Solid waste-based self-compacting super-waterproof backfill material and preparation method thereof

Abstract

The application discloses a solid waste-based self-compacting super-waterproof backfill material and a preparation method thereof, and the solid waste-based self-compacting super-waterproof backfill material is formed by mixing and stirring slag and a solid waste-based high-impervious curing agent and water; the solid waste-based high-impervious curing agent comprises steel slag powder, granulated blast furnace slag, fly ash, red mud, industrial by-product gypsum, hydrophobic organic acid salt, alkali metal lactate, high-performance polycarboxylate water reducer and dispersant. Physical-chemical reactions occur in the mixing and stirring, a large amount of cementing bodies are generated in the curing process, the inter-particle pores of soil are filled, the structure is compacted, the strength is high, and the imperviousness is good; the application focuses on the solid waste resource utilization demand, has the advantages of high solid waste utilization rate, low economic cost, high fluidity, good waterproof performance and the like; and the application changes the need of adding cement clinker in traditional backfill materials, and is more economical and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of building materials, and in particular to a solid waste-based self-compacting ultra-waterproof backfill material and its preparation method. Background Technology

[0002] The selection of backfill materials for pipeline trenches and the control of backfill compaction are crucial factors affecting the quality of pipeline construction. Medium-coarse sand is commonly used for backfilling pipeline foundations. According to the "Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering" (GB50268), backfilling should extend 500mm above the top of the pipe. The moisture content of the backfill material should be strictly controlled during backfilling, adhering to the principles of symmetrical backfilling on both sides of the pipeline and layered compaction. The compaction degree of the trench backfill material is a key quality control indicator; design documents typically specify a minimum of 95%, and strict adherence to the requirements of GB50268 is required to ensure the safety of drainage pipeline projects. However, the following problems are often encountered during the implementation of the project: First, with the depletion of natural river sand resources, the price of high-quality medium-coarse sand materials that are easy to control in terms of quality has gradually increased, and the transportation distance for external purchases is relatively long. In actual construction, materials are often sourced locally for backfilling, making it difficult to control the quality of the project. Second, the backfill soil is not backfilled in layers as required, which covers up the quality hazards such as the presence of large stones in the backfill soil, resulting in the backfill soil not being compacted and causing a large amount of soil settlement after construction. Third, in drainage pipeline projects with limited construction space in urban areas, steel sheet pile foundation pit support schemes are generally adopted. The process of removing steel sheet piles can easily disturb the newly backfill soil around the pipe (especially at the bottom), which can damage the pipe-soil joint force system established by the compaction project. This results in poor durability of the newly built drainage pipeline and makes it easy for structural defects such as joint separation, pipe wall rupture, and pipeline settlement to occur. By improving the properties of trench backfill materials and construction techniques, self-compacting backfill materials can be achieved, thereby increasing the guarantee rate of pipe-soil synergy, improving the stress state of pipelines, reducing backfill material loss, improving drainage pipeline quality, and preventing pipeline rupture and road subsidence. The aggregates for self-compacting backfill materials can generally be sourced locally on-site, or chemically stable, safe, environmentally friendly solid waste that meets engineering performance requirements, such as crushed construction waste, steel slag, mud, and construction waste. To ensure the quality of trench backfilling in drainage pipeline projects, promoting the application of new self-compacting backfill materials and construction techniques is essential for improving the quality of urban drainage pipeline projects. Summary of the Invention

[0003] The technical problem to be solved by this invention is to change the environmental pressure and high cost caused by the use of cement in traditional self-compacting backfill materials, and the poor waterproof performance of previous self-compacting backfill materials. This invention provides a solid waste-based self-compacting super waterproof backfill material and its preparation method. This material has the characteristics of high solid waste utilization rate, low cost, good flowability and waterproof performance.

[0004] The technical solution adopted in this invention is: a solid waste-based self-compacting ultra-waterproof backfill material, comprising solid raw materials and liquid raw materials.

[0005] The solid raw materials, by weight, include: 10 parts of slag and 1.5 parts of solid waste-based high impermeability solidifying agent;

[0006] The liquid raw material is water;

[0007] The mass ratio of solid raw materials to liquid raw materials is 1:2.

[0008] Furthermore, the solid waste-based high impermeability solidifying agent, by weight, comprises the following components:

[0009] 35-50 parts of steel slag powder

[0010] 20-30 parts of granulated blast furnace slag powder

[0011] 5-10 parts fly ash

[0012] 5-10 parts red mud

[0013] 10-15 parts of industrial by-product gypsum

[0014] 0.5-1 part of hydrophobic organic acid salts

[0015] Alkali metal lactate 0.1-0.2 parts

[0016] 1-2 parts of high-performance water-reducing agent

[0017] Dispersant 1-3 parts.

[0018] Furthermore, the slag is screened to a maximum particle size of ≤50mm. If the particle size is too large, the resulting backfill material will be ineffective, its properties will be uneven, and its quality will be difficult to control. The organic matter content is ≤3%, as organic matter will affect the later strength of the backfill material. If the organic matter content is too high, the later strength will not meet the required quality requirements. It also meets the requirements of GB / T 50743-2012 "Technical Specification for Recycling of Construction Waste".

[0019] Furthermore, the steel slag powder meets the requirements for the activity index and fluidity ratio of Grade I steel powder specified in GB / T 20491-2006 "Steel Slag Powder for Cement and Concrete".

[0020] The granulated blast furnace slag powder is S95 grade slag powder, and meets the S95 grade activity index and fluidity ratio requirements specified in GB / T 18046-2017 "Granulated blast furnace slag powder for cement, mortar and concrete".

[0021] The fly ash is Class I fly ash and meets the activity index requirements of Class III or above in GB / T 1596-2017 "Fly Ash for Cement and Concrete".

[0022] The red mud mentioned is Bayer process red mud.

[0023] Furthermore, the industrial by-product gypsum is any one or a mixture of two of desulfurized gypsum and phosphogypsum, and meets the requirements of GB / T 21371-2008 "Industrial by-product gypsum for use in cement"; gypsum sulfate can also activate the activity of granulated blast furnace slag to generate ettringite, and the synergistic activation under the alkaline environment provided by Ca(OH)2 makes the activation effect more obvious.

[0024] The hydrophobic organic acid salt is any one or a mixture of two of calcium stearate and zinc stearate; the hydrophobic organic acid salt is a hydrophobic material that can form a hydrophobic film in the pores of the backfill material, thereby increasing the waterproof and seepage-proof effect of the backfill material.

[0025] The alkali metal lactate is any one or a mixture of two of sodium lactate and calcium lactate. Lactic acid anions can promote the disintegration of slag structure, increase the hydration reaction rate, promote the formation of hydration products such as ettringite and CSH, and significantly improve the pore structure distribution of backfill materials, reduce porosity, increase density, thereby enhancing waterproof performance.

[0026] Furthermore, the high-performance water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water reduction rate of ≥35%.

[0027] Furthermore, the dispersant is any one or a mixture of two of sodium pyrophosphate and sodium oxalate. The dispersant can disperse soil particles, increasing their specific surface area and significantly improving the flowability of the backfill material.

[0028] A method for preparing a solid waste-based self-compacting ultra-waterproof backfill material, characterized by comprising the following steps:

[0029] Step 1: Weigh out the following materials according to requirements: slag and steel slag powder, granulated blast furnace slag powder, fly ash, red mud, industrial by-product gypsum, hydrophobic organic acid salts, alkali metal lactates, high-performance water-reducing agents, and dispersants; measure out the following water according to requirements.

[0030] Step 2: Mix the steel slag powder, granulated blast furnace slag powder, fly ash, red mud, industrial by-product gypsum, hydrophobic organic acid salts, alkali metal lactates, high-performance water-reducing agent, dispersant and measured water weighed in Step 1 for the first time. Stir evenly to obtain a primary mixture.

[0031] Step 3: Mix the primary mixture obtained in step 2 with the slag weighed in step 1 for a second time until it is evenly mixed to obtain a solid waste base self-compacting super waterproof backfill material.

[0032] Traditional backfill materials mostly use cement and lime as raw materials, and require compaction during construction, resulting in poor waterproofing performance. In contrast, this application presents a self-compacting, ultra-waterproof backfill material based on solid waste, using almost entirely solid waste as raw materials, making it economical and environmentally friendly. Adding dispersants increases fluidity to achieve self-compacting; alkali metal lactates increase the hydration reaction rate, promoting the formation of hydration products such as ettringite and CSH, and significantly improve the pore structure distribution of the backfill material, reducing porosity, increasing density, and greatly enhancing waterproofing performance. The addition of hydrophobic organic acid salts forms a hydrophobic film in the pores of the backfill material, thereby increasing its waterproofing and seepage-resistant effects.

[0033] Solid waste-based self-compacting ultra-waterproof backfill material can change the problems of high cost, environmental unfriendliness, and poor waterproof performance caused by the traditional use of cement, which requires compaction during construction. It has the characteristics of low cost, environmental protection, short setting time, no cement clinker, high strength and good waterproof performance, and has broad application prospects in scenarios such as foundation pit backfilling and pipeline filling.

[0034] The present invention has the following advantages over the prior art:

[0035] 1. The raw materials used in this application include solid waste such as slag, steel slag powder, granulated blast furnace slag, fly ash, red mud, and industrial by-product gypsum. The utilization rate of solid waste is close to 100%, which is in line with the national green building materials guidelines. Moreover, the solid waste materials undergo synergistic hydration reactions to generate a large amount of CSH gel and AFt, which interweave and fill with soil particles, enhancing the compactness of the soil and greatly improving the waterproof performance.

[0036] 2. This application changes the traditional requirement to add cement clinker to backfill materials, making it more economical and environmentally friendly.

[0037] 3. The addition of hydrophobic organic acid salts in this application can improve the waterproof performance of the material. The lactic acid anions generated by alkali metal lactates can promote the disintegration of slag structure, increase the hydration reaction rate, promote the formation of hydration products such as ettringite and CSH, and significantly improve the pore structure distribution of backfill material, reduce porosity, and increase density, thereby enhancing waterproof performance. The dispersant can better disperse soil particles and enhance the flowability of backfill material. Detailed Implementation

[0038] The embodiments of the present invention are described in detail below. The embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0039] Example 1

[0040] Step 1: Weigh the following solid raw materials by weight: Solid waste-based high impermeability solidifying agent: 45 parts steel slag powder, 30 parts S95 grade slag powder, 5 parts Grade I fly ash, 5 parts Bayer process red mud, 15 parts desulfurized gypsum, 0.5 parts calcium stearate, 0.1 parts sodium lactate, 1 part high-performance polycarboxylate superplasticizer, and 1 part sodium pyrophosphate; the mass ratio of slag and solid waste-based high impermeability solidifying agent is 10:1.5.

[0041] Measure the liquid raw material: water; the mass ratio of solid raw material to liquid raw material is 1:2;

[0042] Step 2: Mix the steel slag powder, S95 grade slag powder, Grade I fly ash, Bayer red mud, desulfurized gypsum, calcium stearate, sodium lactate, high-performance polycarboxylate superplasticizer, sodium pyrophosphate and measured water in Step 1 for the first time, and stir evenly to obtain a primary mixture.

[0043] Step 3: Mix the primary mixture obtained in step 2 with the slag weighed in step 1 for a second time until it is evenly mixed to obtain a solid waste base self-compacting super waterproof backfill material.

[0044] The specimens were subjected to expansion tests according to GB / T 50080-2016 "Test Methods for Performance of Ordinary Concrete Mixtures". Unconfined compressive strength specimens were cured to standard for 3 days and 28 days according to JTG 3430—2020 "Specifications for Geotechnical Tests for Highways" for unconfined compressive strength tests and permeability coefficient tests.

[0045] The measured spread was 451 mm;

[0046] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 2.32 MPa, and the permeability coefficient was 6.52 × 10⁻⁶. -8 The 28-day unconfined compressive strength is 4.73 MPa, and the permeability coefficient is 1.10 × 10⁻⁶. -8 .

[0047] Example 2

[0048] The difference from Example 1 is as follows:

[0049] Weigh the following parts by weight of solid waste-based high impermeability solidifying agent: 45 parts steel slag powder, 25 parts S95 grade slag powder, 10 parts grade I fly ash, 10 parts Bayer process red mud, 10 parts desulfurized gypsum, 0.8 parts calcium stearate, 0.15 parts sodium lactate, 2 parts high-performance polycarboxylate superplasticizer, and 2 parts sodium pyrophosphate.

[0050] The measured spread was 596 mm;

[0051] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 2.75 MPa, and the permeability coefficient was 4.13 × 10⁻⁶. -8 The 28-day unconfined compressive strength is 5.35 MPa, and the permeability coefficient is 7.52 × 10⁻⁶. -9 .

[0052] Example 3

[0053] The difference from Example 1 is as follows:

[0054] Weigh the following parts by weight of solid waste-based high impermeability solidifying agent: 50 parts steel slag powder, 25 parts S95 grade slag powder, 5 parts grade I fly ash, 10 parts Bayer process red mud, 10 parts desulfurized gypsum, 1 part calcium stearate, 0.2 parts sodium lactate, 2 parts high performance polycarboxylate superplasticizer, and 3 parts sodium pyrophosphate.

[0055] The measured extension was 653 mm;

[0056] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 3.10 MPa, and the permeability coefficient was 1.65 × 10⁻⁶. -8 The 28-day unconfined compressive strength is 5.96 MPa, and the permeability coefficient is 2.67 × 10⁻⁶. -9 .

[0057] Example 4

[0058] The difference from Example 1 is as follows:

[0059] Weigh the following parts by weight of solid waste-based high impermeability solidifying agent: 50 parts steel slag powder, 25 parts S95 grade slag powder, 10 parts grade I fly ash, 5 parts Bayer process red mud, 10 parts desulfurized gypsum, 1 part calcium stearate, 0.2 parts sodium lactate, 2 parts high performance polycarboxylate superplasticizer, and 3 parts sodium pyrophosphate.

[0060] The measured spread was 577 mm;

[0061] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 2.83 MPa, and the permeability coefficient was 3.26 × 10⁻⁶. -8 The 28-day unconfined compressive strength is 4.93 MPa, and the permeability coefficient is 6.75 × 10⁻⁶. -9 .

[0062] Comparative Example 1

[0063] The difference from Example 3 is that calcium stearate was not added.

[0064] The measured spread was 606 mm;

[0065] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 3.00 MPa, and the permeability coefficient was 1.33 × 10⁻⁶.-7 The 28-day unconfined compressive strength is 5.17 MPa, and the permeability coefficient is 4.76 × 10⁻⁶. -8 .

[0066] Comparative Example 2

[0067] The difference from Comparative Example 1 is that: 40 parts of steel slag powder and 35 parts of S95 grade slag powder.

[0068] The measured spread was 581 mm;

[0069] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 1.94 MPa, and the permeability coefficient was 6.86 × 10⁻⁶. -8 The 28-day unconfined compressive strength is 3.55 MPa, and the permeability coefficient is 2.34 × 10⁻⁶. -8 .

[0070] Comparative Example 3

[0071] The difference from Example 4 is that: 45 parts of steel slag powder and 30 parts of S95 grade slag powder were used; sodium pyrophosphate was not added.

[0072] The measured extension was 402 mm;

[0073] Under standard curing conditions, the 3-day unconfined compressive strength was measured to be 2.91 MPa, and the permeability coefficient was 5.19 × 10⁻⁶. -8 The 28-day unconfined compressive strength is 5.66 MPa, and the permeability coefficient is 9.83 × 10⁻⁶. -9 .

[0074] Table 1. Performance test results of solid waste-based self-compacting super waterproof backfill materials prepared in Examples 1-4 and Comparative Examples 1-3

[0075]

[0076] As shown in Table 1, the addition of sodium lactate hydrolyzes to produce bidentate ligand lactic acid anions, which have a chelating effect. These anions can form water-soluble complexes with metal ions in the slag glass, disrupting the glass structure and promoting slag dissolution. This, in turn, promotes the formation of ettringite and CSH. Furthermore, sodium lactate can increase the degree of CSH gel polymerization, making the structure of the solid waste-based self-compacting super waterproof backfill material more compact, thereby increasing its strength, reducing the permeability coefficient, and significantly improving its impermeability. The addition of calcium stearate can generate a hydrophobic membrane in the pores of the backfill material, thereby increasing the waterproof and impermeable effect of the backfill material. The addition of sodium pyrophosphate allows for the formation of a stable adsorption layer after phosphate adsorption, dispersing soil particles and increasing their specific surface area. This promotes the dispersion of the solid waste-based self-compacting super waterproof backfill material, significantly improving its flowability and achieving a self-compacting effect.

Claims

1. A self-compacting, ultra-waterproof backfill material based on solid waste, characterized in that, Including solid and liquid raw materials, The solid raw materials, by weight, include: 10 parts of slag and 1.5 parts of solid waste-based high impermeability solidifying agent; The liquid raw material is water; A method for preparing a solid waste-based self-compacting ultra-waterproof backfill material includes the following steps: Step 1: Weigh the following solid raw materials by weight: Solid waste-based high impermeability solidifying agent: 50 parts steel slag powder, 25 parts S95 grade slag powder, 5 parts Grade I fly ash, 10 parts Bayer red mud, 10 parts desulfurized gypsum, 1 part calcium stearate, 0.2 parts sodium lactate, 2 parts high-performance polycarboxylate superplasticizer with a water reduction rate ≥35%, and 3 parts sodium pyrophosphate; the mass ratio of slag and solid waste-based high impermeability solidifying agent is 10:1.

5. The slag is screened to a maximum particle size ≤50mm and an organic matter content ≤3%. Measure the liquid raw material: water; the mass ratio of solid raw material to liquid raw material is 1:2; Step 2: Mix the steel slag powder, S95 grade slag powder, Grade I fly ash, Bayer red mud, desulfurized gypsum, calcium stearate, sodium lactate, high-performance polycarboxylate superplasticizer, sodium pyrophosphate and measured water in Step 1 for the first time, and stir evenly to obtain a primary mixture. Step 3: Mix the primary mixture obtained in step 2 with the slag weighed in step 1 for a second time until it is evenly mixed to obtain a solid waste base self-compacting super waterproof backfill material.

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