A design method for semi-flexible pavement base asphalt mixture

Abstract

The application provides a semi-flexible pavement matrix asphalt mixture design method, the matrix asphalt mixture is composed of coarse aggregate, fine aggregate, mineral powder and asphalt, according to the skeleton filling theory, the coarse aggregate, the fine aggregate, the mineral powder and the asphalt are filled step by step in the space forming process, the mixing ratio of the coarse aggregate, the fine aggregate, the mineral powder and the asphalt in the matrix asphalt mixture is controlled through the volume parameter change in the filling process; according to the influence of the structure asphalt and the free asphalt in the asphalt on the void, the remaining space of the structure asphalt wrapped around the aggregate and the mineral powder is the void ratio, the free asphalt seals part of the void ratio to form the connected void of the matrix asphalt mixture, and the mixing ratio of the aggregate, the mineral powder and the asphalt is controlled according to the connected void parameter setting. The matrix asphalt mixture design method provided by the application avoids the influence of the material space filling interference, guarantees the volume stability of the matrix asphalt mixture, the designed matrix asphalt mixture has enough connected void, ensures the cement mortar filling degree and saturation, and guarantees that the semi-flexible pavement material has good performance.

Description

Technical Field

[0001] This invention belongs to the field of high-performance pavement materials technology, and in particular relates to a design method for matrix asphalt mixtures for semi-flexible pavements. Technical Background

[0002] Semi-flexible pavement is a type of pavement material formed by injecting high-performance cement-based grout into a large-void asphalt mixture as the skeleton matrix. Its modulus is between that of rigid and flexible pavements. Semi-flexible pavement has good high-temperature resistance and fatigue resistance, and is widely used in areas with high requirements for pavement deformation resistance, such as intersections, BRT lanes, service areas, and toll plazas. With the increasing frequency of continuous high-temperature weather and the rapid increase in the proportion of heavy loads, the application of semi-flexible pavement is becoming more and more widespread.

[0003] The performance of semi-flexible pavement is mainly affected by the matrix asphalt mixture and cement-based grout. The asphalt mixture provides the basic skeleton, and the matrix skeleton, as the carrier, should have good volume stability. The various materials should not interfere with each other in terms of volume composition. At the same time, because of the need to inject cement grout, it should have sufficient interconnected voids to ensure that the cement grout is fully injected, avoiding insufficient grout injection, which can easily lead to cracking, particle loss, deformation and other damage.

[0004] A cold-mix recycled semi-flexible pavement material and its preparation method (CN115108788A) are disclosed. The matrix asphalt mixture is prepared from waste asphalt concrete aggregate, new aggregate, and filler. The proportions of the material composition are given, and the waste asphalt concrete aggregate is divided into five categories. The range of admixture amounts in the gradation design is provided. After the design is completed, the gradation is corrected based on the sieving results of the waste asphalt concrete aggregate. This method uses composite grout for both the matrix skeleton binder and the filling material, and employs shrinkage compensation technology for the filling material to improve the bonding strength of the semi-flexible pavement material and reduce material shrinkage deformation. However, this method does not clearly define the relationship between the components of each raw material in terms of volume composition, and cannot effectively control the volume stability of the matrix asphalt mixture skeleton and the interconnected voids required for the filling grout.

[0005] A semi-flexible pavement material based on hot recycled asphalt mixture (CN112252107A) is disclosed. The asphalt mixture matrix comprises hot recycled asphalt mixture and new asphalt mixture. Following the design method for hot recycled asphalt mixtures, the old material is screened, and the ratio of new to old material is determined according to gradation requirements. Then, a recycling agent, activator, and fusing agent are added to achieve high, stable, and homogeneous matrix performance. However, this method completely relies on the gradation curve trial mixing method in the specification for matrix asphalt mixture design, without considering the volumetric composition relationship between materials. Therefore, the matrix asphalt mixture cannot achieve good stability and effective interconnected voids.

[0006] A semi-flexible pavement material (CN110818358A) includes an asphalt mixture and a cement-based grouting material. The asphalt mixture matrix accounts for 70-80% of the weight of the semi-flexible pavement material. The composition and corresponding proportions of the raw materials of the matrix asphalt mixture are given. Bamboo chips, liquefied resin, and styrene-acrylic emulsion are added to increase the interfacial adhesion between cement and asphalt. However, this method does not provide a design method for the matrix asphalt mixture, does not consider the stability between materials from the perspective of volume composition, and does not provide a method to control the interconnected voids in the matrix asphalt mixture.

[0007] Therefore, existing technologies for designing semi-flexible pavement matrix asphalt mixtures do not consider the spatial composition of the materials in terms of volume structure or the interference between materials, nor do they provide an effective method for controlling the interconnected porosity. There is an urgent need to propose a design method for semi-flexible pavement matrix asphalt mixtures based on the spatial volume structure of the materials, and to determine the blending ratio of raw materials accordingly. Summary of the Invention

[0008] To address the issues of uncontrollable volume stability and unreliable porosity in the spatial composition of semi-flexible pavement matrix asphalt mixtures, this invention provides a design method for semi-flexible pavement matrix asphalt mixtures. By controlling the volume stability and porosity of the matrix asphalt mixture through changes in volume parameters during the spatial composition process, this invention addresses these problems.

[0009] The technical problem to be solved by this invention is achieved by the following technical solution:

[0010] A method for designing a semi-flexible pavement matrix asphalt mixture, wherein the matrix asphalt mixture comprises coarse aggregate, fine aggregate, mineral powder, and asphalt, and the design of the matrix asphalt mixture includes the following steps:

[0011] (1) Screen the coarse aggregate, fine aggregate and mineral powder to determine the gradation composition;

[0012] (2) Calculate the composite gradation and density of coarse aggregate, determine the compacted density of coarse aggregate through aggregate test, and calculate the void ratio (VCA) of coarse aggregate under compacted state.

[0013] (3) Based on the volume composition theory of matrix asphalt mixture, determine the proportional relationship between coarse aggregate, fine aggregate, mineral powder and asphalt. Fine aggregate and mineral powder fill the voids VCA of coarse aggregate. After filling, the voids are the mineral aggregate void ratio VMA. Asphalt fills the mineral aggregate void ratio VMA to form void ratio VV.

[0014] Based on the influence of free asphalt and structural asphalt on the volume composition of matrix asphalt mixtures, the proportional relationship of coarse aggregate, fine aggregate, mineral powder, and asphalt is determined. The porosity VV includes connected voids and closed voids. After asphalt is filled, the asphalt changes, causing the porosity VV to change. Specifically, free asphalt fills the porosity VV, closed voids are blocked by free asphalt, and structural asphalt coats the surface of aggregates and mineral powder to form an asphalt film, which does not affect the connected voids. The porosity VV minus the porosity VMA filled by free asphalt in the aggregate void ratio is the connected porosity Vc.

[0015] Further technology of the present invention:

[0016] Preferably, the proportional relationship between coarse aggregate, fine aggregate, mineral powder, and asphalt is determined according to the following formula based on the theory of volume composition of matrix asphalt mixtures:

[0017] G + g + f = 100%

[0018]

[0019]

[0020] Where: G—coarse aggregate dosage, %; g—fine aggregate dosage, %;

[0021] f—Percentage of mineral powder, %; P a —Asphalt usage, %;

[0022] ρ sc —Compacted density of coarse aggregate, g / cm³ 3 ;ρ g —Density of fine aggregate, g / cm³ 3 ;

[0023] ρ f —Mineral powder density, g / cm³ 3 ;ρ a — Density of asphalt, g / cm³ 3 .

[0024] Preferably, the proportions of coarse aggregate, fine aggregate, mineral powder, and asphalt are determined according to the following formula based on the influence of free asphalt and structural asphalt on the volume composition of the matrix asphalt mixture:

[0025]

[0026] SA=0.41+0.0041a+0.0082b+0.0164c+0.0287d+0.0614e+0.1229f+0.3277g

[0027] In the formula:

[0028] SA—Specific surface area, m² 2 / kg; u—Asphalt film thickness, μm;

[0029] SA G —Specific surface area of ​​coarse aggregate, m² 2 / kg; SA g —Specific surface area of ​​fine aggregate, m² 2 / kg;

[0030] SA f —Specific surface area of ​​mineral powder, m 2 / kg;

[0031] a, b, c, d, e, f, and g represent the passing rates of sieve openings of 4.75 mm and below.

[0032] Preferably, the mineral aggregate interstitial ratio VMA is 26-30, the porosity VV is 19-22, and the interconnected porosity V t Take 15 to 17.

[0033] Preferably, the thickness of the asphalt film formed by the structural asphalt coating the surface of the aggregate and mineral powder is 8-12 μm.

[0034] Preferably, the coarse aggregate has a particle size of 4.75 mm or more and the fine aggregate has a particle size of less than 4.75 mm, and the coarse and fine aggregates are composed of single-grade aggregates or multi-grade aggregates.

[0035] The beneficial technical effects of this invention are:

[0036] (1) The present invention provides a design method for a semi-flexible pavement matrix asphalt mixture, which controls the proportion of raw materials by changing the volume parameters of the matrix asphalt mixture to avoid mutual interference of raw materials when filling space, thereby improving the volume stability of the matrix asphalt mixture.

[0037] (2) The present invention provides a design method for a semi-flexible pavement matrix asphalt mixture. Based on the influence of structural asphalt and free asphalt on voids, the remaining space of the structural asphalt coating aggregates and mineral powder is the void ratio. The free asphalt closes a portion of the voids to form interconnected voids in the matrix asphalt mixture. The proportion of aggregates, mineral powder and asphalt is controlled according to the interconnected void parameters to ensure the interconnected void ratio of the designed matrix asphalt mixture and to ensure the cement grout penetration and saturation. Detailed Implementation

[0038] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further explained below with reference to specific embodiments.

[0039] The sources of all raw materials used in this invention are not particularly limited; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0040] The purity of all raw materials used in this invention is not particularly limited, but analytical grade or conventional purity used in the field of composite materials is preferred.

[0041] Example 1

[0042] The following design uses coarse aggregate, fine aggregate, asphalt, and mineral powder for the matrix asphalt mixture of semi-flexible pavement. The coarse aggregate includes two sizes: 10-15mm and 5-10mm. The fine aggregate has a size of 0-5mm. The aggregate and mineral powder were screened, and the results are shown below:

[0043] Table 1 Raw material screening results

[0044]

[0045] The aggregate density was tested, and the results are shown below:

[0046] Table 2. Aggregate density test results

[0047]

[0048] According to the skeleton structure gradation design method, two grades of coarse aggregate, 10-15mm and 5-10mm, are graded, with the 10-15mm and 5-10mm aggregates graded in a 50:35 ratio. Calculate the composite density ρ of the coarse aggregate. G =2.826g / cm 3 The compacted density of coarse aggregate was determined to be ρ through aggregate tests. sc =1.695g / cm 3 coarse aggregate porosity The design of the matrix asphalt mixture for semi-flexible pavements adopts a void ratio control method. During design, the aggregate void ratio VMA = 28, the porosity VV = 20, and the interconnected porosity V... C =16.

[0049] The specific surface area of ​​the aggregate is calculated using the following formula: SA = 0.41 + 0.0041a + 0.0082b + 0.0164c + 0.0287d + 0.0614e + 0.1229f + 0.3277g

[0050] Table 2 Calculation results of aggregate specific surface area

[0051]

[0052] The coarse aggregate, consisting of 10-15mm and 5-10mm particles, is graded at a ratio of 50:35, resulting in a coarse aggregate specific surface area of ​​0.81 m².2 / kg. Based on the spatial composition of the semi-flexible pavement matrix asphalt mixture, using aggregate void ratio, porosity, and interconnected void ratio as indicators, the composition of each component is controlled, and the proportion of each component is calculated according to the following formula:

[0053] G + g + f = 100%

[0054]

[0055]

[0056]

[0057] Substituting the raw material density, porosity, and specific surface area parameters, and taking the asphalt film thickness as 10µm, the following results are obtained:

[0058] G + g + f = 100%

[0059]

[0060]

[0061]

[0062] Calculations show that the coarse aggregate content G = 84.3%, the fine aggregate content g = 12.5%, the mineral powder content f = 3.2%, and the asphalt content P... a =4.1%.

[0063] The foregoing has shown and described the basic principles, main features, and characteristics of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A design method for a semi-flexible pavement matrix asphalt mixture, wherein the matrix asphalt mixture comprises coarse aggregate, fine aggregate, mineral powder, and asphalt, characterized in that: The design of matrix asphalt mixtures includes the following steps: (1) Screen the coarse aggregate, fine aggregate and mineral powder to determine the gradation composition; (2) Calculate the composite gradation and density of coarse aggregate, determine the compacted density of coarse aggregate through aggregate test, and calculate the void ratio (VCA) of coarse aggregate under compacted state. (3) Based on the volume composition theory of matrix asphalt mixture, determine the proportional relationship between coarse aggregate, fine aggregate, mineral powder and asphalt. Fine aggregate and mineral powder fill the voids VCA of coarse aggregate. After filling, the voids are the mineral aggregate void ratio VMA. Asphalt fills the mineral aggregate void ratio VMA to form void ratio VV. Based on the influence of free asphalt and structural asphalt on the volume composition of matrix asphalt mixtures, the compositional ratio of coarse aggregate, fine aggregate, mineral powder, and asphalt is determined. The porosity VV includes connected voids and closed voids. After asphalt is filled, the asphalt changes, causing the porosity VV to change. Specifically, free asphalt fills the porosity VV, closed voids are blocked by free asphalt, and structural asphalt coats the surface of aggregates and mineral powder to form an asphalt film, which does not affect the connected voids. The porosity VV minus the porosity VMA filled by free asphalt in the aggregate void ratio is the connected porosity Vc. Based on the theory of volume composition of matrix asphalt mixtures, the proportional relationship between coarse aggregate, fine aggregate, mineral powder, and asphalt is determined according to the following formula: G + g + f = 100% Where: G—coarse aggregate dosage, %; g—fine aggregate dosage, %; f—Percentage of mineral powder, %; P a —Asphalt usage, %; ρ sc —Compacted density of coarse aggregate, g / cm³ 3 ;ρ g —Fine aggregate density, g / cm³ 3 ; ρ f —Mineral powder density, g / cm³ 3 ;ρ a — Density of asphalt, g / cm³ 3 ; Based on the influence of free asphalt and structural asphalt on the volume composition of the matrix asphalt mixture, the proportional relationship of coarse aggregate, fine aggregate, mineral powder, and asphalt is determined according to the following formula: SA=0.41+0.0041a+0.0082b+0.0164c+0.0287d+ 0.0614e+0.1229f+0.3277g In the formula: SA—Specific surface area, m² 2 / kg; u—thickness of asphalt film, μm; SA G —Specific surface area of ​​coarse aggregate, m² 2 / kg; SA g —Specific surface area of ​​fine aggregate, m² 2 / kg; SA f —Specific surface area of ​​mineral powder, m 2 / kg; a, b, c, d, e, f, and g represent the passing rates of sieve openings of 4.75 mm and below.

2. The design method for semi-flexible pavement matrix asphalt mixture as described in claim 1, characterized in that: The mineral aggregate interstitial ratio VMA is 26-30, the porosity VV is 19-22, and the interconnected porosity V t Take 15 to 17.

3. The design method for semi-flexible pavement matrix asphalt mixture as described in claim 1, characterized in that: The structural asphalt coating on the surface of aggregates and mineral powder forms an asphalt film with a thickness of 8-12 μm.

4. The design method for semi-flexible pavement matrix asphalt mixture as described in claim 1, characterized in that: The coarse aggregate has a particle size of 4.75 mm or larger, and the fine aggregate has a particle size of less than 4.75 mm. The coarse and fine aggregates are composed of single-grade aggregates or multiple-grade aggregates.

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