Formula of anti-crack concrete for high-speed railway bridge pier column in plateau and alpine region

Abstract

The invention relates to the technical field of concrete materials, in particular to a formula of plateau high-cold high-speed railway bridge pier column anti-crack concrete which comprises the following components: 280-320 kg / m < 3 > of Portland cement, 80-100 kg / m < 3 > of mineral powder, 60-80 kg / m < 3 > of coal ash, 800-850 kg / m < 3 > of machine-made sand with the fineness of 2.6-3.0, 900-1000 kg / m < 3 > of broken stone, 140-160 kg / m < 3 > of water and 4.0-5.0 kg / m < 3 > of polycarboxylic acid water reducing agent. The total use amount of the retarding components in the water reducing agent is 0.8-1.2 kg / m < 3 >, the air entraining agent comprises triterpenoid saponin and a liquid air entraining agent, the total use amount is 0.02-0.05 kg / m < 3 >, and the use amount of the polypropylene fiber is 0.9-1.2 kg / m < 3 >. Through a low water-binder ratio, a composite gelling system, fiber reinforcement and seasonal regulation and control composite admixture technology, the compressive strength, crack resistance and freeze-thaw resistance are remarkably improved, and the composite admixture is suitable for bridge engineering in plateau alpine regions.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete materials, and in particular to a formula of anti-cracking concrete for high-speed railway bridge piers in high-altitude and cold plateaus. Background Art

[0002] The harsh climate in high-altitude, cold regions of the plateau, with diurnal temperature swings exceeding 30°C, dry air, and strong ultraviolet rays, makes concrete structures susceptible to cracking due to temperature stress, shrinkage stress, and freeze-thaw cycles, seriously impacting the durability and safety of bridge piers. Traditional concrete mixes suffer from the following issues: insufficient crack resistance, large early shrinkage, and a susceptibility to plastic shrinkage cracking and temperature cracking; poor freeze-thaw resistance, with a low number of freeze-thaw cycles (typically ≤200), which is difficult to meet the requirements of high-altitude, cold regions; and uneven strength development, with excessively rapid early strength growth, exacerbating the risk of temperature stress cracking. Therefore, optimizing concrete mixes to mitigate cracking remains a technical challenge. Summary of the Invention

[0003] The purpose of the present invention is to provide a formula for anti-cracking concrete for high-speed railway bridge piers in plateau and cold areas, so as to solve the problems raised in the above background technology.

[0004] The technical solution adopted by the present invention is: a formula for anti-cracking concrete for high-speed railway bridge piers in high-altitude and cold plateaus, comprising the following ingredients: silicate cement in an amount of 280-320 kg / m 3 The amount of mineral powder is 80-100 kg / m 3 The amount of fly ash used is 60-80 kg / m 3 The fineness of machine-made sand is 2.6-3.0, and the dosage is 800-850kg / m 3 The amount of crushed stone is 900~1000kg / m 3 , water consumption is 140~160kg / m 3 The dosage of polycarboxylate water reducer is 4.0~5.0kg / m 3 The total amount of retarding component in the water reducer is 0.8~1.2kg / m 3 The air entraining agent components include triterpenoid saponins and liquid air entraining agent, with a total dosage of 0.02-0.05 kg / m 3 , the amount of polypropylene fiber is 0.9~1.2kg / m 3 .

[0005] Preferably, the polycarboxylate water-reducing agent has an air content of 3.0% to 3.5%.

[0006] Preferably, the maximum temperature of the retarder in winter does not exceed 10°C, the total amount of the retarder does not exceed 20kg / ton of water reducer, and the retarder includes the following combination: sodium gluconate does not exceed 10kg / ton of water reducer; sodium tripolyphosphate and citric acid are 10kg / ton of water reducer in total; sodium hexametaphosphate is 5kg / ton of water reducer; and white sugar is prohibited from being used as a retarder.

[0007] Preferably, in spring and autumn when the maximum temperature is 10-15°C, the amount of sugar used is 5 kg / ton of water reducer; when the maximum temperature is 20-25°C, the amount of sugar used is 10 kg / ton of water reducer; the total amount of retarder used does not exceed 40 kg / ton of water reducer.

[0008] Preferably, when the maximum temperature in summer exceeds 25° C., the total retarder dosage does not exceed 60 kg / ton of water reducer, and the sugar dosage is 15 kg / ton of water reducer.

[0009] Preferably, the triterpenoid saponins in the air-entraining agent stabilize microbubbles with a diameter of 20 to 200 μm. The amount of liquid air-entraining agent added to each ton of water-reducing agent is 500 to 1000 grams, and sodium lauryl sulfate is prohibited.

[0010] Preferably, the air entraining agent is allowed to add 5-10 kg of citric acid per ton of water reducer and the dosage of sodium citrate alone is less than 20 kg per ton of water reducer, and sodium citrate is not compounded with polycarboxylate water reducer.

[0011] Preferably, the initial setting time of the concrete is controlled within 6 hours, and the final setting time is within 8 to 9 hours.

[0012] Preferably, the polypropylene fiber is 12 mm in length.

[0013] Preferably, the method comprises the following steps: step 1: dry material mixing, dry mixing cement, mineral powder, fly ash, sand and gravel for 0.5 to 1 minute; step 2: wet mixing, adding an aqueous solution containing a polycarboxylic acid water reducer and an air entraining agent, and stirring for 2 to 3 minutes; step 3: fiber dispersion, slowly adding polypropylene fiber, and continuing to stir for 2 minutes until uniform.

[0014] The beneficial effects of the present invention are as follows: The present invention significantly improves the compressive strength, crack resistance and freeze-thaw resistance through low water-cement ratio, composite cementitious system, fiber reinforcement and seasonally regulated composite admixture technology, and is suitable for bridge projects in plateau and cold areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the mix ratio flow chart of the present invention;

[0016] Figure 2 This is a comparison chart of the effects of the present invention and ordinary C45 concrete. DETAILED DESCRIPTION

[0017] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for purposes of illustration and description and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments are chosen and described to better illustrate the principles of the invention and its practical application, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for specific applications.

[0018] like Figure 1 、 2 As shown: The formula of the anti-cracking concrete for the high-speed railway bridge piers in the plateau and high-cold region of the present invention includes the following ingredients: Portland cement is used in an amount of 280-320 kg / m 3 , preferably 300kg / m 3 , providing early strength; the amount of mineral powder (S95 grade) is 80-100kg / m 3 , preferably 90kg / m 3 , reduce hydration heat and improve later strength; the dosage of fly ash (grade II) is 60-80kg / m 3 , preferably 60kg / m 3 , improve workability and reduce shrinkage; the fineness of machine-made sand (medium sand) is 2.6-3.0, and the dosage is 800-850kg / m 3 , preferably 814kg / m 3 , optimize orthopedic grading; gravel (5-31.5mm continuous grading, 5-10mm:10-20mm:16-31.5mm=1:6:3) dosage is 900-1000kg / m 3 , preferably 994kg / m 3 , improve the density of the skeleton; the water dosage is 140~160kg / m 3 , preferably 153kg / m 3 , control the water-binder ratio not to exceed 0.35; the dosage of polycarboxylate water reducer is 4.0-5.0kg / m 3 , preferably 4.5kg / m 3 , the air content is 3.0% to 3.5%; the total amount of retarding component in the water reducer is 0.8 to 1.2 kg / m 3 , adjust the coagulation time; the air entraining agent components include triterpenoid saponins and liquid air entraining agent, the total dosage is 0.02~0.05kg / m 3 , the air content is 3.5% to 4.0%; the weight of the air entraining agent after dilution at a ratio of 1:99 (air entraining agent: water) is 4.5 kg / m 3 The length of polypropylene fiber is 12mm, and the dosage is 0.9~1.2kg / m 3 , preferably 1.0kg / m3 , inhibiting early plastic shrinkage cracks.

[0019] Low water-binder ratio is the ratio of water to cementitious materials. Cementitious materials include cement, mineral powder and fly ash. The low water-binder ratio is 0.30-0.35, preferably 0.34, which reduces capillary pores and improves density.

[0020] A water reducer is a concrete admixture that reduces the amount of water used in the mix while maintaining a relatively constant slump. It is an anionic surfactant. Adding a water reducer to concrete disperses cement particles and improves workability. This reduces the specific water usage and improves the performance of the concrete mix. Based on their water-reducing capacity and dispersing effect, they are categorized as standard, high-efficiency, and high-performance water reducers.

[0021] Features of polycarboxylic acid high performance water reducer:

[0022] 1. The dosage is low, which is 10% of the cementitious material. The water reduction rate is high (up to 50%). The cement has a strong dispersing ability and can minimize the water consumption of concrete.

[0023] 2. The concrete mixture has high fluidity and good function of maintaining the slump loss of concrete. The slump loss is small and the slump of concrete does not lose in a few hours.

[0024] 3. The strengthening effect is significant. The compressive strength of concrete increases by 50% to 110% in 3 days and by 40% to 80% in 28 days.

[0025] 4. The concrete has excellent workability, no bleeding or segregation, and the concrete appearance color is uniform.

[0026] 5. The air content is moderate, has no adverse effect on the elastic modulus of concrete, and has good frost resistance and durability.

[0027] 6. Low alkali content is beneficial to the durability of concrete.

[0028] 7. Small shrinkage, which is beneficial to preventing concrete cracking.

[0029] 8. The molecular structure is easy to design and it is easy to synthesize products with different performance requirements.

[0030] The core of water-reducing agent compounding is very simple, which is the twelve-word principle, namely "cleverly use retarding setting, cleverly use air entraining, and cleverly use collapse prevention".

[0031] When selecting a retarder, we should not only focus on its retarding effect, but also consider its ability to raise slurry and improve the overall performance of the package. It is strictly forbidden to use a single retarder in combination. The combined use of multiple retarders is very beneficial to improving the adaptability of the water reducer.

[0032] When selecting an air-entraining agent, one should not only consider the amount of air entrained, but also the air-entraining effect, concrete slurry lifting and flow properties, and air content loss. It is advisable to adopt a combination of triterpenoid saponins and liquid air-entraining agents.

[0033] When selecting a slump-retaining agent, one should not only consider its slump-retaining time, but also the workability of the concrete; high-slump-retaining agent has a better slump-retaining effect, but if too much high-slump-retaining agent is added, the concrete will easily bleed water, which puts higher requirements on the water-reducing mother liquor and compounding. It is advisable to adopt a combination of medium-slump-retaining agent and high-slump-retaining agent.

[0034] During summer construction, the combined use of retarders in high-performance concrete can extend the setting time and reduce the loss of slump. At the same time, because retarders can control the hardening speed of concrete and eliminate cold joints by delaying setting, they can reduce construction difficulties. Some retarders (such as tartaric acid, which can easily cause super-retardation and should be used with caution) also have a certain dispersing effect. When used with high-performance water-reducing agents, they can increase the water reduction rate and increase the fluidity of concrete.

[0035] Common retarders include: sugar, sodium gluconate, citric acid, sodium citrate, sodium tripolyphosphate, sodium hexametaphosphate, tartaric acid, etc. When compounding on site, the combined use of multiple retarders is very beneficial to improving the adaptability of the water reducer. It is strictly forbidden to use a single type of retarder for compounding.

[0036] The compatibility of different retarders with high-performance water-reducing agents and cement should be tested before use. The dosage of retarder should be strictly controlled to avoid affecting the early strength of concrete or prolonging the setting time due to excessive retarder.

[0037] The total amount of water reducer and retarder is determined by weather changes or the setting time requirements of concrete during construction. In the absence of special requirements for concrete, the initial setting time of concrete can be easily controlled at around 6 hours, and the final setting time should be 8 to 9 hours, which is convenient for construction.

[0038] This requires precise control of the retarder dosage of water reducer. Taking the weather at 3,800 meters above sea level in the Ruoergai area of Aba, Sichuan Province on the Xicheng Railway as an example, when the water reducer dosage is 1.0%, the maximum retarder dosage in various seasons is: when the maximum temperature in winter does not exceed 10°C during construction, the total retarder dosage shall not exceed 20kg / ton of water reducer; when the temperature in spring and autumn is 10-15°C and 20-25°C during construction, the total retarder dosage shall not exceed 40kg / ton of water reducer; when the maximum temperature in summer exceeds 25°C during construction, the total retarder dosage shall not exceed 60kg / ton of water reducer.

[0039] When compounding concrete water reducers in winter, sugar is sensitive to temperature and cannot be added at will; sodium gluconate has a certain water-reducing function but is easy to ooze water, and has poor slurry lifting and wrapping properties, so it cannot be added too much, and should not exceed 10 kilograms; sodium tripolyphosphate and citric acid have good slurry lifting and wrapping properties for concrete, so they can be added appropriately, about 10 kilograms; and sodium hexametaphosphate, in addition to its good slurry lifting effect, makes the concrete shiny, so it can be added appropriately, about 5 kilograms.

[0040] White sugar primarily acts as a retarder in water reducers. Its viscosity can also be exploited by adding an appropriate amount of white sugar to water reducers to increase the viscosity of concrete. While white sugar as a retarder is indeed effective and can save costs, it is sensitive to temperature and is not suitable for areas with large temperature differences between morning and evening, especially in colder weather. White sugar should not be used as a retarder in water reducers for beams of C50 and above, as it uses a large amount of cementitious material and has a low water-to-cement ratio, resulting in viscous concrete. Therefore, white sugar cannot be used as a retarder in beam concrete water reducers.

[0041] In winter, when compounding water-reducing agent, white sugar is generally not used as a retarder; in spring and autumn when the maximum temperature is 10-15℃, it is advisable to add about 5 kg of white sugar as a retarder; in spring and autumn when the maximum temperature is 20-25℃, it is advisable to add about 10 kg of white sugar as a retarder; in summer when the maximum temperature exceeds 25℃, it is advisable to add about 15 kg of white sugar as a retarder, and the amount of white sugar added needs to be strictly controlled to avoid water seepage.

[0042] Using a certain amount of air-entraining agent (AEA) in high-performance concrete creates small, circular, closed pores within the concrete, further improving its fluidity and reducing segregation and bleeding. This is beneficial for grouting and increasing encapsulation, enhancing concrete uniformity and integrity, and improving its durability, impermeability, and frost resistance. During on-site compounding, the AEA dosage is generally approximately 1% of the water-reducing agent dosage. This small dosage makes direct on-site addition difficult. Therefore, the AEA is diluted to a ratio of 1:99 (AEA:water) before incorporation. If required, concrete air content should be controlled between 3.0 and 3.5%, which does not affect concrete strength or performance. However, air loss is a crucial indicator; significant air loss can severely impact concrete grouting, encapsulation, fluidity, and slump retention.

[0043] Triterpenoid saponins, commonly known as "Huangyin," are nonionic surfactants made primarily from the fruits of wild plants found in southern my country, such as sapodilla and tea seeds. These saponins are refined through extraction, grafting, molecular structure optimization, and synthesis. They appear as pale yellow powders, are easily soluble, and exhibit strong chemical stability to acids, alkalis, and hard water. Huangyin significantly reduces the surface tension of solutions, producing closed, independent bubbles with high numbers, small spacing, and long bubble stability. Huangyin significantly improves the workability of plastic concrete and enhances the durability of hardened concrete, making it a high-quality air-entraining agent with great potential for application in domestic concrete projects.

[0044] The bubbles produced by Huangyin are microspheres, which are used to stabilize the bubbles. Most of the bubbles have a diameter of 20 to 200 μm. This improves the concrete's encapsulation, fluidity, and pumping performance, reduces slump loss, and reduces bleeding and segregation. The mixture is highly cohesive, easy to pump, and vibrate to compact, increasing concrete strength, stability, and durability. When Huangyin is added to concrete with an air content below 3%, the concrete's compressive strength not only does not decrease but actually slightly increases. When Huangyin is added to concrete with an air content of 4%, the concrete's compressive strength remains normal. When Huangyin is added to concrete with an air content of 5%, the concrete's compressive strength loss rate is no more than 5%.

[0045] Liquid air-entraining agents (LAAs) are commonly found in the sodium lauryl sulfate, Hanyin, Clariant, or Kao series. However, sodium lauryl sulfate produces larger bubbles and higher air loss, making its use generally prohibited. However, the addition of 5-10 kg / ton of citric acid to water-reducing agents and sodium citrate is permitted. Single-use LAEs incorporate a novel surfactant into their molecular backbone that effectively reduces surface tension and interfacial energy. This allows the aqueous solution to easily generate numerous tiny, enclosed bubbles during mixing, with most bubbles under 200 μm in diameter. The AEA molecules adsorb onto the bubble surfaces, forming a strong liquid film that stabilizes the bubbles and resists rupture. This not only reduces the cost of traditional AAEs but also enhances their entraining performance. The bubbles are richer, finer, more uniform, and more durable. They are highly effective in improving concrete's durability and freeze-thaw cycle resistance, significantly improving its workability and can also be used in conjunction with antifreeze in winter. When compounding water reducers, liquid lead is usually used in combination with yellow lead, and the amount of liquid lead added to each ton of finished water reducer is 500 to 1000 grams.

[0046] Citric acid and sodium citrate are permitted in air-entraining agents. Citric acid, also known as citric acid and chemically known as 2-hydroxypropane-1,2,3-tricarboxylic acid, is divided into citric acid monohydrate and anhydrous citric acid depending on its water content. Citric acid has an acidic pH value and can neutralize high-alkali cement, providing a favorable reaction environment and conditions for polycarboxylate superplasticizers. This significantly improves the adaptability of superplasticizers and provides excellent concrete slurrying performance. It is commonly used in concrete with low cement content and a high water-cement ratio, but the setting time is slightly longer. It is often used in combination with other retarding materials. The dosage is 5-10kg / ton of superplasticizer. Excessive use can easily lead to prolonged setting time, affecting concrete construction and early strength, and leaving the concrete fluffy.

[0047] Sodium citrate primarily acts as a retarder in concrete. This means it can be added to water reducers as a retarder to improve concrete setting time and enhance workability. Sodium citrate readily adsorbs on the surface of cement particles and forms complexes with calcium ions, inhibiting the exotherm of cement hydration and delaying the formation of hydration products. When used alone as a retarder, the dosage should be carefully considered; the recommended dosage is less than 20 kg per ton of water reducer. Sodium citrate has poor compatibility with other retarding materials and is not suitable for compounding with polycarboxylate water reducers. Compounding sodium citrate with polycarboxylate water reducers not only fails to retard the setting, but can actually accelerate setting.

[0048] The method for preparing crack-resistant concrete for high-speed railway bridge piers in high-altitude and cold plateaus includes the following steps: Step 1: dry material mixing, cement, mineral powder, fly ash, sand, and gravel are dry-mixed for 0.5 to 1 minute; Step 2: wet mixing, an aqueous solution containing a polycarboxylate water reducer and an air-entraining agent is added and stirred for 2 to 3 minutes;

[0049] Step 3: Fiber dispersion: slowly add polypropylene fiber and continue stirring for 2 minutes until uniform.

[0050] like Figure 2 The figure shows a comparison of the effects of the present invention and ordinary C45 concrete. N1 is the mass loss rate of ordinary C45 concrete, and N2 is the mass loss rate of the concrete of the present invention. Compared with ordinary C45 concrete, the present invention has the following advantages:

[0051] Compressive strength: 28-day compressive strength ≥62MPa (increased by 19% to 27%);

[0052] Crack resistance: early cracking area ≤ 0.1㎡ / m 2 (reduced by more than 80%);

[0053] Freeze-thaw resistance: freeze-thaw cycles ≥ 300 times (increased by 50%);

[0054] Durability: Chloride ion diffusion coefficient ≤ 2.0×10-12m 2 / s (reduced by 50%).

[0055] The core of the invention lies in: low water-cement ratio: reducing capillary porosity and improving density; composite cementitious system: using silicate cement and fly ash to optimize hydration heat release; high-performance water reducer and retarding air entraining composite technology: controlling slump loss and improving frost resistance; fiber reinforcement: incorporating polypropylene fiber to inhibit early plastic shrinkage cracks.

[0056] The present invention significantly improves the compressive strength, crack resistance and freeze-thaw resistance through low water-cement ratio, composite cementitious system, fiber reinforcement and seasonally regulated composite admixture technology, and is suitable for bridge projects in plateau and cold areas.

Claims

1. A formula for anti-cracking concrete for high-speed railway bridge piers in high-altitude and cold plateaus, characterized by: It includes the following ingredients: Portland cement dosage is 280~320kg / m 3 The amount of mineral powder is 80-100 kg / m 3 The amount of fly ash used is 60-80 kg / m 3 The fineness of machine-made sand is 2.6-3.0, and the dosage is 800-850kg / m 3 The amount of crushed stone is 900~1000kg / m 3 , water consumption is 140~160kg / m 3 The dosage of polycarboxylate water reducer is 4.0~5.0kg / m 3 The total amount of retarding component in the water reducer is 0.8~1.2kg / m 3 The air entraining agent components include triterpenoid saponins and liquid air entraining agent, with a total dosage of 0.02-0.05 kg / m 3 , the amount of polypropylene fiber is 0.9~1.2kg / m 3 .

2. The formula of the anti-cracking concrete for high-speed railway bridge piers in plateau and high-cold conditions according to claim 1 is characterized by: The polycarboxylate water-reducing agent has an air content of 3.0% to 3.5%.

3. The formula of the anti-cracking concrete for high-speed railway bridge piers in plateau and cold regions according to claim 1 is characterized by: The maximum temperature of the retarder in winter does not exceed 10°C, the total amount of the retarder does not exceed 20kg / ton of water reducer, and the retarder includes the following combination: sodium gluconate does not exceed 10kg / ton of water reducer; sodium tripolyphosphate and citric acid are 10kg / ton of water reducer in total; sodium hexametaphosphate is 5kg / ton of water reducer; and white sugar is prohibited from being used as a retarder.

4. The formula of the anti-cracking concrete for high-speed railway bridge piers in high-altitude and cold plateaus according to claim 3 is characterized by: When the maximum temperature in spring and autumn is 10-15°C, the amount of sugar used is 5kg / ton of water reducer; when the maximum temperature is 20-25°C, the amount of sugar used is 10kg / ton of water reducer; the total amount of retarder used does not exceed 40kg / ton of water reducer.

5. The formula of the anti-cracking concrete for high-speed railway bridge piers in plateau and cold regions according to claim 3 is characterized by: When the maximum temperature in summer exceeds 25°C, the total retarder dosage does not exceed 60kg / ton of water reducer, and the sugar dosage is 15kg / ton of water reducer.

6. The formula of the anti-cracking concrete for high-speed railway bridge piers in plateau and high-cold conditions according to claim 1 is characterized by: The triterpenoid saponin in the air-entraining agent stabilizes microbubbles with a diameter of 20 to 200 μm. The amount of liquid air-entraining agent added to each ton of water-reducing agent is 500 to 1000 grams, and sodium lauryl sulfate is prohibited.

7. The formula of the anti-cracking concrete for high-speed railway bridge piers in high-altitude and cold plateaus according to claim 6 is characterized by: The air entraining agent is allowed to add 5-10 kg of citric acid per ton of water reducer and the single dosage of sodium citrate is less than 20 kg per ton of water reducer, and sodium citrate is not compounded with polycarboxylate water reducer.

8. The formula of the anti-cracking concrete for high-speed railway bridge piers in plateau and high-cold conditions according to claim 1 is characterized by: The initial setting time of the concrete is controlled within 6 hours, and the final setting time is within 8 to 9 hours.

9. The formula of the anti-cracking concrete for high-speed railway bridge piers in high-altitude and cold plateaus according to claim 1 is characterized by: The length of the polypropylene fiber is 12 mm.

10. A method for preparing crack-resistant concrete for high-speed railway bridge piers in high-altitude and cold regions of plateau, characterized by: The following steps are involved: Step 1: Dry material mixing: dry mix cement, mineral powder, fly ash, sand and gravel for 0.5 to 1 minute; Step 2: wet mixing, add the aqueous solution containing polycarboxylate water reducer and air entraining agent, and stir for 2 to 3 minutes; Step 3: Fiber dispersion: slowly add polypropylene fiber and continue stirring for 2 minutes until uniform.

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