Design method of skeleton dense type cement stabilized macadam with fine weathered aggregate

Abstract

The application discloses a skeleton dense type cement stabilized macadam grading design method of mixed fine particle weathered material, relates to the technical field of grading design, and carries out pre-compaction on the fine particle weathered material; the fine particle weathered material after pre-compaction is mixed with each set of aggregate according to the tentative grading curve one; the coarse aggregate vibration density, the fine material tight packing density and the coarse aggregate skeleton gap rate are obtained, and the fine particle weathered material dosage is calculated in combination with the mass fraction relationship of the coarse aggregate, the fine particle weathered material and cement; the grading curve two is generated according to the fine material dosage; the remaining grading curves are obtained by changing the fine material dosage as a benchmark while keeping the internal proportion of the coarse aggregate unchanged; the skeleton dense property of the designed mixture is judged by taking the measured void ratio of the mixture as an evaluation index, and the skeleton dense grading is determined. The application provides the fine particle weathered material dosage expression suitable for the skeleton dense type cement stabilized macadam, the expression optimizes the grading design process, and reduces the grading design test amount.

Description

Technical Field

[0001] This invention relates to the field of pavement base material gradation design technology, and in particular to a method for gradation design of dense-skeletal cement-stabilized crushed stone with added fine-grained weathered aggregate. Background Technology

[0002] Cement-stabilized crushed stone is a commonly used and typical semi-rigid base material for highway pavements, requiring a large amount of stone resources. In areas rich in weathered aggregate resources, replacing some of the stone in cement-stabilized crushed stone with weathered aggregate can reduce stone mining and protect mountain slopes. Because fine-grained weathered aggregate has a high degree of weathering and low strength, it will break during compaction, causing changes in the gradation of the raw materials. Therefore, the impact of gradation changes during the compaction of weathered aggregate must be considered when designing the gradation.

[0003] Existing research and practical applications have shown that skeleton-dense aggregates have good mechanical properties and durability. The existing skeleton-dense cement-stabilized crushed stone gradation design methods mainly include the step-by-step filling method, the experimental method, and the volumetric method. These methods still have problems that need to be improved: (1) Although the step-by-step filling method is easy to understand and operate, the results have large dispersion, the amount of testing is large, and the testing cycle is long. (2) When determining the aggregate gradation, the experimental method lacks consideration of the aggregate structure and does not systematically evaluate whether the coarse aggregate forms a skeleton-dense aggregate. (3) The volumetric method mainly considers the relationship between the voids of the coarse aggregate and the volume of the fine aggregate, without considering the volume and filling effect of cement.

[0004] Patent CN113936751 A discloses a gradation design method for low-dose cement-stabilized crushed stone based on a physical model of aggregate void ratio. Although it provides the ratio of coarse to fine aggregates in a dense aggregate gradation, it does not consider the influence of cement on aggregate gradation in the cement stabilizing material. Therefore, the theoretical dense aggregate structure designed does not represent the actual dense aggregate structure. Furthermore, this method does not consider fine-grained weathered aggregate as a stabilizing material, making it unsuitable for gradation design of cement-stabilized crushed stone with added fine-grained weathered aggregate.

[0005] In summary, current cement-stabilized crushed stone gradation design methods are still mainly empirical, requiring a large number of experiments. There is no existing gradation design method for dense skeletons with added fine-grained weathered aggregates, and the gradation changes of fine-grained weathered aggregates during compaction and the filling effect of cement as fine aggregates are not considered. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a gradation design method for skeleton-dense cement-stabilized crushed stone with added fine-grained weathered aggregate. An expression for the amount of fine-grained weathered aggregate applicable to skeleton-dense cement-stabilized crushed stone is given, which optimizes the gradation design process and reduces the amount of gradation design experiments.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] Embodiments of the present invention provide a method for designing the gradation of skeleton-dense cement-stabilized crushed stone with added fine-grained weathered aggregate, comprising:

[0009] Pre-compacting of fine-grained weathered material based on the principle of equivalent compaction work yields fine-grained weathered material in a stable gradation state.

[0010] According to the proposed gradation curve, the pre-compacted fine-grained weathered material is mixed with each grade of aggregate, and the boundary particle size of coarse and fine materials is set; coarse aggregate and fine material are divided according to the boundary particle size; and the passing rate of the boundary particle size sieve is determined.

[0011] The compacted density of coarse aggregate, the compacted density of fine aggregate, and the gap ratio of coarse aggregate skeleton were measured. Based on the mass fraction relationship between coarse aggregate, fine weathered material, and cement, the amount of fine weathered material was calculated.

[0012] Gradation curve two is generated based on the amount of fine aggregate; while keeping the internal proportion of coarse aggregate unchanged, at least two other gradation curves are obtained by varying the amount of fine aggregate as the benchmark.

[0013] The measured void ratio of the mixture is used as the evaluation index to determine the skeleton compactness of gradation curve 2 and other gradation curves, and to determine the skeleton compactness gradation.

[0014] As a further implementation, the amount of fine-grained weathered material used... Represented as:

[0015]

[0016] in, Indicates the compacted density of coarse aggregate. Indicates the density of tightly packed fine materials. Indicates the gap ratio of coarse aggregate skeleton. This indicates the mass fraction of cement.

[0017] As a further implementation method, the mass fraction of coarse aggregate is , .

[0018] As a further implementation method, the measured void ratios of the mixture corresponding to gradation curve 2 and the other gradation curves are compared, and the gradation curve with the smallest measured void ratio of the mixture is taken as the theoretical skeleton dense gradation.

[0019] As a further implementation method, based on the principle of equivalent compaction work, the compaction work per unit volume formula is used to reflect the compaction situation, and an indoor small road roller is used to simulate the on-site working conditions.

[0020] As a further implementation, a single aggregate with a particle size larger than the boundary between coarse and fine aggregates, or a mixture of aggregates of different sizes mixed in a set ratio, is considered coarse aggregate, while fine weathered aggregate and cement are considered fine aggregate.

[0021] As a further implementation, coarse aggregate serves as the skeleton, with a total skeleton volume of V; fine-grained weathered material and cement are used to fill the gaps formed by the skeleton, and the fine material precisely fills the gaps formed by the coarse aggregate skeleton.

[0022] As a further implementation, if the fine particles do not affect the interlocking method and state of the coarse aggregate particles during the process of filling the gaps in the skeleton, then the gap volume of the skeleton is equal to the volume of the fine particles.

[0023] As a further implementation method, the total volume of the coarse aggregate skeleton for:

[0024]

[0025] in, Indicates the mass fraction of coarse aggregate. This indicates the compacted density of coarse aggregate.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention obtains fine-grained weathered material with stable gradation by pre-compacting it; it also provides an expression for the dosage of fine-grained weathered material suitable for dense-skeletal cement-stabilized crushed stone, which optimizes the gradation design process and reduces the amount of gradation design experiments.

[0028] This invention establishes a system based on A method for designing the gradation of dense-skeletal cement-stabilized crushed stone with fine-grained weathered aggregate is proposed, and the measured porosity of the mixture is introduced. Indicators are used to evaluate the skeleton density of the mixture. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a schematic diagram of the volume composition of cement-stabilized crushed stone with added fine-grained weathered aggregate;

[0031] Figure 2 This is a gradation curve diagram of the preliminary gradation according to one or more embodiments of the present invention;

[0032] Figure 3 This is a gradation curve diagram of the adjusted gradation type II according to one or more embodiments of the present invention;

[0033] Figure 4 This is a gradation curve diagram of the adjusted gradation three according to one or more embodiments of the present invention;

[0034] Figure 5 This is a gradation curve diagram of the adjusted gradation four according to one or more embodiments of the present invention;

[0035] Figure 6 This is a flowchart of the skeleton-dense gradation design method according to one or more embodiments of the present invention. Detailed Implementation

[0036] Example 1:

[0037] This embodiment provides a method for designing the gradation of dense-skeletal cement-stabilized crushed stone with added fine-grained weathered aggregate, such as... Figure 6 As shown, it includes the following steps:

[0038] Step 1: Based on the principle of equivalent compaction work, the compaction condition is reflected by the unit volume compaction formula. A small road roller is used to simulate the on-site working conditions, and relevant parameters are adjusted to pre-compact the fine-grained weathered material and obtain the fine-grained weathered material in the stable gradation state.

[0039] (1)

[0040] In equation (1), E is the compaction work per unit volume; A The amplitude; W It is a static line load; F For excitation force; N This refers to the number of compaction passes. f The vibration frequency; B This refers to the width of the grinding wheel; v This refers to the compaction speed; It is an off-center angle; h This refers to the paving thickness.

[0041] Step 2: Following the "Technical Specifications for Construction of Highway Pavement Base Course" (JTGT F20-2015), draft an S-shaped gradation curve. Based on this, mix the pre-compacted fine-grained weathered aggregate with each grade of aggregate. Set the coarse-fine aggregate boundary particle size to 4.75mm and determine the passing rate of the boundary particle size. Coarse aggregate refers to a single grade of aggregate with a particle size larger than the sieve opening at the boundary between coarse and fine aggregate, or a mixture of aggregates of different grades in a certain proportion. Fine aggregate refers to fine weathered aggregate and cement.

[0042] Step 3: Measure the compacted density of the coarse aggregate. Fine material compaction density Coarse aggregate skeleton gap ratio ,;set up , , These represent the mass fractions of coarse aggregate, fine weathered aggregate, and cement, respectively. And determined based on engineering experience The value of determines the amount of fine material used. .

[0043] Step 4: Based on the structural principle of the dense structure of cement-stabilized crushed stone skeleton and the function of each material in it, establish the formula for the dosage of fine-grained weathered material.

[0044] like Figure 1 As shown, the coarse aggregate in cement-stabilized crushed stone functions as a skeleton, and the total volume of the skeleton (including the interstitial volume between coarse aggregate particles) is set as V; the fine-grained weathered aggregate particles (particle size...) The fine aggregate (4.75mm) is composed of cement and its function is to fill the gaps formed by the skeleton, and it is assumed that the fine aggregate exactly fills the gaps formed by the coarse aggregate skeleton. It is assumed that during the process of the fine aggregate particles filling the skeleton gaps, the fine aggregate particles do not affect the interlocking mode and state of the coarse aggregate particles, and the skeleton gap volume is exactly equal to the fine aggregate volume.

[0045] according to Based on the definition and the above quantitative relationships, establish a system of equations:

[0046]

[0047] Total volume of coarse aggregate skeleton for:

[0048]

[0049] Substituting equation (4) into equation (3), we get:

[0050]

[0051] Combining equations (2) and (5), we obtain the amount of fine-grained weathered material required. :

[0052]

[0053] Equation (6) is the formula for the amount of fine-grained weathered aggregate used in cement-stabilized crushed stone with added fine-grained weathered aggregate. Based on engineering experience with cement-stabilized crushed stone, the cement dosage is generally 3% to 5% of the stone mass. x The value of 3 is 0.03~0.05. In this way, the amount of fine-grained weathered material can be calculated according to formula (6), and the amount of fine material can be determined to guide the gradation design.

[0054] Step 5: Generate gradation curve two based on the amount of fine materials used. This ratio is the theoretical dense skeleton gradation.

[0055] Step 6: While keeping the internal proportions of coarse aggregates unchanged, adjust the amount of fine aggregates... With slight modifications to the baseline, gradation three and gradation four were generated as control groups.

[0056] Step 7: Measure the porosity of the mixture. The evaluation index was used to verify the compactness of the gradation skeleton.

[0057] In this embodiment, three additional gradation curves based on the initial proposed gradation one were obtained through gradation optimization design, namely gradation two, gradation three, and gradation four. Considering that fine-grained weathered material has a certain interference effect on the arrangement of graded crushed stone coarse aggregate, the actual skeleton dense gradation may be within the range covered by the three gradation curves of gradation two, gradation three, and gradation four, and needs to be determined by experiments.

[0058] The skeleton-dense mixture in this embodiment consists of three parts: cement, crushed stone, and fine-grained weathered material. The skeleton density of the three gradations is determined by the measured porosity index of the mixture.

[0059]

[0060] In equation (7): This indicates the maximum dry density of the mixture, in g / cm³. 3 ; The apparent density of the mixture is expressed in g / cm³, which is obtained by combining the apparent density of coarse aggregates and the maximum dry density of fine aggregates. 3 ; This indicates the moisture content of the mixture, expressed as a decimal.

[0061] By comparing the measured void ratios of the mixtures corresponding to gradations 2, 3, and 4, the gradation with the smallest measured void ratio is identified as the theoretically dense skeleton gradation.

[0062] This embodiment provides an expression for the dosage of fine-grained weathered aggregate applicable to dense-structure cement-stabilized crushed stone. This expression optimizes the gradation design process, reduces the amount of gradation design experiments, and establishes a [presumably a specific formula or framework]. A gradation design method for dense-skeletal cement-stabilized crushed stone with added fine-grained weathered aggregate is proposed, and the measured porosity of the mixture is introduced. Indicators used to evaluate the density of the aggregate skeleton.

[0063] Example 2:

[0064] This embodiment illustrates the design method described in Embodiment 1 based on specific parameters, as follows:

[0065] Step 1: Pretreatment of fine-grained weathered material.

[0066] The relevant parameters of a common road roller are shown in Table 1:

[0067] Table 1 Relevant parameters of vibratory roller

[0068]

[0069] Substituting the parameters in Table 1 into Equation (1), we can obtain the unit volume compaction work of one rolling pass as 1166 J / m. 3 .

[0070] The relevant parameters of a commonly used indoor road roller are shown in Table 2:

[0071] Table 2 Relevant parameters of indoor road rollers

[0072]

[0073] Substituting the parameters in Table 2 into Equation (1), we can obtain that the compaction work per unit area for one pass of rolling is 1153 m³ / m². 3 .

[0074] Based on the principle of equivalent compaction work, the unit volume compaction work of the two can be converted. That is, one pass of compaction under field conditions requires one pass of compaction by an indoor roller. Therefore, an indoor roller is used to pre-compact the fine-grained weathered material. According to the field conditions, the fine-grained weathered material is close to a stable state after three passes of compaction. Therefore, it is compacted three times to obtain weathered material with stable gradation.

[0075] Step 2: Develop the gradation curve.

[0076] When designing the gradation of cement-stabilized crushed stone according to the above construction specifications, 1 to 3 gradation curves are proposed within the gradation range; for ease of calculation, this embodiment proposes 1 gradation curve, and the percentage of each sieve opening in the initial proposed gradation is shown in Table 3. Figure 2 The gradation curve showed a passing rate (x) of 32.5% at a sieve aperture of 4.75 mm. The sieving results of the aggregate are shown in Table 4.

[0077] Table 3. Preliminary gradation sieve aperture passing percentage (%)

[0078]

[0079] Table 4. Aggregate screening results (%)

[0080]

[0081] Step 3: Calculate the amount of fine-grained weathered material required for the dense gradation corresponding to the proposed gradation curve. :

[0082] Three grades of coarse aggregate (20-30mm, 10-20mm, and 5-10mm) were mixed in a ratio of 14.0:34.0:15.2. Fine aggregate smaller than 4.75mm was removed by sieving through a 4.75mm sieve. The gap ratio of the coarse aggregate skeleton was then determined by a vibration test. VCA Coarse aggregate compaction density Meanwhile, the treated fine-grained weathered material was sieved through a 4.75mm sieve according to Table 3 to remove coarse aggregate larger than 4.75mm. The sieved fine-grained weathered material was then mixed with cement, and the compaction density of the fine material was tested and calculated using a vibration test method. And calculate the amount of fine-grained weathered material used when the skeleton is dense according to formula (6). The basic data and calculation results of the test are shown in Table 5.

[0083] Table 5. Cement and weathered aggregate dosages for proposed coarse and fine aggregate gradations and dense aggregate aggregate skeletons.

[0084]

[0085] Step 4: Adjust the initial proposed gradation to obtain a dense gradation:

[0086] The calculation result of formula (6) is the amount of fine-grained weathered material. According to the calculation, when the cement dosage is 4%, the amount of fine-grained weathered material is 31.6%, so the amount of fine material is the amount of fine-grained weathered material plus the amount of cement 31.6% + 4% = 35.6%.

[0087] With a fine material content of 35.6%, the resulting gradation ratio is 14.2:34.7:15.5:31.6:4. This ratio is the theoretical dense skeleton gradation. Figure 3 As shown.

[0088] Equation (6) is established under certain assumptions. While keeping the internal proportion of coarse aggregate constant, the amount of fine aggregate is used as the basis for the equation. Generate gradation three and gradation four based on the baseline variation, see Figure 4 and Figure 5 .

[0089] Step 5: Verification of the measured porosity of the mixture with theoretically dense skeleton gradation:

[0090] Through gradation optimization design, three additional gradation curves, gradation two, three, and four, were obtained based on the initial proposed gradation one. Considering the interference effect of fine-grained weathered material on the arrangement of crushed coarse aggregate, the actual skeleton dense gradation may be within the range covered by the three gradation curves, and needs to be determined by experiments.

[0091] The measured void ratio of the mixture can be calculated by formula (7).

[0092] The calculated results of the measured void ratios of graded mixtures II, III, and IV are shown in Table 6.

[0093] Table 6. Calculation results of measured void ratio of three graded mixtures

[0094]

[0095] Measured porosity of the mixture The calculation results show that the porosity is ordered as follows: grade 3 > grade 4 > grade 2, that is, grade 2 is the more ideal dense skeleton grade in practice.

[0096] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for designing the gradation of dense-skeletal cement-stabilized crushed stone with added fine-grained weathered aggregate, characterized in that, include: Pre-compacting of fine-grained weathered material based on the principle of equivalent compaction work yields fine-grained weathered material in a stable gradation state. According to the proposed gradation curve, the pre-compacted fine-grained weathered material is mixed with each grade of aggregate, and the boundary particle size between coarse and fine aggregate is set; coarse aggregate and fine aggregate are divided according to the boundary particle size between coarse and fine aggregate. Obtain the compacted density of coarse aggregate, the compacted density of fine aggregate, and the gap ratio of coarse aggregate skeleton. Combine the mass fraction relationship between coarse aggregate, fine weathered material, and cement to calculate the amount of fine weathered material used. Among them, coarse aggregate refers to a single aggregate with a particle size larger than the boundary between coarse and fine aggregate, or a mixture of aggregates of different grades mixed in a set proportion, while fine weathered material and cement are fine aggregates. Coarse aggregate serves as the skeleton, with a total volume of V. Fine weathered material and cement are used to fill the gaps formed by the skeleton, and the fine material exactly fills the gaps formed by the coarse aggregate skeleton. During the process of setting the gaps between the fine aggregate particles and the skeleton, the fine aggregate particles do not affect the interlocking method and state of the coarse aggregate particles, and the gap volume of the skeleton is equal to the volume of the fine aggregate particles. The amount of fine-grained weathered material Represented as: in, Indicates the compacted density of coarse aggregate. Indicates the density of tightly packed fine materials. Indicates the gap ratio of coarse aggregate skeleton. Indicates the cement mass fraction; coarse aggregate mass fraction is , ; The total volume V of the coarse aggregate skeleton is: in, Indicates the mass fraction of coarse aggregate. Indicates the compacted density of coarse aggregate; Gradation curve two is generated based on the amount of fine aggregate; while keeping the internal proportion of coarse aggregate constant, at least two other gradation curves are obtained by varying the amount of fine aggregate as a benchmark. Among them, the amount of fine materials used ; The measured void ratio of the mixture is used as an evaluation index to determine the skeleton compactness of gradation curve 2 and the remaining gradation curves, and to determine the skeleton compactness gradation.

2. The method for designing the gradation of dense-skeletal cement-stabilized crushed stone with added fine-grained weathered aggregate according to claim 1, characterized in that, Compare the measured void ratios of the mixture corresponding to gradation curve 2 and the other gradation curves, and take the gradation curve with the smallest measured void ratio of the mixture as the theoretical skeleton dense gradation.

3. The method for designing the gradation of dense-skeletal cement-stabilized crushed stone with added fine-grained weathered aggregate according to claim 1, characterized in that, Based on the principle of equivalent compaction work, the compaction condition is reflected by the unit volume compaction formula, and the on-site working conditions are simulated by an indoor small road roller.

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