Method for constructing coal gangue-filled subgrade cement-stabilized base

Abstract

The present invention relates to the technical field of cement-stabilized base construction. Specifically disclosed is a method for constructing a coal gangue-filled subgrade cement-stabilized base. The coal gangue-filled subgrade cement-stabilized base of the present invention comprises a coal gangue aggregate, a cementitious material, straw fibers, and an alkali activator. By means of the incorporation of the straw fibers, when the mixture is subjected to stress, the straw fibers can interact with the mixture in the base to generate a mechanical interlocking force, and the straw fibers exert a transfer effect at the interface, transferring the stress on the internal structure of the mixture in the base to other structures, thereby playing a bridge role in the internal structure. In addition, the straw fibers are freely dispersed inside the mixture in the base to form a spatial network structure, thereby effectively improving the crack resistance of the mixture in the coal gangue base.

Description

A construction method for water-stabilized layer of coal gangue fill roadbed Technical Field

[0001] This invention relates to the field of water-stabilized layer construction technology, and in particular to a method for constructing a water-stabilized layer for coal gangue-filled roadbed. Background Technology

[0002] Water-stabilized layer is short for cement-stabilized crushed stone layer, which is made by using cement-consolidated graded crushed stone, compacted, and cured. Traditional roadbed water-stabilized layer mixtures use sand and gravel as aggregates and lime, cement, etc. as activators, but they have problems such as high environmental and resource pressure and high cost. As the comprehensive utilization of bulk industrial solid waste becomes an important part of my country's construction of a green, low-carbon, and circular economy system, the utilization of solid waste materials such as coal gangue is imperative. Technical issues

[0003] Coal gangue is one of the largest stockpiles of mining waste. Due to its high crushing value and water absorption rate, and taking into full account the seasonal freeze-thaw characteristics of Northeast China as well as the physical, chemical, and engineering properties of coal gangue, roadbeds paved with coal gangue are prone to reflective cracking, affecting the roadbed's bearing capacity.

[0004] Therefore, the present invention provides a construction method for a water-stabilized layer of a coal gangue-filled roadbed, which solves the above-mentioned technical problems by improving the coal gangue base mixture. Technical solutions

[0005] The purpose of this invention is to provide a construction method for a water-stabilized layer in a coal gangue-filled roadbed, in order to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides a water-stabilized layer for roadbed with coal gangue filler, comprising coal gangue aggregate, cementing material, rice straw fiber and alkali activator;

[0007] The particle size of the coal gangue aggregate is 0.075 mm to 19 mm;

[0008] The cementitious material includes cement, slag, fly ash, and gypsum, wherein the mass ratio of cement, slag, fly ash, and gypsum is 55:35:5:5; and the dosage of the cementitious material is 4% to 5.5%.

[0009] The dosage of the alkali activator is 4% of the slag mass;

[0010] The amount of rice straw fiber is 1% to 4%, and the length of the rice straw fiber is 4 mm to 12 mm;

[0011] The moisture content of the mixture of coal gangue aggregate, cementitious material, straw fiber and alkali activator is 8.8% to 9.7%.

[0012] Preferably, the coal gangue aggregate is sieved using standard sieves of 19mm, 9mm, 4.75mm, 2.36mm, 0.6mm, and 0.075mm, respectively.

[0013] Preferably, the coal gangue aggregate further includes natural crushed stone, which accounts for 30% of the total amount of 0-5mm coal gangue aggregate.

[0014] Preferably, the straw fiber is made from rice straw.

[0015] Preferably, the rice straw has no rot or mold on its surface and has a good color.

[0016] Preferably, the rice straw is soaked in a 5% NaOH solution for 12 hours, then washed and air-dried.

[0017] Preferably, the amount of the cementitious material is 5.5%.

[0018] Preferably, the amount of rice straw fiber is 3%.

[0019] Preferably, the length of the straw fiber is 8 mm.

[0020] A construction method for a water-stabilized layer in a coal gangue-filled roadbed includes the following steps:

[0021] Construction preparation, including preparing construction materials and equipment;

[0022] Raw material inspection: Inspecting the raw materials;

[0023] Selection of mix proportions;

[0024] Mixing the ingredients;

[0025] The moisture content and cement dosage of the mixed material are tested. If the cement dosage or moisture content is not up to standard, the mixing process is returned to the mixing step.

[0026] Mixture transportation involves transporting the qualified mixture to the construction site and preparing test specimens.

[0027] Leveling and paving are carried out using a paver, with the paver's travel speed kept below 1.5 m / min;

[0028] Static compaction is performed using a road roller, with the roller's travel speed controlled between 1.5 and 1.7 km / h.

[0029] Elevation and flatness are checked; if the checks fail, manual repairs are carried out.

[0030] The road roller is used for shaping and compaction. The travel speed of the road roller is controlled between 1.8 and 2.5 km / h. The roller is compacted until there are no wheel tracks. The roller overlaps the wheel width by 1 / 2 during compaction.

[0031] If the compaction degree test fails, return to the compaction step of the road roller.

[0032] Health preservation and finished product protection. Beneficial effects

[0033] Compared with the prior art, the present invention has the following advantages and technical effects:

[0034] The construction method for water-stabilized layer of coal gangue filler subgrade provided by the present invention incorporates rice straw fiber. When the mixture is under stress, the rice straw fiber can work together with the base mixture to generate mechanical interlocking force and exert the transfer effect of rice straw fiber at the interface. The force on the internal structure of the base mixture is transferred to other structures through the rice straw fiber, which acts as a bridge between the internal structures. At the same time, the rice straw fiber is freely dispersed in the base mixture to form a spatial network structure, thereby effectively improving the crack resistance of the coal gangue base mixture. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 shows a comparison of the appearance of rice straw before and after alkali treatment modification according to the present invention.

[0037] Figure 2 shows the grading curve of the coal gangue sieve of the present invention;

[0038] Figure 3 shows a comparison of the performance indicators of the coal gangue of the present invention;

[0039] Figure 4 shows the 7-day unconfined compressive strength of the base mixture of the present invention;

[0040] Figure 5 shows the 28-day unconfined compressive strength of the base mixture under freeze-thaw cycles according to the present invention.

[0041] Figure 6 shows the 28-day ultimate flexural failure load of the flexural-tension type load-bearing base course mixture of the present invention.

[0042] Figure 7 shows the 28-day flexural failure load of the composite load-bearing base mixture of the present invention. Embodiments of the present invention

[0043] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] This invention provides a water-stabilized layer for roadbed filled with coal gangue, comprising coal gangue aggregate, cementing material, rice straw fiber and alkali activator;

[0045] The particle size of coal gangue aggregate is 0.075mm to 19mm;

[0046] The cementitious materials include cement, slag, fly ash, and gypsum, with the mass ratio of cement, slag, fly ash, and gypsum being 55:35:5:5; the dosage of the cementitious materials is 4% to 5.5%.

[0047] The dosage of the alkali activator is 4% of the slag mass;

[0048] The amount of rice straw fiber is 1% to 4%, and the length of the rice straw fiber is 4mm to 12mm;

[0049] The moisture content of the mixture of coal gangue aggregate, cementing material, straw fiber and alkali activator is 8.8% to 9.7%.

[0050] This invention incorporates rice straw fiber, which, when the mixture is under stress, works together with the base mixture to generate mechanical interlocking force. Furthermore, the rice straw fiber exhibits a transfer effect at the interface, transmitting the stress on the internal structure of the base mixture to other structures, acting as a bridge between internal structures. Simultaneously, the rice straw fiber freely disperses within the base mixture, forming a spatial network structure, thereby effectively improving the crack resistance of coal gangue base mixtures.

[0051] The solution was further optimized by using rice straw for the rice straw fiber.

[0052] Further optimization of the solution resulted in rice straw with no rot, no mold, and good color.

[0053] To further optimize the process, rice straw was soaked in a 5% NaOH solution for 12 hours, then washed and air-dried. Figure 1 shows a comparison of the appearance of rice straw before and after alkali treatment modification.

[0054] To further optimize the process, coal gangue aggregates were sieved using standard sieves of 19mm, 9mm, 4.75mm, 2.36mm, 0.6mm, and 0.075mm, respectively.

[0055] Further optimization of the scheme includes natural crushed stone as part of the coal gangue aggregate, which accounts for 30% of the total amount of 0-5mm coal gangue aggregate.

[0056] The scheme was further optimized, with the amount of cementitious material added being 5.5%.

[0057] The scheme was further optimized, with the amount of rice straw fiber added being 3%.

[0058] The design was further optimized so that the length of the straw fiber was 8mm. Example

[0059] The coal gangue aggregate of this invention was sieved using standard sieves of 19mm, 9mm, 4.75mm, 2.36mm, 0.6mm, and 0.075mm, respectively. The aggregate gradation design of the coal gangue is shown in Figure 2, where 30% of the 0-5mm coal gangue aggregate is replaced by natural crushed stone. Considering that coal gangue has a relatively high crushing value and water absorption rate, and that the water absorption rate of coal gangue is related to its particle size (the smaller the particle size, the larger its specific surface area, the larger the area in contact with water, and the greater the water absorption rate), this invention addresses the issue. To reduce the crushing value and water absorption rate of the mixture, as shown in Figure 3, which compares the performance indicators of coal gangue, the water absorption rate of coal gangue before replacement was 4.26 and the crushing value was 26.8. By replacing 30% of the 0-5mm coal gangue aggregate with natural crushed stone, the water absorption rate and crushing value of coal gangue were reduced to 3.25 and 24.5, respectively, thereby reducing the water absorption rate and crushing value of coal gangue.

[0060] The alkali activator was prepared using a water glass solution with a modulus of 1.3 solid water glass. The chemical composition of slag, fly ash, cement and coal gangue is shown in Table 1.

[0061] Table 1 Chemical composition of raw materials

[0062]

[0063] The physical properties of coal gangue were measured, and the results are shown in Table 2.

[0064] Table 2 Performance Indicators of Coal Gangue Aggregate

[0065]

[0066] Compaction tests were conducted according to the compaction test method for inorganic binder stabilized materials in JTG E51—2009 "Test Procedure for Inorganic Binder Stabilized Materials in Highway Engineering". Cementitious material content was selected at 4%, 4.5%, 5%, and 5.5%, and the optimum moisture content and maximum dry density were measured. Cylindrical specimens with a compaction degree of 98% and dimensions of ϕ150×150 mm were prepared and cured in a standard curing environment (20℃, 98% humidity) to the specified age. The 7-day unconfined compressive strength was then tested.

[0067] The results of the compaction test show the changes in the optimal moisture content and maximum dry density of coal gangue mixture under different cementitious material dosages, as shown in Table 3.

[0068] Table 3 Compaction Test Results

[0069]

[0070] Table 3 shows that the optimum moisture content and maximum dry density of the coal gangue mixture gradually increase with the increase of cementitious material content. This indicates that the water demand of the coal gangue mixture increases due to the increase of cementitious material, thus increasing the optimum moisture content. As the cementitious material fills the voids in the densely packed coal gangue mixture, the mixture skeleton becomes increasingly compact, and the maximum dry density also increases.

[0071] Unconfined compressive strength tests were conducted on pavement base course mixture specimens with different cementitious material contents added, using the optimal gradation of coal gangue mixture as the standard, and cured under standard conditions for 7 days. The results are shown in Figure 4.

[0072] With the increase of cementitious material content, SiO2 and Al2O3 in coal gangue react with the cement hydration products Ca(OH) and slag powder in a pozzolanic reaction, producing calcium silicate gel that fills the cracks in the aggregate itself and the gaps between aggregates, making the coal gangue mixture more compact. Therefore, the 7-day unconfined compressive strength of the specimens shows an increasing trend. When the cementitious material content is 4%, 4.5%, 5%, and 5.5%, the 7-day compressive strengths are 4.23 MPa, 4.48 MPa, 4.96 MPa, and 5.09 MPa, respectively, all meeting the specifications. When the cementitious material content increases from 4% to 4.5%, the increase in compressive strength is relatively small because the aggregate proportion is large, and the aggregate has a high water absorption rate; a small increase in cementitious material cannot accelerate the setting time of the mixture or fully utilize the hardening strength of the cementitious material. When the content of cementitious material is increased from 4.5% to 5% and 5.5%, the setting time is accelerated and the degree of hardening is increased by 10.7% and 13.6%, respectively.

[0073] Since the road is located in a seasonally frozen zone, the frost resistance of the pavement base material must meet the requirements. A fully automatic low-temperature freeze-thaw testing machine was used for freeze-thaw cycle testing. The machine was used for freezing for 16 hours at a freezing temperature of -18℃, followed by thawing in 20℃ water for 8 hours. After removing the specimens, they were dried, weighed, and the weight was recorded, marking the end of one freeze-thaw cycle. Ten freeze-thaw cycles were performed, with a standard curing period of 28 days. After reaching the required number of freeze-thaw cycles, residual compressive strength was tested. Figure 5 shows the changes in specimens with cementitious material content of 4%, 4.5%, 5%, and 5.5% after 28 days of curing and 10 freeze-thaw cycles.

[0074] After 10 freeze-thaw cycles, the compressive strength of specimens with different cementitious material contents all decreased. The strength of indoor specimens with cementitious material contents of 4%, 4.5%, 5%, and 5.5% decreased by 21.8%, 19.8%, 17.4%, and 15.8%, respectively. This was because the internal expansion of the specimens caused by the freeze-thaw cycles led to the spalling of fine aggregates from the coal gangue and the exposure of coarse aggregates, resulting in a looser overall structure of the specimens and a decrease in compressive strength. The results are shown in Table 4.

[0075] Table 4. BDR index under different cementitious material contents

[0076]

[0077] As shown in Table 4, after 10 freeze-thaw cycles, as the amount of cementitious material increases, the residual compressive strength ratio (BDR) also increases, as shown in Table 5, and all meet the standard of BDR≥70 for severely seasonally frozen areas.

[0078] 28-day base mixture specimens with different straw fiber content and different straw fiber lengths were subjected to flexural ultimate failure load tests (cracks extended to 4 cm). The average value of two specimens in each group was taken. The final results are shown in Figures 6 and 7.

[0079] As shown in Figures 6 and 7, for both the base course mixture specimens with and without straw fiber, the combined failure load is generally greater than the flexural failure load, and the minimum combined failure load is generally greater than the maximum flexural failure load. With increasing amounts of 4mm, 8mm, and 12mm straw fiber, the base course mixture exhibits a trend of first decreasing, then increasing, and then decreasing again. At the same straw fiber content, the ultimate failure load strength of the mixture with 8mm straw fiber is consistently higher than that of the mixture with 4mm and 12mm straw fiber. When 4mm, 8mm, and 12mm rice straw fibers are added at a 1% concentration, comparing the effects of 4mm and 12mm rice straw lengths, the 12mm rice straw fiber has a lower effect on improving the ultimate breaking load strength of the mixture than the 4mm rice straw fiber. This is because the 4mm rice straw fiber has a higher density than the 12mm rice straw fiber, but the straw fibers cannot be evenly distributed in the mixture, resulting in more voids and weak stress areas within the base layer mixture. Furthermore, these numerous small weak stress areas interconnect to form larger weak stress areas, and their impact on the ultimate breaking load outweighs the improvement in toughness of the mixture by the straw fibers themselves. Therefore, the ultimate breaking load of the 4mm base layer mixture is the lowest. At a 2% rice straw content, the ultimate breaking load of the 4mm rice straw fiber is higher than that of the 12mm rice straw fiber. This is because the increased density and relatively uniform dispersion of the 4mm rice straw fiber significantly enhances its toughening effect, resulting in a higher ultimate breaking load for the mixture compared to the 12mm rice straw fiber. When the straw fiber content is 3%, the ultimate failure load of the 8mm straw fiber exceeds that of the unadded straw fiber, showing the greatest increase. When the straw fiber content is 4%, the ultimate failure load of the 4, 8, and 12mm base mixture specimens is significantly reduced. This is because the addition of more straw fiber reduces the contact area between the aggregate and cementitious material in the base mixture, and the straw fiber increases the internal porosity of the mixture.

[0080] Considering the ultimate failure load strength, the addition of rice straw fiber not only significantly increased the ultimate failure load, but also indirectly demonstrated that the addition of rice straw fiber improved the crack resistance of the base mixture. Regardless of the rice straw length (4mm, 8mm, or 12mm), the load strength reached its peak at a 3% rice straw fiber content, therefore the optimal rice straw fiber content is 3%. Under different rice straw fiber contents, the load strength of 8mm rice straw was consistently higher than that of 4mm and 12mm rice straw, indicating that the optimal rice straw fiber length is 8mm.

[0081] In summary, the coal gangue base course mixture exhibits optimal mechanical properties when the cementitious material content is 5.5%, with a 7-day unconfined compressive strength of 5.09 MPa, meeting the requirements of highway base course strength specifications. Furthermore, when the cementitious material content in the pavement base course material is 5.5%, its 28-day unconfined compressive strength still reaches 5.28 MPa after 10 freeze-thaw cycles, demonstrating excellent frost resistance.

[0082] With increasing straw fiber content, the ultimate failure load of the coal gangue base course mixture first increases and then decreases. The addition of straw fiber effectively improves the crack resistance of the coal gangue base course mixture. When the straw fiber content is 3%, its distribution within the base course mixture is relatively uniform, resulting in the best crack resistance. When the straw fiber content is greater than 3%, the fibers tend to aggregate, forming weak areas that are prone to cracking. When the straw fiber content is less than 3%, the fiber distribution is relatively dispersed, and the crack resistance of individual straw fibers is far lower than the stress during cracking, leading to fiber breakage. Therefore, when the straw fiber length is 8mm and the content is 3%, the coal gangue base course mixture achieves the highest resistance to reflective cracking.

[0083] A construction method for a water-stabilized layer in a coal gangue-filled roadbed includes the following steps:

[0084] Construction preparation, including preparing construction materials and equipment;

[0085] Raw material inspection: Inspecting the raw materials;

[0086] Selection of mix proportions;

[0087] Mixing the ingredients;

[0088] The moisture content and cement dosage of the mixed material are tested. If the cement dosage or moisture content is not up to standard, the mixing process is returned to the mixing step.

[0089] Mixture transportation involves transporting the qualified mixture to the construction site and preparing test specimens.

[0090] Leveling and paving are carried out using a paver, with the paver's travel speed kept below 1.5 m / min;

[0091] Static compaction is performed using a road roller, with the roller's travel speed controlled between 1.5 and 1.7 km / h.

[0092] Elevation and flatness are checked; if the checks fail, manual repairs are carried out.

[0093] The road roller is used for shaping and compaction. The travel speed of the road roller is controlled between 1.8 and 2.5 km / h. The roller is compacted until there are no wheel tracks. The roller overlaps the wheel width by 1 / 2 during compaction.

[0094] If the compaction degree test fails, return to the compaction step of the road roller.

[0095] Health preservation and finished product protection.

[0096] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A coal refuse fill subgrade hydro-stable layer characterized by, Including coal gangue aggregate, cementing materials, rice straw fiber, and alkali activator; The particle size of the coal gangue aggregate is 0.075 mm to 19 mm; The cementitious material includes cement, slag, fly ash, and gypsum, wherein the mass ratio of cement, slag, fly ash, and gypsum is 55:35:5:5; and the dosage of the cementitious material is 4% to 5.5%. The dosage of the alkali activator is 4% of the slag mass; The amount of rice straw fiber is 1% to 4%, and the length of the rice straw fiber is 4 mm to 12 mm; The moisture content of the mixture of coal gangue aggregate, cementitious material, straw fiber and alkali activator is 8.8% to 9.7%.

2. The coal refuse fill subgrade hydroseal layer of claim 1, wherein, The coal gangue aggregate was sieved using standard sieves of 19mm, 9mm, 4.75mm, 2.36mm, 0.6mm, and 0.075mm, respectively.

3. The coal refuse fill subgrade hydroseal layer of claim 2, wherein, The coal gangue aggregate also includes natural crushed stone, which accounts for 30% of the total amount of 0-5mm coal gangue aggregate.

4. The coal refuse fill subgrade hydroseal layer of claim 1 wherein, The rice straw fiber is made from rice stalks.

5. The coal refuse fill subgrade hydroseal layer of claim 4, wherein, The rice straw has no rot or mold on its surface and has a good color.

6. The coal refuse fill subgrade hydroseal layer of claim 4, wherein, The rice straw was soaked in a 5% NaOH solution for 12 hours, then washed and air-dried.

7. The coal refuse fill subgrade hydroseal layer of claim 1 wherein, The amount of the cementitious material is 5.5%.

8. The coal refuse fill subgrade hydroseal layer of claim 1 wherein, The amount of rice straw fiber added is 3%.

9. The coal refuse fill subgrade hydroseal layer of claim 8, wherein, The length of the straw fiber is 8 mm.

10. The method of constructing a coal refuse fill subgrade hydroseal layer according to any one of claims 1-9, wherein, Includes the following steps: Construction preparation includes preparing construction materials and equipment. Raw material inspection: Inspecting the raw materials; Selection of mix proportions; Mixing the ingredients; The moisture content and cement dosage of the mixed material are tested. If the cement dosage or moisture content is not up to standard, the mixing process is returned to the mixing step. Mixed material transportation involves transporting the qualified mixed material to the construction site and preparing test specimens. Leveling and paving are carried out using a paver, with the paver's travel speed kept below 1.5 m / min; Static compaction is performed using a road roller, with the roller's travel speed controlled between 1.5 and 1.7 km / h. Elevation and flatness are checked; if the checks fail, manual repairs are carried out. The road roller is used for shaping and compaction. The travel speed of the road roller is controlled between 1.8 and 2.5 km / h. The roller is compacted until there are no wheel tracks. The roller overlaps the wheel width by 1 / 2 during compaction. If the compaction degree test fails, return to the compaction step of the road roller. Health preservation and finished product protection.

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