An acid rain-resistant roadbed material based on waste mud, its preparation method and application

Abstract

The present invention discloses an acid rain-resistant roadbed material based on waste mud, its preparation method and application. The preparation method comprises the following steps: (1) adding a flocculant to the waste mud, stirring to fully mix the waste mud and the flocculant, standing for precipitation, and discharging the supernatant to obtain dehydrated waste mud dried soil; (2) adding Portland cement, sodium hydroxide, sodium silicate and sodium fluorosilicate to the waste mud dried soil, and stirring evenly to prepare the acid rain-resistant roadbed material. The addition amount of the sodium hydroxide is 0.2% - 0.6% of the mass of the waste mud dried soil, the addition amount of the sodium silicate is 0.8% - 1.2% of the mass of the waste mud dried soil, and the addition amount of the sodium fluorosilicate is 0.1% - 0.3% of the mass of the waste dry soil. The treated waste mud is used as the acid rain-resistant roadbed material, which reduces the sand and gravel cost of the roadbed material, reduces environmental pollution, promotes the resource utilization of the waste mud, and has good economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of civil engineering building materials, and particularly relates to an acid-resistant subgrade material based on waste slurry, its preparation method and application, which are applicable to the reprocessing and utilization of waste slurry generated in geotechnical engineering (such as pile foundation drilling, oil and gas drilling, anchoring engineering, slurry shield, etc.). Background Technique

[0002] Waste slurry is the waste and surplus slurry generated during the construction of various buildings (structures), pile foundations, foundation pit retaining structures, slurry shields, pipe network tunneling, etc. Acid rain has direct or potential impacts on soil, building facilities, ecological systems and human health. Therefore, when waste slurry solidified soil is used as a subgrade material, the impact of acid rain cannot be ignored, and its acid resistance needs to be improved.

[0003] However, the existing waste slurry solidification technologies generally only consider the mechanical properties after solidification, and have not considered the acid resistance as a subgrade material, and there are also few relevant engineering practices. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an acid-resistant subgrade material based on waste slurry, its preparation method and application, and overcome the problem of poor acid resistance of existing waste slurry solidified soil as a subgrade material. The present invention adds ordinary Portland cement to waste slurry, and adds acid-resistant modifiers such as sodium hydroxide, sodium silicate and sodium fluorosilicate for treatment. The treated waste slurry is used as a subgrade material, which improves the strength of the waste slurry, makes it acid-resistant, reduces the sand and gravel cost of the subgrade material, reduces environmental pollution, promotes the resource utilization of waste slurry, and has good economic and social benefits.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of an acid-resistant subgrade material based on waste slurry, comprising the following steps:

[0007] (1) Add flocculant polyacrylamide to the waste slurry, and the addition amount is 0.2% - 0.4% of the mass of the dried waste slurry soil, stir to make the waste slurry and the flocculant fully mixed, stand and precipitate for 24 - 30 hours, drain the supernatant, and obtain dehydrated waste slurry dried soil with a moisture content of 35% - 45%;

[0008] (2) Add Portland cement 425, sodium hydroxide, sodium silicate, and sodium fluorosilicate to the dried waste mud soil, stir evenly to make an acid-resistant roadbed material; the addition amount of sodium hydroxide is 0.2% - 0.6% of the mass of the dried waste mud soil, the addition amount of sodium silicate is 0.8% - 1.2% of the mass of the dried waste mud soil, the addition amount of sodium fluorosilicate is 0.1% - 0.3% of the mass of the dried waste mud soil, and the addition amount of Portland cement 425 is 5% - 9% of the mass of the dried waste mud soil;

[0009] The acid-resistant range of the acid-resistant roadbed material is pH3 - pH6.

[0010] As an improvement, in the acid - wet - dry cycling treatment of the acid - resistant roadbed material, when pH is 3, after 3 times, 6 times, and 9 times of acid - wet - dry cycling, the mass loss rates are 1.9%, 3.6%, and 4.0% respectively, and the unconfined compressive strengths are 1056 kPa, 1018 kPa, 973 kPa, and 916 kPa respectively.

[0011] Application of the acid - resistant roadbed material prepared by the above method in highway reconstruction and expansion projects.

[0012] Sodium silicate and sodium fluorosilicate have the function of strengthening coagulation while being used as acid - resistant modifiers. The mechanism is that they react to form silicic acid gel and sodium fluoride. Part of the silicic acid gel and sodium fluoride form a complex, and the other part of the silicic acid gel continuously dehydrates and shrinks to form a high - polymer. The main chemical reaction equations are as follows:

[0013] 2NaO·nSiO2 + Na2SiF6 + 2(n + 1)H2O → 6NaF + (2n + 1)Si(OH)4 (1) Si(OH)4 + NaF → SiO2NaF·H2O + H2O (2) NaO·nSiO2 + 2nH2O + CO2 → Na2CO3 + nSi(OH)4 (3)

[0014] Beneficial effects:

[0015] The acid - resistant roadbed material of the present invention only needs to mix the solidifying material with the dried waste mud soil and stir evenly. The acid - resistant range is pH3 - pH6. After inspection, this material has good curing effect under acid - wet - dry cycling conditions. When pH is 3, after 3 times, 6 times, and 9 times of acid - wet - dry cycling, the mass loss rates are 1.9%, 3.6%, and 4.0% respectively, and the unconfined compressive strengths are 1056 kPa, 1018 kPa, 973 kPa, and 916 kPa respectively. The present invention can efficiently recycle waste mud, reduce the environmental pollution caused by waste mud, promote the resource utilization and reduction of waste mud, and has good economic and social benefits. Description of the drawings

[0016] Figure 1 This is the flow chart of the method for preparing acid - rain - resistant subgrade materials using waste mud in the present invention;

[0017] Figure 2 This is the comparison diagram of the waste mud solidified soil specimens of Example 1 and Comparative Example 1 after 3 acid - wet - dry cycles;

[0018] Figure 3 This is the comparison diagram of the scanning electron microscope images of the waste mud solidified soil specimens of Example 1 and Comparative Example 1 after 3 acid - wet - dry cycles;

[0019] Figure 4 This is the comparison diagram of the mass loss rates of Example 1 and Comparative Examples 1 - 3 after acid - wet - dry cycles;

[0020] Figure 5 This is the comparison diagram of the unconfined compressive strengths of Example 1 and Comparative Examples 1 - 3 after acid - wet - dry cycles. Specific Embodiments

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but it should not be construed as a limitation of the present invention. Modifications or substitutions made to the methods, steps or conditions of the present invention without departing from the spirit and essence of the present invention all fall within the scope of the present invention.

[0022] Preparation and Performance Testing of Acid - Rain - Resistant Subgrade Materials in Example 1

[0023] In this embodiment, the method for preparing acid - rain - resistant subgrade materials using waste mud is used to re - process and utilize the waste mud, which is applied to the waste mud generated from the reconstruction project of the section from Shanghe, Xiaoshan to Anhua, Zhuji on the Hangzhou - Zhuji Highway of National Highway 235. Its maximum dry density is 1.768 g / m 3 .

[0024] Step (1): Mud Dewatering

[0025] Fill the pre - built mud pond with waste mud, uniformly add the flocculant polyacrylamide to the waste mud, with the addition amount being 0.2% of the dry soil mass of the waste mud. Use a mud stirrer to stir to fully mix the mud and the flocculant, let it stand and precipitate for 24 hours, drain the supernatant, and obtain a waste mud dried soil specimen with a water content of about 40%.

[0026] Step (2): Add Acid - Resistant Curing Material

[0027] Uniformly add ordinary Portland cement of grade 425, sodium hydroxide, sodium silicate and sodium fluorosilicate to the dehydrated waste mud dried soil sample. Among them, sodium hydroxide, sodium silicate and sodium fluorosilicate are acid-resistant modifiers, which can improve the acid resistance of waste mud. At the same time, sodium silicate and sodium fluorosilicate also have the function of strengthening coagulation. Stir evenly with a mud mixer to make mud solidified soil. The addition amounts of ordinary Portland cement of grade 425, sodium hydroxide, sodium silicate and sodium fluorosilicate are 9%, 0.4%, 1% and 0.2% of the mass of the dry mud soil respectively.

[0028] Step (3): Curing of solidified soil

[0029] Put the evenly stirred mud solidified soil into a cylindrical mold with a diameter of 39.1 mm and a height of 80 mm in three layers to make a standard sample for unconfined compressive strength test, and cure it in a constant temperature curing box. The curing age is 14 days.

[0030] Step (4): Acidic dry-wet cycling test

[0031] Conduct an acid dry-wet cycling test on the waste mud solidified soil obtained in step (3). The acid dry-wet cycling test is divided into an immersion stage and a drying stage. The immersion experiment uses a mixed acid solution with a pH value of 3 prepared by concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 1:4. The drying test is carried out in an oven at 60 °C. One dry-wet cycle is defined as follows: the waste mud solidified soil sample is first immersed in the above-mentioned mixed acid solution of concentrated sulfuric acid and concentrated nitric acid for 12 hours, and then dried in a constant temperature oven for 12 hours. In this embodiment, the samples are respectively subjected to 3, 6 and 9 acid dry-wet cycling treatments.

[0032] Step (5): Determination of mass loss rate

[0033] Take the dry mass of the cured sample after drying in each dry-wet cycle as the evaluation index of the dry-wet cycle mass loss. The dry mass loss rate C i (%) is calculated by the following formula:

[0034]

[0035] In the formula, M0 is the initial dry mass, and M i is the dry mass of the sample after the i-th cycle (i = 3, 6, 9)

[0036] Step (6): Determination of unconfined compressive strength

[0037] Respectively conduct unconfined compressive strength determination on the waste mud solidified soil samples after 0, 3, 6 and 9 acid dry-wet cycling treatments. The determination method is carried out in accordance with the provisions of the "Standard for Geotechnical Test Methods" BG / T50123-2019 in China.

[0038] Preparation and Property Testing of Waste Slurry without Acid-Resistant Modifier in Comparative Example 1

[0039] For the treatment of waste slurry in this comparative example, sodium hydroxide, sodium silicate and sodium fluorosilicate, the acid-resistant modifiers, are not added, and other conditions are the same as those in Example 1. The addition amount of ordinary Portland cement is 9% of the dry soil mass of the slurry. After 14 days of curing, an acid dry-wet cycle test is carried out on the specimen, and the number of test times is 3 times. The test results are as Figure 2 shown. As can be seen from Figure 2 it that after 3 acid dry-wet cycles, partial peeling occurs in the solidified soil specimen of waste slurry without adding acid-resistant modifiers such as sodium hydroxide, sodium silicate and sodium fluorosilicate, and the integrity is poor, while the solidified soil specimen of waste slurry added with acid-resistant modifiers is relatively complete.

[0040] Scanning electron microscope tests are respectively carried out on the solidified soil specimens of waste slurry with and without adding acid-resistant modifiers such as sodium hydroxide, sodium silicate and sodium fluorosilicate, and 5000-fold scanning electron microscope images of the solidified soil of waste slurry under the two working conditions are obtained, as Figure 3 shown. As can be seen from Figure 3 it that for the solidified soil specimen of waste slurry added with acid-resistant modifiers, the cementitious substances are significantly increased and the pores are denser, indicating that the addition of acid-resistant modifiers can form more effective bonds between clay particles and the strength increases significantly.

[0041] After the specimens are subjected to 3, 6 and 9 acid dry-wet cycle treatments, the mass loss rate and unconfined compressive strength are measured.

[0042] Preparation and Property Testing of Waste Slurry with Acid-Resistant Modifier - Sodium Hydroxide in Comparative Example 2

[0043] For the treatment of waste slurry in this comparative example, sodium silicate and sodium fluorosilicate, the acid-resistant modifiers, are not added, and other conditions are the same as those in Example 1, that is, the added ones are ordinary Portland cement of grade 425 and sodium hydroxide. The addition amounts of ordinary Portland cement and sodium hydroxide are 9% and 0.4% of the dry soil mass of the slurry respectively. After the specimens are subjected to 3, 6 and 9 acid dry-wet cycle treatments, the mass loss rate and unconfined compressive strength are measured.

[0044] Preparation and Property Testing of Waste Slurry with Acid-Resistant Modifiers - Sodium Hydroxide and Sodium Silicate in Comparative Example 3

[0045] For the treatment of waste slurry in this comparative example, sodium fluorosilicate is not added, and other conditions are the same as those in Example 1, that is, the added ones are ordinary Portland cement of grade 425, sodium hydroxide and sodium silicate. The addition amounts of ordinary Portland cement, sodium hydroxide and sodium silicate are 9%, 0.4% and 1% of the dry soil mass of the slurry respectively. After the specimens are subjected to 3, 6 and 9 acid dry-wet cycle treatments, the mass loss rate and unconfined compressive strength are measured.

[0046] The test results of the mass loss rate of the specimens of Example 1 and Comparative Examples 1, 2, and 3 are as follows Figure 4 shown, and the test results of the unconfined compressive strength are as follows Figure 5 shown.

[0047] It can be seen from Figure 4 that for the solidified soil of waste slurry with only ordinary Portland cement added in Comparative Example 1, after 3, 6, and 9 acidic dry-wet cycles, the mass loss rates are 7.6%, 10.5%, and 11.2% respectively; for the solidified soil of waste slurry with ordinary Portland cement and sodium hydroxide added in Comparative Example 2, after 3, 6, and 9 acidic dry-wet cycles, the mass loss rates are 6.2%, 8.8%, and 9.4% respectively; for the solidified soil of waste slurry with ordinary Portland cement, sodium hydroxide, and sodium silicate added in Comparative Example 3, after 3, 6, and 9 acidic dry-wet cycles, the mass loss rates are 4.6%, 6.9%, and 7.4% respectively; for the solidified soil of waste slurry with ordinary Portland cement, sodium hydroxide, sodium silicate, and sodium fluorosilicate added in Example 1 of the present invention, after 3, 6, and 9 acidic dry-wet cycles, the mass loss rates are 1.9%, 3.6%, and 4.0% respectively.

[0048] Thus, it can be seen that the mass loss of the specimens of the solidified soil of waste slurry without adding acid-resistant modifiers increases significantly after acidic dry-wet cycles. After 9 acidic dry-wet cycles, the mass loss rates of the waste slurry under the three conditions of only adding ordinary Portland cement, adding ordinary Portland cement and sodium hydroxide, and adding ordinary Portland cement, sodium hydroxide, and sodium silicate are 2.80 times, 2.35 times, and 1.85 times that of the specimens of the solidified soil of waste slurry under the condition of adding all four curing materials respectively.

[0049] It can be seen from Figure 5It can be seen that for the waste mud solidified soil with only ordinary Portland cement added in Comparative Example 1, after 3, 6, and 9 acidic dry-wet cycles, the unconfined compressive strength decreased from 931 kPa to 828 kPa, 719 kPa, and 605 kPa respectively; for the waste mud solidified soil with ordinary Portland cement and sodium hydroxide added in Comparative Example 2, after 3, 6, and 9 acidic dry-wet cycles, the unconfined compressive strength decreased from 968 kPa to 884 kPa, 789 kPa, and 693 kPa respectively; for the waste mud solidified soil with ordinary Portland cement, sodium hydroxide, and sodium silicate added in Comparative Example 3, after 3, 6, and 9 acidic dry-wet cycles, the unconfined compressive strength decreased from 998 kPa to 931 kPa, 852 kPa, and 766 kPa respectively; for Example 1 of the present invention, the waste mud solidified soil with ordinary Portland cement, sodium hydroxide, sodium silicate, and sodium fluorosilicate added, after 3, 6, and 9 acidic dry-wet cycles, the unconfined compressive strength decreased from 1056 kPa to 1018 kPa, 973 kPa, and 916 kPa respectively. Thus, it can be seen that the unconfined compressive strength of the waste mud solidified soil samples without acid-resistant modifiers added and without all acid-resistant modifiers added decreased significantly after the acidic dry-wet cycle. After 9 acidic dry-wet cycles, the unconfined compressive strength of the waste mud without any additives, with only ordinary Portland cement added, with ordinary Portland cement and sodium hydroxide added, and with ordinary Portland cement, sodium hydroxide, and sodium silicate added decreased by 35.02%, 28.41%, and 23.25% respectively, while the unconfined compressive strength of the waste mud solidified soil sample with all acid-resistant modifiers added, that is, with all four curing materials added, decreased by only 13.26% after 9 acidic dry-wet cycles.

[0050] In addition, from Figure 4 and Figure 5 it can also be seen that the addition of sodium fluorosilicate significantly improved the acid resistance of the waste mud solidified soil. The addition of sodium fluorosilicate reduced the mass loss rate of the waste mud solidified soil under acidic dry-wet cycle conditions by about 50%, and increased the unconfined compressive strength of the waste mud solidified soil after acidic dry-wet cycle by 10% - 20%.

[0051] As can be seen from the above, compared with the waste mud with only ordinary Portland cement added, the waste mud with acid-resistant modifiers such as sodium hydroxide, sodium silicate, and sodium fluorosilicate added performs better in terms of acid resistance and strength. The present invention uses waste mud to prepare acid-resistant roadbed materials, which are applied to projects such as the reconstruction of national highways and the expansion of expressways, facilitating the resource utilization and reduction of waste mud, and having good economic and social benefits.

Claims

1. A method for preparing an acid rain resistant roadbed material based on waste mud, characterized in that: The following steps are involved: (1) Adding polyacrylamide as a flocculant to the waste mud in an amount of 0.2% to 0.4% of the mass of the waste mud dried soil, stirring to fully mix the waste mud and the flocculant, letting it settle for 24 to 30 hours, and discharging the supernatant to obtain dehydrated waste mud dried soil with a moisture content of 35% to 45%; (2) Add 425% silicate cement, sodium hydroxide, sodium silicate and sodium fluorosilicate to the waste mud dried soil and stir evenly to make acid rain resistant roadbed material; the amount of sodium hydroxide added is 0.2%~0.6% of the mass of the waste mud dried soil, the amount of sodium silicate added is 0.8%~1.2% of the mass of the waste mud dried soil, the amount of sodium fluorosilicate added is 0.1%~0.3% of the mass of the waste mud dried soil, and the amount of 425% silicate cement added is 5%~9% of the mass of the waste mud dried soil; The acid-resistant range of the acid rain-resistant roadbed material is pH 3-pH 6.

2. The method for preparing an acid rain resistant roadbed material based on waste mud according to claim 1, characterized in that: In the acidic dry-wet cycle treatment, when the pH value is 3, the mass loss rates of the acid rain resistant roadbed material are 1.9%, 3.6% and 4.0% after 3, 6 and 9 acidic dry-wet cycles, respectively, and the unconfined compressive strengths are 1056 kPa, 1018 kPa, 973 kPa and 916 kPa, respectively.

3. Application of the acid rain resistant roadbed material prepared by the method according to claim 1 in highway reconstruction and expansion projects.

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