Fly ash-based early-strength curing agent as well as preparation method and application thereof

Abstract

The invention discloses a fly ash-based early-strength curing agent as well as a preparation method and application thereof, and belongs to the technical field of building materials. The fly ash-based early-strength curing agent comprises the following components in percentage by mass: 55-65% of low-calcium fly ash, 8-10% of cement, 3-5% of slag, 3-5% of lime, 3-6% of phosphogypsum, 2-4% of a strong oxidant and 8-10% of an alkali activator. The fly ash-based early-strength curing agent is used for soil reinforcement in foundation pit engineering. A deep mixing pile reinforcing technology is adopted for the coal ash-based early-strength curing agent, the coal ash-based early-strength curing agent is fully mixed with soil to be reinforced in a guniting mode, and the doping weight of the early-strength curing agent is 5%-20% of the weight of the soil to be reinforced. According to the preparation method provided by the invention, industrial waste residues such as fly ash are used for replacing or partially replacing the cement curing agent, so that the industrial waste residues are fully utilized, the industrial utilization rate is improved, the early strength of soil curing can be improved, and the problems of serious resource consumption and CO2 emission easily caused by a traditional Portland cement curing agent are solved.

Description

Technical Field

[0001] The invention relates to the technical field of construction, in particular to a fly ash-based early-strength curing agent and a preparation method and application thereof. Background Art

[0002] With the development of curing technology, traditional silicate cement has been one of the most widely used curing agents in the field of soft soil treatment. It has the advantages of high strength, good heat resistance and durability, and is easy to obtain. However, cement curing agents will cause serious consumption of resources and energy during the production process, and are accompanied by the generation of a large amount of CO2, causing serious pollution to the environment.

[0003] At present, industrial waste residues such as slag, fly ash, and gypsum are often used to replace or partially replace traditional silicate cement. Fly ash is an industrial waste residue formed by burning coal in power plants to generate electricity and has a huge output. Therefore, the use of industrial waste fly ash as the main raw material for preparing curing agents has considerable economic and social value. However, due to the properties of fly ash itself, its main crystal phases are quartz, mullite, hematite, magnetite and gypsum, and it lacks active crystalline compounds of calcium, so fly ash-based curing agents are often less active, and their modified soils usually have the disadvantage of low early strength. The application of such curing agents will lead to slow growth in the strength of the modified soil, increase the project duration, and thus increase the engineering time cost.

[0004] Therefore, it is necessary to provide a fly ash-based early-strength curing agent, which can fully utilize industrial waste fly ash and improve the early strength of soil curing. Summary of the invention

[0005] The purpose of the present invention is to provide a fly ash-based early-strength curing agent and a preparation method and application thereof, so that industrial waste residues such as fly ash are used as a substitute or partial substitute for cement curing agent, so as to make full use of industrial waste residues, improve industrial utilization rate, and realize the improvement of early strength of soil curing, thereby solving the problem of serious resource consumption and CO2 emission caused by traditional silicate cement curing agents.

[0006] To achieve the above object, the present invention provides a fly ash-based early-strength curing agent, which contains the following components in percentage by weight: 55% to 65% low-calcium fly ash, 8% to 10% cement, 3% to 5% slag, 3% to 5% lime, 3% to 6% phosphogypsum, 2% to 4% strong oxidant and 8% to 10% alkali activator.

[0007] Preferably, the low-calcium fly ash is a mixture of flue ash, coal slag, copper slag, iron slag and phosphorus slag, and the weight percentages of flue ash, coal slag, copper slag, iron slag and phosphorus slag are 60%:10%:20%:10%, and the specific surface area of ​​the low-calcium fly ash is 250~350m2 / kg, and the fineness is 45μm sieve residue ≤10%.

[0008] Preferably, the cement is ordinary Portland cement of grade 32.5 or 42.5, the fineness of the cement is 80 μm sieve residue ≤ 10%, and the specific surface area of ​​the cement is 300-400 m2 / kg.

[0009] Preferably, the slag has a fineness of 45 μm, a sieve residue ≤ 10%, a specific surface area of ​​350-400 m2 / kg, and a 7d activity index ≥ 70%.

[0010] Preferably, the content of calcium oxide in the lime is above 85%, and the fineness of the lime is 45 μm sieve residue ≤ 10%.

[0011] Preferably, the phosphogypsum is obtained by calcining and grinding solid waste generated by a wet phosphoric acid process, and the phosphogypsum content after calcination is greater than or equal to 55%, the particle size is ≤70 μm, and the specific surface area is 300~400 m2 / kg.

[0012] Preferably, the strong oxidant is potassium permanganate, and the alkaline activator is sodium sulfate.

[0013] The invention provides a method for preparing a fly ash-based early-strength curing agent, which is prepared by mixing low-calcium fly ash, cement, slag, lime, phosphogypsum, a strong oxidant and an alkali activator in proportion.

[0014] The invention also provides an application of a fly ash-based early-strength curing agent, and the fly ash-based early-strength curing agent is used for soil reinforcement in foundation pit engineering.

[0015] Preferably, the fly ash-based early-strength curing agent adopts deep mixing pile reinforcement technology, and the fly ash-based early-strength curing agent is fully mixed with the soil to be reinforced by spraying. Based on the weight of the soil to be reinforced, the weight of the early-strength curing agent is 5% to 20% of the soil to be reinforced, and the water-cement ratio of the early-strength curing agent is 0.4 to 1.0.

[0016] The present invention can be used in the "underground composite support" system, using the solidified soil layer and the engineering piles at the bottom of the pit as the "underground composite support" to play a supporting role before excavation, forming a bidirectional composite force-bearing body. The enclosure structure is embedded below the excavation surface with the solidified soil layer to achieve a rigid connection, which plays a role in preventing "kicking damage".

[0017] Therefore, the present invention adopts the above-mentioned fly ash-based early-strength curing agent and its preparation method and application, which have the following beneficial effects: (1) The present invention makes full use of industrial waste fly ash, reduces environmental pollution, and promotes the recycling of resources.

[0018] (2) It can significantly improve the early strength of the soil in a short period of time, meet the requirements of rapid construction of the project, and shorten the construction period.

[0019] (3) Fly ash is a cheap industrial waste. Using it as a soil solidifier can significantly reduce material costs and thus reduce the cost of the project.

[0020] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the microscopic morphology of the uncured soil in Comparative Example 2; Figure 2 This is a microscopic morphology of the solidified soil prepared with the fly ash-based solidifying agent obtained in Example 1 at a curing age of 7 days; Figure 3 This is a microscopic morphology of the solidified soil prepared with the fly ash-based solidifying agent obtained in Example 1 after 28 days of curing age. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0023] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0024] In addition, it should be understood that although this specification is described according to the implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. These other implementation modes are also covered within the protection scope of the present invention.

[0025] The invention provides a fly ash-based early-strength curing agent, which contains the following components in percentage by weight: 55%-65% of low-calcium fly ash, 8%-10% of cement, 3%-5% of slag, 3%-5% of lime, 3%-6% of phosphogypsum, 2%-4% of a strong oxidant and 8%-10% of an alkali activator.

[0026] Low calcium fly ash is a mixture of flue ash, coal slag, copper slag, iron slag and phosphorus slag. The weight percentage of flue ash, coal slag, copper slag, iron slag and phosphorus slag is 60%: 10%: 20%: 10%. The specific surface area of ​​low calcium fly ash is 250~350m 2 / kg, fineness is 45μm, sieve residue is ≤10%.

[0027] The cement is ordinary Portland cement of grade 32.5 or 42.5, the fineness of the cement is 80μm, the sieve residue is ≤10%, and the specific surface area of ​​the cement is 300~400m 2 / kg.

[0028] The slag fineness is 45μm, the sieve residue is ≤10%, and the specific surface area is 350~400m 2 / kg, 7d activity index ≥70%.

[0029] The calcium oxide content in the lime is above 85%, and the fineness of the lime is 45μm with a sieve residue of ≤10%.

[0030] Phosphogypsum is obtained by calcining and grinding the solid waste produced by the wet phosphoric acid process. The calcined phosphogypsum content is greater than or equal to 55%, the particle size is ≤70μm, and the specific surface area is 300~400 m 2 / kg.

[0031] The strong oxidant is potassium permanganate and the alkaline activator is sodium sulfate.

[0032] The invention provides a fly ash-based early-strength curing agent which is prepared by mixing low-calcium fly ash, cement, slag, lime, phosphogypsum, a strong oxidant and an alkali activator in a certain proportion.

[0033] The invention also provides an application of a fly ash-based early-strength curing agent, and the fly ash-based early-strength curing agent is used for soil reinforcement in foundation pit engineering.

[0034] The fly ash-based early-strength curing agent adopts deep mixing pile reinforcement technology. The fly ash-based early-strength curing agent is fully mixed with the soil to be reinforced by spraying. Based on the weight of the soil to be reinforced, the weight of the early-strength curing agent is 5% to 20% of the soil to be reinforced, and the water-cement ratio of the early-strength curing agent is 0.4 to 1.0.

[0035] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0036] Example 1 A fly ash-based early-strength curing agent is prepared by mixing low-calcium fly ash, cement, slag, lime, phosphogypsum, a strong oxidant and an alkali activator in a certain proportion. The mixing proportion is: The low-calcium fly ash is a mixture of flue ash, coal slag, copper slag, iron slag and phosphorus slag. The weight percentage of flue ash, coal slag, copper slag, iron slag and phosphorus slag is 60%: 10%: 20%: 10%. The specific surface area of ​​the low-calcium fly ash is about 275m 2 / kg, fineness is 45μm, sieve residue is ≤10%.

[0037] The cement is ordinary Portland cement of grade 32.5, the fineness of the cement is 80μm, the sieve residue is ≤10%, and the specific surface area of ​​the cement is about 325m 2 / kg.

[0038] The slag fineness is 45μm, the sieve residue is ≤10%, and the specific surface area is about 335m 2 / kg, 7d activity index ≥70%.

[0039] The calcium oxide content in the lime is above 85%, and the fineness of the lime is 45μm with a sieve residue of ≤10%.

[0040] Phosphogypsum is obtained by calcining and grinding the solid waste produced by the wet phosphoric acid process. The calcined phosphogypsum content is greater than or equal to 55%, the particle size is ≤70μm, and the specific surface area is about 325 m 2 / kg.

[0041] The strong oxidant is potassium permanganate and the alkaline activator is sodium sulfate.

[0042] Example 2 A fly ash-based early-strength curing agent is prepared by mixing low-calcium fly ash, cement, slag, lime, phosphogypsum, a strong oxidant and an alkali activator in a certain proportion. The mixing proportion is: The low calcium fly ash is a mixture of flue ash, coal slag, copper slag, iron slag and phosphorus slag. The weight percentage of flue ash, coal slag, copper slag, iron slag and phosphorus slag is 60%: 10%: 20%: 10%. The specific surface area of ​​the low calcium fly ash is about 315m 2 / kg, fineness is 45μm, sieve residue is ≤10%.

[0043] The cement is 42.5 grade ordinary Portland cement, the fineness of the cement is 80μm, the sieve residue is ≤10%, and the specific surface area of ​​the cement is about 375m 2 / kg.

[0044] The slag fineness is 45μm, the sieve residue is ≤10%, and the specific surface area is about 375m 2 / kg, 7d activity index ≥70%.

[0045] The calcium oxide content in the lime is above 85%, and the fineness of the lime is 45μm with a sieve residue of ≤10%.

[0046] Phosphogypsum is obtained by calcining and grinding the solid waste produced by the wet phosphoric acid process. The calcined phosphogypsum content is greater than or equal to 55%, the particle size is ≤70μm, and the specific surface area is about 395 m 2 / kg.

[0047] The strong oxidant is potassium permanganate and the alkaline activator is sodium sulfate.

[0048] Silt silt clay was selected for solidification test. The silt silt clay was taken from Nanjing City, Jiangsu Province and tested in accordance with the national standard "Standard for Geotechnical Test Methods" (GB / T50123-2019). The physical properties of the silt silt clay used in the test are shown in the table below.

[0049] Physical properties of silty clay

[0050] Among them, samples prepared in Example 1 and Example 2 and comparative examples 1 and 2 were set up for testing, and the results were as follows: Example 1 The soil is silty silty clay, and is solidified by using the fly ash-based solidifying agent prepared in Example 1 of the present invention, with the solidifying agent dosage being 5%.

[0051] At the curing age of 3 days, the axial strain of the modified soil failure is 2.76%; at the curing age of 7 days, the axial strain of the modified soil failure is 2.36%; at the curing age of 14 days, the axial strain of the modified soil failure is 2.23%.

[0052] At a curing age of 3 days, the unconfined compressive strength of the modified soil is 0.38 MPa; at a curing age of 7 days, the unconfined compressive strength of the modified soil is 0.41 MPa; at a curing age of 14 days, the unconfined compressive strength of the modified soil is 0.43 MPa; at a curing age of 28 days, the unconfined compressive strength of the modified soil is 0.47 MPa.

[0053] At a curing age of 3 days, the elastic modulus of the modified soil is 20 MPa, at a curing age of 7 days, the elastic modulus of the modified soil is 21 MPa, at a curing age of 14 days, the elastic modulus of the modified soil is 21.6 MPa, and at a curing age of 28 days, the elastic modulus of the modified soil is 22 MPa.

[0054] In this embodiment, the microscopic morphology of the solidified soil prepared by the fly ash-based solidifying agent at the 7-day curing age is as follows: Figure 2 As shown in the figure, the microscopic morphology of the stabilized soil prepared by fly ash-based stabilizer at 28 days of curing age is as follows Figure 3 shown.

[0055] Example 2 The soil is silty silty clay, and is solidified by using the fly ash-based solidifying agent prepared in Example 2 of the present invention, with the solidifying agent dosage of 20%.

[0056] At the curing age of 3 days, the axial strain of the modified soil failure is 1.68%; at the curing age of 7 days, the axial strain of the modified soil failure is 1.41%; at the curing age of 14 days, the axial strain of the modified soil failure is 1.40%.

[0057] At a curing age of 3 days, the unconfined compressive strength of the modified soil is 1.10MPa; at a curing age of 7 days, the unconfined compressive strength of the modified soil is 1.28MPa; at a curing age of 14 days, the unconfined compressive strength of the modified soil is 1.40MPa; at a curing age of 28 days, the unconfined compressive strength of the modified soil is 1.63MPa.

[0058] At a curing age of 3 days, the elastic modulus of the modified soil is 141 MPa, at a curing age of 7 days, the elastic modulus of the modified soil is 182 MPa, at a curing age of 14 days, the elastic modulus of the modified soil is 208 MPa, and at a curing age of 28 days, the elastic modulus of the modified soil is 226 MPa.

[0059] Comparative Example 1 The soil is silty silty clay, which is solidified using a conventional fly ash-based solidifying agent.

[0060] When the curing agent dosage is 5%, the axial strain of the modified soil failure is 2.23% at the 3-day curing age; the axial strain of the modified soil failure is 2.15% at the 7-day curing age; and the axial strain of the modified soil failure is 1.94% at the 14-day curing age.

[0061] When the curing agent dosage is 20%, the axial strain of the modified soil failure is 2.93% at the 3-day curing age; the axial strain of the modified soil failure is 2.91% at the 7-day curing age; and the axial strain of the modified soil failure is 2.71% at the 14-day curing age.

[0062] When the curing agent dosage is 5%, the unconfined compressive strength of the modified soil is 0.443MPa after 7 days of curing age; and the unconfined compressive strength of the modified soil is 0.488MPa after 28 days of curing age.

[0063] When the curing agent dosage is 20%, the unconfined compressive strength of the modified soil is 0.445MPa at a curing age of 7 days; and the unconfined compressive strength of the modified soil is 0.493MPa at a curing age of 28 days.

[0064] Comparative Example 2 The soil is silty clay, unsolidified, and the microscopic morphology is shown in the figure below. Figure 1 shown.

[0065] The unconfined compressive strength of unsolidified silty clay is 0.22MPa, and the strength does not change much with the increase of curing age.

[0066] The above tests show that the present invention can improve the early strength of soil solidification. Therefore, the present invention adopts a fly ash-based early-strength curing agent and its preparation method and application, and uses fly ash and other industrial waste residues as a substitute or partial substitute for cement curing agent, so as to make full use of industrial waste residues, improve industrial utilization rate, and achieve the improvement of early strength of soil curing, thereby solving the problem of serious resource consumption and CO2 emissions caused by traditional silicate cement curing agents.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A fly ash-based early-strength curing agent, characterized in that: The fly ash-based early-strength curing agent contains the following components in percentage by weight: 55%~65% low-calcium fly ash, 8%~10% cement, 3%~5% slag, 3%~5% lime, 3%~6% phosphogypsum, 2%~4% strong oxidant and 8%~10% alkali activator.

2. A fly ash-based early-strength curing agent according to claim 1, characterized in that: The low-calcium fly ash is a mixture of flue ash, coal slag, copper slag, iron slag and phosphorus slag, wherein the weight percentage of flue ash, coal slag, copper slag, iron slag and phosphorus slag is 60%:10%:20%:10%, and the specific surface area of ​​the low-calcium fly ash is 250-350m 2 / kg, fineness is 45μm, sieve residue is ≤10%.

3. A fly ash-based early-strength curing agent according to claim 1, characterized in that: The cement is ordinary Portland cement of grade 32.5 or 42.5, the fineness of the cement is 80 μm, the sieve residue is ≤10%, and the specific surface area of ​​the cement is 300-400 m 2 / kg.

4. A fly ash-based early-strength curing agent according to claim 1, characterized in that: The slag has a fineness of 45 μm and a sieve residue of ≤10%, and a specific surface area of ​​350-400 m 2 / kg, 7d activity index ≥70%.

5. A fly ash-based early-strength curing agent according to claim 1, characterized in that: The content of calcium oxide in the lime is above 85%, and the fineness of the lime is 45 μm and the residue on the sieve is ≤10%.

6. A fly ash-based early-strength curing agent according to claim 1, characterized in that: The phosphogypsum is obtained by calcining and grinding the solid waste generated by the wet phosphoric acid process. The phosphogypsum content after calcination is greater than or equal to 55%, the particle size is ≤70μm, and the specific surface area is 300~400 m 2 / kg.

7. A fly ash-based early-strength curing agent according to claim 1, characterized in that: The strong oxidant is potassium permanganate, and the alkaline activator is sodium sulfate.

8. A method for preparing a fly ash-based early-strength curing agent as claimed in any one of claims 1 to 7, characterized in that: The invention is prepared by mixing low-calcium fly ash, cement, slag, lime, phosphogypsum, a strong oxidant and an alkali activator in proportion.

9. An application of a fly ash-based early strength curing agent as claimed in any one of claims 1 to 7, characterized in that: Fly ash-based early-strength curing agent is used for soil reinforcement in foundation pit projects.

10. The use of a fly ash-based early strength curing agent according to claim 9, characterized in that: The fly ash-based early-strength curing agent adopts deep mixing pile reinforcement technology. The fly ash-based early-strength curing agent is fully mixed with the soil to be reinforced by spraying. Based on the weight of the soil to be reinforced, the weight of the early-strength curing agent is 5% to 20% of the soil to be reinforced, and the water-cement ratio of the early-strength curing agent is 0.4 to 1.0.

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