Contents of this article
The best formula for concrete anti-segregation agent?
Can citric acid dissolve cement?
What is the effect of needle flake content on concrete?
What are the applicable scopes of concrete pumping agents?
What role does cellulose fiber play in concrete?
Concrete initial setting time and anti-freezing measures?
What is the best formula for concrete anti-segregation agent?
Concrete, as the largest building material, has developed rapidly. In recent years, high-strength and high-performance concrete has been widely used in engineering. The fluidity of concrete has developed from the previous 70~90mm to the current slump of 180~230mm. Some projects also use self-compacting concrete, and the pumping height is getting higher and higher. However, the fluidity and cohesion of concrete are often incompatible, that is, it is difficult for concrete to maintain high cohesion properties under large flow conditions. In this way, concrete that pursues high fluidity is prone to bleeding and segregation. Moreover, with the gradual depletion of river sand resources and mineral resources in my country, the gradation and fineness of river sand fluctuate greatly, ordinary manufactured sand with poor particle size is used on a large scale, the water retention of cement fluctuates, and high water reduction but The more sensitive polycarboxylic acid-type water-reducing admixtures are constantly being promoted, and the quality control of ready-mixed concrete is facing increasingly severe challenges. The existing concrete anti-segregation agents have a strong flocculation effect, which will cause the concrete to settle quickly and the concrete to lose its flow properties instantly, which is detrimental to the workability of concrete. For this reason, we propose an anti-segregation agent for concrete and its preparation method.
Technical implementation elements:
The purpose of the present invention is to provide an anti-segregation agent for concrete and a preparation method thereof to solve the existing concrete anti-segregation problems proposed in the above background technology. The strong flocculation effect of the agent will cause the concrete to settle quickly, causing the concrete to lose its flow properties instantly, which is detrimental to the workability of the concrete.
In order to achieve the above object, the present invention provides the following technical solution: an anti-segregation agent for concrete, the composition of the anti-segregation agent for concrete is as follows:
Fly ash 5- 15 parts, mineral powder 5-15 parts, steel fiber 1-2 parts, polyethylene glycol 1-2 parts, polyhydroxy acid water reducing agent 20-30 parts, tackifier 0.8-1.2 parts, coagulant 0.5- 0.9 parts, 200-300 parts of deionized water, several parts of liquid alkali, 5-10 parts of silicone monomer, 3-5 parts of oxidizing agent, and 1-3 parts of reducing agent.
Preferably, the organosilicon monomer is propyltrichlorosilane or vinyltrichlorosilane or fluorosilicone monomer or a mixture of the three.
Preferably, the coagulant is powdered sodium sulfate.
Preferably, the tackifier is PAM, and the PAM is moistened with methanol or ethanol, deionized water is added for stirring, and the mixture is heated to 55 degrees Celsius during stirring to prepare a solution with a concentration of 4%.
Preferably, the oxidizing agent is one or a mixture of hydrogen peroxide, ammonium persulfate, and potassium persulfate.
Preferably, the reducing agent is ammonium persulfate-anhydrous sodium bisulfite or ammonium persulfate-sodium hypophosphite.
Preferably, the alkali solution is sodium hydroxide.
Preferably, the preparation method of the concrete anti-segregation agent includes the following steps:
S1: Mixing: combine silicone monomer, deionized water, polyhydroxyacid water-reducing agent and polyethylene glycol are added into the reaction kettle for mixing;
S2: Oxidation: Stir until the mixture in step S1 is evenly mixed, and add oxidant for oxidation;
S3: Reduction: Add fly ash, mineral powder and steel fiber to the oxidized mixture in step S2, and then add the reducing agent;
S4: Neutralization: Add a tackifier to the reduced mixture in step S3 and coagulant, stir continuously until the mixture is uniform, and then add liquid caustic soda to adjust the pH so that the pH is between 7-9, and then the anti-segregation agent for concrete can be obtained.
Compared with the existing technology, the beneficial effects of the present invention are: the invention adds fly ash, mineral powder and steel fiber to the anti-segregation agent, which can not only improve the compressive strength of concrete, but also It can also effectively improve the working performance and stratification of concrete, improve the segregation resistance of concrete, and reduce the expansion and slump of concrete. PAM is used as a tackifier because PAM has more -NH2. The tackifier has good hydrophilicity, making the concrete hydrophilic, water-retaining, thickening, resistance-reducing and viscosity-increasing. Adding calcium sulfate as a setting accelerator can promote concrete water splashing, accelerate hardening, and promote condensation. The invention has wide sources of raw materials, low cost, green and environmental protection, and simple operation.
Can citric acid dissolve cement?
No. Citric acid is a strong organic acid with a large degree of dissociation. The dissociated ions have a retarding and dispersing effect on cement slurry, but the effect of citric acid is not only that. Indoor experimental results show that citric acid affects the strength of cement stones. The development of citric acid has a strong retarding effect as the dosage increases at medium and low temperatures, but at high temperatures, the retarding effect shows a curve. When the dosage is greater than 0.8%, the performance is as follows Accelerates coagulation; at various temperatures, citric acid has a dispersing effect on cement slurry, especially for salt water cement slurry; citric acid can improve the water drainage of cement slurry. However, citric acid is easily oxidized by various oxidants, so The effect on the performance of different cement slurry systems is unstable. If the cement admixture contains alcohol or the system temperature is too high, citric acid will react and lose its effect. However, at medium and low temperatures, the performance is relatively low.�: See "10-1-6-3 Air-entraining agent and air-entraining water-reducing agent".
4. Application technical points: (1) The dosage of pumping agent varies greatly from brand to brand. You should carefully understand the instructions in the instructions before use. Overdosing of pumping agent may also cause pump clogging. (2) The performance test of concrete mixed with pumping additives is different from other admixtures. The performance test of pumped concrete should use sand in zone II. The cement dosage: when using pebbles (330±5) kg/m3, when using gravel ( 340±5)kg/m3, sand rate is 42%. The water consumption shall be based on the slump of the blank concrete (8±1) cm and the slump of the tested concrete (18±1) cm. (3) The cohesion and fluidity of concrete mixed with pumping agent should be better, and the bleeding rate should be lower. During the slump test, there should be no coarse aggregate accumulation in the center part of the concrete sample after the slump expansion, and there should be no obvious separation of slurry and free water in the edge part. Turn the slump cylinder upside down and fill it with a concrete sample. After lifting it 30cm, calculate the emptying time of the sample from the cylinder. The shorter the time, the better the fluidity. (4) The temperature of concrete where pumping agent is applied should not be higher than 35°C. (5) The higher the temperature of the concrete and the longer the transportation or pumping distance, the higher the requirements for the quality of the pumping agent.
What role does cellulose fiber play in concrete?
The role of cellulose fiber in concrete:
1. Effectively prevent the occurrence of shrinkage cracks in concrete
Due to the characteristics of cellulose fiber itself, such as natural The hydrophilicity, excellent gripping force, huge fiber specific surface area, and high toughness and strength, etc., after being added to concrete, under the action of water immersion and external force, a large number of evenly distributed fine fibers are formed, which can effectively prevent The plastic shrinkage, drying shrinkage and temperature changes of concrete cause cracks.
2. Significantly improve the mechanical properties of concrete
1. Crack resistance of concrete
Cellulose fibers are three-dimensionally distributed in concrete and can effectively It can reduce the stress concentration at the tip of micro cracks, weaken or eliminate the tensile stress caused by dry shrinkage of concrete or mortar, and prevent the occurrence and expansion of micro cracks.
2. Improvement of the impermeability of concrete
The uniform distribution of cellulose fibers in concrete forms a supporting system, which hinders surface water leakage and aggregate settlement, and reduces The bleeding property of concrete reduces the bleeding channels of concrete and greatly reduces the porosity in concrete, thus significantly improving the anti-permeability performance of concrete.
3. Improvement of freeze-thaw resistance of concrete
The presence of cellulose fibers in concrete can effectively reduce the resistance within concrete caused by multiple freeze-thaw cycles. The concentration of tensile stress prevents further expansion of microcracks. In addition, due to the improvement of concrete's impermeability, it is of course also beneficial to improve its freeze-thaw resistance.
4. Improving the impact resistance and toughness of concrete
Cellulose fibers help absorb the impact of concrete components, and due to the crack resistance effect of the fibers, the fiber in the concrete When subjected to impact loads, fibers can prevent the rapid expansion of internal cracks, so they can effectively enhance the impact resistance and toughness of concrete.
5. Improvement of the durability of concrete
Due to its good crack resistance effect, cellulose fiber greatly reduces the occurrence and development of cracks. The reduction of internal porosity makes the external The erosion and penetration of corrosive water and chemical media in the environment, gas salts, etc. are slowed down. Due to the large reduction in cracks, the channels for corrosion of the main structural steel bars are reduced, thereby greatly improving the durability of the concrete.
6. Improvement of high temperature resistance of concrete
Cellulose fiber is added to concrete, especially high-strength concrete, because it contains a large number of evenly distributed fiber monofilaments. Three-dimensional random distribution, forming a three-dimensional network structure. When the internal temperature of the flame-baked concrete component rises above 165°C, the fibers melt and form internally connected pores for strong high-pressure steam to escape from the inside of the concrete, so it can effectively To avoid explosion in fire environment.
3. Significantly improve the durability of concrete. Cellulose fiber makes the cement more completely hydrated, significantly reduces the voids in the concrete, makes the concrete denser, thereby improving the frost resistance and water penetration resistance of the concrete. , resistant to chloride permeability, giving concrete better durability.
Concrete initial setting time and anti-freezing measures?
The initial setting time of concrete in winter is generally 8 to 12 hours, and the final setting time is 12 to 16 hours. If the temperature is below zero in winter (more than a week after pouring), just do a good job of concrete insulation. If concrete is poured in a negative temperature environment (temperature below minus 5°C), the main thing to pay attention to is early concrete anti-freeze. Antifreeze needs to be operated from two aspects:
1) Use antifreeze: Antifreeze can greatly reduce the freezing point of the mixing water, preventing the moisture inside the concrete from freezing and expanding in the plastic state and early stage, and causing frost damage to the concrete. Antifreeze has no obvious harm to the strength performance of concrete, but some antifreeze contains urea, and the concrete will release ammonia smell for a long time, so special attention is required.
2) Insulation: Use plywood, wooden boards and other formwork with a certain insulation effect as much as possible. Use insulation materials such as quilts, straw curtains or foam insulation boards to cover the exposed concrete surface and wrap the steel formwork to make the concrete Strength develops quickly. For winter construction, use early-strength silicate or ordinary Portland cement because the strength develops quickly and the heat of hydration is relatively high. However, as long as the insulation is good, any cement can be used. The strength develops more slowly, which is better for preventing thermal stress cracks. In an environment with a temperature of 2°C, antifreeze may not be used when pouring concrete, but insulation must be done and the temperature change trend must be paid close attention to. If the temperature continues to drop, it is necessary to strengthen the concrete insulation and pay close attention to the temperature change trend. If the temperature continues to drop, concrete insulation needs to be strengthened.
The heat is relatively high. However, as long as the insulation is good, any cement can be used. The strength develops more slowly, which is better for preventing thermal stress cracks. In an environment with a temperature of 2°C, antifreeze may not be used when pouring concrete, but insulation must be done and the temperature change trend must be paid close attention to. If the temperature continues to drop, it is necessary to strengthen the concrete insulation and pay close attention to the temperature change trend. If the temperature continues to drop, concrete insulation needs to be strengthened. <img src="/upfile/202304/2023041334528065.jpg"/ 
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