Blending method of blast furnace slag powder-fly ash-emulsified asphalt mixture

Abstract

The invention provides a mixing method of a blast furnace slag powder-fly ash-emulsified asphalt mixture, and belongs to the field of road engineering. According to the improved mixing method provided on the basis of the specific surface area of the aggregate, the workability in the mixture mixing process, the difference of the adsorption capacity of the aggregate to the emulsified asphalt and the cement-blast furnace slag powder-fly ash hydration reaction process are fully considered, so that the surfaces of the coarse-grade RAP and the new aggregate can be more wrapped by the emulsified asphalt; therefore, the distribution of the emulsified asphalt is more uniform, the mixing of the regenerated mixture is more uniform, the thickness distribution of asphalt films on the surfaces of different types of aggregates after demulsification of the emulsified asphalt is more uniform, and the phenomenon of'gray material 'of the normal-temperature regenerated mixture is solved; the mixing method is carried out in a distributed manner, so that the hydration reaction of the cement, the blast furnace slag powder and the fly ash is more complete, and the performance of the'blast furnace slag powder-fly ash 'emulsified asphalt normal-temperature regenerated mixture is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of road engineering, and particularly to a mixing method for blast furnace slag powder-fly ash-emulsified asphalt mixture. Background Art

[0002] Emulsified asphalt cold recycling is a commonly used pavement recycling technology, and cement is an important additive therein. However, in the production process of cement, not only non-renewable resources such as limestone are consumed, but also a large amount of carbon emissions are generated. If, on the premise of ensuring road performance, cementitious materials such as blast furnace slag powder and fly ash are used to replace cement, it can not only promote the large-scale disposal of industrial solid waste, but also achieve the purposes of reducing cement production, reducing energy consumption and saving costs. However, research shows that the replacement of cement with blast furnace slag powder-fly ash will lead to the attenuation of road performance. If the mixing method of emulsified asphalt cold recycling mixture of "blast furnace slag powder-fly ash" is improved, the performance of the mixture can be improved, thereby compensating for the performance attenuation caused by the replacement of cement. According to the current conventional method, the mixing method of blast furnace slag powder-fly ash emulsified asphalt cold recycling mixture (conventional mixing method) should be to first mix and stir RAP old materials, new aggregates, mineral powder, cement-blast furnace slag powder-fly ash, etc. in a mixing pot, then add water and mix evenly, and then add the calculated emulsified asphalt all at once for full mixing. The process flow chart of the conventional mixing method is as Figure 1 shown.

[0003] Mixing cold recycling mixture according to the above mixing method will cause the emulsified asphalt to be unevenly distributed in the mixed system, with more emulsified asphalt on the surface of fine aggregates and less emulsified asphalt on the surface of new aggregates, and even no asphalt coating, resulting in pale and white materials.

[0004] For cold recycling mixture without blast furnace slag powder-fly ash, some research has adopted a step-by-step and graded mixing method, adding emulsified asphalt in two steps. First, it is mixed with coarse-grade RAP (10-30 mm), new aggregates (10-20 mm), and part of the water. In the second step, it is mixed with fine RAP (0-5 mm), medium-grade RAP (5-10 mm), mineral powder, cement, and part of the water, and finally mixed with the remaining water. This graded and step-by-step mixing method has also achieved good mixing effects. However, there is no scientific method to determine the addition amount of emulsified asphalt in the two-step process, and the mixing method of cold recycling mixture with "blast furnace slag powder-fly ash" is not considered. Summary of the Invention

[0005] The present invention provides a mixing method for blast furnace slag powder-fly ash-emulsified asphalt mixture. The blast furnace slag powder-fly ash-emulsified asphalt mixture mixed by using the mixing method of the present invention is more uniform and has good dry splitting strength, water stability, high-temperature stability and low-temperature crack resistance.

[0006] The present invention provides a mixing method for blast furnace slag powder-fly ash-emulsified asphalt mixture, comprising the following steps:

[0007] Perform a first mixing on coarse RAP, new aggregates, a part of emulsified asphalt, a part of blast furnace slag powder, a part of fly ash, a part of cement and a first part of water to obtain a first mixture;

[0008] Perform a second mixing on the said first mixture, fine RAP, medium RAP, mineral powder, the remaining emulsified asphalt, the remaining blast furnace slag powder, the remaining fly ash, the remaining cement and a second part of water to obtain a second mixture;

[0009] Perform a third mixing on the said second mixture and the remaining water;

[0010] The mass percentage of the part of emulsified asphalt in the total amount of emulsified asphalt, the mass percentage of the part of blast furnace slag powder in the total amount of blast furnace slag powder, the mass percentage of the part of fly ash in the total amount of fly ash and the mass percentage of the part of cement in the total amount of cement are independently A±0.5%;

[0011]

[0012] In formula (1):

[0013] S1, S2, S3, S4, S5, S6, S7, S8 are respectively the specific surface areas of coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement, with the unit m 2 / kg;

[0014] P1, P2, P3, P4, P5, P6, P7, P8 are respectively the percentages of coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement in the total mass of coarse RAP, new aggregates, fine RAP, medium RAP and mineral powder.

[0015] Preferably, the calculation methods of the specific surface areas of the coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement are as shown in formula (2):

[0016] s = 0.41 + 0.0041P 4.75 + 0.0082P 2.36 + 0.0164P 1.18 + 0.0287P 0.6 + 0.0614P 0.3 + 0.1229P0.15 +0.3277P 0.075 Equation (2);

[0017] In Equation (2):

[0018] P 4.75 、P 2.36 、P 4.75 、P 1.18 、P 0.6 、P 0.3 、P 0.15 、P 0.075 are the passing rates of coarse RAP, new aggregate, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash or cement through sieves with particle sizes of 4.75 mm, 2.36 mm, 4.75 mm, 1.18 mm, 0.6 mm, 0.3 mm, 0.15 mm, 0.075 mm respectively.

[0019] Preferably, the raw materials of the blast furnace slag powder-fly ash-emulsified asphalt mixture include: powder materials and admixtures;

[0020] By mass fraction, the powder materials include:

[0021]

[0022] The admixtures include: one or more of cement, blast furnace slag powder and fly ash, water, emulsified asphalt;

[0023] The mass of one or more of the cement, blast furnace slag powder and fly ash is 1.5% of the mass of the powder materials;

[0024] The mass of the water is 4.9% of the mass of the powder materials;

[0025] The mass of the emulsified asphalt is 3.6% of the mass of the powder materials.

[0026] Preferably, the particle size of the coarse RAP is 10 - 30 mm or 10 - 26.5 mm; the particle size of the new aggregate is 10 - 20 mm; the particle size of the fine RAP is 0 - 5 mm, and the particle size of the medium RAP is 5 - 10 mm.

[0027] Preferably, both the first part of water and the second part of water are 1 / 3 of the total amount of water.

[0028] Preferably, the stirring speed of the first mixing is 45 - 55 r / min, and the time is 60 s.

[0029] Preferably, the stirring speed of the second mixing is 45 - 55 r / min, and the time is 60 s.

[0030] Preferably, the stirring speed of the third mixing is 45-55 r / min, and the time is 30 s.

[0031] Preferably, the density of the blast furnace slag powder is 2.88 g / cm 3 ; the density of the fly ash is 2.39 g / cm 3 , and the density of the cement is 3.15 g / cm 3 .

[0032] Preferably, the coating area of the emulsified asphalt and the new aggregate > 2 / 3.

[0033] The improved mixing method proposed based on the specific surface area of the aggregate in the present invention fully considers the workability during the mixing process of the mixture, the difference in the adsorption capacity of the aggregate for the emulsified asphalt, and the hydration reaction process of cement-blast furnace slag powder-fly ash, enabling the coarse-grade RAP and the surface of the new aggregate to be more coated with the emulsified asphalt. This makes the distribution of the emulsified asphalt more uniform, the mixing of the recycled mixture more uniform, and the thickness distribution of the asphalt film on the surfaces of different types of aggregates more uniform after the emulsified asphalt demulsifies, solving the phenomenon of "variegated materials" in the cold recycled mixture; and the mixing method of the present invention is carried out step by step, making the hydration reaction of cement-blast furnace slag powder-fly ash more complete, enhancing the bonding and strengthening effects of gels such as C-S-H and AFt at the interfaces of aggregate-asphalt mortar, etc., improving the overall stability and interface structure performance of the asphalt mortar, and further enhancing the performance of the "blast furnace slag powder-fly ash" cold recycled mixture with emulsified asphalt (for example: dry splitting strength, water stability, high-temperature stability, and low-temperature crack resistance). Description of the Drawings

[0034] Figure 1 is the process flow chart of the conventional mixing method;

[0035] Figure 2 is the process flow chart of the mixing method of the embodiment of the present invention;

[0036] Figure 3 is the process flow chart of the mixing method of Comparative Example 1;

[0037] Figure 4 is the process flow chart of the mixing method of Comparative Example 2;

[0038] Figure 5 are the test results of the void ratio of the mixture with different mixing methods and different alternative schemes;

[0039] Figure 6 are the test results of the dry splitting strength of the mixture with different mixing methods and different alternative schemes;

[0040] Figure 7 are the test results of the low-temperature splitting strength of the mixture with different mixing methods and different alternative schemes;

[0041] Figure 8 Freeze-thaw splitting strength ratio TSR test results of mixtures with different mixing methods and different replacement schemes;

[0042] Figure 9 For the dynamic stability test results of mixtures with different mixing methods and different replacement schemes;

[0043] Figure 10 For the SIP test results of mixtures with different mixing methods and different replacement schemes;

[0044] Figure 11 For the SS test results of mixtures with different mixing methods and different replacement schemes;

[0045] Figure 12 For the G f test results of mixtures with different mixing methods and different replacement schemes;

[0046] Figure 13 For the K IC test results of mixtures with different mixing methods and different replacement schemes. Detailed implementation method

[0047] The present invention provides a mixing method for blast furnace slag powder-fly ash-emulsified asphalt mixture, comprising the following steps:

[0048] Mix the coarse RAP, new aggregates, part of the emulsified asphalt, part of the blast furnace slag powder, part of the fly ash, part of the cement with the first part of water for the first mixing to obtain the first mixture;

[0049] Mix the first mixture with the fine RAP, medium RAP, mineral powder, remaining emulsified asphalt, remaining blast furnace slag powder, remaining fly ash, remaining cement and the second part of water for the second mixing to obtain the second mixture;

[0050] Mix the second mixture with the remaining water for the third mixing;

[0051] The mass percentages of part of the emulsified asphalt in the total amount of emulsified asphalt, part of the blast furnace slag powder in the total amount of blast furnace slag powder, part of the fly ash in the total amount of fly ash, and part of the cement in the total amount of cement are independently A±0.5%;

[0052]

[0053] In formula (1):

[0054] S1, S2, S3, S4, S5, S6, S7, and S8 are the specific surface areas of coarse RAP, new aggregate, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash, and cement, respectively, with the unit m 2 / kg;

[0055] P1, P2, P3, P4, P5, P6, P7, and P8 are the percentages of coarse RAP, new aggregate, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash, and cement in the total mass of coarse RAP, new aggregate, fine RAP, medium RAP, and mineral powder, respectively.

[0056] In the present invention, by mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 33% of fine RAP; the particle size of the fine RAP is preferably 0 - 5 mm;

[0057] By mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 19% of medium RAP; the particle size of the medium RAP is preferably 5 - 10 mm;

[0058] By mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 36% of coarse RAP; the particle size of the coarse RAP is preferably 10 - 30 mm or 10 - 26.5 mm;

[0059] By mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 10% of new aggregate; the particle size of the new aggregate is preferably 10 - 20 mm;

[0060] By mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 2% of mineral powder; Mineral powder has multiple functions in asphalt mixtures, including filling voids, increasing density, improving pore structure, enhancing impermeability, strengthening stability, durability, and anti - aging performance, etc., and can reduce pavement problems such as cracking and deformation, and extend service life.

[0061] By mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 1.5% of blast furnace slag powder - fly ash; After adding blast furnace slag powder, fly ash and cement and other cementitious materials to the emulsified asphalt cold recycling mixture, the hydraulicity, pozzolanic activity and other hydration activities can be exerted, and a large amount of gelatinous hydration products are generated to strengthen the interface strength of the asphalt mortar and promote the demulsification of the emulsified asphalt

[0062] By mass fraction, the raw materials of the blast furnace slag powder - fly ash - emulsified asphalt mixture preferably include 4.9% of water;

[0063] In terms of mass fraction, the raw materials of the blast furnace slag powder-fly ash-emulsified asphalt mixture preferably include 3.6% of emulsified asphalt

[0064] In the present invention, the coarse RAP, new aggregates, part of the emulsified asphalt, part of the blast furnace slag powder, part of the fly ash, part of the cement and the first part of water are subjected to the first mixing to obtain the first mixture. At least one of the blast furnace slag powder, fly ash and cement is not zero.

[0065] In the present invention, the first part of water is preferably 1 / 3 of the total amount of water.

[0066] In the present invention, the mass percentage of the part of the emulsified asphalt in the total amount of emulsified asphalt, the mass percentage of the part of the blast furnace slag powder in the total amount of blast furnace slag powder, the mass percentage of the part of the fly ash in the total amount of fly ash and the mass percentage of the part of the cement in the total amount of cement are independently A±0.5%;

[0067]

[0068] In formula (1):

[0069] S1, S2, S3, S4, S5, S6, S7, S8 are the specific surface areas of the coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement respectively, with the unit m 2 / kg;

[0070] P1, P2, P3, P4, P5, P6, P7, P8 are the percentages of the coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement in the total mass of the coarse RAP, new aggregates, fine RAP, medium RAP and mineral powder respectively;

[0071] In the present invention, the calculation method of the specific surface areas S of the coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement is preferably as shown in formula (2):

[0072] s = 0.41 + 0.0041P 4.75 + 0.0082P 2.36 + 0.0164P 1.18 + 0.0287P 0.6 + 0.0614P 0.3 + 0.1229P 0.15 + 0.3277P 0.075 Formula (2);

[0073] In formula (2):

[0074] P 4.75 、P 2.36 、P 4.75 、P 1.18 、P 0.6 、P 0.3 、P 0.15 、P 0.075 are the passing rates of coarse-grade RAP, new aggregates, fine RAP or medium-grade RAP through particle sizes of 4.75 mm, 2.36 mm, 4.75 mm, 1.18 mm, 0.6 mm, 0.3 mm, 0.15 mm, and 0.075 mm respectively.

[0075] In the present invention, the stirring speed of the first mixing is preferably 45 - 55 r / min, and the time is preferably 60 s. In specific embodiments of the present invention, the stirring speed of the first mixing can be 45 r / min, 50 r / min, or 55 r / min.

[0076] After obtaining the first mixture, the present invention mixes the first mixture with fine RAP, medium-grade RAP, mineral powder, remaining emulsified asphalt, remaining blast furnace slag powder, remaining fly ash, remaining cement, and the second part of water for the second mixing to obtain a second mixture.

[0077] In the present invention, the second part of water is preferably 1 / 3 of the total amount of water.

[0078] In the present invention, the stirring speed of the second mixing is preferably 45 - 55 r / min, and the time is preferably 60 s. In specific embodiments of the present invention, the stirring speed of the second mixing can be 45 r / min, 50 r / min, or 55 r / min.

[0079] After obtaining the second mixture, the present invention mixes the second mixture with the remaining water for the third mixing.

[0080] In the present invention, the stirring speed of the third mixing is preferably 45 - 55 r / min, and the time is preferably 30 s. In specific embodiments of the present invention, the stirring speed of the third mixing can be 45 r / min, 50 r / min, or 55 r / min..

[0081] The following combines examples to detail the mixing method of the blast furnace slag powder - fly ash - emulsified asphalt mixture provided by the present invention, but they should not be construed as limiting the protection scope of the present invention.

[0082] The process flow chart of the mixing method of the embodiment of the present invention is as Figure 2 shown.

[0083] Example 1

[0084] The raw materials and their ratios of the emulsified asphalt cold recycling mixture of Improved Process 1, Improved Process 2 and the comparative process are shown in Table 1.

[0085] Table 1 Raw materials and their ratios of the emulsified asphalt cold recycling mixture

[0086]

[0087] The RAP material uses the milled material of the old asphalt surface layer selected from a certain highway reconstruction and expansion project in Inner Mongolia. The content of the old asphalt in each grade of RAP old material is shown in Table 2.

[0088] Table 2 Test results of the old asphalt content in the RAP old material

[0089]

[0090] The detection indexes of the emulsified asphalt are shown in Table 3.

[0091] Table 3 Test results of the detection indexes of the emulsified asphalt

[0092]

[0093]

[0094] The technical indexes of the new aggregate (10 - 20mm) are shown in Table 4:

[0095] Table 4 Test results of the technical indexes of the 10 - 20mm new aggregate

[0096] Test Technical Indexes Test Results Specification Requirements Test Methods Relative Density (Apparent) 2.77 ≮2.5 T0308 Water Absorption / % 1.9 ≯3.0 T0308 Crushing Value / % 17.4 ≯28 T0316 Los Angeles Abrasion Loss / % 21 ≯30 T0317 <0.075 Particle content / % 0.05 ≯1.0 T0302 Soundness / % 6.2 ≯12 T0314

[0097] For the S95 blast furnace slag powder, Class F Grade II fly ash and P·O 42.5 cement of the present invention, the test results of the density indexes are shown in Table 5.

[0098] Table 5 Test results of the density of the blast furnace slag powder, fly ash and cement

[0099] Raw Materials Ground Granulated Blast-Furnace Slag Fly Ash Cement <![CDATA[Density (g / cm 3 )]]> 2.88 2.39 3.15

[0100] The mineral powder is limestone mineral powder, and the test results of the technical indexes are shown in Table 6.

[0101] Table 6 Test results of the technical indexes of the mineral powder

[0102]

[0103] According to the "structural asphalt" calculation formula given in JTG F40 - 2004 "Technical Specifications for Construction of Highway Asphalt Pavements", the asphalt film thickness is calculated as shown in Equation (3):

[0104]

[0105] In the formula: DA is the effective thickness of the asphalt film, with the unit of μm; P be is the effective asphalt content, dimensionless; γ b is the relative density of asphalt (at 25°C), dimensionless; SA refers to the total specific surface area of the aggregate, with the unit of m 2 / kg.

[0106] After the emulsified asphalt and the mineral aggregate are mixed, they will wrap around the surface of the aggregate, forming an asphalt-coated film called "structural asphalt". "Structural asphalt" is one of the important influencing factors for the strength of the emulsified asphalt cold recycling mixture. Outside the "structural asphalt" is the "free asphalt" that has not undergone chemical adsorption. The asphalt film formed by combining with the aggregate must reach a sufficient thickness to ensure that the cold recycling mixture has qualified road performance. Therefore, during the mixing process of the cold recycling mixture, it is necessary to accurately control the thickness of the asphalt film on the surface of the aggregate. It should be noted that the asphalt film thickness mentioned here refers to the new asphalt film thickness formed on the surface of the aggregate after the emulsified asphalt breaks.

[0107] According to the "Technical Specifications for Construction of Highway Asphalt Pavements (JTG F40 - 2004)" and the calculation method given by the National Center for Asphalt Technology (NCAT) in the United States, by considering the aggregate as a perfect spherical solid, the specific surface area coefficients of each size of aggregate are calculated, and the results are shown in Table 7.

[0108] Table 7 Specific surface area coefficients of aggregates with different particle sizes

[0109] Sieve Opening Size (mm) >4.75 2.36 1.18 0.6 0.3 0.15 0.075 <![CDATA[Specific surface area coefficient (m 2 / g)]]> 4.1 8.2 16.4 28.7 61.4 1229 3277

[0110] The specific surface area S of aggregates with different gradations is calculated by Equation 2.

[0111]

[0112] In Equation (2): S is the specific surface area of the aggregate, with the unit of m 2 / kg, and Pi is the passing percentage (%) of various particle sizes of the aggregate.

[0113] Taking the gradation of a test section of a cold recycling project on a certain highway in Inner Mongolia as an example, the screening results of fine RAP, medium RAP, coarse RAP, new aggregate, mineral powder, cement, blast furnace slag powder, and fly ash are shown in Table 8.

[0114] Table 8 Screening results of fine RAP, medium RAP, coarse RAP, new aggregate, mineral powder, blast furnace slag powder - fly ash

[0115]

[0116]

[0117] According to Table 8 and Equation (2), the specific surface areas of fine RAP, medium RAP, coarse RAP, new aggregates, mineral powder, and cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash were calculated, and the results are shown in Table 9.

[0118] Table 9 Specific Surface Areas of Fine RAP, Medium RAP, Coarse RAP, New Aggregates, Mineral Powder, and Blast Furnace Slag Powder - Fly Ash

[0119]

[0120] According to Table 1, Table 9, and Equation (1), the proportion of the specific surface areas of coarse RAP and new aggregates in the emulsified asphalt cold recycled mixture can be calculated (taking "10 - 26.5 mm RAP and new aggregates" as an example, the calculation method is 0.77×36% + 0.98×10%), and the calculation results are shown in Table 10.

[0121] Table 10 Proportion of Specific Surface Areas of Coarse RAP and New Aggregates in the Emulsified Asphalt Cold Recycled Mixture

[0122]

[0123] The improved process proposed by the present invention: First, new aggregates, 10 - 26.5 mm RAP, part of the emulsified asphalt, part of the cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash, and part of the water are mixed, then the remaining cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash, emulsified asphalt, part of the water, fine RAP, medium RAP, and mineral powder are added and mixed, and finally the remaining water is added and mixed. In the improved process, the new aggregates, 10 - 26.5 mm RAP, and part of the cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash added first need to be coated with an appropriate proportion of emulsified asphalt to obtain a suitable asphalt film thickness, and the fine RAP, medium RAP, mineral powder, and the remaining cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash added later also need to be coated with sufficient emulsified asphalt. Therefore, based on the specific surface area of the aggregates, the present invention determines the following experimental scheme for the addition ratio distribution:

[0124] As can be seen from Table 10, the proportion of the specific surface areas of new aggregates and RAP materials in the total is 9.5%. Considering that a small amount of cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash with a relatively large specific surface area will also be added, the proportion of the specific surface area in the total is taken as 10%; that is, in order to make the asphalt film thickness on the surfaces of new aggregates and coarse RAP more uniform, 10% of the emulsified asphalt is added in the first step, and 90% of the emulsified asphalt is added in the second step.

[0125] Add the coarse RAP, new aggregates, water (one-third of the externally added water), cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash (total dosage 10%), and emulsified asphalt (total dosage 10%) according to the proportions in Table 1 into the mixing pot, and mix at a stirring speed of 50 r / min for 60 s;

[0126] Add the fine RAP, medium RAP, mineral powder, water (one-third of the externally added water), cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash (total dosage 90%), and emulsified asphalt (total dosage 90%), and mix at a stirring speed of 50 r / min for 60 s;

[0127] Add water (one-third of the externally added water), and mix at a stirring speed of 50 r / min for 30 s to complete the mixing.

[0128] (Recorded as improved process 2)

[0129] The summary of the two-time addition ratios of emulsified asphalt and cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash is shown in Table 11.

[0130] Table 11 Two-time addition ratios of emulsified asphalt and cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash for cold recycled mixture

[0131]

[0132] Control ratio 1 (improved process 1)

[0133] (1) Add the coarse RAP, new aggregates, water (one-third of the externally added water), cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash (total dosage 50%), and emulsified asphalt (total dosage 50%) in Table 1 into the mixing pot, and mix at a stirring speed of 50 r / min for 60 s;

[0134] Add the fine RAP, medium RAP, mineral powder, water (one-third of the externally added water), cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash (total dosage 50%), and emulsified asphalt (total dosage 50%) in Table 1 to the mixing pot, and mix at a stirring speed of 50 r / min for 60 s;

[0135] Add water (one-third of the externally added water) to the mixing pot, mix for 30 s, and complete the mixing at a stirring speed of 50 r / min.

[0136] The process flow chart of the mixing method for control ratio 1 is as Figure 3 shown.

[0137] Control ratio 2 (comparative process)

[0138] Mix the RAP old materials (coarse RAP, fine RAP, medium RAP), new aggregates, mineral powder, cement / cement + blast furnace slag powder + fly ash / blast furnace slag powder + fly ash in a mixing pot at a stirring speed of 50 r / min for 60 s, then add water and continue to mix at a stirring speed of 50 r / min for 60 s, and then immediately add emulsified asphalt and mix at a stirring speed of 50 r / min for 30 s.

[0139] The process flow chart of the mixing method of Comparative Example 2 is as Figure 4 shown.

[0140] The combined replacement plan of blast furnace slag powder + fly ash for cement, that is, use blast furnace slag powder + fly ash with equal mass in the cold recycled mixture to gradually replace different proportions of cement until complete replacement. The specific combined replacement plan is shown in Table 12. The mixing methods of different plans under the same mixing process are the same (for example, in Table 13, the mixing methods of Plans 1-5 in the comparison process are the same).

[0141] Table 12 Replacement Plan of Blast Furnace Slag Powder + Fly Ash for Cement

[0142] Raw Materials Scheme 1 Scheme 2 Scheme 3 Scheme 4 Scheme 5 Cement 100％ 75％ 50％ 25％ 0％ Fly Ash 0％ 12.5％ 25％ 37.5％ 50％ Ground Granulated Blast-Furnace Slag 0 12.5％ 25％ 37.5％ 50％

[0143] (1) Void ratio

[0144] The void ratio is one of the key design indexes of the cold recycled mixture, which determines the performance of the mixture such as fatigue and water damage resistance to a certain extent. According to the relevant test methods introduced in the previous section, four groups of Marshall specimens are formed for each replacement plan formed by each mixing method. The void ratio results obtained from the tests are shown in Table 13 and Figure 5 shown.

[0145] Table 13 Test Results of Void Ratio of Mixtures with Different Mixing Methods and Different Replacement Plans

[0146]

[0147] Figure 5 are the test results of void ratio of mixtures with different mixing methods and different replacement plans.

[0148] From Figure 5As can be seen from Table 13, whether it is the comparative or improved process, with the increase in the cement replacement amount, the porosity shows a certain increasing trend. When using the comparative mixing method, the overall porosity of the specimens is relatively high. The porosity reaches the highest value of 10.2% when the cement is replaced by 100%, indicating that there are more pore distributions in the formed mixture. When using the two improved processes, the porosity index shows an obvious narrowing. When no cement is replaced, the porosity decreases by 0.3% and 0.2% respectively, and when the cement is replaced by 100%, the porosity decreases by 0.4% and 0.6%. When using Improved Process 2 and replacing 50% of the cement, the porosity drops to the lowest value of 9.1%, comprehensively demonstrating that using the improved process for forming can significantly improve the volume parameter index of the specimens. At the same time, it is noted that when using the comparative mixing method, the difference between the maximum and minimum values of the specimen porosity is as high as 1%, and the standard deviation is 0.004, indicating that the porosity increases significantly with the increase in the cement replacement amount. However, when using the improved process, the overall porosity does not exceed 10.0%, and the extreme value differences are 0.7% and 0.5% respectively, and the standard deviations are 0.03 and 0.001 respectively, indicating that using the improved process can effectively reduce the growth rate of the specimen porosity and cut down the pore increase phenomenon caused by cement replacement to a certain extent.

[0149] In summary, with the increase in the cement replacement amount, the porosity shows a certain increasing trend; the improved process can improve the phenomenon of increased hydration pores caused by cement replacement, control the increase amplitude of the porosity, and effectively reduce the overall porosity of the specimens.

[0150] (2) Dry splitting strength at 15°C

[0151] The dry splitting strength at 15°C can characterize the tensile properties of the mixture. According to the relevant test methods introduced in the previous section, four groups of Marshall specimens are formed for each replacement scheme formed by each mixing method. The test results of the dry splitting strength are shown in Table 14 and Figure 6 as follows.

[0152] Table 14 Test results of dry splitting strength of mixtures with different mixing methods and different replacement schemes

[0153]

[0154] Figure 6 are the test results of dry splitting strength of mixtures with different mixing methods and different replacement schemes.

[0155] From Figure 6As can be seen from Table 14, when the comparative mixing method is adopted, the dry splitting strength is not good, and the strength of each specimen is not higher than 0.86 MPa. The standard deviation as high as 0.063 indicates that the dry splitting strength decays significantly with the increase of the replacement amount of cement. When the cement is replaced by 100%, the dry splitting strength is only 0.77 MPa, which is 10.5% lower than that without cement replacement. The maximum dry splitting strengths of the specimens with the improved process are 0.91 MPa and 0.94 MPa, which are significantly improved compared with the comparative mixing method. The minimum values are 0.85 MPa and 0.88 MPa respectively, which are equal to or even exceed the maximum value of the comparative mixing method, indicating that the dry splitting strength index is overall better than the comparative mixing method. When the improved process 2 is adopted, the standard deviation is only 0.023, indicating that the replacement amount of different blast furnace slag powder-fly ash has little effect on the dry splitting strength of the specimens. When the cement is replaced by 100%, the dry splitting strength of the specimens only decreases by 5.3%, which is much narrower than the 10.5% decrease of the comparative process, proving that the improved process based on the specific surface area of aggregates can effectively improve the tensile properties of the mixture.

[0156] In summary, when the comparative mixing method is adopted, the dry splitting strength is low and is significantly affected by the cement replacement amount. The dry splitting strength of the specimens with the improved process is significantly improved and is less affected by the cement replacement amount.

[0157] (3) Low-temperature splitting strength

[0158] The low-temperature splitting strength can characterize the low-temperature cracking resistance of the mixture. According to the relevant test methods introduced in the previous section, four groups of Marshall specimens are formed for each replacement scheme formed by each mixing method. The test results of the low-temperature splitting strength are shown in Table 15 and Figure 7 as follows.

[0159] Table 15 Test results of low-temperature splitting strength of mixtures with different mixing methods and different replacement schemes

[0160]

[0161] Figure 7 are the test results of the low-temperature splitting strength of mixtures with different mixing methods and different replacement schemes.

[0162] From Figure 7It can be found from Table 15 that the overall performance shows a similar pattern to that of the dry splitting test: when the comparative mixing method is adopted, the low-temperature splitting strength index is relatively low, the data is concentrated in the range of 1.20 - 1.30 MPa, and the standard deviation is relatively high; when 100% replaces cement, the low-temperature splitting strength is 1.17 MPa, which is 10% lower than that of the specimen without cement replacement, indicating that the low-temperature splitting strength also decreases significantly as the cement replacement amount increases. When the improved process is adopted, the maximum low-temperature splitting strengths are 1.36 MPa and 1.39 MPa, which are significantly improved compared with the comparative mixing method; the minimum values are also overall better than those of the comparative mixing method; the standard deviations of the two improved processes are significantly narrower than those of the comparative mixing method, and with the increase of the cement replacement amount, the low-temperature splitting does not show a large decrease, indicating that the mixing improvement process helps to improve the low-temperature cracking resistance of the cold recycled mixture.

[0163] In summary, when the comparative mixing method is adopted, the low-temperature splitting strength is relatively low and is significantly affected by the cement replacement amount; when the improved process is adopted, the low-temperature splitting strength index is overall better than that of the comparative mixing method, and the decrease affected by the change of the cement replacement amount is not obvious. This shows that the improved process improves the coating effect of the aggregate and promotes the hydration reaction process of the raw materials, thus improving the dry splitting and low-temperature splitting strengths of the cold recycled mixture.

[0164] (4) Freeze-thaw splitting strength ratio TSR

[0165] TSR can evaluate the water stability performance of the mixture. According to the relevant test methods introduced in the previous section, four groups of Marshall specimens are formed for each mixing method and each replacement scheme, and the obtained TSR results are shown in Table 16 and Figure 8 as follows.

[0166] Table 16 Test results of freeze-thaw splitting strength ratio TSR of mixtures with different mixing methods and different replacement schemes

[0167]

[0168] Figure 8 Test results of freeze-thaw splitting strength ratio TSR of mixtures with different mixing methods and different replacement schemes

[0169] From Figure 8As can be seen from Table 16, the improved process significantly improves the TSR index of the mixture. When using the comparative mixing method, with the increase of the cement replacement amount, the TSR decays significantly. When the cement is replaced by 100%, the TSR is only 71%, which is 9 percentage points lower than the highest value and has fallen below the requirements of the specification technical standard. When using the improved process, especially the improved process 2, the TSR index is significantly improved, and the TSR index of all specimens exceeds 80%, fully meeting the requirements of the relevant technical standards; although the TSR also shows a certain decay with the increase of the cement replacement amount, the decay amplitude is significantly narrowed. The analysis is that the improved process enhances the coating effect of the aggregate and the hydration of the raw materials, improving the water damage resistance under freeze-thaw cycles.

[0170] Through the preliminary comparison of the volume parameters, mechanical strength, low-temperature performance and water stability performance of the cold recycled mixture specimens formed under three different mixing methods and different replacement schemes, the following conclusions can be obtained:

[0171] (1) Under the three different mixing methods, the continuous increase of the replacement ratio of blast furnace slag powder - fly ash for cement has a certain negative impact on the performance of the cold recycled mixture, and some performance indicators show decay: among them, the performance decay amplitude is larger when using the comparative mixing method, while when using the improved process, due to the more sufficient reaction between raw materials such as blast furnace slag powder - fly ash and emulsified asphalt and better hydration effect, the performance decay amplitude is significantly narrowed.

[0172] (2) The two improved processes significantly improve the volume parameters and road performance of the mixture. Among them, the improved process 2 (cement - blast furnace slag powder - fly ash and emulsified asphalt are added in portions according to the specific surface area ratio of the aggregate) has the most obvious performance improvement in splitting strength, low temperature and water stability, significantly superior to the comparative mixing method and the improved process 1.

[0173] The analysis is that the improved process fully considers the "mixing workability" of the cold recycled mixture and the differences in the adsorption capacity of emulsified asphalt by each size of aggregate, making the coating effect of emulsified asphalt in the mixed mixture better. At the same time, it promotes the hydration reaction of the raw materials, optimizes the quality and structural form of the hydration products, and obtains a cold recycled mixture with excellent performance. Therefore, the improved process 2 is selected as the relatively better improved process, and further road performance tests of the mixture will be carried out for the comparative mixing method and the improved process 2 in the future.

[0174] Analysis of the Influence of Different Mixing Methods and Different Replacement Schemes on the Performance of Cold Recycled Mixtures

[0175] After conducting a preliminary analysis of the road performance of blast furnace slag powder-fly ash-emulsified asphalt cold recycled mixture and optimizing the improved process 2 (hereinafter referred to as the improved process), this section compares the high-temperature performance, water stability performance, and low-temperature performance of the blast furnace slag powder-fly ash-emulsified asphalt cold recycled mixture specimens formed under two different mixing methods and different replacement schemes of the comparative and improved processes.

[0176] (1) High-temperature rutting test

[0177] The main index for evaluating the high-temperature performance of asphalt mixture in the high-temperature rutting test is the dynamic stability DS. According to the relevant test methods introduced in the previous section, three parallel experiments are carried out for each replacement scheme formed by each mixing method, and the average value is taken as the rutting test result. The dynamic stability obtained from the test is shown in Table 17 and Figure 9 as follows.

[0178] Table 17 Test results of dynamic stability of mixtures with different mixing methods and different replacement schemes

[0179]

[0180] Figure 9 For the test results of dynamic stability of mixtures with different mixing methods and different replacement schemes

[0181] From Figure 9 and Table 17, it can be seen that when the improved process is adopted, the dynamic stability indexes of all replacement schemes show an increase of more than 15%. This shows that the improved process has a very obvious effect on improving the dynamic stability. The analysis is that the improved process significantly improves the coating effect of aggregates, promotes the hydration reaction of raw materials, and then improves the bonding effect of the cementitious products in the mixture, enhancing the deformation resistance ability of the mixture to loads under high-temperature conditions, and the macroscopic manifestation is a significant increase in the dynamic stability index. At the same time, it can be found that whether it is the comparative process or the improved process, with the increase of the cement replacement amount, the dynamic stability index shows a certain downward trend. The dynamic stability of the specimens with 100% cement replacement is 13% and 10% lower than that of the specimens without cement replacement respectively, indicating that using blast furnace slag powder-fly ash to replace cement will have a certain negative impact on the high-temperature performance of the cold recycled mixture; however, the dynamic stability of the specimens with the comparative mixing method and no cement replacement is lower than that of the specimens with the improved process and 100% cement replacement, indicating that the improved process has a stronger effect on improving the dynamic stability than the negative impact brought by cement replacement, that is, when the improved process is adopted, even if cement is completely replaced, the high-temperature performance of the mixture can be improved to a certain extent.

[0182] (2) Hamburg rutting test

[0183] The main indicators of the Hamburg rutting test include the stripping inflection point SIP and the stripping slope SS. According to the relevant test methods introduced in the previous section, each alternative formed by each mixing method was tested, and the SIP and SS were obtained by fitting the deformation curves in the creep stage and the stripping stage. The results are shown in Table 18 and Figures 10 - 11 as follows.

[0184] Table 18 Hamburg rutting test results of mixtures with different mixing methods and different alternatives

[0185]

[0186] Figure 10 are the SIP test results of mixtures with different mixing methods and different alternatives. *Note: The stripping stage did not appear in the test of the improved process plan, and the data in the figure are only for comparison and have no practical significance

[0187] Figure 11 are the SS test results of mixtures with different mixing methods and different alternatives.

[0188] Since SS is closely related to the gradation in the specimen under the action of the steel wheel and the results show no obvious pattern, the analysis mainly focuses on the stripping inflection point SIP.

[0189] From Figures 10 - 11 and Table 18, it can be seen that the overall pattern of SIP is similar to that of dynamic stability. The improved process has a significant effect on improving the SIP index. Among them, the specimens without replacing cement did not show the stripping stage at all in the test. The improvement amplitude of the specimens of the other alternative plans is about 20% compared with the comparative mixing method, and the improvement amplitude is greater for higher temperature rutting. The analysis is that because the experimental conditions of the Hamburg rutting test are more stringent, and the improved process enhances the deformation resistance of the mixture to the load under high temperature conditions, and the effect is more obvious under the coupling action of high temperature and high humidity, that is, it is more difficult for water to invade the asphalt-aggregate interface, and it is difficult for the mixture to suffer from water damage, resulting in a more significant improvement in the deformation resistance of the asphalt mixture. On the other hand, with the increase of the cement replacement amount, the SIP index of both the comparative and improved process specimens also shows a certain downward trend, indicating that using blast furnace slag powder-fly ash to replace cement will also affect the water stability performance under high temperature conditions; when the improved process is adopted, the downward amplitude is greatly reduced, only showing a slight downward trend, indicating that the improved process can basically offset the negative impact brought by replacing cement in terms of high temperature performance.

[0190] (3) SCB test

[0191] The main performance indicators of the SCB test include the fracture energy G f and the fracture toughness K ICWith stiffness S. According to the relevant test methods introduced in the previous section, the SCB test was carried out for each alternative formed by each mixing method, and G f , K IC and S results are shown in Table 19 and Figures 12 - 13 . Since there is no obvious law for stiffness S and the variability is large, no further analysis will be done in the following, and the analysis will be mainly carried out on the fracture energy and fracture toughness data.

[0192] Table 19 SCB test results of mixtures with different mixing methods and different alternatives

[0193]

[0194] Figure 12 are the test results of G f for mixtures with different mixing methods and different alternatives;

[0195] Figure 13 are the test results of K IC for mixtures with different mixing methods and different alternatives.

[0196] From Figure 12 , it can be seen that the improvement of the process has a very obvious effect on improving the low-temperature performance of the mixture, and the average improvement amplitude of the specimens with different replacement amounts is about 15%. When examining the influence of the mixing method on G f , it can be found that whether comparing the mixing methods or improving the process, with the increase of the cement replacement amount, the fracture energy index shows a certain downward trend. The G f of the specimens with 100% cement replacement is reduced by 17% and 9% respectively compared with the specimens without cement replacement; at the same time, it is noted that the G f of the specimens with 75% and 100% cement replacement under the two mixing methods are basically the same, indicating that when the cement replacement amount exceeds 75%, the test results of the fracture energy index have tended to be stable.

[0197] From Figure 13 , similar to the fracture energy, the improvement of the process also has an obvious effect on improving the low-temperature performance of the mixture. When examining the influence of the mixing method on K IC , it can be found that the fracture toughness variability of the specimens formed by the comparison mixing method is large, showing a trend of first significantly decreasing, rising midway and then slightly decreasing again, without an obvious law; the K IC of the specimens formed by the improved process generally reaches a relatively stable level, with a standard deviation of only 0.025, and the difference between the maximum value and the minimum value is only 0.11 MPa·m 0.5 , proving that the improvement of the process for the fracture toughness can offset the negative impact of cement replacement to a certain extent and pull the overall low-temperature performance of the mixture to a better level.

[0198] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A mixing method for blast furnace slag powder-fly ash-emulsified asphalt mixture, characterized in that, Including the following steps: Carry out a first mixing of coarse RAP, new aggregates, a part of emulsified asphalt, a part of blast furnace slag powder, a part of fly ash, a part of cement and a first part of water to obtain a first mixture; Carry out a second mixing of the said first mixture with fine RAP, medium RAP, mineral powder, the remaining emulsified asphalt, the remaining blast furnace slag powder, the remaining fly ash, the remaining cement and a second part of water to obtain a second mixture; Carry out a third mixing of the said second mixture with the remaining water; The mass percentage of the part of emulsified asphalt in the total amount of emulsified asphalt, the mass percentage of the part of blast furnace slag powder in the total amount of blast furnace slag powder, the mass percentage of the part of fly ash in the total amount of fly ash and the mass percentage of the part of cement in the total amount of cement are independently A±0.5%; In formula (1): S1, S2, S3, S4, S5, S6, S7, and S8 are the specific surface areas of coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash, and cement, respectively, with the unit of m 2 / kg; P1, P2, P3, P4, P5, P6, P7, P8 are respectively the percentages of coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement in the total mass of coarse RAP, new aggregates, fine RAP, medium RAP and mineral powder.

2. The mixing method according to claim 1, characterized in that, The calculation methods of the specific surface areas of the said coarse RAP, new aggregates, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash and cement are as shown in formula (2): S = 0.41 + 0.0041P 4.75 + 0.0082P 2.36 + 0.0164P 1.18 + 0.0287P 0.6 + 0.0614P 0.3 + 0.1 1 229P 0.15 + 0.3277P 0.075 Equation (2); In formula (2): P 4.75 、P 2.36 、P 4.75 、P 1.18 、P 0.6 、P 0.3 、P 0.15 、P 0.075 are the passing rates of coarse RAP, new aggregate, fine RAP, medium RAP, mineral powder, blast furnace slag powder, fly ash or cement when the particle sizes are 4.75 mm, 2.36 mm, 4.75 mm, 1.18 mm, 0.6 mm, 0.3 mm, 0.15 mm, 0.075 mm respectively.

3. The mixing method according to claim 1 or 2, characterized in that, The raw materials of the blast furnace slag powder-fly ash-emulsified asphalt mixture include: powder materials and admixtures; By mass fraction, the said powder materials include: The said admixtures include: one or more of cement, blast furnace slag powder and fly ash, water, emulsified asphalt; The mass of one or more of the said cement, blast furnace slag powder and fly ash is 1.5% of the mass of the powder materials; The mass of the said water is 4.9% of the mass of the powder materials; The mass of the said emulsified asphalt is 3.6% of the mass of the powder materials.

4. The mixing method according to claim 3, characterized in that, The particle size of the said coarse RAP is 10 - 30mm or 10 - 26.5mm; the particle size of the new aggregates is 10 - 20mm; the particle size of the fine RAP is 0 - 5mm, and the particle size of the medium RAP is 5 - 10mm.

5. The mixing method according to claim 1, characterized in that, Both the first part of water and the second part of water are 1 / 3 of the total amount of water.

6. The mixing method according to claim 1, characterized in that, The stirring speed of the first mixing is 45 - 55r / min, and the time is 60s.

7. The mixing method according to claim 1, characterized in that, The stirring speed of the second mixing is 45 - 55r / min, and the time is 60s.

8. The mixing method according to claim 1, characterized in that The stirring speed of the third mixing is 45 - 55r / min, and the time is 30s.

9. The mixing method according to claim 3, characterized in that, The density of the blast furnace slag powder is 2.88 g / cm 3 ; the density of the fly ash is 2.39 g / cm 3 , and the density of the cement is 3.15 g / cm 3 .

10. The mixing method according to claim 3, wherein The coating area of the emulsified asphalt and the new aggregates > 2 / 3.

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