Recycled concrete precast pile mix proportion improvement method considering acid salt erosion influence

Abstract

The invention discloses a recycled concrete precast pile mix proportion improvement method considering acid salt erosion influence, which comprises the following steps: firstly, determining an initial replacement rate and a water cement ratio of a building solid waste recycled concrete precast pile, and then establishing a mechanical property estimation model and a durability estimation model; judging whether the concrete mechanical property and durability of the precast pile meet the design standard or not under the condition of acid salt erosion; if so, completing the mix proportion improvement; if not, the concrete mix proportion is adjusted, and the mechanical property and the durability are evaluated again according to the pre-estimation model until the optimal mix proportion meeting the design requirement is found. The design of the building solid waste recycled concrete precast pile is optimized, and scientific basis and technical support are provided for practical engineering application. The problem that in the prior art, research on building solid waste recycled aggregate in soft soil foundation treatment application is insufficient is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials science and technology, and particularly relates to a method for improving the mix proportion of recycled concrete precast piles considering the influence of acid-salt erosion and its application. Background Art

[0002] At present, there are the following three application ways for construction waste recycled aggregates (hereinafter referred to as recycled aggregates): First, replacing natural aggregates to prepare recycled concrete; Second, being used to produce building materials for various purposes such as hollow blocks, permeable bricks, and lightweight walls; Third, being used in road projects for subgrade, pavement, and ancillary facilities. In addition, in recent years, out of the consideration of resource conservation and environmental protection in foundation treatment, some scholars have started research on building waste piles. However, existing research mostly focuses on the general performance evaluation of recycled concrete. As precast piles for soft soil foundation treatment consume a large amount of natural concrete, such as crushed stones, sand, etc., there are few scholars who have done research on using recycled concrete as precast piles.

[0003] Using recycled aggregates to replace natural aggregates as precast pile materials can significantly improve the recycling rate of construction waste, reduce the accumulation of solid waste, and lower the consumption of natural resources. However, current research on recycled aggregates in foundation treatment is limited. Due to the low strength and unstable performance of recycled aggregates, the variation law of pile body performance is not clear. The mechanical properties and durability of recycled concrete vary in different environments, especially in foundation projects that require long-term stability. This uncertainty limits its application. In inland saline areas and coastal soft soil foundations, the soil moisture content is high, and it contains erosive sulfate ions and humus. These conditions exacerbate the durability problems of precast piles under acid and salt ion erosion, becoming a key factor affecting project safety. There is a lack of performance evaluation and improvement methods for acid-salt erosion environments in the existing technology, making it difficult to design high-performance precast pile concrete materials suitable for such environments in actual construction. In view of this, it is necessary to establish a set of mix proportion improvement methods for building waste precast piles applicable to acid-salt ion erosion environments. Summary of the Invention

[0004] The present invention provides a method for improving the mix proportion of recycled concrete precast piles considering the influence of acid-salt erosion, which improves the concrete based on the physical and chemical characteristics of recycled aggregates, environmental erosion factors, and long-term stability to ensure the reliability and durability of precast piles in complex environments.

[0005] The technical solution adopted by the present invention is that the method for improving the mix proportion of recycled concrete precast piles considering the influence of acid-salt erosion includes the following steps:

[0006] S1. Determine the initial replacement rate and water-cement ratio of the recycled concrete precast pile;

[0007] S2. Establish a mechanical property prediction model for recycled concrete precast piles to evaluate the mechanical properties of the concrete in the initial mix proportion of precast piles under erosion conditions;

[0008] S3. Establish a durability prediction model for recycled concrete precast piles to evaluate the durability of the concrete in the initial mix proportion of precast piles under erosion conditions;

[0009] S4. Determine whether the concrete properties of the initial mix proportion of precast piles and the durability of precast piles under acid-salt erosion conditions meet the design values; if they meet the design values, the mix proportion improvement is completed; if not, adjust the concrete mix proportion of the precast piles and re-predict the mechanical properties and durability based on the prediction models in S2 and S3 until the design value requirements are met.

[0010] Furthermore, the mechanical property prediction model for recycled concrete precast piles includes a compressive strength prediction model under erosion conditions, a splitting tensile strength prediction model under erosion conditions, an elastic modulus prediction model, and a slump prediction model.

[0011] Furthermore, the compressive strength prediction model under erosion conditions is specifically:

[0012]

[0013] where f cu is the compressive strength; t is the erosion time; f cu0 is the initial value of the compressive strength; f cuu is the stable value of the compressive strength under erosion conditions; w / c is the water-cement ratio; R c is the replacement rate; A 1 , B 1 , C 1 , D 1 , E 1 , A 2 , B 2 are fitting parameters; the fitting parameters of the compressive strength prediction model under erosion conditions are obtained by fitting the data of the compressive strength of recycled concrete precast pile specimens varying with the mix proportion in the erosion environment.

[0014] Furthermore, the splitting tensile strength prediction model under erosion conditions is specifically:

[0015] f ts0 =(A 1 (w / c)+B 1 (w / c) 2 +C 1 )×(D 1 R c +E 1 )

[0016]

[0017] Among them, f ts is the splitting tensile strength; t is the erosion time; f ts0 is the initial value of the splitting tensile strength; f tsu is the stable value of the splitting tensile strength under erosion conditions; w / c is the water-cement ratio; R c is the replacement rate; A 1 , B 1 , C 1 , D 1 , E 1 , A 2 , B 2 are fitting parameters, among which the fitting parameters of the splitting tensile strength prediction model under erosion conditions are obtained by fitting the data of the splitting tensile strength of recycled concrete precast pile specimens changing with the mix ratio in the erosion environment.

[0018] Furthermore, the elastic modulus prediction model is specifically:

[0019] E = Ae B(w / c)+C ×(DR c + E)

[0020] Among them, E is the elastic modulus; w / c: water-cement ratio; R c is the replacement rate; A, B, C, D, E are fitting parameters; among them, the fitting parameters of the elastic modulus prediction model are obtained by fitting the data of the elastic modulus of recycled concrete precast pile specimens changing with the mix ratio.

[0021] Furthermore, the slump prediction model is specifically:

[0022] S = (A(w / c) B + C)×(DR c + E)

[0023] Among them, S is the slump; w / c: water-cement ratio; R c is the replacement rate; A, B, C, D, E are fitting parameters; among them, the fitting parameters of the slump prediction model are obtained by fitting the data of the slump of recycled concrete precast pile specimens changing with the mix ratio.

[0024] Furthermore, the durability prediction model of the precast pile includes:

[0025] Durability prediction model of the precast pile in a clear water environment:

[0026]

[0027] Among them, m represents the quality index, t represents the erosion time, and a, b, c, and d are fitting parameters; among them, the fitting parameters in the durability prediction model of precast piles in a clear water environment are obtained by fitting based on the data of the quality of precast recycled concrete pile body specimens changing with the erosion time in a clear water environment;

[0028] Durability prediction model of precast piles in an erosion environment:

[0029]

[0030] Among them, e is the base of the natural logarithm, t represents the erosion time, and a, b, c, and d are fitting parameters; the fitting parameters in the durability prediction model of precast piles in an erosion environment are obtained by fitting based on the data of the quality of precast recycled concrete pile body specimens changing with the erosion time in an erosion environment.

[0031] Furthermore, it is characterized in that the determination methods of the data of the compressive strength of precast recycled concrete pile body specimens changing with the mix ratio, the splitting tensile strength of precast recycled concrete pile body specimens changing with the mix ratio, the elastic modulus of precast recycled concrete pile body specimens changing with the mix ratio, the slump of precast recycled concrete pile body specimens changing with the mix ratio, and the data of the quality of precast recycled concrete pile body specimens changing with the erosion time in an erosion environment are specifically as follows:

[0032] step1: Select the materials of precast recycled concrete pile body specimens and determine various mix ratios;

[0033] step2: Prepare precast recycled concrete pile body specimens and conduct tests on the compressive strength, splitting tensile strength, elastic modulus and slump test of the specimens; Fit the experimental results into a curve changing with the mix ratio; Determine the optimal mix ratio of the performance of precast recycled concrete pile body specimens;

[0034] step3: Simulate the erosion environment;

[0035] step4: Use the optimal mix ratio obtained in step2 to prepare precast recycled concrete pile body specimens for elastic modulus test, slump test and conduct compressive strength, splitting tensile strength and quality change tests under erosion conditions to obtain the data of the compressive strength of precast recycled concrete pile body specimens changing with the mix ratio, the data of the splitting tensile strength of precast recycled concrete pile body specimens changing with the mix ratio, the data of the elastic modulus of precast recycled concrete pile body specimens changing with the mix ratio, the data of the slump of precast recycled concrete pile body specimens changing with the mix ratio, and the data of the quality of precast recycled concrete pile body specimens changing with the erosion time in an erosion environment.

[0036] The beneficial effects of the present invention are:

[0037] The present invention proposes a method for improving the mix proportion of recycled concrete precast piles against the influence of acid-salt erosion. First, the initial replacement rate and water-cement ratio of the recycled concrete precast piles are determined, and prediction models for mechanical properties and durability performance are established to evaluate the performance of precast piles under different erosion conditions. By iteratively adjusting the mix proportion of the precast pile concrete until the design requirements are met, the long-term stability and reliability of the precast piles in the erosion environment are ensured. The present invention provides an improved path adapted to the characteristics of recycled concrete, including multiple mechanical property prediction models such as compressive strength, splitting tensile strength, elastic modulus, and slump, as well as durability prediction models in a clear water environment and an erosion environment. These models are obtained by fitting experimental data and can accurately predict the performance changes of recycled concrete precast piles under different conditions, providing a solid theoretical basis for practical engineering applications.

[0038] By considering the influence of different water-cement ratios and replacement rates on mechanical properties, the present invention can find the optimal mix proportion to optimize the mechanical properties of recycled concrete precast piles. In addition, durability performance prediction formulas are developed, enabling engineers to predict the service life of precast piles in a specific erosion environment during the design stage, enhancing the reliability and feasibility of the design scheme.

[0039] The present invention uses recycled aggregates to replace natural aggregates, which can not only improve the recycling rate of construction waste, reduce the accumulation of solid waste, but also reduce the consumption of natural resources. This is in line with the current global concept of green building and circular economy, and helps to promote the development of the construction industry towards a more environmentally friendly direction.

[0040] In summary, the present invention not only fills the technical gap in the application of recycled concrete precast piles in an acid-salt erosion environment, but also lays a foundation for the wide application of recycled concrete materials in the field of foundation treatment through scientific methodology and practical verification. Brief Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0042] Figure 1 It is the test results and fitting curves of the compressive strength of precast piles varying with the replacement rate under different water-cement ratios.

[0043] Figure 2 It is the test results and fitting curves of the splitting tensile strength of precast piles varying with the replacement rate under different water-cement ratios.

[0044] Figure 3 The test results and fitting curves of the elastic modulus of precast piles with the change of replacement ratio under different water-cement ratios.

[0045] Figure 4 The test results and fitting curves of the slump of precast piles with the change of replacement ratio under different water-cement ratios.

[0046] Figure 5 The test results and fitting curves of the compressive strength of precast piles with the change of water-cement ratio under different replacement ratios.

[0047] Figure 6 The test results and fitting curves of the splitting tensile strength of precast piles with the change of water-cement ratio under different replacement ratios.

[0048] Figure 7 The test results and fitting curves of the elastic modulus of precast piles with the change of water-cement ratio under different replacement ratios.

[0049] Figure 8 The test results and fitting curves of the slump of precast piles with the change of water-cement ratio under different replacement ratios.

[0050] Figure 9 The test results and fitting curves of the compressive strength of precast piles with the change of erosion time under different erosion environments.

[0051] Figure 10 The test results and fitting curves of the splitting tensile strength of precast piles with the change of erosion time under different erosion environments.

[0052] Figure 11 The change situation and fitting curves of the quality of precast piles with the change of erosion time in a clear water environment.

[0053] Figure 12 The change situation and fitting curves of the quality of precast piles with the change of erosion time under different erosion environments.

[0054] Figure 13 The compressive strength of precast piles with the change of replacement ratio under different water-cement ratios.

[0055] Figure 14 The splitting tensile strength of precast piles with the change of replacement ratio under the same water-cement ratio.

[0056] Figure 15 The elastic modulus of precast piles with the change of replacement ratio under different water-cement ratios.

[0057] Figure 16 The slump of precast piles with the change of replacement ratio under different water-cement ratios.

[0058] Figure 17 The flow chart of the mixing ratio improvement method of this embodiment. Specific implementation mode

[0059] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0060] This embodiment aims to determine the optimal mix ratio of precast pile concrete under the condition of acid salt erosion by systematically evaluating the mechanical properties and durability of recycled concrete. Specifically, the process first establishes a mechanical property prediction model for recycled concrete precast piles and uses the prediction model to comprehensively evaluate the performance of recycled concrete. After the evaluation, it will be judged whether the mechanical properties and durability of recycled concrete meet the design standards under the condition of acid salt erosion according to the obtained data. If the requirements are not met, the mix ratio of the concrete will be adjusted based on the evaluation results, and the established model will be used to conduct a performance evaluation again until a mix ratio plan that meets the design requirements is obtained.

[0061] In some specific embodiments, the method for establishing the mechanical property prediction model of recycled concrete precast piles is as follows: First, test the mechanical properties of recycled concrete with different mix ratios, and the mix ratios include replacement rate and water-cement ratio. In this embodiment, the components of precast pile concrete specifically include cement, water, fine aggregate, coarse aggregate, and necessary admixtures.

[0062] Example 1

[0063] S11, determination of specimen materials

[0064] There are 2 types of coarse aggregates used in this example: ① Recycled coarse aggregate with a particle size of 4.75 - 19 mm; ② Natural coarse aggregate with a particle size of 4.75 - 19 mm. The raw material of the recycled coarse aggregate is obtained by crushing and screening the demolition waste from a construction site in Changsha City. The raw material of the natural coarse aggregate is basalt. The apparent density, water absorption rate, moisture content, etc. of the recycled coarse aggregate and natural coarse aggregate are measured through apparent density test, crushing test, water absorption test, etc. The indexes are shown in Table 1.

[0065] Table 1 Various indexes of coarse aggregates

[0066]

[0067]

[0068] S12: Cement: Select ordinary Portland 52.5 cement from Zhucheng Yangchun Cement Co., Ltd. The performance indexes of the cement are shown in Table 2.

[0069] Water reducing agent: HLX (standard type) polycarboxylate high-performance water reducing agent is selected, and its performance indicators are shown in Table 3.

[0070] Fine aggregate: Natural river sand is selected, which is medium sand with a fineness modulus of 2.63.

[0071] Water: The water used in the test is tap water from Changsha City.

[0072] Table 2 Cement performance indicators

[0073]

[0074] Table 3 Polycarboxylate high-performance water reducing agent performance indicators

[0075]

[0076] S2, Mix proportion design of recycled concrete precast pile specimens

[0077] When designing the mix proportion of recycled concrete, due to the high water absorption rate of recycled aggregates, additional water needs to be added to achieve the required water-cement ratio. By this method, the consistency and adaptability of the concrete can be ensured to meet the engineering and structural requirements.

[0078] Since the main component of natural coarse aggregate is basalt, and the natural aggregates are mainly in two grades of 4.75mm - 9.5mm and 9.5mm - 19mm, in order to keep the same particle size as the natural aggregates, recycled aggregates of 4.75 - 9.5mm and 9.5 - 19mm are used in a ratio of 1:1. The replacement rate of recycled aggregates and the water-cement ratio are used as two variables in the design. The replacement rate gradually increases from 0% to 100%, and five water-cement ratios of 0.6, 0.55, 0.5, 0.45, and 0.4 are designed with reference to the application of precast piles in actual projects. Different replacement rates and water-cement ratios are used in the pile body of the precast pile, so as to systematically evaluate the influence of the replacement rate and the water-cement ratio on the performance of recycled concrete and find the best balance point between economic benefits and environmental benefits. The mix proportion designs under different replacement rates with water-cement ratios of 0.6, 0.55, 0.5, 0.45, and 0.4 are shown in Tables 4 - 8 as follows:

[0079] Table 4 Mix proportion of pile body with water-cement ratio of 0.6

[0080]

[0081]

[0082] Table 5 Mix proportion of pile body with water-cement ratio of 0.55

[0083]

[0084] Table 6 Mix proportion of pile body with water-cement ratio of 0.5

[0085]

[0086]

[0087] Table 70.45 Water-cement ratio for pile body

[0088]

[0089] Table 80.4 Water-cement ratio of pile body

[0090]

[0091] S3: Determine the best mix ratio

[0092] S31: Prepare specimens and conduct tests.

[0093] S311: According to different design parameters such as replacement rate, water-cement ratio, etc., cement, water, fine aggregate, coarse aggregate and necessary admixtures, i.e. water reducer, are proportioned, and after mixing the dry materials, water is added and stirred thoroughly.

[0094] S312: Immediately thereafter, a slump test is performed on the fresh mix to assess whether its fluidity is as expected.

[0095] S313: Then the freshly mixed material is placed into a three-piece test mold coated with a release agent to make test blocks and conduct test tests. The size of the compressive strength test and splitting tensile strength test specimens is 100mm×100mm×100mm, and the size of the elastic modulus test specimen is 100mm×100mm×300mm.

[0096] Place the three-unit test mold filled with the mixture in an indoor environment at a temperature of 20±5℃ for 24 to 48 hours for initial curing, then demould and number it. Then immediately place it in a standard curing room with a temperature of 20±2℃ and a relative humidity of more than 95% for standard curing.

[0097] In some specific embodiments, the tests include compressive strength, splitting tensile strength, elastic modulus test, and slump test.

[0098] S32: Analysis of test results.

[0099] In the test design, three samples were set for each group of data to ensure the reliability of the results, and the average value was taken as the final test data. Based on the test results, the relationship between the mechanical properties and replacement rate of the recycled aggregate prefabricated pile test block was determined as follows:

[0100] y=ax+b

[0101] Among them, y represents the mechanical property index, x represents the replacement rate, and a and b are parameters obtained by data fitting; the compressive strength, splitting tensile strength, elastic modulus and slump of the precast pile specimens made of recycled aggregate under different water-cement ratios are fitted according to the relationship between the performance of the precast pile specimens made of recycled aggregate and the replacement rate Figures 1-4 The fitting curves are obtained by Figures 1-4 It can be seen from the analysis of the test results in

[0102] Figures 1-4 that the compressive strength of recycled concrete is lower than that of natural concrete (replacement rate is 0%) in Figure 1 、 2 . It can be known from

[0103] that when the water-cement ratio is 0.45, the compressive strength and splitting tensile strength of recycled concrete are the highest. When the water-cement ratio is 0.6 and the replacement rate is 100%, the compressive strength and splitting tensile strength of recycled concrete reach the lowest values of 32.93 MPa and 4.76 MPa respectively Figure 1 It can be known from

[0104] that the compressive strength of recycled concrete with different replacement rates under different water-cement ratios all reaches more than 30 MPa, meeting the minimum requirement for the concrete strength of precast piles in the "Technical Code for Building Pile Foundations" (JGJ 94-2008). When the water-cement ratio is 0.55 and 0.6, the compressive strength of recycled concrete with a 100% replacement rate is 29.3% and 29.7% lower than that of natural concrete respectively Figure 2 It can be known from

[0105] that under the condition of a higher water-cement ratio, the influence of the replacement rate on the splitting tensile strength of concrete is not significant. The splitting tensile strength of recycled concrete with a 100% replacement rate is 6.9% and 2.1% lower than that of natural concrete respectively. When the water-cement ratio is 0.4, 0.45 and 0.5, the decrease in the splitting tensile strength is relatively large Figure 3 It can be known from

[0106] that the results of the elastic modulus are consistent with the change law of the strength. The elastic modulus of recycled concrete is lower than that of natural concrete (replacement rate is 0%). When the water-cement ratio is 0.45, the elastic modulus of recycled concrete is the highest. When the water-cement ratio is 0.6 and the replacement rate is 100%, the elastic modulus of recycled concrete reaches the lowest value of 26.2 GPa Figure 4It can be seen that as the replacement rate of recycled aggregate increases, the slump of recycled concrete shows a linear decreasing trend. As the water-cement ratio increases, the slump of recycled concrete shows a linear increasing trend. The slump of recycled concrete is lower than that of natural concrete (replacement rate of 0%). When the water-cement ratio is 0.6, the slump of recycled concrete is the highest, and the decrease in slump is relatively slow at this water-cement ratio. When the water-cement ratio is 0.4 and the replacement rate is 100%, the slump of recycled concrete reaches the lowest value of 34 mm.

[0107] Based on Figures 1-4 The corresponding coefficients of the prediction formulas for various compressive strengths (Table 9), the corresponding coefficients of the prediction formula for splitting tensile strength (Table 10), the corresponding coefficients of the prediction formula for elastic modulus (Table 11), and the corresponding coefficients of the prediction formula for slump (Table 12) are obtained.

[0108] Table 9 Corresponding coefficients of the prediction formula for compressive strength varying with replacement rate

[0109] Water-cement ratio Coefficient a Coefficient b <![CDATA[Fitting coefficient R 2 > 0.4 -0.19 61.29 0.99 0.45 -0.2 63.43 0.99 0.5 -0.12 54.91 0.96 0.55 -0.14 50.37 0.97 0.6 -0.14 48.53 0.97

[0110] Table 10 Corresponding coefficients of the prediction formula for splitting tensile strength varying with replacement rate

[0111]

[0112]

[0113] Table 11 Corresponding coefficients of the prediction formula for elastic modulus varying with replacement rate

[0114] Water-cement ratio Coefficient a Coefficient b <![CDATA[Fitting coefficient R 2 > 0.4 -0.064 36.31 0.99 0.45 -0.07 37.13 0.99 0.5 -0.063 35.03 0.88 0.55 -0.075 33.99 0.97 0.6 -0.05 31.09 0.94

[0115] Table 12 Corresponding coefficients of the prediction formula for slump varying with replacement rate

[0116] Water-cement ratio Coefficient a Coefficient b <![CDATA[Fitting coefficient R 2 > 0.4 -0.26 59.58 0.99 0.45 -0.25 61.25 0.99 0.5 -0.29 70.05 0.99 0.55 -0.31 74.34 0.98 0.6 -0.32 84.25 0.99

[0117] Determine the relationship between the compressive strength and water-cement ratio of recycled concrete according to the fitting curve:

[0118]

[0119] In the formula: f cu represents the compressive strength index, x represents the water-cement ratio, and a, b, c, and d are parameters obtained through data fitting. Based on the above formula, the compressive strength data of the precast pile specimens of recycled aggregate under different replacement rates are respectively fitted to obtain Figure 5 , and the corresponding coefficients of the prediction formula for compressive strength under different replacement rate conditions can be obtained, as shown in Table 13.

[0120] Table 13 Corresponding coefficients of the prediction formula for compressive strength varying with water-cement ratio

[0121] Replacement rate Coefficient a Coefficient b Coefficient c Coefficient d <![CDATA[Fitting coefficient R 2 <!-- 9 -->]]> 0％ 16.39 47.65 0.05 0.43 0.99 10％ 14.96 47.11 0.05 0.43 0.99 20％ 14.73 46.27 0.05 0.43 0.99 30％ 12.93 45.55 0.06 0.44 0.99 40％ 13.08 42.08 0.06 0.44 0.99 50％ 12.86 40.32 0.07 0.44 0.99 60％ 11.67 39.53 0.08 0.43 0.99 70％ 12.12 38.72 0.06 0.44 0.99 80％ 13.72 34.44 0.08 0.45 0.98 90％ 11.24 35.12 0.06 0.45 0.99 100％ 12.52 31.52 0.07 0.45 0.99

[0122] Determine the relationship between the splitting tensile strength and the water-cement ratio of recycled concrete according to the fitting curve:

[0123] f ts =(a + bx + cx 2 ) -1

[0124] In the formula: f ts represents the splitting tensile strength index, x represents the water-cement ratio, and a, b, and c are parameters obtained through data fitting.

[0125] According to the above formula, the splitting tensile strength of the precast pile body specimens of recycled aggregate under different replacement rates is respectively fitted to obtain Figure 6 , and the corresponding coefficients of the splitting tensile strength prediction formula under different replacement rates can be obtained (Table 14).

[0126] Table 14 Corresponding coefficients of the prediction formula for the change of splitting tensile strength with water-cement ratio

[0127] Replacement rate Coefficient a Coefficient b Coefficient c <![CDATA[Fitting coefficient R 2 > 0％ 0.8 -3.03 3.42 0.97 10％ 0.75 -2.76 3.08 0.99 20％ 0.71 -2.58 2.9 0.99 30％ 0.6 -2.06 2.29 0.98 40％ 0.64 -2.22 2.43 0.89 50％ 0.63 -2.2 2.48 0.99 60％ 0.8 -2.89 3.17 0.99 70％ 0.73 -2.6 2.92 0.95 80％ 0.68 -2.33 2.61 0.85 90％ 0.71 -2.42 2.65 0.79 100％ 0.71 -2.32 2.51 0.69

[0128] According to the test data, the relationship between the elastic modulus and the water-cement ratio of recycled concrete:

[0129]

[0130] In the formula: E represents the elastic modulus index, x represents the water-cement ratio, and a, b, c, and d are parameters obtained through data fitting.

[0131] According to the above formula, the elastic modulus of the precast pile body specimens of recycled aggregate under different replacement rates is respectively fitted to obtain Figure 7 , and the corresponding coefficients of the compressive strength prediction formula under different replacement rates can be obtained. See Table 15.

[0132] Table 15 Corresponding coefficients of the prediction formula for the change of elastic modulus with water-cement ratio

[0133] Replacement rate Coefficient a Coefficient b Coefficient c Coefficient d <![CDATA[Fitting coefficient R 2 > 0％ 15.9 20.86 0.17 0.45 0.99 30％ 6.38 28.72 0.08 0.43 0.94 50％ 8.83 24.78 0.11 0.44 0.99 70％ -4.78 32.37 0.06 0.57 0.99 100％ 4.92 25.59 0.07 0.45 0.98

[0134] According to the test data, the relationship between the slump and the water-cement ratio of recycled concrete:

[0135] S = ax b

[0136] In the formula: S represents the slump index, x represents the water-cement ratio, and a, b are parameters obtained through data fitting.

[0137] According to the above formula, the slump of the precast pile body specimens of recycled aggregate under different replacement rates is respectively fitted to obtain Figure 8 , and the corresponding coefficients of the slump prediction formula under different replacement rates can be obtained. See Table 16.

[0138] Coefficient corresponding to the estimated formula for the change of slump with water-cement ratio in Table 16

[0139]

[0140]

[0141] According to the test data, considering the workability, strength and economy of concrete, the water-cement ratio is determined to be 0.45 and the replacement rate of recycled aggregate is 30% as the optimal mix ratio. Under this replacement rate and water-cement ratio, the recycled aggregate concrete has the best comprehensive performance, which can not only meet the engineering requirements but also reduce the dependence on natural resources and achieve sustainable development.

[0142] After determining the optimal mix ratio, in this embodiment, the mixture for the recycled aggregate precast pile is prepared by using the aforementioned determined optimal mix ratio, and long-term erosion immersion tests are carried out by simulating the immersion, sulfate erosion and fulvic acid (humic acid) erosion environments. For comparative analysis, a control group is set up, and the natural aggregate precast pile with the same water-cement ratio is used as a reference. All specimens are made strictly according to the design mix ratio and are respectively placed in specific erosion solutions for long-term immersion treatment. Subsequently, the mass change rate test, compressive strength test and splitting tensile strength test are carried out on each group of pile bodies to comprehensively evaluate the performance differences between the recycled aggregate precast pile and the natural aggregate precast pile under different erosion environments.

[0143] S41. Simulate the erosion environment according to the erosion test simulation conditions set in Table 17:

[0144] Table 17 Action levels of sulfates and acids in water bodies

[0145]

[0146] VI-C, VI-D, VI-E indicate that the environmental levels are divided into moderate, severe and very severe.

[0147] This embodiment considers three representative erosion conditions: immersion, sulfate erosion and fulvic acid erosion as shown in Table 18. These conditions are set to simulate the chemical and physical erosion effects similar to the actual engineering environment, so as to evaluate the durability performance and its deterioration trend of the recycled concrete precast pile in these environments. Using industrial anhydrous sodium sulfate and fulvic acid as test reagents, the reagents are added with water and mixed evenly, placed in a corrosion-resistant plastic box, and sealed with a plastic cover to prevent the solution from evaporating. The chemical solutions prepared for the test are shown in Table 19.

[0148] Table 18 Setting of erosion test simulation conditions

[0149]

[0150] Table 19 Concentrations of Solutions of Different Types

[0151] Type Condition environment Sulfate - moderate <![CDATA[SO 4 2- solution with a concentration of 1000 mg / L]]> Sulfate - very severe <![CDATA[SO 4 2- Solution with a concentration of 10,000 mg / L]]> Humic acid - moderate Humic acid solution with pH value of 6 Humic acid - severe Humic acid solution with pH value of 5

[0152] S42: Specimens are fabricated and tested.

[0153] The test object is a recycled concrete precast pile, and the control group is a natural concrete precast pile with the same water-cement ratio. The best mix ratio determined in S3 is selected to prepare test blocks of recycled concrete precast piles. The mix ratio of the test blocks in this embodiment is shown in Table 20.

[0154] Table 20 Mix Ratio of Precast Piles (kg / m 3 )

[0155]

[0156] A total of 140 groups of 100mm×100mm×100mm test blocks of natural concrete precast piles and recycled concrete precast piles are fabricated according to the mix ratio in Table 18 above, with three test blocks in each group. After the specimens initially set for 24 hours at room temperature, they are demolded and transferred to standard curing conditions (temperature 20±2°C, relative humidity not less than 95%) for curing. After reaching 28 days of age, they are placed in the prepared solution for long-term erosion immersion.

[0157] The compressive strength test and splitting tensile strength test are carried out on the said specimens. At the set age, the compressive strength test and splitting tensile strength test are carried out respectively, and the average values of the compressive strength and splitting tensile strength of each group of specimens are obtained.

[0158] The mass change rate test is used to test the mass change of each pile body test block in the solution. The test blocks reaching the curing age are immersed in different erosion solutions and the original mass M of the test blocks is recorded 0 , and when reaching the test age, the specimens are taken out, the surface liquid is wiped off, and they are immediately weighed to obtain the mass M of the pile body test blocks at each age i . Calculate the mass change rate m:

[0159]

[0160] In the formula: m——mass change rate;

[0161] M i ——the mass of the pile body test block at any age;

[0162] M 0 ——the initial mass of the pile body test block.

[0163] S43: Analysis of Test Results.

[0164] Through the analysis of the test results, refer to Figure 9 、10 、11、12, CW-P NAC represents the natural concrete precast pile soaked in fresh water, CW-P RAC represents the recycled concrete precast pile soaked in fresh water; it can be seen that in the fresh water environment, with the increase of the erosion age, the compressive strength and splitting tensile strength of recycled concrete and natural concrete show a linear increasing trend, and the growth rate shows a decreasing trend. With the increase of the erosion age, the mass of recycled concrete and natural concrete shows a linear increasing trend, showing an obvious increase in mass within the first 30 days. The early mass increase is due to the water absorption and further hydration of the cement paste, because the hydration in 28 days may not be sufficient, and the mass of recycled concrete and natural concrete continues to increase during the 180-day soaking time, reaching about 0.7% and 0.4% growth respectively. The mass increase of recycled concrete is larger, which is due to the higher water absorption of recycled aggregates than natural aggregates.

[0165] Under the condition of sulfate erosion, with the increase of the erosion age, the compressive strength and splitting tensile strength of recycled concrete and natural concrete show a linear decreasing trend. This is mainly because the sulfate ions in the sulfate solution react with the calcium ions in the concrete to form ettringite, resulting in stress inside the concrete. With the continuous sulfate erosion and the continuous accumulation and expansion of the products, the micropores and microcracks inside the concrete expand and extend, leading to the reduction of the concrete strength. Under long-term sulfate erosion, the decrease of the compressive strength and splitting tensile strength of recycled concrete is more significant than that of natural concrete, and the decrease amplitude is faster and larger in the high-concentration sulfate solution. The main reasons are as follows: on the one hand, there is more old mortar in recycled concrete, and old mortar is more vulnerable to the influence of erosion products than new mortar. On the other hand, the high-concentration solution accelerates the chemical reaction between sulfate ions and cement hydration products. Taking the data of 180 days as an example, in the 1g / L SO 4 2- environment and 10g / L SO 4 2- environment, the compressive strength of recycled concrete decreased by 19.9% and 32.5% respectively, and the compressive strength of natural concrete decreased by 12% and 24.4% respectively. The compressive strength of recycled concrete decreased to a minimum of 39.3MPa. In the 1g / L SO 4 2- environment and 10g / L SO 4 2-Under the environment, the splitting tensile strength of recycled concrete decreased by 15.1% and 28.4% respectively, and that of natural concrete decreased by 9.5% and 15% respectively. The splitting tensile strength of recycled concrete decreased to a minimum of 5.21 MPa. With the increase of the erosion age, the mass of natural concrete and recycled concrete showed a trend of first increasing and then decreasing. The mass of recycled concrete decreased more significantly than that of natural concrete, and the decrease rate was faster and larger in high-concentration sulfate solution. Taking the data of 180 days as an example, in the 1g / L SO4 2- environment and 10g / L SO4 2- environment, the mass of recycled concrete decreased by 0.1% and 0.5% respectively, and the mass of natural concrete decreased by 0.06% and 0.3% respectively.

[0166] Under the condition of fulvic acid erosion, with the increase of the erosion age, the compressive strength and splitting tensile strength of natural concrete and recycled concrete showed a linear decreasing trend. This was mainly due to the strength loss caused by the corrosion of alkaline components in concrete by fulvic acid. The compressive strength and splitting tensile strength of recycled concrete decreased more significantly than those of natural concrete, and the decrease rate was faster and larger in the fulvic acid solution with a pH value of 5. This was because recycled concrete contained more micropores and microcracks, providing more channels for fulvic acid erosion. Taking the data of 180 days as an example, in the fulvic acid solution with a pH value of 6 and a pH value of 5, the compressive strength of recycled concrete decreased by 21% and 29.9% respectively, and the compressive strength of natural concrete decreased by 16.2% and 23.7% respectively. The compressive strength of recycled concrete decreased to a minimum of 40.8 MPa. In the fulvic acid solution with a pH value of 6 and a pH value of 5, the splitting tensile strength of recycled concrete decreased by 15.1% and 23.6% respectively, and the splitting tensile strength of natural concrete decreased by 14.3% and 20.2% respectively. The splitting tensile strength of recycled concrete decreased to a minimum of 5.56 MPa. With the increase of the erosion age, the mass of natural concrete and recycled concrete showed a trend of first increasing and then decreasing. Under the long-term fulvic acid erosion, the mass of recycled concrete decreased more significantly than that of natural concrete, and the decrease rate was faster and larger in the fulvic acid solution with a pH value of 5. Taking the data of 180 days as an example, in the fulvic acid solution with a pH value of 6 and a pH value of 5, the mass of recycled concrete decreased by 0.4% and 0.6% respectively, and the mass of natural concrete decreased by 0.3% and 0.5% respectively. From the above experimental data analysis, it can be seen that without external influencing factors, when the erosion age reaches 180 days, the erosion deterioration degree of concrete has tended to be stable. When the water-cement ratio is 0.45 and the replacement rate of recycled aggregate is 30%, the compressive strength of recycled concrete precast piles in different erosion environments reaches more than 30 MPa, meeting the minimum requirements for the concrete strength of precast piles in the "Technical Code for Building Pile Foundations" (JGJ 94-2008).

[0167] S44: Obtain the durability performance prediction formula and fit the mechanical property curve.

[0168] According to the test data, the relationship between the mechanical properties and the erosion time of the precast piles of recycled concrete under different erosion conditions can be expressed as:

[0169]

[0170] In the formula: s represents the mechanical property index, t represents the erosion time, and a, b, c, and d are parameters obtained through data fitting.

[0171] According to the above formula, the compressive strength and splitting tensile strength of the precast piles of recycled concrete under different erosion environments are respectively fitted to obtain Figure 9 、 10 , and the corresponding coefficients of each compressive strength prediction formula can be obtained, as shown in Table 21, and the corresponding coefficients of the splitting tensile strength prediction formula, as shown in Table 22.

[0172] Table 21 Corresponding coefficients of the prediction formula for the change of compressive strength with erosion time

[0173]

[0174]

[0175] Table 22 Corresponding coefficients of the prediction formula for the change of splitting tensile strength with erosion time

[0176] Erosion environment Coefficient a Coefficient b Coefficient c Coefficient d <![CDATA[Fitting coefficient R 2 > <![CDATA[CW-P NAC > 7.67 7.88 2.54 65.8 0.99 <![CDATA[CW-P RAC > 7.28 7.67 1.3 122.53 0.99 <![CDATA[1g / LSO 4 2- -P NAC > 7.67 6.62 2.41 122.05 0.98 <![CDATA[1g / LSO 4 2- -P RAC > 7.28 5.78 1.63 90.67 0.99 <![CDATA[10g / LSO 4 2- -P NAC > 7.66 5.98 1.56 104.13 0.99 <![CDATA[10g / LSO 4 2- -P RAC > 7.28 0.56 1.12 356.03 0.99 <![CDATA[PH6FA-P NAC > 7.66 6.39 2.31 73.15 0.99 <![CDATA[PH6FA-P RAC > 7.24 6.17 4.59 73.3 0.99 <![CDATA[PH5FA-P NAC > 7.65 5.17 1.72 128.55 0.99 <![CDATA[PH5FA-P RAC > 7.26 4.94 1.99 104.25 0.99

[0177] According to the test data, the relationship between the mass and the erosion time of the precast piles of recycled concrete in a clear water environment is as follows:

[0178]

[0179] In the formula: m represents the mass index, t represents the erosion time, and a, b, c, and d are parameters obtained through data fitting.

[0180] The relationship between the mass and the erosion time of the precast piles of recycled concrete in an erosion environment is as follows:

[0181]

[0182] In the formula: m represents the mass index, t represents the erosion time, and a, b, c, and d are parameters obtained through data fitting.

[0183] In this embodiment, the relationship between the mass and the erosion time is the durability prediction model of the precast piles of recycled concrete.

[0184] According to the above formula, the data of the mass of the recycled concrete precast pile specimens varying with the erosion time under the fresh water environment and the sulfate and fulvic acid erosion environments were respectively fitted to obtain Figure 11 and Figure 12 . The corresponding coefficients of the mass prediction formula under the fresh water environment can be obtained. See Table 23. The corresponding coefficients of the durability prediction formula under the sulfate and fulvic acid erosion environments can be obtained. See Table 24.

[0185] Table 23 Corresponding Coefficients of the Durability Prediction Formula for Recycled Concrete Precast Piles in Fresh Water Environment

[0186] Erosion environment Coefficient a Coefficient b Coefficient c Coefficient d <![CDATA[Fitting coefficient R 2 > <![CDATA[Clean water CW-P NAC > 2547.5 2558.17 5.16 21.65 0.99 <![CDATA[Clear water CW-P RAC > 2413.8 2429.75 0.89 1.17 0.99

[0187] Table 24 Corresponding Coefficients of the Prediction Formula for the Mass Varying with Erosion Time under Sulfate and Fulvic Acid Erosion Environments

[0188] Erosion environment Coefficient a Coefficient b Coefficient c Coefficient d <![CDATA[Fitting coefficient R 2 > <![CDATA[1g / LSO 4 2- -P NAC > 7.67 2532.08 32.47 53.81 0.97 <![CDATA[1g / LSO 4 2- -P RAC > 11.12 2405.97 35.88 52.88 0.98 <![CDATA[10g / LSO 4 2- -P NAC > 10.55 2510.59 56.73 39.27 0.99 <![CDATA[10g / LSO 4 2- -P RAC > 15.23 2408.34 58.6 31.66 0.99 <![CDATA[PH6FA-P NAC > 10.93 2550.18 47.87 40.92 0.99 <![CDATA[PH6FA-P RAC > 12.27 2435 49.48 40.23 0.99 <![CDATA[PH5FA-P NAC > 14.31 2557.17 57.9 26.22 0.99 <![CDATA[PH5FA-P RAC > 16.1 2422.28 55.52 26.56 0.99

[0189] S5. Establish a mechanical property prediction model for recycled concrete precast piles

[0190] Using the specimens and experimental environment as in S4, the mechanical property tests of the specimens with different mix ratios under erosion conditions were carried out; According to Figure 9 , 13 . The relationship between the stable value of the compressive strength of the recycled concrete precast pile under erosion conditions and the replacement rate and water-cement ratio is:

[0191]

[0192] f cu : Compressive strength; t: Erosion time; f cu0 : Initial value of compressive strength; f cuu : Stable value of compressive strength under erosion conditions; w / c: Water-cement ratio; R c : Replacement rate; A 1 , B 1 , C 1 , D 1 , E 1 , A 2 , B 2 : Fitting parameters, as shown in Tables 24 and 26.

[0193] Table 25 Corresponding Coefficients of the Compressive Strength Prediction Model under Different Erosion Conditions -

[0194] <![CDATA[Coefficient A 1 > <![CDATA[Coefficient B 1 > <![CDATA[Coefficient C 1 > <![CDATA[Coefficient D 1 > <![CDATA[Coefficient E 1 > <![CDATA[Fitting coefficient R 2 > 5.01 -1.26 1.58 -0.0124 4.28 0.91

[0195] Table 26 Corresponding Coefficients of the Compressive Strength Prediction Model under Different Erosion Conditions - II

[0196] Erosion environment <![CDATA[Coefficient f cu0 > <![CDATA[Coefficient f cuu > <![CDATA[Coefficient A 2 > <![CDATA[Coefficient B 2 > <![CDATA[Fitting coefficient R 2 > <![CDATA[CW-P NAC > 63.4 67.76 36.9 1.78 0.99 <![CDATA[CW-P RAC > 58.2 62.04 37.07 2.21 0.99 <![CDATA[1g / LSO 4 2- -P NAC > 63.57 54.84 82 3.03 0.99 <![CDATA[1g / LSO 4 2- -P RAC > 58.32 45.73 64.8 2.72 0.99 <![CDATA[10g / LSO 4 2- -P NAC > 63.2 39.99 112.25 1.63 0.99 <![CDATA[10g / LSO 4 2- -P RAC > 58.08 36.14 67.28 1.97 0.99 <![CDATA[PH6FA-P NAC > 63.4 49.49 99.06 1.97 0.99 <![CDATA[PH6FA-P RAC > 57.75 45.1 74.04 3.28 0.99 <![CDATA[PH5FA-P NAC > 62.74 45.9 93.01 2.99 0.99 <![CDATA[PH5FA-P RAC > 57.4 39.92 79.34 4 0.99

[0197] According toFigure 14 and Figure 10 According to the test data, the relationship between the stable value of the splitting tensile strength of recycled concrete precast piles under different erosion conditions and the replacement ratio and water-cement ratio can be expressed as:

[0198] f ts0 =(A 1 (w / c)+B 1 (w / c) 2 +C 1 )×(D 1 R c +E 1 )

[0199]

[0200] f ts : splitting tensile strength; t: erosion time; f ts0 : initial value of splitting tensile strength; f tsu : stable value of splitting tensile strength under erosion conditions; w / c: water-cement ratio; R c : replacement ratio; A 1 、B 1 、C 1 、D 1 、E 1 、A 2 、B 2 : fitting parameters, as shown in Tables 27 and 28.

[0201] Table 27 Corresponding Coefficients of the Estimation Model for Splitting Tensile Strength under Different Erosion Conditions -

[0202] <![CDATA[Coefficient A 1 > <![CDATA[Coefficient B 1 > <![CDATA[Coefficient C 1 > <![CDATA[Coefficient D 1 > <![CDATA[Coefficient E 1 > <![CDATA[Fitting coefficient R 2 > -3713.59 4212.63 462.72 0.000037 -0.02 0.9

[0203] Table 28 Corresponding Coefficients of the Estimation Model for Splitting Tensile Strength under Different Erosion Conditions -

[0204]

[0205]

[0206] According to Figure 15 the test data, the relationship between the elastic modulus of recycled concrete precast piles and the replacement ratio and water-cement ratio can be expressed as:

[0207] E = Ae B(w / c)+C ×(DR c +E)

[0208] E: elastic modulus; w / c: water-cement ratio; R c : replacement ratio; A, B, C, D, E: fitting parameters, as shown in Table 29.

[0209] Table 29 Coefficients of Elastic Modulus Prediction Model

[0210] Coefficient A Coefficient B Coefficient C Coefficient D Coefficient E <![CDATA[Fitting coefficient R 2 > -118.92 -0.78 -14.54 1639.86 -886097.48 0.92

[0211] According to Figure 16 the test data, the relationship between the slump of recycled concrete precast piles and the replacement ratio and water-cement ratio can be expressed as:

[0212] S=(A(w / c) B +C)×(DR c +E)

[0213] S: slump; w / c: water-cement ratio; R c : replacement ratio; A, B, C, D, E: fitting parameters.

[0214] Table 30 Coefficients of Slump Prediction Model

[0215] Coefficient A Coefficient B Coefficient C Coefficient D Coefficient E <![CDATA[Fitting coefficient R 2 > 15.5 4.05 3 -0.07 17.24 0.98

[0216] To sum up, the present invention conducts research on using recycled aggregates to replace natural aggregates for precast piles, and studies the variation laws of the pile body performance of recycled concrete precast piles under long-term immersion, sulfate erosion and fulvic acid erosion conditions respectively, and compares with natural concrete precast piles under the same conditions, and draws the following conclusions:

[0217] 1. Recycled aggregates have higher water absorption rate and lower apparent density compared with natural aggregates. The differences in these physical properties have a significant impact on the workability and mechanical properties of recycled concrete. With the increase of the recycled aggregate replacement ratio, the mechanical properties of recycled concrete basically show a linear decreasing trend. With the increase of the water-cement ratio, the mechanical properties of recycled concrete show a trend of first increasing and then decreasing. When the water-cement ratio is 0.45 and the recycled aggregate replacement ratio is 30%, the comprehensive performance is the best. When the water-cement ratio is 0.6 and the replacement ratio is 100%, the compressive strength of recycled concrete reaches the lowest value of 32.93 MPa. When the water-cement ratio is 0.6 and the replacement ratio is 70%, the splitting strength of recycled concrete reaches the lowest value of 4.43 MPa. The compressive strength of recycled concrete with different replacement ratios at different water-cement ratios all reaches more than 30 MPa, meeting the minimum requirement for the concrete strength of precast piles in the Technical Code for Building Pile Foundations (JGJ94-2008).

[0218] 2. By simulating various erosion environments (immersion in water, sulfate erosion, and fulvic acid erosion), it is found that under the immersion environment, the mass, compressive strength, and splitting tensile strength of recycled concrete all show a trend of first increasing and then leveling off with the increase of erosion age. Under the sulfate and fulvic acid erosion environments, the mass of recycled concrete shows a trend of first increasing and then decreasing with the increase of erosion age, and the compressive strength and splitting tensile strength show a decreasing trend, and the decline is faster and greater in the 10 g / L sodium sulfate solution and the pH 5 fulvic acid solution. Therefore, appropriate protective measures should be taken in environments rich in sulfates and fulvic acids. Moreover, for the recycled concrete precast piles with a water-cement ratio of 0.45 and a recycled aggregate replacement rate of 30%, the compressive strength under different erosion environments reaches more than 30 MPa, meeting the minimum requirements for the concrete strength of precast piles in the "Technical Code for Building Pile Foundations" (JGJ 94-2008). Generally speaking, considering the mechanical properties and durability, concrete containing recycled aggregates is suitable for making precast piles.

[0219] Example 2

[0220] Such as Figure 17 , a method for improving the mix proportion of recycled concrete precast piles considering the influence of acid salt erosion, which is specifically carried out according to the following steps:

[0221] S1. Set the stable value of the minimum compressive strength required by the design to 30 MPa, the stable value of the minimum splitting tensile strength required by the design to 4 MPa, the stable value of the minimum elastic modulus required by the design to 30 GPa, and the slump required by the design to 40 mm to 60 mm.

[0222] S2. Select the mix proportion of recycled concrete precast piles with a recycled aggregate replacement rate of 100% and a water-cement ratio of 0.4.

[0223] S3. Substitute the mix proportion into the prediction formula for calculation, and find that the stable value of the compressive strength after 180 days of erosion in the pH 5 fulvic acid solution environment is 40.09 MPa, the stable value of the splitting tensile strength after 180 days of erosion in the pH 5 fulvic acid solution environment is 5.13 MPa, the elastic modulus is 30.46 GPa, and the slump is 34 mm. It is found that the slump does not meet the design value, and the mix proportion is readjusted to the mix proportion of recycled concrete precast piles with a recycled aggregate replacement rate of 30% and a water-cement ratio of 0.45.

[0224] S4. Substitute the adjusted mix proportion into the prediction formula for calculation, and find that the stable value of the compressive strength after 180 days of erosion in the pH 5 fulvic acid solution environment is 40.43 MPa, the stable value of the splitting tensile strength after 180 days of erosion in the pH 5 fulvic acid solution environment is 5.39 MPa, the elastic modulus is 33.95 GPa, and the slump is 54.67 mm. All four indicators meet the design values, and the recycled concrete precast piles under the conditions of a 30% replacement rate and a water-cement ratio of 0.45 can be used for this project.

[0225] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for the related parts, reference can be made to the partial description of the method embodiment.

[0226] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. A method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion, characterized in that: The following steps are involved: S1. Determine the initial replacement rate and water-cement ratio of recycled concrete precast piles; S2. Establish a model for estimating the mechanical properties of recycled concrete precast piles to evaluate the concrete mechanical properties of the initial mix ratio of precast piles under erosion conditions; S3. Establish a durability estimation model for recycled concrete precast piles to evaluate the durability of concrete of the initial mix ratio of precast piles under erosion conditions; S4. Determine whether the concrete performance of the initial mix ratio of the precast piles and the durability performance of the precast piles under acid salt erosion conditions meet the design values; if they meet the design values, the mix ratio is improved; if not, the precast pile concrete mix ratio is adjusted and the mechanical properties and durability performance are re-estimated based on the estimation models of S2 and S3 until the design value requirements are met.

2. The method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to claim 1, characterized in that: The mechanical property prediction model of the recycled concrete precast pile includes a compressive strength prediction model under erosion conditions, a splitting tensile strength prediction model under erosion conditions, an elastic modulus prediction model, and a slump prediction model.

3. A method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to claim 2, characterized in that: The compressive strength estimation model under the erosion conditions is specifically as follows: Among them, f cu is the compressive strength; t is the erosion time; f cu0 is the initial value of compressive strength; f cuu is the stable compressive strength under erosion conditions; w / c is the water-cement ratio; R c is the replacement rate; A1, B1, C1, D1, E1, A2, and B2 are fitting parameters; the fitting parameters of the compressive strength estimation model under erosion conditions are obtained based on the data of compressive strength of recycled concrete precast pile specimens changing with mix ratio under erosion environment.

4. The method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to claim 2, characterized in that: The splitting tensile strength estimation model under the erosion condition is specifically as follows: f ts0 =(A1(w / c)+B1(w / c) 2 +C1)×(D1R c +E1) Among them, f ts is the splitting tensile strength; t is the erosion time; f ts0 is the initial value of splitting tensile strength; f tsu is the stable value of splitting tensile strength under erosion conditions; w / c is the water-cement ratio; R c is the replacement rate; A1, B1, C1, D1, E1, A2, and B2 are fitting parameters, among which the fitting parameters of the splitting tensile strength estimation model under erosion conditions are obtained based on the data of the splitting tensile strength of the recycled concrete precast pile specimens changing with the mix ratio under erosion environment.

5. The method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to claim 2, characterized in that: The elastic modulus estimation model is specifically: And=Ae B(w / c)+C ×(DR c +E) Where, E is elastic modulus; w / c: water-cement ratio; R c is the replacement rate; A, B, C, D, and E are fitting parameters; the fitting parameters of the elastic modulus estimation model are obtained based on the data of the elastic modulus of the recycled concrete precast pile specimen changing with the mix ratio.

6. The method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to claim 2, characterized in that: The slump prediction model is specifically: S=(A(w / c) B +C)×(DR c +E) Where S is slump; w / c: water-cement ratio; R c is the replacement rate; A, B, C, D, and E are fitting parameters; among them, the fitting parameters of the slump prediction model are obtained based on the data of slump change of recycled concrete precast pile specimens with mix ratio.

7. The method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to claim 1, characterized in that: The precast pile durability prediction model includes: Durability prediction model of precast piles in clear water environment: Wherein, m represents the quality index, t represents the erosion time, and a, b, c, and d are fitting parameters; wherein, the fitting parameters in the durability estimation model of precast piles in a clean water environment are obtained by fitting the data of the mass variation of the recycled concrete precast pile body test block in a clean water environment with the erosion time; Durability prediction model of precast piles in erosive environment: Wherein, e is the base of the natural logarithm, t represents the erosion time, and a, b, c, and d are fitting parameters; the fitting parameters in the durability estimation model of precast piles under erosion environment are obtained by fitting based on the data of the mass change of recycled concrete precast pile body test block under erosion environment with erosion time.

8. A method for improving the mix ratio of recycled concrete precast piles considering the influence of acid salt erosion according to any one of claims 3 to 7, characterized in that: The method for determining the data of compressive strength of recycled concrete precast pile body test block under the corrosive environment as a function of mix ratio, the data of splitting tensile strength of recycled concrete precast pile body test block under the corrosive environment as a function of mix ratio, the data of elastic modulus of recycled concrete precast pile body test block as a function of mix ratio, the data of slump of recycled concrete precast pile body test block as a function of mix ratio, and the data of mass of recycled concrete precast pile body test block under the corrosive environment as a function of erosion time is specifically as follows: Step 1. Select the recycled concrete prefabricated pile test block material and determine various mix ratios; Step 2, prepare recycled concrete prefabricated pile test blocks and conduct compressive strength, splitting tensile strength, elastic modulus and slump tests on the test blocks; fit the experimental results into a curve that changes with the mix ratio; determine the optimal mix ratio of the recycled concrete prefabricated pile test block performance; Step 3, simulate erosion environment; step4. Use the best mix ratio obtained in step 2 to prepare recycled concrete precast pile test blocks for elastic modulus test, slump test, and compressive strength, splitting tensile strength, and mass change tests under erosion conditions to obtain data on compressive strength of recycled concrete precast pile test blocks changing with mix ratio under erosion environment, splitting tensile strength of recycled concrete precast pile test blocks changing with mix ratio under erosion environment, elastic modulus of recycled concrete precast pile test blocks changing with mix ratio, slump of recycled concrete precast pile test blocks changing with mix ratio, and mass of recycled concrete precast pile test blocks changing with erosion time under erosion environment.

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