Series grading asphalt mixture design method

Abstract

The invention discloses a series grading asphalt mixture design method. The mineral aggregate gradation can be designed according to the performance requirements of the asphalt mixture, and the accuracy and operability of the gradation design are improved; the composition of the mixture is quantitatively designed according to the Marshall stability requirement, so that the workload of composition design is greatly reduced, and the controllability of the high pavement performance of the asphalt mixture is improved; the high-temperature stability and the water stability of the mixture are checked according to the preset composition, blindness of mixture composition adjustment is avoided, the success rate of pavement performance verification of the mixture is improved, and the performance verification period is shortened. According to the method, the composition design of the asphalt mixture can be guided, the composition of the mixture can be accurately controlled, the pavement performance of the mixture can be quantitatively designed and controlled, and the pavement performance of the asphalt mixture can be efficiently and comprehensively coordinated.

Description

Technical Field

[0001] The invention belongs to the technical field of asphalt mixture design, production and application, and particularly relates to a method for designing graded asphalt mixture. Background Art

[0002] Asphalt mixture gradation and composition are the fundamental guarantee for achieving its road performance. Extensive research has been conducted both domestically and internationally on the relationship between the composition, structure, and road performance of asphalt mixtures, accumulating rich experience that plays a significant role in the design of asphalt mixture compositions and the realization of road performance. Asphalt mixture composition design primarily includes three stages: raw material selection, mixture volume design, and mixture road performance verification. Currently, in the asphalt mixture composition design process both domestically and internationally, raw material selection, mineral aggregate gradation design, mixture volume design, and road performance design primarily rely on experience. Conflicts or omissions in road performance are common, and the workload for mixture composition design testing and road performance verification is substantial.

[0003] A method for designing asphalt mixtures with a graded structure has not been reported in China or abroad. Drawing on experience gained in asphalt mixture composition design and road performance verification, this method proposes a method for designing asphalt mixtures with a graded structure. This method uses a series method to design the aggregate gradation, a Marshall stability design method to determine the volumetric composition of the mixture, and dynamic stability and freeze-thaw splitting residual strength ratio to adjust the mixture composition. This method provides technical support for the design of asphalt mixture aggregate gradation, volumetric indicators, and road performance. Summary of the Invention

[0004] The purpose of this invention is to propose a method for designing graded asphalt mixtures, which takes road performance as the design goal, designs mineral gradation using a graded method, and controls the selection of raw materials, mixture volume indicators, and road performance indicators.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A method for designing a graded asphalt mixture comprises the following steps:

[0007] S1. Design the aggregate gradation of the mixture using the progression method, including: constructing the progression gradation formula, determining the gradation classification method, determining the coordination number adjustment method, and determining the gradation range;

[0008] S2. Determine the mixture composition based on Marshall stability design, including: establishing the Marshall stability design formula, designing raw material parameters, and designing the mixture volume composition;

[0009] S3. Design and adjust the mixture composition based on dynamic stability and water stability.

[0010] Furthermore, step S1 includes:

[0011] (1) Construct the gradation formula, the calculation formula is:

[0012]

[0013] Where V i is the cumulative volume percentage on the sieve hole No. i, %; m is the number of series; n is the average coordination number of particles; k is the ratio of the diameters of adjacent sieve holes;

[0014] (2) Determine the grading method: take the standard sieve hole sequence with the adjacent sieve hole diameter ratio k=0.5 as 38mm, 19mm, 9.5mm, 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm, 0.15mm and 0.075mm, take the standard sieve hole with a nominal maximum particle size of more than 2 times as the sieve hole number 0, take the sieve hole of 0.075mm as the sieve hole number m, and the numbers of other sieve holes are as follows:

[0015]

[0016] Where, d i is the standard sieve hole diameter, mm; d0 is the maximum standard sieve hole diameter, mm; k is the ratio of adjacent standard sieve hole diameters;

[0017] (3) Determine the coordination number adjustment method: Based on the ratio of adjacent sieve hole diameters, the theoretical coordination number n is 6.0. The actual coordination number n is adjusted within the range of 5.0 to 6.0 so that the percentage of particles passing through 0.075 mm is equal to the volume percentage of the filler;

[0018] (4) Determine the gradation range: the maximum particle size passing percentage is 100%, the nominal maximum particle size passing percentage is 90% to 100%, and the coordination number is adjusted according to the range of filler volume change to determine the gradation range.

[0019] Furthermore, step S2 includes:

[0020] (1) Establish the Marshall stability design formula as follows:

[0021]

[0022] Where, MS is the Marshall stability, kN; h is the specimen thickness, mm; D is the specimen diameter, mm; FL is the Marshall test flow value, mm; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J; S v is the volume of solid in the mixture; λ is the linear concentration of solid particles; P a is the mass ratio of asphaltene in the mixture; d ais the average particle size of asphaltene, m;

[0023] (2) Raw material parameter design, including: determining the average adhesion work of asphalt and mineral aggregate in air, determining the asphaltene content in asphalt, determining the gel content in asphalt, determining the mass ratio of asphaltene in the mixture, and determining the average particle size of asphaltene;

[0024] a. Determine the average adhesion work A of asphalt and mineral aggregate in air 12 , determined by the following formula:

[0025]

[0026] Where A 11 is the adhesion work of asphalt. When the asphalt penetration is 10-120 (0.1 mm), the value is 8.0×10 -20 J~8.4×10 -20 J, when the needle penetration is low, take a high value; A 22 is the average adhesion work of the ore;

[0027] b. Determine the asphalt content in asphalt according to the asphalt penetration:

[0028] A=36.735-4.748lnP

[0029] Where A is the mass percentage of asphalt in asphalt, %; P is the asphalt penetration, 0.1 mm;

[0030] c. Determine the gel content in asphalt according to the asphalt penetration:

[0031] G=28.469+2.136lnP

[0032] Where, G is the mass percentage of gel in asphalt, %; P is the asphalt penetration, 0.1mm;

[0033] d. Determine the mass ratio of asphaltene in the mixture according to the following formula:

[0034] P a =aA

[0035] Where, P a is the mass ratio of asphaltene in the mixture, %; a is the oil-to-stone ratio of the mixture, %; A is the mass percentage of asphaltene in asphalt, %;

[0036] e. Determine the average size of asphaltene particles. The smallest particle size determines the strength of the mixture. The average size of the smallest asphaltene particles is taken as d a is 3nm, that is, d a =3×10 -9 m;

[0037] (3) Mixture volume composition design, including: mixture composition calculation; mixture volume index calculation; Marshall stability calculation;

[0038] a. Mixture composition calculation, using the absolute volume method, including the volume of mineral aggregate, asphalt and mineral powder:

[0039] 1) Calculate the volume of mineral aggregate based on compaction degree, porosity, oil-stone ratio and powder-rubber ratio:

[0040]

[0041] Where: V k is the volume percentage of the ore, %; V m is the maximum compaction degree, %; V p is the void ratio of the mixture, %; a is the oil-stone ratio, %; f is the powder-rubber ratio; ρ a ,ρ f and ρ k are the relative densities of asphalt, mineral powder and mineral aggregate, respectively, determined by actual measurement;

[0042] 2) Calculate the volume of asphalt V based on the oil-stone ratio, powder-rubber ratio and mineral volume a :

[0043]

[0044] 3) Calculate the volume of mineral powder V according to the oil-stone ratio, powder-rubber ratio and mineral volume f :

[0045]

[0046] b. Calculation of mixture volume indicators, including aggregate void ratio, asphalt saturation, volume concentration and linear concentration:

[0047] 1) Calculate the aggregate void ratio (VMA) of the compacted asphalt mixture based on the asphalt-to-stone ratio, powder-to-rubber ratio, and aggregate volume:

[0048]

[0049] 2) Calculate the asphalt saturation VFA based on the asphalt volume and mineral void ratio:

[0050] VFA=100V A / VMA

[0051] 3) Volume concentration includes the volume of all solids per unit volume S V , the calculation formula is:

[0052] S V =0.01[V k +AVa +V f ]

[0053] 4) Calculate the linear concentration λ based on the maximum volume concentration and the actual volume concentration:

[0054] λ=[(S Vm / S V ) 1 / 3 -1] -1

[0055] Where S Vm is the maximum volume concentration, S Vm =0.01V m ;

[0056] c. Marshall stability calculation, including: determining the Marshall stability test plan, estimating the Marshall test flow value and calculating the Marshall stability:

[0057] 1) The Marshall stability test uses the standard Marshall test or the large Marshall test to determine the specimen diameter D and thickness h, in mm;

[0058] 2) Based on experience, five different oil-to-stone ratios were selected, the Marshall test flow value was estimated, the Marshall stability was calculated, and the optimal oil-to-stone ratio was determined;

[0059] 3) Fix the optimal oil-stone ratio, select different powder-rubber ratios, estimate the Marshall test flow value, calculate the Marshall stability, and determine the optimal powder-rubber ratio;

[0060] 4) Optimize the composition and volume indicators of the mixture so that the Marshall stability and flow value meet the design target requirements and determine the composition of the mixture.

[0061] Furthermore, step S3 includes:

[0062] (1) According to the mixture composition, the dynamic stability of the mixture is calculated using the following formula:

[0063]

[0064] Where DS is the dynamic stability, times / mm; h is the thickness of the rutting plate, mm; σ0 is the load stress of the dynamic stability test (MPa), σ0 = 0.7 MPa; t is the load action time (s), t = 0.0147 s; η1 is the viscosity of the mixture, MPa.s; E2 is the elastic modulus of the asphalt mortar, MPa; t r is the characteristic time (s), t r =η2 / E2; η2 is the viscosity of asphalt mortar, MPa.s;

[0065] (2) According to the composition of the mixture, the water-immersion Marshall residual stability is calculated using the following formula:

[0066]

[0067] Where M s is the residual stability of the Marshall test after immersion in water, %; FL is the flow value of the Marshall test after immersion in water, mm; D is the diameter of the Marshall specimen, mm; B1 is the spalling rate of the Marshall test after immersion in water, %; A 132 is the average adhesion work of asphalt and mineral aggregate in water, J; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J;

[0068] (3) According to the composition of the mixture, the freeze-thaw splitting residual strength ratio is calculated using the following formula:

[0069]

[0070] Where, TSR is the freeze-thaw splitting residual strength ratio, %; B2 is the spalling rate of the freeze-thaw splitting test, %; A 132 is the average adhesion work of asphalt and mineral aggregate in water, J; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J.

[0071] Furthermore, the viscosity η1 of the mixture is calculated as:

[0072]

[0073] Where η a is the viscosity of asphalt, MPa.s; k is an empirical constant, taken as 14.5; S Vk is the volume ratio of mineral materials in the mixture; S Vf is the volume ratio of filler in asphalt mortar;

[0074] The viscosity η2 of asphalt mortar is calculated as follows:

[0075]

[0076] Where η a is the viscosity of asphalt, MPa.s; k is an empirical constant, taken as 14.5; S Vs is the volume ratio of fine aggregate in asphalt mortar; S Vf is the volume ratio of filler in asphalt mortar;

[0077] The viscosity of asphalt is determined based on the asphalt penetration and viscosity-temperature curve. The calculation formula is:

[0078] lnη a =A+B / T

[0079] Where T is the thermodynamic temperature, K; A and B are empirical constants, and their relationship with needle penetration is:

[0080] A=2.2615lnP-38.331

[0081] B=-1204lnP+16339

[0082] When calibrating A and B, the unit of viscosity is Pa.s, and P is the needle penetration at 25°C, 0.1mm.

[0083] The beneficial effects of the present invention are:

[0084] 1. The present invention provides a method for designing graded asphalt mixtures, which uses grades to represent aggregate gradation, adjusts the grade terms and coordination numbers, and achieves complete control over the gradation. An infinite number of gradations can be designed, and the mixture composition and volume index can be controlled to achieve material composition optimization and quantitative design of road performance, thus having enormous technical and economic benefits.

[0085] 2. The present invention provides a method for designing graded asphalt mixtures, which adopts the Marshall stability design method to determine the mixture composition, realizes the quantitative design and control of Marshall stability, establishes the relationship between Marshall stability and road performance, greatly reduces the workload of asphalt mixture composition design, and improves the quality of mixture composition design and the controllability of road performance.

[0086] 3. The present invention provides a method for designing graded asphalt mixtures, which quantitatively controls the dynamic stability and water stability of the asphalt mixture, avoids blind adjustment of the mixture composition, coordinates the road performance of the asphalt mixture, and can greatly improve the success rate of the mixture road performance verification and shorten the cycle of the mixture road performance verification. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1-3 This is an example of Marshall stability design for asphalt mixture. Figure 1 is the relationship between the interstitial ratio and void ratio of the mineral material; Figure 2 is the relationship between asphalt saturation and void ratio; Figure 3 is the relationship between Marshall stability and void ratio.

[0088] Figure 4-7 This is an example of dynamic stability verification of asphalt mixture. Figure 4 is the relationship between dynamic stability and oil-stone ratio; Figure 5 is the relationship between dynamic stability and powder-to-rubber ratio; Figure 6 is the relationship between dynamic stability and void ratio; Figure 7 is the relationship between dynamic stability and sand ratio. DETAILED DESCRIPTION

[0089] The following will be combined with specific embodiments of the present invention to clearly and completely describe the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0090] This invention provides a method for designing graded asphalt mixtures. This method can guide asphalt mixture composition design, accurately manipulate mixture composition, quantitatively design and control the mixture's road performance, and achieve rapid and efficient comprehensive coordination of the asphalt mixture's road performance. The overall process for one implementation is as follows: aggregate gradation design; Marshall stability design; and mixture road performance verification.

[0091] 1. Mineral gradation design

[0092] The design of the gradation of the mixture using the series method includes: constructing the series gradation formula; determining the gradation classification method; determining the coordination number adjustment method; and determining the gradation range.

[0093] 1. Construct the gradation formula. The calculation formula is as follows:

[0094]

[0095] Where V i is the cumulative volume percentage on the sieve hole No. i, %; m is the number of series; n is the average coordination number of particles; k is the ratio of the diameters of adjacent sieve holes.

[0096] (1) The general formula for the series represents the volume percentage of the sieve hole No. i:

[0097]

[0098] (2) The ratio k of the diameters of adjacent sieve holes is between 0.414 and 0.732, and k is taken as 0.50, so that the theoretical coordination number is equal to 6.

[0099] 2. Determine the grading method, including: determining the standard sieve hole size; determining the maximum diameter of the standard sieve hole; determining the number of grading levels; and the correspondence between the number of grading levels and the sieve holes.

[0100] (1) Determine the standard sieve size. When the adjacent sieve size ratio is 0.5, the standard sieve sizes are 38 mm, 19 mm, 9.5 mm, 4.75 mm, 2.36 mm, 1.18 mm, 0.6 mm, 0.3 mm, 0.15 mm and 0.075 mm.

[0101] (2) The maximum diameter of the standard sieve hole should be greater than twice the nominal maximum particle size of the mixture so that the particles with the nominal maximum particle size can participate in the coordination. For AC-25, AC-20, AC-16, AC-13 and AC-10 mixtures, the d0 value is 38 mm;

[0102] (3) The method for determining the number of grading grades is calculated according to formula (3):

[0103]

[0104] Where, d i is the standard sieve hole diameter, mm; d0 is the maximum standard sieve hole diameter, mm; k is the ratio of adjacent standard sieve hole diameters;

[0105] (4) The correspondence between the grade number and the sieve aperture is determined by formula (2). The standard sieve aperture corresponds to the integer term of m in the grade formula. The cumulative volume percentage corresponding to the non-integer m value can be interpolated between two adjacent integer standard sieve apertures.

[0106] 3. Determine the coordination number adjustment method. The adjustment goal is to make the actual coordination number close to the theoretical coordination number and make the calculated result at the critical particle size meet the target value.

[0107] (1) The actual coordination number takes into account the influence of particle angularity and is less than the theoretical coordination number of 6. The actual coordination number n is adjusted between 5.0 and 6.0 to calculate the subtotal volume percentage and cumulative volume percentage;

[0108] (2) Particles smaller than the critical particle size cannot form this level of coordination. The diameter ratio of the critical particle size is ≤0.155. The critical particle size of coarse and fine aggregates is 2.36 mm or 4.75 mm, and the critical particle size of fillers is 0.075 mm.

[0109] (3) Adjust the coordination number so that the sand ratio in the ore grading is close to the target value and the passing percentage of 0.075 mm is equal to the volume percentage of the filler.

[0110] 4. Determine the gradation range so that the gradation range of the maximum particle size of the mixture, the nominal maximum particle size, the controlled particle size and the filler particle size meet the design target requirements. Among them:

[0111] (1) According to the definition of maximum particle size, the passing percentage of the maximum particle size is limited to 100%; according to the definition of nominal maximum particle size, the passing percentage of the nominal maximum particle size is limited to 90% to 100%;

[0112] (2) Calculate V at different coordination numbers using formula (1) i value, so that the percentage of passing the controlled particle size meets the requirements of the design target, and V9 corresponds to a 0.075 mm sieve hole, and its percentage of passing is equal to the volume percentage of the filler;

[0113] (3) For sieve apertures with non-integer m values, the cumulative volume percentage is interpolated between two adjacent integer standard sieve apertures, and the cumulative volume percentage is converted into the passing mass percentage to obtain the design gradation range of the mineral material for different mixtures.

[0114] 2. Marshall stability design

[0115] Determine the mixture composition based on Marshall stability design, including: establishing the Marshall stability design formula; raw material parameter design; mixture volume composition design.

[0116] 1. Establish the Marshall stability design formula, using contact mechanics and particle mechanics theory. The calculation formula is:

[0117]

[0118] Where, MS is the Marshall stability, kN; h is the specimen thickness, mm; D is the specimen diameter, mm; FL is the Marshall test flow value, mm; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J; S v is the volume of solid in the mixture; λ is the linear concentration of solid particles; P a is the mass ratio of asphaltene in the mixture; d a is the average particle size of asphaltene, m.

[0119] 2. Raw material parameter design, including: determining the average adhesion work of asphalt and mineral aggregate in air; determining the asphaltene content in asphalt; determining the gel content in asphalt; determining the mass ratio of asphaltene in the mixture; and determining the average particle size of asphaltene. Among them:

[0120] (1) Determine the average adhesion work of asphalt and mineral aggregate in air. Based on the adhesion work of asphalt and mineral aggregate, the average adhesion work is determined according to formula (5):

[0121]

[0122] Where A 11 is the adhesion work of asphalt. When the asphalt penetration is 10-120 (0.1 mm), the value is 8.0×10 -20 J~8.4×10 -20 J, when the needle penetration is low, take a high value; A 22 is the average adhesion work of the ore, which is taken from Table 1:

[0123] Table 1 Average adhesion work of mineral materials

[0124]

[0125] (2) Determine the asphalt content in asphalt according to the asphalt penetration, using formula (6):

[0126] A=36.735-4.748lnP (6)

[0127] Where A is the mass percentage of asphalt in asphalt, %; P is the asphalt penetration, 0.1 mm.

[0128] (3) Determine the gel content in asphalt according to the asphalt penetration using formula (7):

[0129] G=28.469+2.136lnP (7)

[0130] Where G is the mass percentage of gel in asphalt, %; P is the asphalt penetration, 0.1 mm.

[0131] (4) Determine the mass ratio of asphaltene in the mixture according to formula (8):

[0132] P a =aA (8)

[0133] Where, P a is the mass ratio of asphaltene in the mixture, %; a is the oil-to-stone ratio of the mixture, %; A is the mass percentage of asphaltene in asphalt, %.

[0134] (5) Determine the average size of asphaltene particles. The smallest particle size determines the strength of the mixture. The average size of the smallest asphaltene particles is taken as d a is 3nm, that is, d a =3×10 -9 m.

[0135] 3. Mixture volume composition design includes: mixture composition calculation; mixture volume index calculation; Marshall stability calculation. Among them:

[0136] (1) The mixture composition is calculated using the absolute volume method, including the volume of mineral aggregate, asphalt and mineral powder:

[0137] 1) Calculate the volume of mineral aggregate based on compaction degree, porosity, oil-stone ratio and powder-rubber ratio:

[0138]

[0139] Where: V k is the volume percentage of the ore, %; V m is the maximum compaction degree, %; V p is the void ratio of the mixture, %; a is the oil-stone ratio, %; f is the powder-rubber ratio; ρ a ,ρ f and ρ kThey are the relative densities of asphalt, mineral powder and mineral aggregate, respectively, determined by actual measurement.

[0140] 2) Calculate the volume of asphalt V based on the oil-stone ratio, powder-rubber ratio and mineral volume a :

[0141]

[0142] 3) Calculate the volume of mineral powder V according to the oil-stone ratio, powder-rubber ratio and mineral volume f :

[0143]

[0144] (2) Calculation of mixture volume indicators, including aggregate void ratio, asphalt saturation, volume concentration, and linear concentration:

[0145] 1) Calculate the aggregate void ratio (VMA) of the compacted asphalt mixture based on the asphalt-to-stone ratio, powder-to-rubber ratio, and aggregate volume:

[0146]

[0147] 2) Calculate the asphalt saturation VFA based on the asphalt volume and mineral void ratio:

[0148] VFA=100V A / VMA (13)

[0149] 3) Volume concentration includes the volume of all solids per unit volume S V , the calculation formula is:

[0150] S V =0.01[V k +AV a +V f ] (14)

[0151] 4) Calculate the linear concentration λ based on the maximum volume concentration and the actual volume concentration:

[0152] λ=[(S Vm / S V ) 1 / 3 -1] -1 (15)

[0153] Where S Vm is the maximum volume concentration, S Vm =0.01V m .

[0154] (3) Marshall stability calculation, including: determining the Marshall stability test plan, estimating the Marshall test flow value and calculating the Marshall stability:

[0155] 1) The Marshall stability test can be carried out using the standard Marshall test or the large Marshall test to determine the specimen diameter D and thickness h in mm;

[0156] 2) Based on experience, five different oil-to-stone ratios were selected, the Marshall test flow value was estimated, the Marshall stability was calculated, and the optimal oil-to-stone ratio was determined;

[0157] 3) Fix the optimal oil-stone ratio, select different powder-rubber ratios, estimate the Marshall test flow value, calculate the Marshall stability, and determine the optimal powder-rubber ratio;

[0158] 4) Optimize the composition and volume indicators of the mixture so that the Marshall stability and flow value meet the design target requirements and determine the composition of the mixture.

[0159] 3. Verification of Mixture Road Performance

[0160] Adjust the mixture composition based on dynamic stability and water stability, including: high temperature stability verification; water stability verification.

[0161] 1. High temperature stability is verified by the dynamic stability formula, and the dynamic stability calculation formula is:

[0162]

[0163] Where DS is the dynamic stability, times / mm; h is the thickness of the rutting plate, mm; σ0 is the dynamic stability test load stress, MPa; t is the load action time per time, s; t r is the characteristic time, s; η1 is the viscosity of the mixture, MPa.s; E2 is the elastic modulus of the asphalt mortar, MPa.

[0164] (1) Verification of the dynamic stability of the mixture. The test parameters are determined as follows:

[0165] 1) Dynamic stability test load stress, σ0 = 0.7 MPa. The test load stress can be adjusted for non-standard tests.

[0166] 2) The duration of each load action is calculated based on the loading speed and wheel track contact area, t = 0.0147s.

[0167] 3) The viscoelastic characteristic time is determined by the viscosity of the asphalt mortar and the elastic modulus of the mortar:

[0168] t r =η2 / E2 (17)

[0169] Where: η2 is the viscosity of asphalt mortar, MPa.s; E2 is the elastic modulus of asphalt mortar, MPa.

[0170] (2) Verification of the dynamic stability of the mixture. The viscosity parameters of the mixture are determined as follows:

[0171] 1) The viscosity of the mixture η1 is calculated as follows:

[0172]

[0173] Where η a is the viscosity of asphalt, MPa.s; k is an empirical constant, taken as 14.5; S Vk is the volume ratio of mineral materials in the mixture; S Vf is the volume ratio of filler in asphalt mortar;

[0174] 2) The viscosity η2 of asphalt mortar is calculated as follows:

[0175]

[0176] Where η a is the viscosity of asphalt, MPa.s; k is an empirical constant, taken as 14.5; S Vs is the volume ratio of fine aggregate in asphalt mortar; S Vf is the volume ratio of filler in asphalt mortar;

[0177] 3) The viscosity of asphalt is determined based on the asphalt penetration and viscosity-temperature curve. The calculation formula is:

[0178] lnη a =A+B / T (20)

[0179] Where T is the thermodynamic temperature, K; A and B are empirical constants, and their relationship with needle penetration is:

[0180] A=2.2615lnP-38.331 (21)

[0181] B=-1204lnP+16339 (22)When calibrating A and B, the unit of viscosity is Pa.s, and P is the needle penetration at 25℃, 0.1mm.

[0182] (3) Verification of the dynamic stability of asphalt mixture. The elastic parameters are determined as follows:

[0183] 1) The elastic parameter E1 of asphalt mixture is calculated as follows:

[0184]

[0185] Where, E k ,E f ,E a are the elastic modulus of aggregate, filler and asphalt, MPa;

[0186] 2) The elastic parameter E2 of asphalt mortar is calculated as follows:

[0187]

[0188] Where V s is the volume of fine aggregate in asphalt mixture; E s is the elastic modulus of fine aggregate, MPa; the rest of the meanings are the same as before.

[0189] 2. According to the composition of the mixture, calculate the water-immersion Marshall residual stability. The calculation formula is:

[0190]

[0191] Where M s is the residual stability of the Marshall test after immersion in water, %; FL is the flow value of the Marshall test after immersion in water, mm; D is the diameter of the Marshall specimen, mm; B1 is the spalling rate of the Marshall test after immersion in water, %; A 132 is the average adhesion work of asphalt and mineral aggregate in water, J; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J. Where:

[0192] (1) The spalling rate of the immersion Marshall test can be determined according to the type of ore and its adhesion work using the following formula:

[0193] B1=150.0-93.2A 132 (26)

[0194] Where A 132 is the average adhesion work of asphalt and mineral aggregate in water, ×10 -20 J can be determined by referring to Table 2:

[0195] Table 2 Average adhesion work of asphalt and mineral aggregate in water

[0196]

[0197] (2) The flow value of the Marshall test can be estimated based on the oil-rock ratio and experience, and its value has little effect on the residual stability; the average adhesion work of asphalt and mineral aggregate in air is determined according to formula (5).

[0198] 3. According to the composition of the mixture, calculate the freeze-thaw splitting residual strength ratio. The calculation formula is:

[0199]

[0200] Where, TSR is the freeze-thaw splitting residual strength ratio, %; B2 is the spalling rate of the freeze-thaw splitting test, %. 132 is the average adhesion work of asphalt and mineral aggregate in water, J; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J. Where:

[0201] (1) The spalling rate B2 of the freeze-thaw splitting test can be taken as 1.15 to 1.30 times of B1;

[0202] (2) The average adhesion work of asphalt and mineral aggregate in air is calculated according to formula (5); the average adhesion work of asphalt and mineral aggregate in water is taken according to Table 2. Specific embodiment:

[0204] 1. Mineral Grading Design Example

[0205] The coordination number is adjusted according to the filler dosage, and the design results are shown in Table 3. In the table, AC-25 represents asphalt mixture with a nominal maximum particle size of 25 mm, and the numbers represent the nominal maximum particle size; V f is the volume percentage of filler in the total mineral material; the coordination number n is accurate to the third decimal place; the particle size d i is the aggregate sieve hole diameter, mm; the maximum particle size d0 is 38 mm, the adjacent sieve hole diameter ratio k = 0.5, the integer m is the classification number, and the non-integer m is used for interpolation between two adjacent integer sieve holes.

[0206] Aggregate gradation is expressed as volume percentage. When gradation is expressed using aggregates of varying densities and expressed as mass percentage, it's easy to convert volume percentages to mass percentages. The coordination number is highly sensitive to gradation design results. When the coordination number is accurately determined, aggregate gradation can be precisely designed, ensuring that filler dosage meets control targets and that the percentages of 4.75mm and 2.36mm passing through meet empirical targets. To prevent interference between coarse and fine aggregates at the boundary particle size, a discontinuity between 2.36mm and 4.75mm can be added to the coarse aggregate content of the previous level.

[0207] Table 3 Asphalt mixture aggregate gradation design results

[0208]

[0209]

[0210] 2. Marshall Stability Design Example

[0211] Route 70 petroleum asphalt is used, with a relative density of 1.02; limestone is used for both coarse and fine aggregates, and limestone powder is used as filler, both with a relative density of 2.70. The design control targets are: void ratio 3% to 6%, aggregate interstitial ratio 13% to 15%, flow value 3.0mm, asphalt saturation 55% to 70%, and minimum Marshall stability ≥ 8.0kN. An example of Marshall stability design is shown below. Figure 1 As shown. Among them: Figure 1 is the relationship between the interstitial ratio and void ratio of the mineral material; Figure 2 is the relationship between asphalt saturation and void ratio; Figure 3 is the relationship between Marshall stability and void ratio.

[0212] Depend on Figure 1 It can be seen that when the designed void ratio is 4% to 5%, the oil-stone ratio of 3.5% to 4.0% can meet the requirement of a maximum void ratio of 15%. Figure 2 It can be seen that when the designed void ratio is 5%, the saturation can only meet the requirement of not less than 55% when the oil-stone ratio is ≥3.8%. Figure 3 It can be seen that when the maximum void ratio is 6%, the Marshall stability ≥ 8.0kN and the oil-stone ratio ≥ 3.9% can meet the design requirements. Based on the above analysis, the optimal oil-stone ratio is 3.9%.

[0213] The proposed method for designing graded asphalt mixtures uses Marshall stability design to rapidly determine the optimal asphalt-to-aggregate ratio, ensuring that the design results fully meet technical specifications and design objectives. This design method allows for precise control of mixture composition and road performance, enabling quantitative design of asphalt mixtures, significantly reducing testing workload and accelerating the design process and increasing the success rate of mixture composition.

[0214] 3. Asphalt mixture road performance verification example

[0215] The road was constructed using No. 70 petroleum asphalt with a relative density of 1.02. Both the coarse and fine aggregates were limestone, and the filler was limestone powder, both with a relative density of 2.70. The dynamic stability control target was DS ≥ 1000 times / mm.

[0216] (1) Verification of high temperature stability of mixture

[0217] Figure 4 The relationship between dynamic stability and oil-stone ratio is shown in Figure 2. When the optimal oil-stone ratio is 3.9%, the DS is 1390 times / mm, which meets the target requirements. Figure 5 The relationship between dynamic stability and powder-rubber ratio is that when the oil-stone ratio is optimal, appropriately increasing the powder-rubber ratio can improve the dynamic stability of the mixture and ensure that the dynamic stability of the mixture meets the requirements; Figure 6 The relationship between dynamic stability and void ratio is shown in Figure 2. Dynamic stability meets the requirements when the void ratio is within the range of 3% to 6%. Figure 7 The relationship between dynamic stability and sand ratio is that increasing the sand ratio appropriately can improve dynamic stability. Therefore, it is not the case that the more coarse aggregate is used, the better.

[0218] (2) Verification of mixture water stability

[0219] 1) Calculation of Marshall residual stability after immersion

[0220] In this embodiment, the Marshall residual stability design target is M s ≥80%. The asphalt is No. 70 asphalt, and the adhesion work in the air is A11 =8.32×10 -20 J; the ore material is limestone, A 22 =12.64×10 -20 J; Calculate the adhesion work A between asphalt and mineral material according to formula (5) 12 =10.25×10 -20 J.

[0221] From Table 2, we can find A 132 =1.49×10 -20 J, the peeling rate calculated according to formula (26) is B1=11.13%. The Marshall test flow value is taken as 3mm and the specimen size is 101.6mm. Substituting each parameter into formula (25), the Marshall test residual stability is obtained as 79.46%<80%, which does not meet the requirements and needs to be improved. It can be improved by adding slaked lime or cement, or the penetration of asphalt can be appropriately reduced to increase the adhesion work of asphalt. In this embodiment, the flow value can be reduced to 2mm, and the Marshall residual stability is calculated to be 80.27%≥80%, which meets the design requirements.

[0222] 2) Freeze-thaw splitting residual strength ratio

[0223] In this embodiment, the freeze-thaw splitting residual strength ratio is designed to be TSR ≥ 75%. The asphalt is No. 70 asphalt, and the adhesion work in air is A 11 =8.32×10 -20 J; the ore material is limestone, A 22 =12.64×10 -20 J; Calculate the adhesion work A between asphalt and mineral material according to formula (5) 12 =10.25×10 -20 J.

[0224] From Table 2, we can find A 132 =1.49×10 -20 J, the spalling rate calculated by formula (26) is B1 = 11.13%. In the freeze-thaw splitting test, the spalling rate increases to 1.3 times, B2 = 14.47%, and the calculated TSR is 76.8> 75%, which meets the design target requirements.

[0225] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for designing graded asphalt mixture, characterized in that: The following steps are involved: S1. Design the aggregate gradation of the mixture using the progression method, including: constructing the progression gradation formula, determining the gradation classification method, determining the coordination number adjustment method, and determining the gradation range; S2. Determine the mixture composition based on Marshall stability design, including: establishing the Marshall stability design formula, designing raw material parameters, and designing the mixture volume composition; S3. Design and adjust the mixture composition based on dynamic stability and water stability.

2. A method for designing graded asphalt mixture according to claim 1, characterized in that: Step S1 includes: (1) Construct the gradation formula, the calculation formula is: Where V i is the cumulative volume percentage on the sieve hole No. i, %; m is the number of series; n is the average coordination number of particles; k is the ratio of the diameters of adjacent sieve holes; (2) Determine the grading method: take the standard sieve hole sequence with the adjacent sieve hole diameter ratio k=0.5 as 38mm, 19mm, 9.5mm, 4.75mm, 2.36mm, 1.18mm, 0.6mm, 0.3mm, 0.15mm and 0.075mm, take the standard sieve hole with a nominal maximum particle size of more than 2 times as the sieve hole number 0, take the sieve hole of 0.075mm as the sieve hole number m, and the numbers of other sieve holes are as follows: Where, d i is the standard sieve hole diameter, mm; d0 is the maximum standard sieve hole diameter, mm; k is the ratio of adjacent standard sieve hole diameters; (3) Determine the coordination number adjustment method: Based on the ratio of adjacent sieve hole diameters, the theoretical coordination number n is 6.

0. The actual coordination number n is adjusted within the range of 5.0 to 6.0 so that the percentage of particles passing through 0.075 mm is equal to the volume percentage of the filler; (4) Determine the gradation range: the maximum particle size passing percentage is 100%, the nominal maximum particle size passing percentage is 90% to 100%, and the coordination number is adjusted according to the range of filler volume change to determine the gradation range.

3. A method for designing graded asphalt mixture according to claim 1, characterized in that: Step S2 includes: (1) Establish the Marshall stability design formula as follows: Where, MS is the Marshall stability, kN; h is the specimen thickness, mm; D is the specimen diameter, mm; FL is the Marshall test flow value, mm; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J; S v is the volume of solid in the mixture; λ is the linear concentration of solid particles; P a is the mass ratio of asphaltene in the mixture; d a is the average particle size of asphaltene, m; (2) Raw material parameter design, including: determining the average adhesion work of asphalt and mineral aggregate in air, determining the asphaltene content in asphalt, determining the gel content in asphalt, determining the mass ratio of asphaltene in the mixture, and determining the average particle size of asphaltene; a. Determine the average adhesion work A of asphalt and mineral aggregate in air 12 , determined by the following formula: Where A 11 is the adhesion work of asphalt. When the asphalt penetration is 10-120 (0.1 mm), the value is 8.0×10 -20 J~8.4×10 -20 J, when the needle penetration is low, take a high value; A 22 is the average adhesion work of the ore; b. Determine the asphalt content in asphalt according to the asphalt penetration: A=36.735-4.748lnP Where A is the mass percentage of asphalt in asphalt, %; P is the asphalt penetration, 0.1 mm; c. Determine the gel content in asphalt according to the asphalt penetration: G=28.469+2.136lnP Where, G is the mass percentage of gel in asphalt, %; P is the asphalt penetration, 0.1mm; d. Determine the mass ratio of asphaltene in the mixture according to the following formula: Q a =aA Where, P a is the mass ratio of asphaltene in the mixture, %; a is the oil-to-stone ratio of the mixture, %; A is the mass percentage of asphaltene in asphalt, %; e. Determine the average size of asphaltene particles. The smallest particle size determines the strength of the mixture. The average size of the smallest asphaltene particles is taken as d a is 3nm, that is, d a =3×10 -9 m; (3) Mixture volume composition design, including: mixture composition calculation; mixture volume index calculation; Marshall stability calculation; a. Mixture composition calculation, using the absolute volume method, including the volume of mineral aggregate, asphalt and mineral powder: 1) Calculate the volume of the aggregate based on compaction, porosity, oil-stone ratio and powder-rubber ratio: Where: V k is the volume percentage of the ore, %; V m is the maximum compaction degree, %; V p is the void ratio of the mixture, %; a is the oil-stone ratio, %; f is the powder-rubber ratio; ρ a ,ρ f and ρ k are the relative densities of asphalt, mineral powder and mineral aggregate, respectively, determined by actual measurement; 2) Calculate the volume of asphalt V based on the oil-stone ratio, powder-rubber ratio and mineral volume a : 3) Calculate the volume of mineral powder V according to the oil-stone ratio, powder-rubber ratio and mineral volume f : b. Calculation of mixture volume indicators, including aggregate void ratio, asphalt saturation, volume concentration and linear concentration: 1) Calculate the aggregate void ratio (VMA) of the compacted asphalt mixture based on the asphalt-to-stone ratio, powder-to-rubber ratio, and aggregate volume: 2) Calculate the asphalt saturation VFA based on the asphalt volume and mineral void ratio: VFA=100V A / VMA 3) Volume concentration includes the volume of all solids per unit volume S V , the calculation formula is: S V =0.01[V k +OFF a +V f ] 4) Calculate the linear concentration λ based on the maximum volume concentration and the actual volume concentration: λ=[(S Vm / S V ) 1 / 3 -1] -1 Where S Vm is the maximum volume concentration, S Vm =0.01V m ; c. Marshall stability calculation, including: determining the Marshall stability test plan, estimating the Marshall test flow value and calculating the Marshall stability: 1) The Marshall stability test uses the standard Marshall test or the large Marshall test to determine the specimen diameter D and thickness h, in mm; 2) Based on experience, five different oil-to-stone ratios were selected, the Marshall test flow value was estimated, the Marshall stability was calculated, and the optimal oil-to-stone ratio was determined; 3) Fix the optimal oil-stone ratio, select different powder-rubber ratios, estimate the Marshall test flow value, calculate the Marshall stability, and determine the optimal powder-rubber ratio; 4) Optimize the composition and volume indicators of the mixture so that the Marshall stability and flow value meet the design target requirements and determine the composition of the mixture.

4. A method for designing graded asphalt mixture according to claim 1, characterized in that: Step S3 includes: (1) According to the mixture composition, the dynamic stability of the mixture is calculated using the following formula: Where DS is the dynamic stability, times / mm; h is the thickness of the rutting plate, mm; σ0 is the load stress of the dynamic stability test (MPa), σ0 = 0.7 MPa; t is the load action time (s), t = 0.0147 s; η1 is the viscosity of the mixture, MPa.s; E2 is the elastic modulus of the asphalt mortar, MPa; t r is the characteristic time (s), t r =η2 / E2; η2 is the viscosity of asphalt mortar, MPa.s.; (2) According to the composition of the mixture, the water-immersion Marshall residual stability is calculated using the following formula: Where M s is the residual stability of the Marshall test after immersion in water, %; FL is the flow value of the Marshall test after immersion in water, mm; D is the diameter of the Marshall specimen, mm; B1 is the spalling rate of the Marshall test after immersion in water, %; A 132 is the average adhesion work of asphalt and mineral aggregate in water, J; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J; (3) According to the composition of the mixture, the freeze-thaw splitting residual strength ratio is calculated using the following formula: Where, TSR is the freeze-thaw splitting residual strength ratio, %; B2 is the spalling rate of the freeze-thaw splitting test, %; A 132 is the average adhesion work of asphalt and mineral aggregate in water, J; A 12 is the average adhesion work of asphalt and mineral aggregate in air, J.

5. A method for designing graded asphalt mixture according to claim 4, characterized in that: The viscosity η1 of the mixture is calculated as follows: Where η a is the viscosity of asphalt, MPa.s; k is an empirical constant, taken as 14.5; S Vk is the volume ratio of mineral materials in the mixture; S Vf is the volume ratio of filler in asphalt mortar; The viscosity η2 of asphalt mortar is calculated as follows: Where η a is the viscosity of asphalt, MPa.s; k is an empirical constant, taken as 14.5; S Vs is the volume ratio of fine aggregate in asphalt mortar; S Vf is the volume ratio of filler in asphalt mortar; The viscosity of asphalt is determined based on the asphalt penetration and viscosity-temperature curve. The calculation formula is: lnη a =A+B / T Where T is the thermodynamic temperature, K; A and B are empirical constants, and their relationship with needle penetration is: A=2.2615lnP-38.331 B=-1204lnP+16339 When calibrating A and B, the unit of viscosity is Pa.s, and P is the needle penetration at 25°C, 0.1mm.

Images