Method for reducing content of soluble salt in alkaline residue and preventing and treating dissolving sinking disease of alkaline residue limestone soil of base layer

Abstract

The invention belongs to the technical field of road and bridge construction, and particularly discloses a method for reducing the content of soluble salts in alkaline residues and preventing and treating base-layer alkaline residue lime soil dissolving sinking diseases, which comprises the following steps: determining the alkaline residue mixing amount x1 at a medium and strong salinization alkaline residue lime soil boundary; determining the maximum alkali residue mixing amount x2 meeting the strength standard; taking one of x1 and x2 as the maximum allowable mixing amount x3 of the alkali residues in the alkali residue lime soil; under the condition of x1, x2, x3 and the alkali residue mixing amount, the dissolution sinking coefficient of the alkali residue limestone soil is measured, and if the dissolution sinking obtained through calculation is larger than 1.5%, improvement is needed; the mixing amount of the alkaline residues is x3, the mixing amount of the soil is 100%-x3, 12% of lime is added, and the strength and the melt sinking coefficient of the alkaline residues with different soluble salt contents are tested respectively; and performing fitting analysis on the result in the step (5), and selecting the alkaline residues with the optimal soluble salt content as a prevention and treatment scheme according to the strength and the melt sinking coefficient. According to the method, the content of soluble salt in the alkaline residues is reduced appropriately through a water washing process creatively, so that the purpose of preventing and treating the dissolving sinking disease of the alkaline residue limestone soil is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of road and bridge construction, relates to the prevention and treatment of salinization diseases of road base materials, and specifically relates to a method for reducing the soluble salt content of alkali slag to prevent and treat the dissolution disease of alkali slag lime soil in the base. Background Art

[0002] Alkali residue is the alkaline solid waste residue discharged during the alkali production process of the ammonia-soda process. According to statistics, for every ton of soda ash produced by the alkali plant, about 10m3 of soda residue is discharged. 3 The waste liquid contains 300-600kg of alkali residue. There are more than 50 alkali-making enterprises in China, and the annual alkali residue discharge reaches 7.8-10 million tons. Alkali residue is often directly discharged on the surface and discharged into the sea, which not only occupies precious land resources, but also causes soil salinization and pollutes the surrounding soil and water environment.

[0003] In the process of using alkali slag and lime to prepare alkali slag lime soil for roads, it was found that alkali slag lime soil specimens with different alkali slag dosages would produce different degrees of precipitation of soluble salt crystals, which is similar to the salt precipitation phenomenon of saline soil, and the higher the alkali slag content, the more salt precipitated. Analysis shows that the alkali slag has a high content of soluble salts, and the alkali slag soil exhibits similar salinization characteristics. With the dissolution and precipitation of salts, the roadbed or subbase paved with alkali slag soil may experience dissolution and collapse characteristics in the later stage. At present, there are relatively rich research results on the mechanical properties of alkali slag lime soil for roads and its construction technology and methods, but there are no reports on the salinization and collapse of alkali slag lime soil.

[0004] A large number of tests have shown that with the increase of the amount of alkali slag, the alkali slag lime soil specimens will be damaged to varying degrees when they come into contact with water. Analysis shows that the alkali slag contains a large amount of soluble salts, which are mainly chloride salts. As the specimens are immersed in water, water enters the interior of the specimens along the pores, and the soluble salt particles dissolve in water, causing the internal pores to increase and dissolution damage to occur. Therefore, when dissolution damage occurs in the alkali slag lime soil base, it will cause the surface to swell and the road surface to deform and damage, thus creating traffic safety hazards. According to the provisions of the "Guidelines for the Design and Construction of Highways in Saline Soil Areas", the dissolution coefficient value of the road base material should be less than 1.5%.

[0005] Studies have shown that adding an appropriate amount of cement, lime and other materials to alkali slag can effectively control the salinization degree and dissolution disease of alkali slag. However, in the context of large-scale utilization of alkali slag, when the alkali slag content increases, the control of salinization and dissolution disease of alkali slag soil requires the addition of a large amount of cementitious materials such as lime and cement, which leads to an increase in the cost of road materials and an increase in the cost burden. In order to deal with the dissolution and cost control of alkali slag lime soil under the condition of high alkali slag content, other material processing and dissolution control methods must be adopted.

[0006] Practice has proved that appropriate alkali slag dosage can effectively improve the mechanical properties of alkali slag lime soil in the base layer. However, when the alkali slag dosage is too high, the mechanical properties of the alkali slag lime soil decrease. In addition, too high alkali slag dosage will lead to an increase in the soluble salt content of the alkali slag lime soil, resulting in dissolution damage in the base layer. Therefore, it is particularly important to control dissolution when using alkali slag to prepare alkali slag lime soil. Summary of the invention

[0007] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer. The present invention considers the source of the dissolution disease of alkali slag lime soil. The fundamental reason for the dissolution is the excessively high soluble salt content. Starting from the control of soluble salts, it is proposed to reduce the soluble salt content of alkali slag lime soil by washing the alkali slag raw materials, thereby effectively controlling the soluble salt content of alkali slag lime soil, and finally achieving the goal of preventing and controlling the dissolution disease of alkali slag lime soil for roads. The present invention will effectively prevent and control the dissolution disease caused by alkali slag lime soil, make it meet the national road construction standards, and provide guarantee for the quality control of alkali slag lime soil base.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer, comprising the following steps:

[0010] Step (1): Determine the alkali slag dosage x at the boundary between medium and strong salinized alkali slag lime soil 1

[0011] Prepare alkali slag lime soil with different dosages, separate the soluble salts in the alkali slag lime soil by washing and drying, and calculate the total amount of soluble salts in the alkali slag lime soil; perform curve fitting on the total amount of soluble salts in the alkali slag lime soil with different dosages to obtain a fitting curve of alkali slag dosage and soluble salt total amount; determine the alkali slag dosage x corresponding to the boundary line between medium and strong salinization alkali slag lime soil through the fitting curve. 1 ;

[0012] Step (2): Determine the maximum alkali residue content x that meets the strength standard 2

[0013] Prepare alkali slag lime soil with different alkali slag content and test its strength; perform curve fitting on the unconfined compressive strength values ​​of alkali slag lime soil with different alkali slag content to obtain the alkali slag content-strength fitting curve; through the fitting curve, determine that the maximum alkali slag content corresponding to the alkali slag lime soil that meets the standard strength is x 2 ;

[0014] Step (3): Determine the maximum allowable amount of alkali slag in alkali slag lime soil x 3

[0015] Compare x 1 and x 2The smaller one is the maximum allowable amount of alkali slag in alkali slag lime soil x 3 , that is, x 3 =min{x 1 , x 2};

[0016] Step (4): x 3 Under the alkali slag dosage, measure and calculate the dissolution coefficient of alkali slag lime soil. If the calculated dissolution coefficient is less than 1.5%, no improvement is required. If it is greater than 1.5%, improvement is required.

[0017] Step (5): Prepare five kinds of alkali residues with different soluble salt contents by water washing, and design five groups of experiments. The alkali residue dosage is x 3 , soil content is 100% - x 3 , adding 12% lime, and testing the strength and dissolution coefficient of alkali slag with different soluble salt contents;

[0018] Step (6): Perform fitting analysis on the results in step (5), combine the strength and dissolution coefficient, and select the alkali slag with the best soluble salt content as the prevention and control plan.

[0019] A further improvement of the present invention is:

[0020] The preparation process of alkali slag lime soil with different admixtures in step (1) is as follows: the soil and alkali slag are designed to be 100 parts by weight in total, alkali slag: soil = x: (100-x), and 12% of lime is added, wherein the ratio of alkali slag to soil is the percentage of dry mass of the material; the mass of alkali slag, plain soil and required water for each test group is calculated according to the target moisture content, the alkali slag and plain soil are first mixed evenly, water is evenly sprayed on them, and then mixed evenly, and then bagged and sealed for 24 hours; the alkali slag soil mixture after being stuffed is put into a constant temperature oven, dried at a constant temperature of 100-110° C., and ground through a 1 mm standard sieve for standby use; using the above method, 8-10 groups of alkali slag lime soil with different admixtures are designed.

[0021] Furthermore, the process of calculating the total amount of soluble salt in step (1) is as follows:

[0022] a. Weigh the dried alkali residue soil mixture that passes through a 1mm sieve, put it into a dry wide-mouth plastic bottle, add deionized water at a soil-water ratio of 1:5, and filter immediately after shaking to obtain the test solution;

[0023] b. Use a pipette to absorb the leaching solution and inject it into a porcelain evaporating dish that has been dried to a constant volume at 105-110℃. Cover it with a watch glass and place it on a boiling water bath to evaporate to dryness. Perform three sets of parallel experiments. If the residue after evaporation is yellow-brown, add 15% H 2 O 2 1~3mL, continue to evaporate to dryness in a water bath, repeat the process until the yellow-brown color disappears;

[0024] c. Place the evaporating dish in an oven at 105-110°C and dry for 4-8 hours. Take it out and place it in a desiccator to cool for 0.5 hours, then weigh it. Repeat the drying process for 2-4 hours, cool it for 0.5 hours, and weigh it with an analytical balance. Repeat this process until the difference between the two weights is no more than 0.0001 g.

[0025] d. Calculate the total amount of soluble salts according to the formula and take the average value of the three groups.

[0026] Furthermore, the formula for calculating the total amount of soluble salt is:

[0027]

[0028] Where: m 2 ——Mass of the evaporating dish plus the dried residue (g), calculated to 0.001;

[0029] m 1 ——Mass of evaporating dish (g);

[0030] m s ——Mass of dry soil sample in 50mL of leaching solution (g).

[0031] Furthermore, the strength test process of the alkali slag lime soil with different dosages in step (2) is as follows:

[0032] a. Weighing

[0033] During the weighing process, the material holding device must be kept dry. Before each weighing, the material must be reset. The required water, air-dried alkali residue and soil must be measured according to the experimental ratio.

[0034] b. Stuffing

[0035] Mix the weighed experimental materials to ensure that they are evenly mixed. Spread the materials flat and evenly spray the required amount of water. Pour the mixed materials into a convenient bag, tie the bag tightly, soak the experimental materials for later use, and keep the materials for at least 6 hours;

[0036] c.Moulding

[0037] Put the steamed material into the mold. Before putting it into the mold, you need to brush the inside of the mold with oil to ensure that the test block and the mold do not stick together when demolding;

[0038] d. Compaction

[0039] In order to ensure the density of the test piece, the assembled mold is placed in the press, the distance between the upper and lower gaskets of the press is adjusted, and the mold is moved to be pressed tightly until the test piece in the mold is completely pressed into the mold. The compaction process lasts for 3 to 4 minutes.

[0040] e. Demolding

[0041] Place the pressed mold on the demoulding instrument, turn on the demoulding instrument, and wait until the specimen is completely out of the mold, then take out the specimen;

[0042] f. Maintenance

[0043] Place the demoulding specimen in a curing box and cure for 7 days under standard conditions of 20±2℃ and ≥95% humidity. On the last day of the curing period, take out the specimen from the high-temperature curing room, cool it to room temperature, open the plastic bag and take out the specimen, observe whether the specimen has defects, measure the height and weight, and immerse it in a 20±2℃ constant temperature water tank with the water surface 2.5cm higher than the top of the specimen. After immersion for 24 hours, take out the specimen, wipe off the visible free water with a soft cloth, weigh the weight and height, and immediately conduct an unconfined compressive strength test.

[0044] g. Strength test

[0045] Turn on the press switch, connect the computer and the press, place the specimen on the press base, use the handle to control the press plate to almost contact the specimen, keep the loading rate at 1mm / min, and record the maximum pressure P (N) when the specimen is destroyed.

[0046] Furthermore, the process of determining the solubility coefficient of alkali slag lime soil in step (4) is as follows:

[0047] a. Pass the test materials alkali residue and soil through a 2.00mm standard sieve respectively, take representative test materials to determine their air-dried moisture content, calculate the mass of each group of test alkali residue, soil and required water according to the target moisture content of the mixture, first mix the alkali residue and soil evenly, spray water evenly, mix again evenly, and then bag and seal for 24 hours;

[0048] b. Prepare the dissolution specimen at room temperature of 20℃, use light compaction, add the mixture into the compaction cylinder in 3 layers, hammer 29 times for each layer, roughen one layer after compaction, and compact the next layer to make a cylindrical specimen with an inner diameter of 152mm and a height of 120mm. Push out the compacted soil with a demoulding instrument, then place the cutting edge of the ring knife downward on the compacted soil sample, press vertically downward, and cut while pressing until the soil sample extends out of the ring knife. Cut off the excess soil at both ends and make it flat;

[0049] c. Clean the outer wall of the ring cutter with the sample prepared, put the cutter blade downward into the guard ring, put the lower permeable stone and filter paper on the bottom plate, put the guard ring and the sample into the container, cover the soil sample with the filter paper and the permeable stone, then put down the pressure guide ring and the pressure transmission piston, make all parts in close contact and keep stable, put the compression container in the center of the pressure frame, close the pressure transmission piston and the crossbeam, pre-apply 1.0kPa pressure, make all parts of the consolidation instrument in close contact, install the dial indicator, and adjust the reading to zero;

[0050] d. The load range of the test is 12.5kPa~400kPa, among which the specific loads are 12.5kPa, 25kPa, 50kPa, 100kPa, 200kPa, 300kPa and 400kPa. 25kPa~50kPa is the first-level load, which is loaded step by step. The dial indicator reading is read at intervals of 10min~30min between each level of load until the deformation of the load is stable. The deformation stability standard is that the deformation per hour is not more than 0.01mm. Based on the test steps, another sample is immersed in water after each level of load is added, and the corresponding deformation is read, and the dissolution coefficient is calculated according to the formula.

[0051] Furthermore, the formula for calculating the dissolution coefficient of alkali slag lime soil in step 4 is:

[0052]

[0053] Where: δss——solution coefficient, calculated to 0.001;

[0054] h p ——Height of the specimen after deformation stabilizes under pressure P (mm);

[0055] h' p ——The height of the sample after the water immersion and filtration deformation stabilizes under the pressure P (mm);

[0056] h 0 ——Initial height of the specimen (mm).

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] By washing the alkali slag with water, the soluble salt content of the alkali slag is reduced, thereby reducing the salinization degree of the alkali slag lime soil and preventing and controlling the dissolution disease. However, according to research, too many times of washing will destroy the internal structure of the alkali slag, and the appropriate amount of soluble salt content can promote the strength of the alkali slag lime soil, which is beneficial to the road performance of the alkali slag lime soil. Therefore, the present invention combines the allowable alkali slag dosage designed for the strength of the alkali slag lime soil, and proposes a design process and method for the control target amount of the soluble salt content of the alkali slag that takes into account both the strength and dissolution targets. Controlling the soluble salt content of the alkali slag within a certain allowable range can not only keep the material strength within the specified range, but also prevent and control dissolution.

[0059] Different from the traditional method of reducing the amount of alkali slag to control the dissolution disease of alkali slag lime soil, the present invention innovatively proposes to appropriately reduce the soluble salt content of the alkali slag through a water washing process, thereby achieving the goal of preventing and controlling the dissolution disease of alkali slag lime soil.

[0060] The method of the present invention determines the maximum alkali slag dosage that needs to be improved based on the salinization degree, strength and dissolution degree of alkali slag lime soil, and selects the alkali slag after washing to reduce the soluble salt content to replace the original alkali slag for improvement, and determines the optimal soluble salt content alkali slag through the improved strength value and dissolution coefficient. This method will effectively solve the dissolution disease problem caused by alkali slag lime soil with a high alkali slag dosage, and provide technical guarantee for the quality of road construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a flow chart of the method of the present invention;

[0062] Figure 2 It is the fitting curve of the total amount of soluble salt in alkali slag lime soil with different proportions;

[0063] Figure 3 The UCS fitting curves of different proportions of alkali slag lime soil;

[0064] Figure 4 Fitting the UCS curve of alkali slag lime soil under different soluble salt contents;

[0065] Figure 5 The curve fitting of the maximum dissolution coefficient of alkali slag lime soil under different soluble salt contents is given. DETAILED DESCRIPTION

[0066] The present invention is described in detail below in conjunction with specific embodiments.

[0067] Example 1

[0068] Step 1: Determine the alkali slag dosage x at the boundary between medium and strong salinized alkali slag lime soil 1

[0069] (1) Determination of the total amount of soluble salt in alkali slag lime soil with different proportions

[0070] The fresh alkali residue and soil were preliminarily crushed manually and placed in a ventilated place to dry naturally. The dried materials were sieved and passed through a 2mm standard sieve, and then their natural moisture content was measured. The natural moisture content of the raw soil was 4.51%, and the natural moisture content of the alkali residue was 34.79%.

[0071] Nine groups of different proportions of alkali slag test groups were designed, with 1 to 10 samples. Each group of samples was designed to have 100 parts of soil and alkali slag, and lime was added at 12%. The alkali slag in each group was 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40% respectively, and the corresponding content of each group of plain soil was 100%, 95%, 90%, 85%, 80%, 75%, 70%, 65% and 60%. Group 1 was the control group, and the specific experimental proportions of each group were shown in Table 1.

[0072] Table 1 Test mix ratio scheme

[0073]

[0074] According to the natural moisture content of alkali residue of 34.79%, the natural moisture content of raw soil of 4.51%, and the target moisture content of the sample of 18.8%, the mass of alkali residue, raw soil and the mass of water required for each test group are calculated. According to the amount of materials, the alkali residue and raw soil are mixed evenly, sprayed with water evenly, mixed evenly again, and then packed and sealed for 24 hours. The alkali residue soil mixture after stuffing is placed in a constant temperature oven, dried at a constant temperature of 105℃, and ground through a 1mm standard sieve for use.

[0075] Refer to the corresponding specifications of "Highway Geotechnical Test Code" (JTG3430-2020) to prepare the soluble salt test solution and test the total amount of soluble salt. The specific operations are as follows:

[0076] a. Weigh 50g of the dried alkali-slag soil mixture that has passed a 1mm sieve hole, put it into a dry 1000ml wide-mouth plastic bottle, add deionized water at a soil-water ratio of 1:5, cover the bottle stopper, shake it on a shaker for 3 minutes, and then filter it immediately to obtain the test solution.

[0077] b. Use a pipette to draw 50 mL of the leaching solution and inject it into a porcelain evaporating dish that has been dried at 105-110°C to a constant weight (the difference between the two masses is no more than 1 mg). Cover it with a watch glass and place it on a boiling water bath to evaporate to dryness. Perform three parallel experiments. If the residue after evaporation is yellow-brown, add 15% H 2 O 2 1~3mL, continue to evaporate to dryness in a water bath, repeat the process until the yellow-brown color disappears. Figure 2 shown.

[0078] c. Place the evaporating dish in an oven at 105-110°C and dry for 4-8 hours, take it out and place it in a desiccator to cool for 0.5 hours, and weigh it. Repeat the drying process for 2-4 hours, cooling for 0.5 hours, and weighing it with an analytical balance, and repeat until the difference between the two weights is no more than 0.0001g.

[0079] The experimental results are shown in Table 2.

[0080] Table 2 Test results of total soluble salt

[0081]

[0082] (2) Fitting the total amount of soluble salt in alkali slag lime soil with different proportions

[0083] The alkali residue dosage and the total amount of soluble salt in alkali residue soil were curve fitted, and the fitting formula of alkali residue dosage and alkali residue soil soluble salt was obtained. The alkali residue dosage required for different salinization degrees of alkali residue soil was inferred, and the alkali residue dosage and the total amount of soluble salt in alkali residue soil were fitted. Figure 2 As shown in Figure 3, the fitting formula for the amount of alkali slag added and the total amount of soluble salt in alkali slag soil is shown in Figure 3.

[0084] y=0.6533+0.1422*x+(6.04618E -4 )*x 2 (3)

[0085] Where: y——the total amount of soluble salt under a certain alkali residue dosage (%);

[0086] x——alkali slag dosage (%).

[0087] (3) Determine the alkali slag dosage x at the boundary between medium and strong salinized alkali slag lime soil 1

[0088] Referring to the corresponding specifications of the "Highway Geotechnical Test Code" (JTG3430-2020), alkali slag soil belongs to artificially prepared fine-grained chloride-saline soil. The soluble salt content of 0.3%-1.0% belongs to weak saline soil, 1.0%-5.0% belongs to moderate saline soil, 5.0%-8.0% belongs to strong saline soil, and >8.0% belongs to over-salinized soil. According to formula 3, the alkali slag dosage of alkali slag soil at different salinization degrees is deduced, see Table 3.

[0089] Table 3 Alkali residue dosage for different salinization degrees of alkaline residue soil

[0090]

[0091] The alkali slag lime soil with an alkali slag content of 3% to 27% is medium saline soil. The alkali slag content at the boundary between medium and strong salinization alkali slag lime soil is x 1 It is 27%.

[0092] Step 2: Determine the maximum alkali slag content x that meets the strength standard 2

[0093] (1) Determination of strength of alkali slag lime soil with different proportions

[0094] Refer to T0805-2018 Test Method for Unconfined Compressive Strength of Inorganic Binder Stabilized Materials in "Test Code for Inorganic Binder Stabilized Materials for Highway Engineering" (JTG E51-2009).

[0095] The sample preparation process mainly includes weighing, stuffing, mold loading, compaction, demoulding, and curing.

[0096] a. Weighing

[0097] During the weighing process, the material holding device must be kept dry, and the zeroing operation must be performed before each weighing. Measure the required water, alkali residue and soil in the air-dried state according to the experimental ratio.

[0098] b. Stuffing

[0099] Mix the weighed experimental materials to ensure that they are evenly mixed, and evenly spray the required amount of water after the materials are flattened. Then pour the mixed materials into a convenient bag, tie the convenient bag tightly, soak the experimental materials for later use, and keep them in a simmering state for no less than 6 hours.

[0100] c.Moulding

[0101] Put the steamed material into the mold. Before putting it into the mold, you need to brush the inside of the mold with oil to ensure that the test block and the mold do not stick together when demolding.

[0102] d. Compaction

[0103] In order to ensure the density of the test piece, place the assembled mold in the press, adjust the distance between the upper and lower gaskets of the press, move to compact the mold, and press the test piece in the mold until it is completely pressed into the mold. The compaction process lasts for 3 to 4 minutes.

[0104] e. Demolding

[0105] Place the pressed mold on the demoulding instrument, turn on the demoulding instrument, and wait until the specimen is completely out of the mold, then take out the specimen.

[0106] f. Maintenance

[0107] Place the demoulding specimen in a curing box and cure for 7 days under standard conditions of 20±2℃ and ≥95% humidity. On the last day of the curing period, take out the specimen from the high-temperature curing room, cool it to room temperature (about 2h), open the plastic bag and take out the specimen, observe whether the specimen has defects, measure the height and weight, and immerse it in a 20±2℃ constant temperature water tank with the water surface 2.5cm higher than the top of the specimen. After immersion in water for 24h, take out the specimen, wipe off the visible free water with a soft cloth, weigh the weight and height, and immediately conduct an unconfined compressive strength test.

[0108] g. Strength test

[0109] Turn on the press, connect the computer to the press, place the specimen on the press base, and use the handle to control the upper plate of the press to almost touch the specimen (but not completely), and keep the loading rate at 1mm / min. Record the maximum pressure P (N) when the specimen is destroyed.

[0110] The experimental results are shown in Table 4.

[0111] Table 4 UCS of alkali slag lime soil

[0112]

[0113] (2) Strength fitting of alkali slag lime soil with different proportions

[0114] The unconfined compressive strength values ​​of alkali slag lime soil with different alkali slag content were fitted by curve fitting, and the alkali slag content-UCS fitting formula was obtained. In order to have engineering research significance, the alkali slag content range that meets the standard strength was calculated according to the fitting formula. The alkali slag content-UCS fitting curve is shown in Figure 3 As shown, the fitting formula is shown in Formula 4.

[0115] y=0.74018-0.00138*x-0.000322078*x 2 (4)

[0116] Where: y——UCS under a certain alkali residue dosage;

[0117] x——Alkali residue dosage (%)

[0118] When UCS is greater than 0.5MPa, the amount of alkali slag added is 0-25.25%.

[0119] (3) Determine the maximum alkali slag content x of alkali slag lime soil that meets the strength standard 2

[0120] By fitting the curve, the maximum alkali slag content x corresponding to the alkali slag lime soil that meets the standard strength (strength greater than 0.5MPa) is determined. 2 is 25%.

[0121] Step 3: Determine the maximum allowable amount of alkali slag in alkali slag lime soil x 3

[0122] The alkali slag lime soil material must not only meet the requirements of not being a highly saline soil, but also meet the strength standards. Therefore, it is necessary to compare x 1 and x 2 The smaller one is the maximum allowable amount of alkali slag in alkali slag lime soil x 3 , so we can get x 3 is 25%.

[0123] Step 4: Verify that when the alkali slag dosage is x 3 Whether the alkali slag lime soil will dissolve or not (if no dissolution occurs, no improvement is needed)

[0124] Combining steps 1, 2 and 3, it can be concluded that the maximum allowable amount of alkali slag in alkali slag lime soil is 25%.

[0125] (1) Determination of the solubility coefficient of alkali slag lime soil

[0126] Referring to the corresponding specifications of the "Highway Geotechnical Test Code" (JTG3430-2020), alkali slag lime soil with an alkali slag content of 25% was selected for dissolution test. The specific operations are as follows:

[0127] a. Pass the test materials alkali residue and soil through a 2.00mm standard sieve respectively, take representative samples to determine the air-dried moisture content of alkali residue (34.79%) and the air-dried moisture content of bare soil (4.51%), calculate the mass of each group of test alkali residue, bare soil and required water according to the target moisture content of the mixture, first mix the alkali residue and bare soil evenly, spray water evenly, mix again evenly, and then bag and seal for 24 hours.

[0128] b. Prepare the dissolution specimen at room temperature of 20℃. Use light compaction. Add the mixture into the compaction cylinder in 3 layers. Hammer each layer 29 times. After compacting one layer, roughen it and compact the next layer. Make a cylindrical specimen with an inner diameter of 152mm and a height of 120mm. Push the compacted soil out with a demoulding instrument. Figure 5 As shown, place the cutting edge of the ring knife downward on the compacted soil sample and press it vertically downward, while the ring knife is pressing and cutting until the soil sample extends out of the ring knife. Cut off the excess soil at both ends and smooth them.

[0129] c. Clean the outer wall of the ring cutter with the sample prepared, and place it into the guard ring with the blade facing downward. Place the lower permeable stone and filter paper on the bottom plate. Place the guard ring and the sample into the container, cover the soil sample with the filter paper and the permeable stone, then lower the pressure guide ring and the pressure transmission piston to make all parts in close contact and keep stable. Place the compression container in the center of the pressure frame, close the pressure transmission piston and the crossbeam, pre-apply 1.0kPa pressure, make all parts of the consolidation instrument in close contact, install the dial indicator, and adjust the reading to zero.

[0130] d. The load range of the test is 12.5kPa~400kPa, and the specific loads are 12.5kPa, 25kPa, 50kPa, 100kPa, 200kPa, 300kPa, and 400kPa. 25kPa~50kPa is the first-level load, which is loaded step by step. The dial indicator reading is read every 10min~30min when each level of load is applied until the deformation of the load is stable. The deformation stability standard is that the deformation per hour is not more than 0.01mm. Another sample is immersed in water after each level of load is added according to this test procedure, and the corresponding deformation is read.

[0131] The dissolution coefficient of saline soil was calculated according to Formula 2. The experimental results are shown in Table 5.

[0132] Table 5 Maximum dissolution coefficient

[0133]

[0134] It can be seen from the data that when the alkali slag dosage is 25%, the maximum dissolution coefficient of the alkali slag lime soil is 2.5%, which is greater than 1.5%, and dissolution occurs.

[0135] (2) Determine the allowable design dosage x of alkali slag lime soil 3

[0136] Verify whether the alkali slag lime soil will dissolve when the alkali slag content is 25% (the dissolution coefficient is greater than 1.5%). If no dissolution occurs, no improvement is required. If dissolution occurs, determine the alkali slag lime soil that needs to be improved. 3 is 25%.

[0137] Step 5: Determine the strength and dissolution results of alkali-lime soil under different soluble salt content alkali-lime conditions

[0138] According to the above process, the alkali slag lime soil with an alkali slag content of 25% needs to be prevented and treated. The soluble salt content of the original alkali slag is 19.862%. After washing, five alkali slags with different soluble salt contents are prepared, which are 16%, 12%, 9%, 5% and 2%, respectively. Five groups of tests were designed, with an alkali slag content of 25%, a soil content of 75%, and 12% lime added. The strength and dissolution coefficient of alkali slag with different soluble salt contents were tested. The test proportions are shown in Table 6.

[0139] Table 6 Alkali slag lime soil ratio under different soluble salt content

[0140]

[0141] Referring to the test methods of step 2 and step 3, the strength values ​​and dissolution coefficients of these five groups were tested, as shown in Table 7.

[0142] Table 7 Alkali slag lime soil ratio under different soluble salt content

[0143]

[0144] Draw the UCS curve and fit it, such as Figure 4 As shown; draw the maximum dissolution coefficient and fit it, as shown Figure 5 shown.

[0145] The UCS fitting curve is shown in Formula 5:

[0146] y=0.33517+0.03382x-0.00129x 2 (5)

[0147] It can be seen from the chart that when the soluble salt content of alkali slag is appropriately reduced, the material strength will be improved, but too little soluble salt content will lead to insufficient strength. When the soluble salt content of alkali slag is within the range of (6.5%, 19.7%), the strength meets the standard.

[0148] The fitting curve of the dissolution coefficient is shown in Formula 6:

[0149] y=(3.84589E-4)+(6.52148E-4)*x+(3.57143E-5)*x 2 (6)

[0150] The fitting results show that when the soluble salt content of alkali slag is less than 13%, the dissolution coefficient is less than 1.5%.

[0151] Step 6: Determine the optimal soluble salt content of alkali residue control plan

[0152] Based on the fitting analysis results in step 5, combined with the strength and dissolution coefficient, the optimal soluble salt content of the alkali slag is selected to be 6.5% to 13%.

[0153] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer, characterized in that: The following steps are involved: Step (1): Determine the alkali slag dosage x1 at the boundary between medium and strong salinized alkali slag lime soil Prepare alkali slag lime soil with different dosages, separate and obtain the soluble salt in the alkali slag lime soil by washing and evaporation, and calculate the total amount of soluble salt in the alkali slag lime soil; perform curve fitting on the total amount of soluble salt in the alkali slag lime soil with different dosages, and obtain a fitting curve of alkali slag dosage and soluble salt total amount; determine the alkali slag dosage x1 corresponding to the boundary line between medium and strong salinization alkali slag lime soil through the fitting curve; Step (2): Determine the maximum alkali residue content x2 that meets the strength standard Prepare alkali slag lime soil with different alkali slag content and test its strength; perform curve fitting on the unconfined compressive strength values ​​of alkali slag lime soil with different alkali slag content to obtain an alkali slag content-strength fitting curve; determine the maximum alkali slag content corresponding to the alkali slag lime soil that meets the standard strength as x2 through the fitting curve; Step (3): Determine the maximum allowable amount of alkali slag in alkali slag lime soil x3 Compare the sizes of x1 and x2, and take the smaller one as the maximum allowable amount of alkali slag in alkali slag lime soil x3, that is, x3 = min{x1, x2}; Step (4): Under the condition of x3 alkali slag dosage, the dissolution coefficient of the alkali slag lime soil is measured and calculated. If the calculated dissolution coefficient is less than 1.5%, no improvement is required; if it is greater than 1.5%, improvement is required; Step (5): Prepare five kinds of alkali slag with different soluble salt contents by water washing, design five groups of tests, with the alkali slag dosage being x3, the soil dosage being 100%-x3, and 12% lime added externally, and test the strength and dissolution coefficient of the alkali slag with different soluble salt contents respectively; Step (6): Perform fitting analysis on the results in step (5), combine the strength and dissolution coefficient, and select the alkali slag with the best soluble salt content as the prevention and control plan.

2. The method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer according to claim 1, characterized in that: The preparation process of alkali slag lime soil with different admixtures in step (1) is as follows: the soil and alkali slag are designed to be 100 parts by weight in total, alkali slag: soil = x: (100-x), and 12% of lime is added, wherein the ratio of alkali slag to soil is the percentage of dry mass of the material; the mass of alkali slag, plain soil and required water for each test group is calculated according to the target moisture content, the alkali slag and plain soil are first mixed evenly, water is evenly sprayed on them, and then mixed evenly, and then bagged and sealed for 24 hours; the alkali slag soil mixture after being stuffed is put into a constant temperature oven, dried at a constant temperature of 100-110° C., and ground through a 1 mm standard sieve for standby use; using the above method, 8-10 groups of alkali slag lime soil with different admixtures are designed.

3. The method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer according to claim 1, characterized in that: The process of the test calculation of the total amount of soluble salt in step (1) is as follows: a. Weigh the dried alkali slag soil mixture that passes through a 1 mm sieve, put it into a dry wide-mouth plastic bottle, add deionized water at a soil-water ratio of 1:5, and filter immediately after shaking to obtain a test solution; b. Use a pipette to absorb the leaching solution and inject it into a porcelain evaporating dish that has been dried to a constant volume at 105-110℃, cover it with a watch glass, and place it on a boiling water bath to evaporate to dryness. Perform three parallel experiments. If the residue after evaporation is yellow-brown, add 15% H2O2 1-3mL and continue to evaporate in a water bath. Repeat the process until the yellow-brown color disappears. c. Place the evaporating dish in an oven at 105-110°C and dry for 4-8 hours. Take it out and place it in a desiccator to cool for 0.5 hours, then weigh it. Repeat the drying process for 2-4 hours, cool it for 0.5 hours, and weigh it with an analytical balance. Repeat this process until the difference between the two weights is no more than 0.0001 g. d. Calculate the total amount of soluble salts according to the formula and take the average value of the three groups.

4. A method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer according to claim 3, characterized in that: The formula is: Where: m2——mass of evaporating dish plus evaporated residue (g), calculated to 0.001; m1——mass of evaporating dish (g); m s ——Mass of dry soil sample in 50mL of leaching solution (g).

5. The method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer according to claim 1, characterized in that: Step (2) The strength test process of alkali slag lime soil with different dosages is as follows: a. Weighing During the weighing process, the material holding device must be kept dry. Before each weighing, the material must be reset. The required water, air-dried alkali residue and soil must be measured according to the experimental ratio. b. Stuffing Mix the weighed experimental materials to ensure that they are evenly mixed. Spread the materials flat and evenly spray the required amount of water. Pour the mixed materials into a convenient bag, tie the bag tightly, soak the experimental materials for later use, and keep the materials for at least 6 hours; c.Moulding Put the steamed material into the mold. Before putting it into the mold, you need to brush the inside of the mold with oil to ensure that the test block and the mold do not stick together when demolding; d. Compaction In order to ensure the density of the test piece, the assembled mold is placed in the press, the distance between the upper and lower gaskets of the press is adjusted, and the mold is moved to be pressed tightly until the test piece in the mold is completely pressed into the mold. The compaction process lasts for 3 to 4 minutes. e. Demolding Place the pressed mold on the demoulding instrument, turn on the demoulding instrument, and wait until the specimen is completely out of the mold, then take out the specimen; f. Maintenance Place the demoulding specimen in a curing box and cure for 7 days under standard conditions of 20±2℃ and ≥95% humidity. On the last day of the curing period, take out the specimen from the high-temperature curing room, cool it to room temperature, open the plastic bag and take out the specimen, observe whether the specimen has defects, measure the height and weight, and immerse it in a 20±2℃ constant temperature water tank with the water surface 2.5cm higher than the top of the specimen. After immersion for 24 hours, take out the specimen, wipe off the visible free water with a soft cloth, weigh the weight and height, and immediately conduct an unconfined compressive strength test. g. Strength test Turn on the press switch, connect the computer and the press, place the specimen on the press base, use the handle to control the press plate to almost contact the specimen, keep the loading rate at 1mm / min, and record the maximum pressure P (N) when the specimen is destroyed.

6. The method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer according to claim 1, characterized in that: The process of determining the solubility coefficient of alkali slag lime soil in step (4) is as follows: a. Pass the test materials alkali residue and soil through a 2.00mm standard sieve respectively, take representative test materials to determine their air-dried moisture content, calculate the mass of each group of test alkali residue, soil and required water according to the target moisture content of the mixture, first mix the alkali residue and soil evenly, spray water evenly, mix again evenly, and then bag and seal for 24 hours; b. Prepare the dissolution specimen at room temperature of 20℃, use light compaction, add the mixture into the compaction cylinder in 3 layers, hammer 29 times for each layer, roughen one layer after compaction, and compact the next layer to make a cylindrical specimen with an inner diameter of 152mm and a height of 120mm. Push out the compacted soil with a demoulding instrument, then place the cutting edge of the ring knife downward on the compacted soil sample, press vertically downward, and cut while pressing until the soil sample extends out of the ring knife. Cut off the excess soil at both ends and make it flat; c. Clean the outer wall of the ring cutter with the sample prepared, put the cutter blade downward into the guard ring, put the lower permeable stone and filter paper on the bottom plate, put the guard ring and the sample into the container, cover the soil sample with the filter paper and the permeable stone, then put down the pressure guide ring and the pressure transmission piston, make all parts in close contact and keep stable, put the compression container in the center of the pressure frame, close the pressure transmission piston and the crossbeam, pre-apply 1.0kPa pressure, make all parts of the consolidation instrument in close contact, install the dial indicator, and adjust the reading to zero; d. The load range of the test is 12.5kPa~400kPa, among which the specific loads are 12.5kPa, 25kPa, 50kPa, 100kPa, 200kPa, 300kPa and 400kPa. 25kPa~50kPa is the first-level load, which is loaded step by step. The dial indicator reading is read at intervals of 10min~30min between each level of load until the deformation of the load is stable. The deformation stability standard is that the deformation per hour is not more than 0.01mm. Based on the test steps, another sample is immersed in water after each level of load is added, and the corresponding deformation is read, and the dissolution coefficient is calculated according to the formula.

7. The method for reducing the soluble salt content of alkali slag to prevent and control the dissolution disease of alkali slag lime soil in the base layer according to claim 6, characterized in that: Step 4 The formula for calculating the dissolution coefficient of alkali slag lime soil is: Where: δss——solution coefficient, calculated to 0.001; h p ——Height of the specimen after deformation stabilizes under pressure P (mm); h' p ——The height of the sample after the water immersion and filtration deformation stabilizes under pressure P (mm); h0——The initial height of the sample (mm).

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