Method for preparing pre-soaked CFG pile with modified recycled aggregate and method for evaluating long-term performance thereof

Abstract

The application discloses a preparation method and a long-term performance evaluation method of a pre-soaking slurry modified recycled aggregate CFG pile, and the preparation method comprises the following steps: mixing sodium hydroxide solution and modified admixture according to a mass ratio of 1:0.05-1:0.2, uniformly stirring, and standing for 2-10 min, so that the two mixtures are fully reacted to obtain an alkaline slurry; pouring the air-dried recycled coarse aggregate into the alkaline slurry, soaking for 2-10 h, taking out and airing, and reserving for use. A water absorption rate prediction formula and a compressive strength prediction formula are established to perform long-term performance evaluation. The application can judge the water absorption rate and strength change of the pre-soaking slurry modified recycled aggregate CFG pile in different periods under an engineering application environment, and determine the design strength of the modified recycled aggregate CFG pile meeting the engineering requirements under the environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of recycled aggregate pile performance evaluation, and relates to a preparation method and long-term performance evaluation method of pre-soaking slurry modified recycled aggregate CFG piles. BACKGROUND

[0002] Soft soil foundation is widely distributed in China, and has the characteristics of high water content and large settlement. Therefore, soft soil foundation treatment is often carried out before road engineering construction. CFG pile is an effective and economical pile used for soft soil foundation treatment at present, but a large amount of natural aggregate such as gravel and sand is consumed. At the same time, with the emphasis of the state on environmental protection, the Ministry of Natural Resources, the Ministry of Ecology and Environment and other departments have successively issued documents to strictly limit behaviors such as mountain quarrying and river sand cutting. It can be predicted that the materials such as sand and gravel required for future engineering construction will be in serious shortage.

[0003] Recycled aggregate is used to replace natural aggregate for CFG pile body material, which can realize the recycling of recycled aggregate to a greater extent, effectively consume construction solid waste, and reduce the consumption of natural resources. However, the recycled aggregate has lower strength than the natural aggregate, the performance change rule of the pile body is not clear, the aggregate performance is unstable, and a large amount of old cement mortar remains on the surface of the recycled aggregate. In addition, a large number of fine cracks are generated in the aggregate during the crushing process, the overall water absorption rate is high, and the strength is low. Therefore, these shortcomings limit the popularization and use of recycled aggregate. It is very important to take appropriate modification treatment on the recycled aggregate to reduce the water absorption rate and crushing value. At present, the modification effect of physical modification (such as mechanical grinding method, pre-heating method, etc.) is general and the cost is high; the modification period of microbial modification (such as bacillus precipitation method, bacterial degradation method, etc.) is usually long; chemical modification (such as hydrochloric acid soaking, low-concentration sulfuric acid pretreatment, etc.) brings environmental pollution problems; and most of the existing modified materials and modification methods do not consider the economy, environmental protection and periodicity.

[0004] Therefore, it is necessary to establish a long-term performance evaluation method of modified recycled aggregate CFG pile. SUMMARY

[0005] In order to solve the above problems, the application provides a preparation method and long-term performance evaluation method of pre-soaking slurry modified recycled aggregate CFG pile, which judges the water content and strength change of the pre-soaking slurry modified recycled aggregate CFG pile at different periods in the engineering application environment, and determines the design strength of the modified recycled aggregate CFG pile meeting the engineering requirements in the environment.

[0006] The technical scheme adopted by the application is a preparation method of pre-soaking slurry modified recycled aggregate CFG pile, comprising the following steps:

[0007] S1, mixing sodium hydroxide solution and modified admixture according to mass ratio 1:0.05-1:0.2, stirring uniformly, standing for 2-10 min, making two mixtures fully react, obtaining alkaline slurry;

[0008] S2, soaking the air-dried recycled coarse aggregate in the alkaline slurry for 2-10 h, taking out and airing, standby.

[0009] Further, the modified admixture is silica fume, slag powder or steel slag.

[0010] Further, the particle size of the recycled coarse aggregate is 5-20 mm.

[0011] Further, the mass fraction of the sodium hydroxide solution is 5-15%.

[0012] A long-term performance evaluation method of a pre-soaking slurry modified recycled aggregate CFG pile, the pre-soaking slurry modified recycled aggregate CFG pile is prepared by the method of claim 1, comprising the following steps:

[0013] The mass change of the pre-soaking slurry modified recycled aggregate CFG pile body test block under water immersion condition at different ages is tested to obtain the corresponding water absorption rate, and then the water absorption rate of the pre-soaking slurry modified recycled aggregate CFG pile body test block under water immersion condition is fitted to obtain the fitting formula of water absorption rate and time:

[0014] W=-Ae (-t / B) +C

[0015] Wherein, W represents the water absorption rate of the pre-soaking slurry modified recycled aggregate CFG pile body under water immersion condition, t represents time, A, B and C are fitting parameters.

[0016] Further, the following steps are further included:

[0017] The compressive strength change of the pre-soaking slurry modified recycled aggregate CFG pile body test block under water immersion condition at different ages is tested, and then the compressive strength of the pre-soaking slurry modified recycled aggregate CFG pile body test block under water immersion condition is fitted to obtain the fitting formula of compressive strength and time:

[0018]

[0019] Wherein, q represents the compressive strength of the pre-soaking slurry modified recycled aggregate CFG pile body under water immersion condition, t represents time, D, M and N are fitting parameters, and dx represents the slope of the compressive strength change.

[0020] Further, if the engineering site is completely water immersion condition, the fitting formula of water absorption rate and time is:

[0021] W=-2.18e (-t / 23.28) +2.29.

[0022] Further, if the engineering site is completely immersed in water, the compressive strength and time fitting formula is:

[0023]

[0024] Further, the mass change of the pile test block is calculated according to the following formula:

[0025]

[0026] In the formula: m - mass change rate;

[0027] M i - the mass of the pile test block at any age;

[0028] M0 - the initial mass of the pile test block.

[0029] The application respectively adopts three different alkaline slurries to modify the recycled coarse aggregate, observes the micro morphology of the modified recycled coarse aggregate by using a Zeiss EVO18 type scanning electron microscope, analyzes the change of the crushing value and water absorption rate of the recycled aggregate under different mixing amounts and different modification times of the three modified materials, and proposes that the silica ash modification is the most ideal modification method. The CFG pile mixture is prepared by using the silica ash modified recycled aggregate, the recycled aggregate and the natural aggregate respectively, the simulation conditions of the immersion environment are set according to the experimental requirements, the experimental objects are under the completely immersed condition and under the curing room condition as the control group, the test pieces are made according to the designed mixing ratio, and are respectively immersed in the water plastic bucket for a long time and cured under the standard curing condition. Then, the mass change rate test and the compressive strength test are carried out on each pile body, and the water absorption rate prediction formula of the pre-soaking slurry modified recycled aggregate CFG pile under the immersion condition is obtained: W=A e (-t / B) +C, wherein A, B and C are constants, and the compressive strength prediction formula of the pre-soaking slurry modified recycled aggregate CFG pile body test block is obtained by fitting the compressive strength: In the formula: D, M and N are constants, and dx represents the slope of the change of the compressive strength.

[0030] The beneficial effects of the application are:

[0031] 1. The application can obtain more economical and efficient pre-soaking slurry recycled aggregate modification methods through specific modification methods, improve the pile body performance of the recycled aggregate CFG pile, and take into account the economy, environmental protection and periodicity.

[0032] 2. The application provides a scientific basis for engineering design of the modified recycled aggregate CFG pile, and the strength stability value of the modified recycled aggregate CFG pile in a long-term immersion working environment can be determined through the compression strength estimation formula, and then the design strength of the modified recycled aggregate CFG pile meeting engineering requirements in the environment can be determined.

[0033] 3. The application provides a channel for how to consume construction solid waste, and the construction solid waste is used in the CFG pile and applied to foundation treatment, so that the construction solid waste can be consumed in a large amount and effectively utilized.

[0034] 4. The compression strength of the recycled aggregate CFG pile in a long-term immersion working environment decreases with time, and a certain degree of maintenance is needed in the later period to ensure normal work of the pile body, and the method provided by the application can provide calculation services for determining whether the maintenance standard is met and whether the work requirements of the pile body are met in the construction and maintenance process of the recycled aggregate CFG pile, and the safety of the recycled aggregate CFG pile is improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can be obtained without creative labor on the basis of these drawings.

[0036] Figure 1a is the physical map of the modified raw material silica ash in the embodiment of the application.

[0037] Figure 1b is the physical map of the modified raw material slag powder in the embodiment of the application.

[0038] Figure 1c is the physical map of the modified raw material steel slag in the embodiment of the application.

[0039] Figure 2a is the physical map of the unmodified recycled aggregate in the embodiment of the application.

[0040] Figure 2b is the physical map of the recycled aggregate modified by silica ash in the embodiment of the application.

[0041] Figure 2c is the physical map of the recycled aggregate modified by slag powder in the embodiment of the application.

[0042] Figure 2d is the physical map of the recycled aggregate modified by steel slag in the embodiment of the application.

[0043] Figure 3a is the electron microscope map of the unmodified recycled aggregate in the embodiment of the application.

[0044] Figure 3b is the electron microscope graph of the modified recycled aggregate by silica ash in the embodiment of the present application.

[0045] Figure 3c is the electron microscope graph of the modified recycled aggregate by slag powder in the embodiment of the present application.

[0046] Figure 3d is the electron microscope graph of the modified recycled aggregate by steel slag in the embodiment of the present application.

[0047] Figure 4a is the change of the crushing value of the recycled aggregate with time when the modifier content is 10% in the embodiment of the present application.

[0048] Figure 4b is the change of the water absorption rate of the recycled aggregate with time when the modifier content is 10% in the embodiment of the present application.

[0049] Figure 4c is the change of the crushing value of the recycled aggregate with time when the modifier content is 20% in the embodiment of the present application.

[0050] Figure 4d is the change of the water absorption rate of the recycled aggregate with time when the modifier content is 20% in the embodiment of the present application.

[0051] Figure 4e is the change of the crushing value of the recycled aggregate with time when the modifier content is 30% in the embodiment of the present application.

[0052] Figure 4f is the change of the water absorption rate of the recycled aggregate with time when the modifier content is 30% in the embodiment of the present application.

[0053] Figure 4g is the change of the crushing value of the recycled aggregate with time when the modifier content is 40% in the embodiment of the present application.

[0054] Figure 4h is the change of the water absorption rate of the recycled aggregate with time when the modifier content is 40% in the embodiment of the present application.

[0055] Figure 5 is the comparison of the test results before and after the modification of the recycled aggregate in the embodiment of the present application.

[0056] Figure 6a is the change of the mass of the CFG pile test block of the modified recycled aggregate by pre-impregnation paste in the embodiment of the present application before and after the immersion.

[0057] Figure 6b is the change of the mass of the CFG pile test block of the recycled aggregate in the embodiment of the present application before and after the immersion.

[0058] Figure 6cis the mass change of the CFG pile test block of the natural aggregate in the embodiment of the present application before and after immersion.

[0059] Figure 7 is the fitting curve of the moisture content of the pre-soaked slurry modified recycled aggregate changing with time in the embodiment of the present application.

[0060] Figure 8 is the water absorption change of the test block in the embodiment of the present application.

[0061] Figure 9 is the compressive strength change of the test block in the embodiment of the present application.

[0062] Figure 10 is the fitting curve of the compressive strength of the pre-soaked slurry modified recycled aggregate changing with time in the embodiment of the present application. DETAILED DESCRIPTION

[0063] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0064] Embodiment 1,

[0065] A preparation method of a pre-soaked slurry modified recycled aggregate CFG pile, comprising the following steps:

[0066] Selecting modified raw materials;

[0067] Recycled aggregate: select recycled coarse aggregate with a particle size of 5-20 mm, and the indexes are shown in Table 1.

[0068] Table 1 Test indexes of recycled coarse aggregate

[0069] Particle size (mm) Water absorption rate (%) Crushing value (%) Apparent density (kg / m 3 )]]> 5-10 8.63 29.3 1912 10-20 8.39 27.6 1962

[0070] Modified material: through investigation and analysis, considering factors such as economy, environmental protection and acquisition method, three kinds of industrial solid wastes or by-products, i.e., silica fume, slag powder and steel slag, are selected as the modified material in this test.

[0071] (1) Silica fume: silica fume (Silica Fume, abbreviated as SF) produced by Hebei Sirui Company is used in this test, which is gray powder with a refractoriness >1600℃ and a density of 1680kg / m 3 , wherein more than 80% of the fineness is less than 1μm, and the average particle size is 0.1-0.3μm.

[0072] (2) Slag powder: S95 slag powder (SP) produced by Hebei Tianhui Technology Co., Ltd. was used in the experiment. The appearance was white powder, the density was 2850 kg / m 3 , the flow ratio was 98%, and the fineness was 400 mesh.

[0073] (3) Steel slag: Steel slag (SS) produced by Henan Dingnuo Co., Ltd. was used in the experiment. The appearance was black gray powder, the density was 3270 kg / m 3 , the specific surface area was 400 m 2 / kg, the fineness was 150 mesh, the Cl ion content was 0.02%, and the 7-day and 28-day activity indexes were 71.63% and 84.27%, respectively.

[0074] The chemical compositions of the three modified materials are shown in Table 2, and the physical comparison is shown in Table 3. Figures 1a-1c

[0075] Table 2 Chemical composition of three modified materials (mass fraction %)

[0076] Group SiO2 CaO Al2O3 Fe2O3 MgO MnO Others Silica fume 90.0 5.4 1.2 1.1 0.8 —— 1.5 Slag powder 34.1 39.1 16.5 0.3 6.8 0.2 3.0 Steel slag 14.2 40.1 2.2 27.1 10.5 2.6 3.3

[0077] Three different alkaline slurries were used for the modification treatment of recycled coarse aggregate. The alkaline slurry was a mixture of alkaline aqueous solution and modified admixture. The alkaline aqueous solution was a sodium hydroxide solution with a mass fraction of 5-15%, and the modified admixture was one of the following three: (I) silica fume, (II) slag powder, and (III) steel slag.

[0078] S1, the sodium hydroxide solution with a mass fraction of 5-15% and the modified admixture were mixed in a mass ratio of 1:0.05-1:0.2, stirred uniformly, and allowed to stand for 2-10 min to allow the two mixtures to react fully, obtaining an alkaline slurry;

[0079] S2, the air-dried recycled coarse aggregate was soaked in the alkaline slurry for 2-10 h, the mass ratio of recycled aggregate to alkaline slurry was 1:2, and then it was taken out and dried, ready for use.

[0080] Cement fly ash gravel pile (CFG pile) is a pile body made by mixing gravel, stone chips, fly ash, and water.

[0081] ​In this embodiment, the sodium hydroxide solution with a mass fraction of 10% is used, and the modified material content is 10%, 20%, 30% and 40% of the mass of the recycled aggregate. When the modified material content is 10% of the mass of the recycled aggregate, the corresponding mass ratio of the sodium hydroxide solution to the modified material is 1:0.05; when the modified material content is 20% of the mass of the recycled aggregate, the corresponding mass ratio of the sodium hydroxide solution to the modified material is 1:0.1; when the modified material content is 30% of the mass of the recycled aggregate, the corresponding mass ratio of the sodium hydroxide solution to the modified material is 1:0.15; and when the modified material content is 40% of the mass of the recycled aggregate, the corresponding mass ratio of the sodium hydroxide solution to the modified material is 1:0.2.

[0082] To ensure that the recycled aggregate can be fully soaked, the mass of the sodium hydroxide solution is twice the mass of the recycled aggregate, and the soaking time is 2, 4, 6, 8 and 10 hours, respectively.

[0083] The recycled coarse aggregate used in this test has a particle size of 5-20 mm. As shown in Figures 2a-2d , the pre-soaking slurry silica ash slurry modification method balances the economic, environmental and periodic problems, and finds a modification method that is both economical and effective, environmentally friendly and short in cycle, which can save cost and improve the modification effect.

[0084] Modification effect analysis:

[0085] (1) Microscopic analysis

[0086] The test uses a Zeiss EVO18 type scanning electron microscope of Shanghai Jielu Company to observe the microstructure of the modified recycled coarse aggregate. The sample preparation process is as follows: sample the recycled coarse aggregate modified by three different modification methods and the unmodified recycled coarse aggregate, and soak the sample in anhydrous ethanol for 24 hours for dehydration. When testing, the sample soaked in anhydrous alcohol is placed in an oven at 60°C and pre-dried to constant weight, and the sample surface is covered before scanning electron microscope inspection, as shown in Figures 3a-3d .

[0087] As can be clearly seen from Figures 3a-3d , under the same magnification of 2000 times, the surface of the unmodified recycled aggregate is very rough and has many large-pore pores, which is the reason for the high crushing value and water absorption rate of the recycled aggregate. The surface of the recycled aggregate modified by slag powder is much smoother than that of the recycled aggregate, and the corners are wrapped by the slag powder slurry to become smoother. Compared with the slag powder modification, the surface of the recycled aggregate modified by steel slag is smoother and more compact, most of the pores are filled with steel slag slurry, and there are a small number of small-pore pores. For silica ash modification, the modified recycled aggregate is very smooth, and the number and degree of aggregate cracks are greatly reduced, and almost no pores can be seen.

[0088] (2) Index evaluation

[0089] Figures 4a-4h The change of the crushing value and water absorption of the recycled aggregate under different mixing amount and different modification time of the three modified materials is given. In the figure, RA-SF represents the silica fume modified recycled aggregate; RA-SP represents the slag powder modified recycled aggregate; and RA-SS represents the steel slag modified recycled aggregate. It can be seen from the figure that with the increase of the modification time, the crushing value and water absorption of the recycled aggregate are gradually reduced. For the slag powder modification, the crushing value and water absorption rapidly decrease within 0-4h after modification. After 4h, the crushing value and water absorption tend to be stable. At the same time, with the increase of the mixing amount of the modified material, the crushing value and water absorption of the recycled aggregate can be reduced and stabilized by 20% of the mixing amount of the slag powder, and the two indexes are finally stabilized at about 23.5% and 7.06% respectively. For the silica fume modification, the crushing value and water absorption rapidly decrease within 0-4h after modification by 10% of the mixing amount, and the crushing value and water absorption tend to be stable after 4h. For the mixing amount of 20% and above, the crushing value and water absorption rapidly decrease within 0-6h after modification, and the crushing value and water absorption tend to be stable after 6h. The two indexes are finally stabilized at about 19.4% and 5.89% respectively. For the steel slag modification, the crushing value and water absorption rapidly decrease within 0-8h after modification. After 8h, the crushing value and water absorption tend to be stable. At the same time, with the increase of the mixing amount of the modified material, the crushing value and water absorption of the recycled aggregate can be reduced and stabilized by 30% of the mixing amount of the slag powder, and the two indexes are finally stabilized at about 21.7% and 6.48% respectively.

[0090] The test results of the above three optimal modification methods are compared as shown in Figure 5 It can be clearly seen from the figure that the silica fume modification is the most ideal modification method. The water absorption and crushing value of the recycled aggregate are lower than those of the other two modification methods. At the same time, under the mixing amount of 20% of the silica fume, the pre-soaking slurry modified recycled aggregate obtained by 6h of modification has the most significant improvement in reducing the water absorption and crushing value.

[0091] The recycled aggregate modified by the pre-soaking slurry is applied to the CFG pile material (the alkaline aqueous solution is 10% concentration of sodium hydroxide solution, and the modified material is silica fume), compared with the CFG pile of the unmodified recycled aggregate, the compressive strength is improved by about 17%, and the flexural strength is improved by about 7%.

[0092] The experiment shows that the three selected modified materials can improve the recycled aggregate to a certain extent. Among the three, the best modified material is silica fume, which can reduce the water absorption rate of the modified recycled aggregate by 31.2%, and the crushing value by 32.3%. The second is steel slag, which can reduce the water absorption rate of the modified recycled aggregate by 24.0% at most, and the crushing value by 24.7% at most. The improvement degree of slag powder on the recycled aggregate is relatively the smallest, and the reduction rates of the water absorption rate and the crushing value are both below 20%, and the modification effect is not obvious. Therefore, the silica fume modification is the most ideal method.

[0093] When the recycled aggregate is modified in the embodiment of the application, silica fume, slag powder and steel slag are used as the modified admixture, and the alkaline environment is provided by soaking in alkaline water. With the increase of the modification time, the crushing value and the water absorption rate of the recycled aggregate are gradually reduced, and the modification effect is improved.

[0094] Embodiment 2,

[0095] A long-term performance evaluation method of a pre-soaking slurry modified recycled aggregate CFG pile, comprising the following steps:

[0096] Performance change research on a pre-soaking slurry modified recycled aggregate CFG pile:

[0097] The test object is a pre-soaking slurry modified recycled aggregate CFG pile, and the control group is a recycled aggregate CFG pile and a natural aggregate CFG pile under the same conditions. In the production process, cement, fly ash, coarse aggregate and fine aggregate are weighed according to the designed mixing ratio, and then stirred uniformly (the specific mixing ratio of each component is shown in Table 4). In the erosion test, the mass growth rate test piece and the compressive strength test test piece are formed by using a 100mm*100mm*100mm test mold, and then taken out from the mold after 24 hours, and then directly placed in a plastic box containing clean water for long-term soaking. At the same time, the control group is placed in the standard curing condition (humidity ≥ 95%, temperature 20℃) for curing. The test piece under the long-term soaking condition is compared with the control group, as shown in Tables 3-4.

[0098] Table 3: Erosion test simulation condition setting

[0099] Type Environmental condition Curing room Temperature 20±2℃, humidity 95% Water Temperature 20±2℃, completely immersed

[0100] Table 4: Erosion test simulation condition setting

[0101]

[0102] In Table 4, "kg / m 3 " represents the mass of each component in each cubic meter of pile test piece. RA P MRA represents a recycled aggregate CFG pile; P MRA represents a pre-soaking slurry modified recycled aggregate CFG pile; PNA This indicates a natural aggregate CFG pile.

[0103] Quality change rate test:

[0104] This method is used to test the mass change of each pile specimen in solution. The specimens are molded according to the designed mix ratio, demolded and numbered after 24 hours, and the initial mass M0 of each specimen is recorded. Without curing in a curing room, they are directly immersed in clean water. Upon reaching the test age, the specimens are removed, the surface liquid is wiped off, and they are immediately weighed. The mass M of each pile specimen at different ages is measured. i The rate of change of mass, m, is calculated using the following formula, and the water absorption rate is then calculated based on the rate of change of mass.

[0105] mass change rate m:

[0106]

[0107] Where: m — rate of change of mass;

[0108] M i —The mass of a pile test block at any age;

[0109] M0—Initial mass of the pile test block.

[0110] Compressive strength test:

[0111] According to the relevant provisions of the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2019), compressive strength tests were conducted at the set age, and the average compressive strength of each group of specimens was calculated.

[0112] Table 5. Changes in immersion time and water absorption rate of CFG piles with pre-impregnated modified aggregate.

[0113]

[0114] Table 6. Changes in Immersion Time and Water Absorption Rate of CFG Piles with Recycled Aggregate

[0115]

[0116] Table 7 Changes in Immersion Time and Water Absorption Rate of Natural Aggregate CFG Piles

[0117]

[0118]

[0119] Compare Table 5-7, Figures 6a-6c and Figure 7The experimental results of each pile body are fitted to the water absorption rate of the pre-soaking slurry modified recycled aggregate CFG pile body test block under the immersion condition; specifically, the water contents of the immersion time of 3d, 14d, 40d, 60d, 80d, 100d and 120d are selected, the non-linear curve data fitting is carried out by using Origin software, and the fitting formula of the water absorption rate and time is obtained:

[0120] W = -2.18e (-t / 23.28) + 2.29

[0121] W represents the water absorption rate of the pre-soaking slurry modified recycled aggregate CFG pile body under the immersion condition, and t represents time; the fitting parameters 2.18, 23.28 and 2.29 are related to the working environment of the modified recycled aggregate CFG pile, and the fitting degree is greater than 0.99. In actual application, if the engineering site is also completely immersed, the three constants measured by the formula can be directly applied; if it is not completely immersed, three groups of the above water absorption rate experiments can be carried out according to the actual situation of the engineering site, and the constants A, B and C in the actual engineering application can be calculated.

[0122] According to Figure 6a It can be intuitively analyzed that the mass change of the test block before and after immersion at which immersion time is greater, that is, the water absorption rate is greater, and then the water absorption rate of the test block in the long-term immersion time tends to be stable according to the water absorption rate change trend. This is consistent with the change trend of the obtained water absorption rate fitting formula, which can play a verification role, thereby indicating that the water absorption rate prediction formula obtained by the application is consistent with the actual experimental situation.

[0123] Figure 6b The mass change of the recycled aggregate CFG pile test block before and after immersion is given, and the pre-soaking slurry modified recycled aggregate CFG pile body test block is compared, and the Figure 6a , Figure 6b According to the specific experimental data, with the increase of the immersion time, the water absorption rate of the pre-soaking slurry modified recycled aggregate test block is stable at about 2.2% at 60 days, which is decreased by 27.9% compared with the recycled aggregate CFG pile. Therefore, it is fully explained that the water absorption rate of the recycled aggregate after modification is reduced, and the modification effect is obvious.

[0124] According to the experimental data of Figure 8 , Figure 9 , Figure 10 The compressive strength of the pre-soaking slurry modified recycled aggregate CFG pile body test block under the immersion condition is fitted; specifically, the compressive strengths of the immersion time of 28d, 50d, 70d, 90d and 110d are selected, and the non-linear curve data fitting is carried out by using Origin software, and the fitting formula of the compressive strength and time is obtained:

[0125]

[0126] wherein q represents the compressive strength of the pre-soaked slurry modified recycled aggregate CFG pile body under the condition of water immersion, t represents time; the constants 3.88, 18.36, 41.68 and 25.77 are fitting parameters, which are related to the working environment of the modified recycled aggregate CFG pile. The fitting degree is greater than 0.99. In actual application, if the engineering site is also completely immersed in water, the four constants determined by the formula can be directly applied; if it is not completely immersed in water, three groups of the above compressive strength experiments can be conducted according to the actual situation of the engineering site, and the constants D, E, M and N in the actual engineering application can be calculated by substitution.

[0127] In combination with Figure 8 and Figure 9 Further analysis shows that the compressive strength of the pre-soaked slurry modified aggregate CFG pile and the recycled aggregate CFG pile body test block under the condition of water immersion has a close relationship with the water absorption rate. The water absorption rate of the test block rises and the compressive strength decreases at the same time. When the water absorption rate tends to be stable, the strength also decreases and reaches a stable stage. Therefore, the change of the compressive strength can be analyzed according to the change of the water absorption rate of the pile body, and the compressive strength prediction formula is verified by combining the compressive strength fitting result, which shows that the compressive strength prediction formula obtained by the present application is consistent with the actual experimental situation.

[0128] At present, the output of building solid waste is large, the management mechanism is not perfect, and it is randomly stacked to pollute the environment. In addition, the materials such as sand and gravel needed for engineering construction are also in serious shortage. In order to dispose of building solid waste, building solid waste is used for CFG pile and applied to foundation treatment. The compressive strength of non-building solid waste CFG pile body is basically not affected by the water absorption rate and the water absorption rate of the pile body is extremely low. However, the water absorption rate of the building solid waste CFG pile increases under the condition of water immersion due to the special material of the building solid waste and the working environment of long-term water immersion. In the process of increasing the water absorption rate, the compressive strength decreases. This problem exists all the time in the process of using building solid waste. However, the change rule is unknown. In addition, compared with natural aggregate, the strength of recycled aggregate CFG pile is lower and the performance is poorer. The use of building solid waste in CFG pile and in soft soil foundation with high water content may exist engineering safety problems, and the change of the compressive strength is unknown, which leads to great technical difficulties in the use of building solid waste in CFG pile and in soft soil foundation with high water content. In addition, the strength of the pile body buried in soft soil in engineering practice is difficult to measure. In view of the above application environment, the present application embodiment adopts a rigorous, perfect and reliable prediction method to obtain the water absorption rate and compressive strength prediction formula of the building solid waste CFG pile under the condition of water immersion. Moreover, the function model used in the prediction formula is highly fitted with the data obtained by the actual experiment, and the presentation form is universal, which is convenient for application in engineering.

[0129] The embodiment of the present application considers the actual water immersion working environment of the building solid waste CFG pile, uses the water immersion periodical test mode of the pile body model test block to measure the change of the water content and the strength, obtains the corresponding fitting formula, reveals the change relationship between the compressive strength and the water absorption rate of the building solid waste CFG pile, and proposes the corresponding water absorption rate estimation formula and the compressive strength estimation formula, has higher fitting degree, quantifies the relationship between the water absorption rate and the compressive strength, provides matching basis for the engineering design of the building solid waste CFG pile, and can overcome the problems existing in the practical application of the building solid waste CFG pile.

[0130] The embodiment of the present application discloses the change relationship between the water content, the compressive strength and the time of the modified recycled aggregate CFG pile under long-term (years, decades, etc.) water immersion working conditions, and the change relationship between the water content and the compressive strength. The water content and the strength change of the modified recycled aggregate CFG pile in different periods under pre-soaking slurry are judged by the water content estimation formula and the compressive strength estimation formula under the engineering application environment; the specific values of the water content and the compressive strength under the time parameter can be directly calculated, and the obtained formula can also reveal that the compressive strength and the water content of the pile body will eventually tend to be stable with time, so as to determine the strength stable value of the modified recycled aggregate CFG pile under the long-term water immersion working environment, and further determine the design strength of the modified recycled aggregate CFG pile meeting the engineering requirements under the environment, so as to provide a scientific basis for the engineering design of the modified recycled aggregate CFG pile and the application in the soft soil foundation, and has important value and significance.

[0131] The above only describes the preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application is included in the protection scope of the present application.

Claims

1. A method for long-term performance evaluation of preimpregnated slurry modified recycled aggregate (CFG) piles, characterized in that, The preparation method of preimpregnated slurry modified recycled aggregate CFG piles includes the following steps: S1. Mix sodium hydroxide solution and modified admixture at a mass ratio of 1:0.05 to 1:0.2, stir evenly, and let stand for 2 to 10 minutes to allow the two mixtures to react fully and obtain an alkaline slurry. S2, after air-drying, the recycled coarse aggregate is soaked in alkaline slurry for 2-10 hours, then removed and dried for later use; The modified admixture is silica fume, slag powder, or steel slag; The long-term performance evaluation method includes the following steps: The mass changes of pre-impregnated slurry modified recycled aggregate (CFG) pile specimens at different ages under immersion conditions were obtained through testing, and the corresponding water absorption rates were calculated. Furthermore, the water absorption rate of the pre-impregnated slurry modified recycled aggregate (CFG) pile specimens under immersion conditions was fitted to obtain a fitting formula for the water absorption rate versus time. ； Where W represents the water absorption rate of the pre-impregnated slurry modified recycled aggregate CFG pile under immersion conditions, t represents time, and A, B and C are all fitting parameters; The compressive strength of CFG pile specimens modified with pre-impregnated slurry aggregate under immersion conditions was tested and obtained at different ages. Then, the compressive strength of the CFG pile specimens under immersion conditions was fitted, and a fitting formula for compressive strength versus time was obtained: ； Where q represents the compressive strength of the pre-impregnated slurry modified recycled aggregate CFG pile under immersion conditions, t represents time, D, M and N are fitting parameters, and dx represents the slope of the compressive strength change. In the corrosion test, the specimens for both the mass growth rate test and the compressive strength test were molded using a test mold. After 24 hours, the specimens were removed from the mold and then placed directly into clean water for long-term immersion. Meanwhile, the control group was cured under standard curing conditions.

2. The long-term performance evaluation method for preimpregnated slurry modified recycled aggregate CFG piles according to claim 1, characterized in that, If the construction site is completely submerged, the fitting formula for the water absorption rate versus time is: 。 3. The long-term performance evaluation method for preimpregnated slurry modified recycled aggregate CFG piles according to claim 1, characterized in that, If the construction site is completely submerged, the fitting formula for compressive strength versus time is: 。 4. The long-term performance evaluation method for preimpregnated slurry modified recycled aggregate CFG piles according to claim 1, characterized in that, The mass change of the pile body test block is calculated according to the following formula: ； Where: m — rate of change of mass; M i —The mass of a pile test block at any age; M0—Initial mass of the pile test block.

5. The long-term performance evaluation method for pre-impregnated slurry modified recycled aggregate CFG piles according to claim 1, characterized in that, The particle size of the recycled coarse aggregate is 5-20 mm.

6. The long-term performance evaluation method for preimpregnated slurry modified recycled aggregate CFG piles according to claim 1, characterized in that, The sodium hydroxide solution has a mass fraction of 5-15%.

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