Based on our understanding of the properties of various admixtures, it is also crucial to further rationally select and correctly use various admixtures. Therefore, we must also understand and master the “Technical Specifications for the Application of Concrete Admixtures” (GBJ119-88), which stipulates the scope of application of various types of admixtures and formulates basic and specific regulations on the application technology of various types of admixtures. . Basic regulations:
1. The selection of admixture varieties should be based on the main purpose of using admixtures and determined through technical and economic comparison.
2. The dosage of admixtures should be determined through experiments according to their varieties and based on usage requirements, construction conditions, concrete raw materials and other factors.
3. The amount of admixture (calculated on a solid basis) should be expressed as a percentage of cement weight, and the weighing error should not exceed 2% of the specified measurement.
4. The cement used in concrete mixed with admixtures can be silicic acid, ordinary Portland cement, slag, volcanic ash, fly ash cement.
5. The coarse and fine aggregate used in concrete mixed with admixtures should comply with the current national standards.
6. The mix ratio design of admixtures can be implemented in accordance with the regulations of JGJ-55-2000.
Specific provisions:
① In concrete projects, lignosulfonate can be used Similar water-reducing agents, polycyclic aromatic sulfonate-based water-reducing agents, water-soluble resin sulfonate-based water-reducing agents, and others such as corrosive acid-based water-reducing agents.
② Water reducing agent can be used for cast-in-place precast concrete, reinforced concrete and prestressed concrete.
③ Ordinary water-reducing admixtures should be used for concrete construction where the daily minimum temperature is above 5℃, and should not be used alone for steam-cured concrete.
④ High-efficiency water-reducing admixture can be used for concrete construction where the daily minimum temperature is above 0℃, and is suitable for preparing high-fluidity concrete, high-strength concrete and steam-cured concrete.
⑤ In cement using anhydrite or industrial waste gypsum as the setting agent, the cement should be adapted first when adding lignosulfonate water-reducing agent. It can be used only after passing the sex test.
⑥ The suitable dosage of ordinary water reducing agent is 0.2~0.3%. With the temperature, the dosage can be increased or decreased appropriately, but it should not be greater than 0.5%. , the suitable dosage of high-efficiency water reducing agent is 0.5%-0.7%, which can be increased or decreased appropriately according to the needs of the project.
⑦ The water-reducing agent should be added in solution, and the amount of water in the solution should be deducted from the mixing water amount.
⑧ The water-reducing agent should be added to the mixer at the same time as mixing. When using a mixer truck to transport concrete, it can be added to the mixer truck before unloading. Discharge after uniformity.
⑨ For the concrete mixture mixed with water-reducing agent, during the period from when the mixer is unloaded to the completion of pouring, the pouring and vibration methods are the same as those without water-reducing agent. of concrete.
⑩ According to the needs of the project, the water-reducing agent can be used in combination with other admixtures, and the dosage must be determined based on the test. When preparing solutions, if flocculation or precipitation occurs, solutions should be prepared separately and added to the mixer separately.
⑾ When natural curing is used for concrete mixed with water-reducing agent, initial curing should be strengthened. When steam curing is used for concrete mixed with superplasticizer, the concrete should have the necessary structural strength to heat up. The steam curing system is determined through experiments.
2. General provisions for air-entraining agents and air-entraining water-reducing agents
① In concrete In the project, the following air-entraining agents or air-entraining water-reducing agents can be used; rosin resins, alkyl benzene sulfonates, fatty alcohol sulfonates, modified lignin sulfonates, alkyl aromatic sulfonates Salts, and composite agents composed of various air-entraining agents and water-reducing agents.
② Air-entraining agent and air-entraining water-reducing agent can be used for anti-freeze concrete, impermeable concrete, sulfate-resistant concrete, concrete with severe bleeding, and poor concrete. Special seats for gray concrete, lightweight aggregate concrete and concrete with requirements for corrosion surfaces.
③ Air-entraining agents should not be used for steam-cured concrete and prestressed concrete.
④ Concrete with high requirements for freeze-thaw resistance must be mixed with air-entraining agent or air-entraining water-reducing agent. The amount should be based on the air content of the concrete. Requirements are determined through testing.
The air content of concrete mixed with air-entraining or air-entraining water-reducing admixtures should not exceed the following requirements:
Air content of concrete mixed with air-entraining agent and air-entraining water-reducing agent
Maximum particle size of coarse aggregate cm3 10 15 20 25 40 50 80 150
Concrete air content (%) 7.0 6.0 5.5 5.0 4.5 4.0 3.5 3.0
⑤ Air-entraining agent The air-entraining water-reducing agent should be added as a solution and added to the mixing water when used. The amount of water in the solution should be deducted from the mixing water.
⑥ The air-entraining agent and air-entraining water-reducing agent must be fully dissolved when preparing the solution. If flocculation or precipitation occurs, it should be heated to dissolve it before use. .
⑦ Air entraining agent and its�When admixtures are used in combination, if flocculation or precipitation occurs in the prepared solution, the solutions should be prepared separately and added to the mixer respectively.
⑧ During construction, the air content of concrete should be strictly controlled. When the materials or construction conditions change, the air-entraining agent or air-entraining water-reducing agent should be increased or decreased accordingly. dosage.
⑨ To test the air content of the air-entraining agent or air-entraining water-reducing agent, sampling should be carried out at the mixer outlet, and consideration should be given to the transportation and impact of the concrete. loss of air content during the process.
⑩ Air-entraining agent and air-entraining water-reducing agent concrete must be mixed mechanically. The mixing time should not be more than 5 minutes and less than 3 minutes. The parking time from discharging to pouring should not be too long. When using a plug-in vibrator, the vibration time should not exceed 20 seconds. </p
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