Effect evaluation and proportion optimization method for solid waste in sludge soft soil treatment

Abstract

The invention discloses a solid waste utility evaluation and proportion optimization method in sludge soft soil treatment in the technical field of inorganic composite materials. The method comprises the following steps: S1, carrying out a pH value test and an x fluorescence test on industrial solid wastes to be adopted, and dividing the industrial solid wastes to be adopted into two types: the type I is silicon-aluminum-based waste residues or alkaline waste residues, and the type II is gypsum-based waste residues; s2, constructing a strength prediction model of the pure cement sludge solidified soil, and carrying out coefficient calibration; s3, on the basis of the strength prediction model of the pure cement sludge solidified soil, constructing a strength prediction model of the waste residue-based sludge solidified soil, and carrying out coefficient calibration; and S4, optimizing and adjusting the ratio of various waste residues according to the waste residue-based sludge solidified soil strength prediction model. According to the utility evaluation and proportion optimization method, based on the strength prediction model of the waste residue-based sludge solidified soil, rapid and effective evaluation of the strength of the sludge solidified soil under different waste residue proportions can be realized, and the waste residue proportion in the solidified sludge soil can also be optimized.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic composite materials, and in particular to a method for evaluating the effectiveness and optimizing the proportion of solid waste in sludge soft soil treatment. Background Art

[0002] Every year, my country carries out a large number of river and lake desilting and ocean dredging projects, which produces a large amount of dredged mud with high water content and low strength. Due to the extremely poor engineering properties, a large amount of dredged mud is discarded. Inland dredged mud is usually stored on land for building cofferdams, while ocean dredged mud is abandoned offshore. The disposal of dredged mud causes a waste of resources and poses a threat to the environment. Chemical solidification treatment is an effective method for the recycling of dredged mud. Through chemical modification, dredged mud can be converted into good-quality soil and used for engineering filling construction. The solidification treatment method has the advantages of high treatment efficiency and short construction period, but it usually uses high-energy consumption resources such as cement, has a high economic cost, and greatly increases carbon emissions.

[0003] With the rapid development of urban construction, a large amount of industrial waste has been piled up for a long time due to ineffective utilization, which not only occupies land resources, but also has serious impacts on the environment. Bulk solid waste is large in volume and wide in scope, has prominent environmental impacts, and has broad prospects for utilization. It is the core area of ​​comprehensive resource utilization. In 2019, the comprehensive utilization rate of bulk solid waste in my country reached 55%, an increase of 5 percentage points from 2015. Among them, the comprehensive utilization rates of coal gangue and fly ash reached 70% and 78% respectively. Despite this, the disposal of bulk solid waste in my country is still in a severe situation. At present, the cumulative stockpile of bulk solid waste is about 60 billion tons, and the annual new stockpile is nearly 3 billion tons. In particular, the utilization rate of solid wastes such as red mud and phosphogypsum is still low, which is the focus and difficulty of the resource utilization of bulk solid waste. Industrial solid waste has potential chemical activity, especially under the activation of cement chemical environment, it often plays a beneficial role. If industrial solid waste is combined and utilized in cement solidified sludge, it can reduce the amount of cement and absorb the stock of industrial solid waste at the same time, which has great economic and environmental benefits.

[0004] However, due to the large number of types of industrial solid waste, standardization is difficult. This is mainly due to the different effects of industrial waste residues in cement-based materials, and the lack of classification and universal methods. The evaluation of the role of solid waste requires specific indoor tests, and the selection of the proportions in the test is also relatively blind. Therefore, the utilization efficiency of industrial solid waste in the treatment of silt and soft soil is very low. In addition, when the amount of waste residue is too high, it often causes negative effects and even engineering accidents. For example, when too much phosphogypsum is added to the roadbed, expansion and cracking often occur. Summary of the invention

[0005] To solve or partially solve the above problems, the present application provides a method for evaluating the utility and optimizing the proportion of solid waste in the treatment of silt and soft soil, which is used to evaluate the utility of solid waste in the treatment of silt and soft soil, and optimize the proportion between different waste residues by methods such as obtaining the maximum strength.

[0006] The embodiment of the present application provides a method for evaluating the utility and optimizing the proportion of solid waste in the treatment of silt and soft soil, including the following steps:

[0007] S1: Conduct pH value tests and X-ray fluorescence tests on the industrial solid waste to be used to obtain the acidity and alkalinity and chemical composition characteristics of the industrial solid waste; according to the acidity and alkalinity and chemical composition characteristics, classify the industrial solid waste to be used into two categories: type I waste residue and type II waste residue, where the type I waste residue is a silicon-aluminum-based waste residue or an alkaline waste residue, and the type II waste residue is a gypsum-based waste residue;

[0008] S2: Construct a strength prediction model for pure cement silt solidified soil and calibrate the coefficients. The specific expression of the strength prediction model for pure cement silt solidified soil is:

[0009]

[0010] where: q u is the uniaxial compressive strength; w is the initial water content of the silt soil; w / c is the water-cement ratio of the solidified silt, that is, the ratio of the initial water content of the silt soil to the cement content; A, n are fitting coefficients based on Abrams’ law; λ is the influence coefficient of the structure of the solidified soil;

[0011] S3: Based on the strength prediction model of pure cement silt solidified soil, construct a strength prediction model for waste residue-based silt solidified soil and calibrate the coefficients. The specific expression of the strength prediction model for waste residue-based silt solidified soil is as follows:

[0012]

[0013] where q and r are the dosages of type I waste residue and type II waste residue respectively, k 1 is the pozzolanic enhancement coefficient of type I waste residue, m 1 is the ettringite filling and enhancement coefficient of type II waste residue, d 1 is the cementation damage coefficient of type II waste residue;

[0014] S4: According to the strength prediction model of waste residue-based silt solidified soil, optimize and adjust the proportion of various waste residues in the industrial solid waste.

[0015] The beneficial effects of the above embodiments are as follows: In this utility evaluation and proportion optimization method, the industrial waste residues to be used are classified into two categories by pH test and X-ray fluorescence test: I - silicon-aluminum-based alkaline waste residues and II - gypsum-based waste residues. In the solidified silt soil, the type I waste residues mainly promote the pozzolanic reaction, while the type II waste residues mainly promote the formation of ettringite. Based on the roles of the waste residues, the pozzolanic enhancement effect k, the ettringite filling enhancement effect m, and the cementation damage effect d in the silt solidified soil are defined. The above effects can be quantified through the unconfined compressive strength test, so as to adjust the dosage ratio of the waste residues through the strength prediction formula. The strength prediction model of the waste residue-based silt solidified soil in this utility evaluation and proportion optimization method can not only quickly and effectively evaluate the strength of the silt solidified soil under different waste residue ratios, but also reasonably control the cementation and filling effects in the solidified silt soil and optimize the waste residue ratio.

[0016] Based on the above embodiments, the present application can be further improved as follows:

[0017] In one embodiment of the present application, in step S1, the discrimination criterion for the alkaline waste residue is that the pH is greater than 10; the discrimination criterion for the silicon-aluminum-based waste residue is that the sum of the contents of Al 2 O 3 and S i O 2 is greater than 50%; the discrimination criterion for the gypsum-based waste residue is that the content of SO 3 is greater than 40% and the content of CaO is greater than 20%.

[0018] In one embodiment of the present application, in step S1, for industrial solid wastes with significant chemical composition characteristics, the pH test and X-ray fluorescence test may not be performed. For example, fly ash and blast furnace slag can be directly classified as type I silicon-aluminum-based waste residues, and red mud can be directly classified as type I alkaline waste residues; phosphogypsum and desulfurized gypsum can be directly classified as type II waste residues.

[0019] In one embodiment of the present application, in step S2, based on the strength prediction model of the pure cement silt solidified soil, multiple groups of unconfined compressive strength tests of the pure cement silt solidified soil are carried out to determine A, n, and λ in formula (1).

[0020] In one embodiment of the present application, in step S2, when multiple groups of unconfined compressive strength tests of the pure cement silt solidified soil are carried out, at least two different initial water contents and at least two different water-cement ratios are included in multiple groups of the pure cement silt solidified soil.

[0021] In one embodiment of the present application, in step S3, according to the strength prediction model of the waste residue-based silt solidified soil, multiple groups of unconfined compressive strength tests with different waste residue dosage combinations are carried out to determine k in formula (2)1 , m 1 , d 1 .

[0022] In one embodiment of the present application, when conducting the unconfined compressive strength test in steps S2 and S3, the same curing age is selected. The influence of the curing age is not considered in both formula (1) and formula (2). Therefore, the same curing age should be selected when calibrating the coefficient through the unconfined compressive strength test.

[0023] In one embodiment of the present application, in step S3, k 1 mainly represents the promoting effect of the active ions directly provided by the ionic-based waste residue and the active ions in the silt clay minerals with enhanced alkalinity dissolution on the pozzolanic reaction. Since more cementitious substances such as calcium silicate hydrate are generated, the bonding strength between particles and aggregates is increased; m 1 mainly represents the promoting effect of the calcium sulfate hydrate provided by the gypsum-based waste residue on the formation reaction of ettringite. Since the quantity of ettringite increases, the filling and compaction effect of ettringite is enhanced, the contact between particles is increased, and the micro-density is improved, which is equivalent to reducing the moisture content and void ratio; d 1 mainly represents the damaging effect of the expansion of ettringite on the formed cementitious substances and bonding structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0025] Figure 1 is the step flow chart of a method for evaluating the utility and optimizing the ratio of solid waste in the treatment of silt soft soil in an embodiment of the present application;

[0026] Figure 2 is the trend chart of the unconfined compressive strength of silt solidified soil varying with the solid waste ratio in an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following further clarifies the present invention in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. After reading the present invention, those skilled in the art's various equivalent modifications of the present invention all fall within the scope defined by the appended claims of this application.

[0028] Embodiment:

[0029] As Figure 1As shown in the figure, a method for utility evaluation and ratio optimization of solid waste in silt and soft soil treatment includes the following steps:

[0030] S1: Conduct pH value tests and X-ray fluorescence tests on the industrial solid waste to be used to obtain the acidity, alkalinity and chemical composition characteristics of the industrial solid waste; according to the acidity, alkalinity and chemical composition characteristics, classify the industrial solid waste to be used into two categories: type I waste residue and type II waste residue. Type I waste residue is silico-aluminum-based waste residue or alkaline waste residue, and type II waste residue is gypsum-based waste residue;

[0031] Among them, the discrimination criterion for alkaline waste residue is that the pH is greater than 10; the discrimination criterion for silico-aluminum-based waste residue is that the sum of the contents of Al 2 O 3 and S i O 2 is greater than 50%; the discrimination criterion for gypsum-based waste residue is that the content of SO 3 is greater than 40% and the content of CaO is greater than 20%.

[0032] For industrial solid waste with significant chemical composition characteristics, pH value tests and X-ray fluorescence tests may not be required. For example, fly ash and blast furnace slag can be directly classified as type I silico-aluminum-based waste residue, and red mud can be directly classified as type I waste residue; phosphogypsum and desulfurized gypsum can be directly classified as type II waste residue.

[0033] S2: Construct a strength prediction model for pure cement silt solidified soil and conduct coefficient calibration. The specific expression of the strength prediction model for pure cement silt solidified soil is:

[0034]

[0035] Among them: q u is the uniaxial compressive strength; w is the initial water content of the silt soil; w / c is the water-cement ratio of the solidified silt, that is, the ratio of the initial water content of the silt soil to the cement content; A and n are fitting coefficients based on Abrams’ law; λ is the influence coefficient of the structure of the solidified soil;

[0036] Based on the strength prediction model of pure cement silt solidified soil, conduct unconfined compressive strength tests on multiple groups of pure cement silt solidified soil to determine A, n and λ in formula (1). Among them, when conducting unconfined compressive strength tests on multiple groups of pure cement silt solidified soil, at least 2 different initial water contents and at least 2 different water-cement ratios are included in multiple groups of pure cement silt solidified soil.

[0037] S3: Based on the strength prediction model of pure cement silt solidified soil, construct a strength prediction model for waste residue-based silt solidified soil and conduct coefficient calibration. The specific expression of the strength prediction model for waste residue-based silt solidified soil is as follows:

[0038]

[0039] wherein, q and r are the dosages of Class I waste residue and Class II waste residue respectively, and k 1 is the pozzolanic enhancement coefficient of Class I waste residue, and m 1 is the ettringite filling and enhancement coefficient of Class II waste residue, and d 1 is the cementation damage coefficient of Class II waste residue;

[0040] According to the strength prediction model of waste residue-based silt solidified soil, unconfined compressive strength tests with multiple groups of different waste residue dosage combinations are carried out to determine k 1 , m 1 , d 1 in formula (2).

[0041] Among them, k 1 mainly represents the promotion effect of active ions directly provided by ionic group waste residue and active ions in silt clay minerals dissolved by alkaline enhancement on the pozzolanic reaction. Since more cementitious substances such as hydrated calcium silicate are generated, the bonding strength between particles and aggregates is increased; m 1 mainly represents the promotion effect of calcium sulfate hydrate provided by gypsum-based waste residue on the ettringite formation reaction. Since the amount of ettringite increases, the filling and compaction effect of ettringite is enhanced, the contact between particles is increased, and the microscopic density is improved, which is equivalent to reducing the water content and void ratio; d 1 mainly represents the damage effect of the expansion of ettringite on the formed cementitious substances and cementation structure.

[0042] S4: Optimize and adjust the proportion of various waste residues according to the strength prediction model of waste residue-based silt solidified soil.

[0043] Furthermore, the influence of curing age is not considered in both formula (1) and formula (2). Therefore, the same curing age should be selected when calibrating the coefficients through unconfined compressive strength tests in steps S2 and S3.

[0044] The method for evaluating the utility and optimizing the proportion of solid waste in the treatment of silt and soft soil proposed by the present invention considers from the essential strength characteristics of solidified soil. The strength of solidified silt is determined by the cementation strength and the fabric characteristics. Among them, the cementation strength is determined by the water-cement ratio (w / c), and the water-cement ratio reflects the amount of cement per unit volume. Since the water content in silt is relatively high, it is generally considered that the hydration reaction and the pozzolanic reaction are sufficient. Therefore, the water-cement ratio can reflect the density of the cementation product. The fabric characteristics are mainly determined by characteristics such as pores, and the initial water content is the decisive index for determining the pore characteristics of solidified silt. Therefore, the strength expression of pure cement solidified silt is obtained by modifying the traditional Abrams’ law. The solid waste used in the treatment of silt and soft soil mainly affects the strength of solidified silt in two aspects. One is that it provides an alkaline environment to promote the dissolution of active silicon and aluminum ions in silt minerals or directly provides active silicon and aluminum ions, thus promoting the pozzolanic reaction and increasing the cementation strength. Therefore, this part of the effect is equivalent to increasing the cement content. The other is that it provides sulfate ions, thus promoting the formation of ettringite. Ettringite is an expansive mineral, and its formation and growth process can play a role in filling pores and promoting densification. Therefore, it is equivalent to reducing the water content. The expansion of ettringite will also damage the existing cementation, resulting in the deterioration of the microstructure and the reduction of the cementation strength, thus equivalent to reducing the cement content.

[0045] The present invention innovatively proposes an evaluation method for considering the solid waste effect from two aspects of cementation and fabric. Based on this strength evaluation and prediction method, the dosages of I-silicon-aluminum-based alkaline waste residue and II-gypsum-based waste residue can be optimized by obtaining the maximum value, etc.

[0046] The following uses an actual case to introduce in more detail the method for evaluating the utility and optimizing the proportion of industrial solid waste in cement solidified silt of the present invention. This case uses industrial solid waste red mud and phosphogypsum combined with cement to reinforce the marine silt in Lianyungang. The purpose is to optimize the proportion of red mud and phosphogypsum. The basic physical property indexes of the marine silt in Lianyungang are shown in Table 1. The cement used is standard Portland cement with a grade of 42.5.

[0047]

[0048] The specific implementation steps are as follows:

[0049] 1) Conduct pH value tests and x-ray fluorescence tests on the industrial solid waste to be used to obtain the acidity and alkalinity and chemical composition characteristics of the industrial solid waste. The measured pH values of red mud and phosphogypsum are 10.3 and 3.2 respectively, and the chemical compositions of red mud and phosphogypsum are shown in Table 2. According to the test results of acidity and alkalinity and chemical composition, the red mud is classified as type I waste residue, and the phosphogypsum is classified as type II waste residue.

[0050]

[0051] 2) Determine the coefficients in the strength prediction model of pure cement-silt solidified soil, namely the coefficients A, λ, and n in formula (1). Conduct three groups of tests, select 3 groups with different water contents and water-cement ratios for the tests, as shown in Table 3, and conduct unconfined compressive strength tests under standard curing conditions (20±2°C, 95% humidity).

[0052]

[0053] Solve according to the test results. When solving, use the Solver function in Excel to find the minimum value of the sum of squares of the differences between the predicted values and the measured values. Finally, the undetermined coefficients are obtained as A = 168783, λ = 3, and n = 1. Then formula (1) is:

[0054]

[0055] 3) Conduct 5 groups of unconfined compressive strength tests with different ratios of red mud to phosphogypsum for two different water contents and cement dosages respectively. The results are shown in Table 4.

[0056]

[0057]

[0058] Solve according to the test results. When solving, use the Solver function in Excel to find the minimum value of the sum of squares of the differences between the strength prediction values (i.e., formula (2), where A = 168783, λ = 3, and n = 1) and the strength measured values (test values), so as to determine the coefficients k 1 , m 1 , d 1 . Obtain:

[0059] When the initial water content is 80% and the cement dosage is 8%, formula (2) is:[[]]

[0060]

[0061] That is, k 1 = 0.133, m 1 = 0.05, d 1 = 0.045;

[0062] When the initial water content is 120% and the cement dosage is 12%, formula (2) is:[[]]

[0063]

[0064] That is, k 1 = 0.047, m 1 = 0.193, d 1 = 0.046.

[0065] 4) According to formula (2), the strength variation with the content of waste residue can be obtained, as Figure 2 shown. Figure 2 It is the strength variation of the silt solidified soil with the content of red mud under two water contents and cement contents (keeping the total amount of red mud and phosphogypsum as 10% of the dry soil mass). According to Figure 2 the evolution law of the strength can be obtained, and according to Figure 2 the optimal ratio of red mud to phosphogypsum here can be approximately obtained as 9:1, and based on this, the engineering practice can be guided to ensure the strength.

[0066] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for evaluating the effectiveness and optimizing the proportion of solid waste in sludge and soft soil treatment, characterized in that: The following steps are involved: S1: Conduct pH value test and x-ray fluorescence test on the industrial solid waste to be used, and divide the industrial solid waste to be used into two categories: Class I waste residue and Class II waste residue, wherein Class I waste residue is silicon-aluminum-based waste residue or alkaline waste residue, and Class II waste residue is gypsum-based waste residue; S2: Construct a strength prediction model for pure cement sludge-solidified soil and perform coefficient calibration; S3: Based on the strength prediction model of pure cement sludge solidified soil, a strength prediction model of waste residue-based sludge solidified soil is constructed, and coefficients are calibrated; S4: According to the waste residue-based silt solidified soil strength prediction model, the proportions of various types of waste residues are optimized and adjusted.

2. The utility evaluation and ratio optimization method according to claim 1, characterized in that: In the step S1, the criterion for determining the alkaline waste residue is that the pH value is greater than 10; the criterion for determining the silicon-aluminum-based waste residue is that the content of Al2O3 and S i The sum of the O2 contents is greater than 50%; the criteria for determining the gypsum-based waste residue are that the SO3 content is greater than 40% and the CaO content is greater than 20%.

3. The utility evaluation and ratio optimization method according to claim 1, characterized in that: In the step S1, the industrial solid waste with significant chemical composition characteristics can be directly classified.

4. The utility evaluation and ratio optimization method according to claim 1, characterized in that: The specific expression of the strength prediction model of pure cement sludge solidified soil is: Where: q u is the uniaxial compressive strength; w is the initial moisture content of silt soil; w / c is the water-cement ratio of solidified silt, that is, the ratio of the initial moisture content of silt soil to the cement content; A and n are fitting coefficients based on Abelm's law; λ is the influence coefficient of the solidified soil structure.

5. The utility evaluation and ratio optimization method according to claim 4 is characterized in that: The specific expression of the strength prediction model of the waste residue-based silt-solidified soil is as follows: Among them, q and r are the dosages of Class I waste slag and Class II waste slag respectively, k1 is the volcanic ash enhancement coefficient of Class I waste slag, m1 is the calcium aluminate filling enhancement coefficient of Class II waste slag, and d1 is the cementation damage coefficient of Class II waste slag.

6. The utility evaluation and ratio optimization method according to claim 5, characterized in that: In the step S2, based on the strength prediction model of the pure cement silt stabilized soil, multiple groups of unconfined compressive strength tests of the pure cement silt stabilized soil are carried out to determine A, n and λ in formula (1).

7. The utility evaluation and ratio optimization method according to claim 6, characterized in that: In the step S2, when the unconfined compressive strength test of multiple groups of pure cement sludge stabilized soil is carried out, the multiple groups of pure cement sludge stabilized soil contain at least 2 different initial moisture contents and at least 2 different water-cement ratios.

8. The utility evaluation and ratio optimization method according to claim 6, characterized in that: In step S3, according to the waste residue-based sludge solidified soil strength prediction model, multiple groups of unconfined compressive strength tests with different waste residue dosage combinations are carried out to determine k1, m1, and d1 in formula (2).

9. The utility evaluation and ratio optimization method according to claim 8, characterized in that: When carrying out the unconfined compressive strength test in steps S2 and S3, the same curing age is selected.

10. The utility evaluation and ratio optimization method according to claim 5, characterized in that: In step S3, k1 represents the promoting effect of active ions directly provided by ion-based waste slag and active ions in silt clay minerals dissolved by alkalinity on the volcanic ash reaction; m1 represents the promoting effect of hydrated calcium sulfate provided by gypsum-based waste slag on the formation reaction of ettringite; d1 represents the damaging effect of the expansion effect of ettringite on the generated cementitious material and cementing structure.

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