6 safety measures

Strengthen the training and improve the safety awareness of all participants. Concrete intelligent curing system safety precautions (1) by a professional electrician to connect the three-phase power supply, connected to the power box, the general letter L on behalf of the firewire. (2) Intelligent maintenance system host stainless steel wheels must be pressed on the ground for grounding conductors in addition to static electricity, the site installation of equipment this wheel shall not be suspended. (3) Intelligent maintenance system is prohibited without water to start, no water should immediately stop running. (4) Intelligent maintenance system placed in the outdoor use must be covered on its top surface to prevent rain and sun. (5) ambient temperature below 0 ℃, should stop the system host operation.

7 Environmental Protection Measures

Waste water, waste slurry, waste residue, etc. generated during construction cannot be discharged indiscriminately and are handled according to regulations. The maintenance girder yard reasonably sets up the catchment canal and catchment pool, the water for spraying and maintenance flows down from the girder board to be maintained and then collects through the catchment canal, and enters the catchment pool to be used again as the water for maintenance after precipitation.

8 Resource saving

Adopting technologically advanced and economically reasonable construction equipment, it promotes the process of standardization and refinement management while improving technological advancement and intelligence, and saves all kinds of costs. Changed the backward process of manual maintenance in the past, improving the quality of concrete maintenance, reducing pollution and protecting the ecological environment. Reduced personnel to perform the construction process cumbersome procedures, on behalf of the implementation of the program to improve labor efficiency.

9 Benefit Analysis

9.1 Technical Benefits

(1) On-site real-time monitoring of ambient temperature and humidity as well as the temperature and humidity of the beam surface, and automatically according to the monitoring results of the implementation of the conservation measures, so that on-site concrete curing conditions inclined to the standard curing room curing, the realization of the site of the concrete curing standardization, refinement, intelligence. Overcome the artificial measurement of temperature and humidity of the actual number of times and the actual number of curing difficult to ensure the problem. (2) Setting program according to the amount of hydration heat release to guide the hydration heat can be released smoothly. (3) According to the specifications and conservation program established procedures for conservation construction, the process is standardized, spraying reasonable. (4) The curing process is standardized and reasonable, with high strength of concrete and few cracks. (5) The system can automatically complete the full cycle of curing construction and can simultaneously carry out automatic curing of multiple beams of different ages.

9.2 Economic Benefits

Equipment can be used for more than 8 years with one-time input, compared with the traditional manual maintenance, intelligent maintenance can be installed once to realize the full cycle of maintenance, work efficiency can be improved by more than 5 times, labor savings of 70%. At the same time, the quality of maintenance has been qualitatively improved to ensure that the temperature and humidity in the field of concrete component maintenance process, try to avoid the production of maintenance cracks, reduce the structure of the later maintenance costs, the economic benefits are incalculable.9.3 Social BenefitsThe quality of concrete curing is to ensure the safety of the concrete components and durability of the key processes, is the lifeline of the structural safety. Through automation, intelligent means to control the temperature and humidity of concrete curing, so as to improve the safety and durability of concrete components, changing the traditional manual curing method, realizing the improvement of technical process, with good social benefits.

10 Conclusion

The cement concrete intelligent curing system is adopted on site and used with the self-controlled hot water boiler. Changing the manual curing to intelligent mechanical automatic curing, it improves the curing efficiency and quality of curing, promotes the construction progress of the project, prolongs the service life of the concrete components, saves the maintenance cost in the later stage, and has good economic benefits, social benefits and promotion prospects.

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