Preparation method of replacement slurry for improving peat soil foundation

Abstract

The present invention discloses a preparation method of a replacement slurry for improving a peat soil foundation, and belongs to the technical field of soft soil foundation reinforcement treatment. The replacement slurry of the present invention is an admixture for the peat soil to be reinforced, and the mass percentage of the admixture is 20% to 30% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fraction: 100 to 300 parts of cement, 200 to 600 parts of sand, 35 to 60 parts of quicklime, 20 to 50 parts of alkaline admixture, 1 to 15 parts of polyurethane superplasticizer, and 1 to 15 parts of polycarboxylic acid water reducer. The formula of the present invention is scientific and reasonable. The replacement slurry replaces and improves the peat soil, reduces the organic matter content and acidity of the soil body, and increases the water content. While ensuring that the replacement slurry has a certain fluidity, it can also have more mixed solid particles, synergistically, further improve the processing performance and crack resistance of the slurry, and achieve better reinforcement effect.

Description

Technical Field

[0001] The invention relates to the technical field of soft soil foundation treatment, and in particular to a replacement slurry for improving a peat soil foundation and a preparation method thereof. Background Art

[0002] This application takes the East Coast Project of Malaysia as the background. The peat soil along the East Coast Rail Project of Malaysia is affected by factors such as climate, vegetation type, sedimentation age and groundwater environment. The organic matter content is generally greater than 10%, and some organic matter content even reaches more than 80%. At the same time, the peat soil in the project area is mostly located in swamps, which are rich in water for a long time. The soil is acidic and the pH value of the soil is in the range of 3-6. It will combine with the alkaline substances in the cement and seriously affect the quality of cement soil piles. Therefore, the amount of mud required for direct cement injection to reinforce peat soil is extremely large. For example, the cement content of some test piles reaches 530kg / m3, and some pile sections are still not piled, which has a very low cost performance.

[0003] With the rapid development of underground engineering construction such as coastal transportation, more and more peat soil reinforcement problems have emerged and need to be solved urgently. In the prior art, traditional cement mixing pile technology can improve the strength of foundation soil to a certain extent. However, for peat soil with high organic matter content, single cement, lime, fly ash and other commonly used curing agents have many problems when curing high organic matter soil, such as low strength, slow strength growth, poor stability, and difficulty in pile formation when used in actual engineering. Therefore, based on cement as the main raw material, fully understanding the structural characteristics of peat soil and seeking a replacement slurry that can significantly improve the reinforcement strength of peat soil is the preferred way to solve the geological problems of peat soil with high organic matter content. Summary of the invention

[0004] The purpose of the present invention is to provide a replacement slurry and a preparation method for improving peat soil foundation, to solve the technical problems mentioned in all the above background technologies, to replace and improve peat soil, to reduce the organic matter content and acidity of the soil, to increase the water content, and to ensure that the replacement slurry has a certain fluidity while having more mixed solid particles.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A replacement slurry for improving a peat soil foundation, wherein the replacement slurry is an admixture for the peat soil to be reinforced, wherein the mass percentage of the admixture is 20% to 30% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fractions: 100 to 300 parts of cement, 200 to 600 parts of sand, 35 to 60 parts of quicklime, 20 to 50 parts of alkaline admixture, 1 to 15 parts of polyurethane superplasticizer, and 1 to 15 parts of polycarboxylic acid water reducer;

[0007] The preparation method of the replacement slurry comprises the following steps:

[0008] S01 determines the mass of the peat soil to be reinforced, calculates the mass of the admixture according to the mass percentage of the admixture being 20% ​​to 30% of the peat soil to be reinforced, and then obtains the cement, sand, quicklime, alkaline admixture, polyurethane superplasticizer and polycarboxylate water reducer of the mass required for the peat soil to be reinforced according to the specific component formula of the admixture;

[0009] S02: adding all the components of the admixture in step S01 to water at a water-cement ratio of 0.4 to 0.8 and stirring to prepare a replacement slurry;

[0010] S03: adding the replacement slurry obtained in step S02 into the peat soil to be reinforced and mixing evenly, and then solidifying to form a cement mixing pile.

[0011] The polyurethane ester superplasticizer mentioned in the above admixture is a high-performance cement plasticizer that can improve the fluidity, strength and durability of concrete at a lower water-cement ratio. In the peat soil foundation reinforcement treatment, it can improve the bearing capacity and stability of the soil by adjusting the consolidation time and expansion. Polycarboxylate water reducer is a complex of dispersant and adsorbent, which can control the interaction between cement particles by changing the surface charge and dispersion mechanism of concrete, thereby achieving the effect of reducing the water-cement ratio and improving the strength of concrete.

[0012] As a preferred technical solution of the present invention, the replacement slurry is an admixture for the peat soil to be reinforced, the mass percentage of the admixture is 25-30% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fractions: 200-250 parts of cement, 300-500 parts of sand, 50-60 parts of quicklime, 30-40 parts of alkaline admixture, 3-8 parts of polyurethane superplasticizer, and 3-8 parts of polycarboxylic acid water reducer.

[0013] According to a further preferred technical solution, the alkaline admixture is a mixture of calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1.

[0014] As a preferred technical solution of the present invention, in step S02, all components of the admixture of step S01 are added to water at a water-cement ratio of 0.45 to 0.5 and stirred to prepare a replacement slurry.

[0015] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. Reduce the organic matter content and acidity of peat soil and have a certain fluidity: cement and sand are the main raw materials for replacement slurry. Adding quicklime can adjust the pH value of peat soil to a certain extent, making it neutral or alkaline, which helps prevent corrosion and environmental pollution. At the same time, quicklime reacts chemically with water in the soil to form slaked lime. In the process of forming slaked lime, a large amount of heat is generated, which can further evaporate part of the water and play a solidifying role. Adding an appropriate amount of polycarboxylate water reducer can improve the fluidity of cement slurry and prevent slurry from clogging pipes. Since polycarboxylate water reducer is acidic, adding alkaline admixtures will generally partially decompose polycarboxylate water reducer. However, the present application uses calcium hydroxide and aluminum hydroxide as alkaline admixtures, wherein calcium hydroxide is a relatively neutral alkaline substance that can not only neutralize the acidic substances in the peat soil foundation, correct its pH value, make it close to neutral or slightly alkaline, and improve the stability and corrosion resistance of the mixture, wherein a small amount of aluminum hydroxide, in addition to correcting the pH value, mainly plays a role in increasing the compressive strength and stability of the polycarboxylate water reducer, and reducing the risk of the polycarboxylate water reducer being decomposed. The combination of calcium hydroxide and aluminum hydroxide can neutralize the organic acid in the soil, improve the strength and stability of the soil, and will not affect the use effect of the polyurethane superplasticizer and the polycarboxylate water reducer.

[0017] 2. Synergistic effect, good effect: In the reinforcement treatment of peat soil foundation, the combined addition of polycarboxylate water reducer and polyurethane superplasticizer can realize multiple mechanisms such as surfactants, dispersants and adsorbents, effectively control the interaction between cement and peat soil, thereby reducing the viscosity and cohesion of the slurry, and increasing its fluidity and permeability; at the same time, it can form a protective film to control the friction between cement particles, thereby reducing the viscosity and cohesion of the slurry; polycarboxylate water reducer cooperates with polyurethane superplasticizer to make cement particles react better with peat soil particles and reduce the generation of excessive voids, gaps and looseness. It should be mentioned that the addition of aluminum hydroxide can further improve the processing performance and crack resistance of the slurry for the use of polycarboxylate water reducer, and achieve better reinforcement effect.

[0018] 3. The composition ratio of the replacement slurry in this application is scientific and reasonable: cement, sand, quicklime, which promote the hardening reaction in the slurry, enhance the compressive strength and durability of the mixture, and the replacement slurry has more mixed solid particles; this formula also reduces the organic matter content and acidity of the soil, appropriately increases the water content, ensures the best quality of piles, and the slurry is alkaline; quicklime and polycarboxylate water reducer can control the interaction between cement and peat soil, prevent solid particles from settling or agglomerating in water, and reduce rheological properties; the polycarboxylate water reducer used in this application is polycarboxylate water reducer stock solution, which is acidic, with a pH value of 6-7, avoiding the addition of other auxiliary materials and causing The pH of the finished product is relatively high, which has little effect on the overall acidity and alkalinity; in addition, polyurethane superplasticizers belong to a class of high-efficiency surfactants, and their molecular structure contains a large number of carboxylic acid groups and hydrophobic groups, which can improve the fluidity and working performance of concrete by adsorbing on the surface of concrete particles. Since the carboxylic acid group itself has a certain acidity, polyurethane superplasticizers usually also show a certain acidity, but this acidity does not have an adverse effect on the performance and durability of the replacement slurry, and can undergo a certain neutralization reaction with the alkaline substances in the replacement slurry, thereby further improving the stability of the structure after peat soil solidification treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of the method for preparing a displacement slurry. DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] The specific implementation process is as follows:

[0022] A replacement slurry for improving a peat soil foundation, wherein the replacement slurry is an admixture for the peat soil to be reinforced, wherein the mass percentage of the admixture is 20% to 30% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fractions: 100 to 300 parts of cement, 200 to 600 parts of sand, 35 to 60 parts of quicklime, 20 to 50 parts of alkaline admixture, 1 to 15 parts of polyurethane superplasticizer, and 1 to 15 parts of polycarboxylic acid water reducer;

[0023] The preparation method of the replacement slurry comprises the following steps:

[0024] S01 determines the mass of the peat soil to be reinforced, calculates the mass of the admixture according to the mass percentage of the admixture being 20% ​​to 30% of the peat soil to be reinforced, and then obtains the cement, sand, quicklime, alkaline admixture, polyurethane superplasticizer and polycarboxylate water reducer of the mass required for the peat soil to be reinforced according to the specific component formula of the admixture;

[0025] S02: adding all the components of the admixture in step S01 to water at a water-cement ratio of 0.4 to 0.8 and stirring to prepare a replacement slurry;

[0026] S03: adding the replacement slurry obtained in step S02 into the peat soil to be reinforced and mixing evenly, and then solidifying to form a cement mixing pile.

[0027] In a further preferred embodiment, the replacement slurry is an admixture for the peat soil to be reinforced, the mass percentage of the admixture is 25-30% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fractions: 200-250 parts of cement, 300-500 parts of sand, 50-60 parts of quicklime, 30-40 parts of alkaline admixture, 3-8 parts of polyurethane superplasticizer, and 3-8 parts of polycarboxylic acid water reducer.

[0028] In a further preferred embodiment, the alkaline admixture is a mixture of calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1.

[0029] In a further preferred embodiment, in step S02, all components of the admixture in step S01 are added to water at a water-cement ratio of 0.4 to 0.8 and stirred to prepare a replacement slurry;

[0030] The method for preparing the replacement slurry for improving the peat soil foundation comprises the following steps:

[0031] S01 determines the mass of the peat soil to be reinforced, calculates the mass of the admixture according to the mass percentage of the admixture being 20% ​​to 30% of the peat soil to be reinforced, and then obtains the cement, sand, quicklime, alkaline admixture, polyurethane superplasticizer and polycarboxylate water reducer of the mass required for the peat soil to be reinforced according to the specific component formula of the admixture;

[0032] S02: adding all the components of the admixture in step S01 to water at a water-cement ratio of 0.4 to 0.8 and stirring to prepare a replacement slurry;

[0033] S03: adding the replacement slurry obtained in step S02 into the peat soil to be reinforced and mixing evenly, and then solidifying to form a cement mixing pile.

[0034] Embodiment 1:

[0035] The replacement slurry for improving the peat soil foundation is an admixture of the peat soil to be reinforced, and the mass percentage of the admixture is 30% of the peat soil to be reinforced. The admixture is composed of the following components in mass fraction: 150 parts of cement, 200 parts of sand, 40 parts of quicklime, 50 parts of alkaline admixture, 5 parts of polyurethane superplasticizer, and 8 parts of polycarboxylic acid water reducer. The alkaline admixture is made of calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1. Water is added and stirred according to a water-cement ratio of 0.5 to prepare a replacement slurry, and the obtained replacement slurry is mixed into the peat soil to be reinforced and mixed evenly to obtain a cement mixing pile.

[0036] Embodiment 2:

[0037] The replacement slurry for improving the peat soil foundation is an admixture of the peat soil to be reinforced, and the mass percentage of the admixture is 35% of the peat soil to be reinforced. The admixture is composed of the following components in mass fraction: 300 parts of cement, 600 parts of sand, 60 parts of quicklime, 50 parts of alkaline admixture, 15 parts of polyurethane superplasticizer, and 15 parts of polycarboxylic acid water reducer. The alkaline admixture is calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1. Water is added and stirred according to a water-cement ratio of 0.8 to prepare a replacement slurry, and the obtained replacement slurry is mixed into the peat soil to be reinforced and mixed evenly to obtain a cement mixing pile.

[0038] Embodiment 3:

[0039] The replacement slurry for improving the peat soil foundation is an admixture of the peat soil to be reinforced, and the mass percentage of the admixture is 20% of the peat soil to be reinforced. The admixture is composed of the following components in mass fraction: 100 parts of cement, 200 parts of sand, 35 parts of quicklime, 20 parts of alkaline admixture, 1 part of polyurethane superplasticizer, and 1 part of polycarboxylic acid water reducer. The alkaline admixture is made of calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1. Water is added and stirred according to a water-cement ratio of 0.4 to prepare a replacement slurry, and the obtained replacement slurry is mixed into the peat soil to be reinforced and mixed evenly to obtain a cement mixing pile.

[0040] Embodiment 4:

[0041] The replacement slurry for improving the peat soil foundation is an admixture of the peat soil to be reinforced, and the mass percentage of the admixture is 25% of the peat soil to be reinforced. The admixture is composed of the following components in mass fraction: 200 parts of cement, 300 parts of sand, 50 parts of quicklime, 30 parts of alkaline admixture, 3 parts of polyurethane superplasticizer, and 3 parts of polycarboxylic acid water reducer. The alkaline admixture is calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1. Water is added and stirred according to a water-cement ratio of 0.45 to prepare a replacement slurry, and the obtained replacement slurry is mixed into the peat soil to be reinforced and mixed evenly to obtain a cement mixing pile.

[0042] Embodiment 5:

[0043] The replacement slurry for improving the peat soil foundation is an admixture of the peat soil to be reinforced, and the mass percentage of the admixture is 30% of the peat soil to be reinforced. The admixture is composed of the following components in mass fraction: 250 parts of cement, 500 parts of sand, 60 parts of quicklime, 40 parts of alkaline admixture, 8 parts of polyurethane superplasticizer, and 8 parts of polycarboxylic acid water reducer. The alkaline admixture is made of calcium hydroxide and aluminum hydroxide in a mass ratio of 2:1. Water is added and stirred according to a water-cement ratio of 0.5 to prepare a replacement slurry, and the obtained replacement slurry is mixed into the peat soil to be reinforced and mixed evenly to obtain a cement mixing pile.

[0044] In addition, two groups of control examples were set up, control example 1 only mixed with cement, and control example 2 mixed with cement and quicklime.

[0045] Indoor formulation tests were conducted on the above-mentioned embodiments 1-5 and the control example: the designed pile length was L=4m, OPC52.5 cement was used, the unconfined compressive strength of cement soil at 28d age was not less than 1.5MPa, and the designed water-cement ratio used in the control example was 0.5 for pile testing.

[0046] The cement content of control example 1 is 55kg / m (empirical value), and the designed water-cement ratio is 0.5 for pile testing. The unconfined compressive strength of the specimen after 7 days of testing is only 0.5MPa. The unconfined compressive strength of the specimen after 28 days of testing is 0.9MPa, which does not meet the design requirements. In addition, additional tests were conducted, and the cement content was increased to 80kg / m. Although the cement dosage increased, the unconfined compressive strength of the specimen after 28 days of testing was 1.5MPa, which just met the design requirements. The cement dosage was too large, which was not economical and there was a phenomenon of pile burning, resulting in the pile body strength not meeting the design requirements. The test results also show that the reinforcement effect of using only cement as a curing agent is very poor.

[0047] In Control Example 2, cement and quicklime (mixed solid content 55kg / m3) were used for indoor formulation test. The dosage of quicklime and lime was determined according to 0.4:1. The unconfined compressive strength of the specimens after 7 days of test was 0.65MPa, and the unconfined compressive strength of the specimens after 28 days of test was 1.2MPa, which did not meet the design requirements. Although the addition of quicklime can improve the unconfined compressive strength to a certain extent, it still cannot meet the design requirements.

[0048] The reinforcement measures for the test piles obtained in Examples 1 to 5 are verified below, and the unconfined compressive strength (MPa) of the test pieces at 7d, 14d, and 28d of age for all examples are compared, as shown in the following table:

[0049]

[0050]

[0051] The above table shows that the water-cement ratio and the amount of admixture added play a key role in the reinforcement effect. The unconfined compressive strength of Examples to Example 5 at the age of 14 days meets the design requirement of 1.5MPa, and the unconfined compressive strength at the age of 28 days falls in the range of 1.78 to 3.18MPa, which not only meets the design requirements, but also has better compressive resistance, forming a sharp contrast with the control example. It has the following characteristics: (1) The addition of admixtures has a more significant reinforcement effect than adding only cement or cement and quicklime; (2) The strength of the peat soil to be reinforced increases with the increase of the amount of admixture added; (3) Under the conditions of the same amount of admixture added and the water-cement ratio, the components in the admixture increase in proportion according to the formula, and the strength of the peat soil to be reinforced also gradually increases. In addition, the organic matter content of the soil sample in this test reaches 50%. Under the synergistic effect of the components of the admixture, it can be seen from the table that the treatment effect of the soil sample is significant, which can be compared with Example 1 and Example 5. Indoor experiments have proved that the addition of the admixture of the present invention has a good pile-forming effect. After the completion of some projects, the roadbed is stable and flat, without cracking, sinking and the like. The soft soil properties of the peat soil foundation of the project to which the present invention is applied are different. The reinforcement method of the present invention is adopted for this purpose, and its reinforcement effect can be also guaranteed. It has the advantages of reducing the organic matter content and acidity of the soil, increasing the water content, ensuring that the replacement slurry has a certain fluidity, and having more mixed solid particles. The components work synergistically to improve the processing performance and crack resistance of the slurry, thereby achieving a better reinforcement effect.

[0052] It should be understood that the above-mentioned embodiments are one or more embodiments of the present invention. There are many other embodiments and variations based on the present invention. For those skilled in the art, various changes, modifications, substitutions and variations of these implementations are made without departing from the principle and spirit of the present invention, and they still fall within the protection scope of the present invention.

Claims

1. A method for preparing a replacement slurry for improving a peat soil foundation, characterized in that: The replacement slurry is an admixture for the peat soil to be reinforced, the mass percentage of the admixture is 20% to 35% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fraction: 100 to 300 parts of cement, 200 to 600 parts of sand, 35 to 60 parts of quicklime, 20 to 50 parts of alkaline admixture, 1 to 15 parts of polyurethane superplasticizer, and 1 to 15 parts of polycarboxylic acid water reducer; The preparation method of the replacement slurry comprises the following steps: S01 determines the mass of the peat soil to be reinforced, calculates the mass of the admixture according to the mass percentage of the admixture being 20% ​​to 30% of the peat soil to be reinforced, and then obtains the cement, sand, quicklime, alkaline admixture, polyurethane superplasticizer and polycarboxylate water reducer of the mass required for the peat soil to be reinforced according to the specific component formula of the admixture; The alkaline admixture is a mixture of calcium hydroxide and aluminum hydroxide, and their mass ratio is 2:1; S02: adding all the components of the admixture in step S01 to water at a water-cement ratio of 0.4 to 0.8 and stirring to prepare a replacement slurry; S03: adding the replacement slurry obtained in step S02 into the peat soil to be reinforced and mixing them evenly, and then solidifying to form cement mixing piles.

2. The method for preparing a replacement slurry for improving a peat soil foundation according to claim 1, characterized in that: The replacement slurry is an admixture for the peat soil to be reinforced, the mass percentage of the admixture is 25-30% of the peat soil to be reinforced, and the admixture is composed of the following components in mass fractions: 200-250 parts of cement, 300-500 parts of sand, 50-60 parts of quicklime, 30-40 parts of alkaline admixture, 3-8 parts of polyurethane superplasticizer, and 3-8 parts of polycarboxylic acid water reducer.

3. The method for preparing a replacement slurry for improving a peat soil foundation according to claim 1, characterized in that: In step S02, all the components of the admixture in step S01 are added to water at a water-cement ratio of 0.45 to 0.5 and stirred to prepare a replacement slurry.

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