A RAP-steel slag hot recycled asphalt mixture and its preparation method and application

Abstract

The present invention discloses a RAP-steel slag hot-regenerated asphalt mixture and a preparation method and application thereof. The preparation method comprises: (1) primary regeneration: mixing RAP fine aggregate with an asphalt regeneration agent, and regenerating at a temperature not exceeding 60° C., so that the softening point of aged asphalt in the RAP fine aggregate is reduced by more than 15%, thereby obtaining recycled RAP fine aggregate; (2) secondary thermal regeneration: heating the recycled RAP fine aggregate to 130° C. to 150° C., heating the steel slag coarse aggregate to 200° C. to 220° C., and adding new asphalt and mineral powder while hot, and mixing to obtain the RAP-steel slag hot-regenerated asphalt mixture; wherein the recycled RAP fine aggregate accounts for 15wt% to 45wt% of the total aggregate, and the steel slag accounts for 55wt% to 85wt% of the total aggregate. The method adopts two regeneration processes, which can significantly improve the utilization rate of RAP fine aggregate, and the asphalt mixture prepared with the RAP fine aggregate in an amount exceeding 30wt% has good road performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of highway asphalt pavement, and more specifically, relates to a RAP-steel slag hot regenerated asphalt mixture and a preparation method and application thereof. Background Art

[0002] After construction, service and recycling, asphalt mixture will produce a large amount of old asphalt mixture, which will cause great pollution to the environment and soil. Although the asphalt in the old asphalt mixture has aged and its performance has declined, its aggregate performance still has great utilization value. The recycling of asphalt mixture is conducive to reducing the mining of natural aggregates. It is an economical, environmentally friendly and sustainable road repair technology, and it is also a hot spot in existing research. In recent years, with the development of asphalt pavement recycling technology, it is divided into hot recycled asphalt mixture, cold mix recycled asphalt mixture and warm mix recycled asphalt mixture according to the regeneration temperature.

[0003] Currently, the most researched is warm mix recycled asphalt mixture. Warm mix asphalt mixture is achieved by adding warm mix agent to new asphalt to reduce the high temperature viscosity of asphalt, thereby recycling old asphalt mixture. RAP can be mixed at a temperature below 150°C, but it mainly utilizes the properties of aggregates in old asphalt mixture. The amount of new asphalt added is large and the cost is high. The aggregates in the old asphalt mixture are themselves wrapped by asphalt binder and are also mixed with crushed pure asphalt binder, which has good reuse value.

[0004] Thermally regenerated asphalt mixture is made by adding asphalt regeneration agent to recycled old asphalt mixture RAP and heating it to a high temperature of 150℃-180℃ for mixing and regeneration with new asphalt and mineral materials. Thermal regeneration can restore the performance of aged asphalt in the old asphalt mixture to a certain extent. However, existing thermal regeneration technology often uses high-temperature treatment of 170℃-180℃ for thermal regeneration. During the thermal regeneration process at 170℃-180℃, asphalt is prone to secondary aging, resulting in poor road performance of thermally regenerated asphalt mixture, which makes the dosage of recycled old asphalt mixture RAP low, generally not exceeding 30wt% of aggregate. For example, in patent CN113511842A, the proportion of old asphalt mixture replacing aggregate is 27-29%. Although the proportion of old asphalt mixture added in CN109021595A exceeds 30wt%, a large number of studies have shown that the anti-skid performance of asphalt mixture prepared with RAP dosage exceeding 30wt% is significantly reduced. In addition, although cold-mix recycled asphalt mixture avoids the problem of secondary aging of asphalt caused by high temperature, its road performance is poor and it is difficult to use in high-demand asphalt pavement. Therefore, a hot recycled asphalt mixture with high RAP content and good road performance is studied to make full use of the performance of asphalt and aggregate in the recycled old asphalt mixture and maximize its reuse value. Summary of the invention

[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a RAP-steel slag hot-regenerated asphalt mixture and its preparation method and application, the purpose of which is to use RAP fine aggregate and steel slag coarse aggregate to completely replace natural aggregate to prepare hot-regenerated asphalt mixture, and to improve the road performance of hot-regenerated asphalt mixture through two regeneration treatments, wherein the RAP fine aggregate is firstly added with an asphalt regeneration agent and regenerated once at a temperature not exceeding 60°C to reduce the softening point of aged asphalt by more than 15%, thereby obtaining recycled RAP fine aggregate, and then a secondary hot regeneration treatment is used to prepare hot-regenerated asphalt mixture. The secondary thermal regeneration can further restore the performance of aged asphalt. The recycled RAP fine aggregate is heated at 130℃~150℃ to avoid secondary aging of asphalt in RAP caused by high temperature above 150℃, which is beneficial to increase the RAP dosage. The steel slag coarse aggregate is heated at 200℃~220℃ to reduce the volume expansion of steel slag powder and improve the stability of steel slag powder. At the same time, the prepared hot-recycled asphalt mixture has good road performance, thereby solving the technical problem of poor road performance of asphalt mixture prepared by completely replacing natural aggregate with high dosage of RAP fine aggregate and steel slag coarse aggregate.

[0006] To achieve the above object, according to one aspect of the present invention, a method for preparing a small-size RAP-steel slag hot-regenerated asphalt mixture is provided, which comprises the following steps:

[0007] (1) Preparation of recycled RAP fine aggregate by one-time regeneration: The RAP fine aggregate obtained by recycling and screening is mixed with an asphalt regeneration agent and regenerated at a temperature not exceeding 60°C, so that the softening point of the aged asphalt in the RAP fine aggregate is reduced by more than 15%, the needle penetration is increased by more than 30%, or the ductility is increased by more than 50%, thereby obtaining recycled RAP fine aggregate;

[0008] (2) Preparation of asphalt mixture by secondary thermal regeneration: the recycled RAP fine aggregate obtained in step (1) is heated to 130°C to 150°C, the steel slag coarse aggregate is heated to 200°C to 220°C, and new asphalt and mineral powder are added while hot, and mixed to obtain a small-particle RAP-steel slag thermally recycled asphalt mixture;

[0009] The recycled RAP fine aggregate accounts for 15wt% to 45wt% of the total aggregate, and the steel slag coarse aggregate accounts for 55wt% to 85wt% of the total aggregate.

[0010] Preferably, in the method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture, the steel slag coarse aggregate comprises 40wt% to 50wt% of coarse aggregate of 4.75mm to 9.5mm and 50wt% to 60wt% of coarse aggregate of 9.5mm to 16mm.

[0011] Preferably, in the method for preparing the small-size RAP-steel slag hot-regenerated asphalt mixture, when the performance of the aged asphalt in the regenerated RAP fine aggregate is restored to a level close to that of new asphalt, the new asphalt is added according to the following calculation:

[0012] m a =A·[(ω 1 +ω 2 +ω 3 )·γ-ω 1 α];

[0013] Where A is the total design mass of all mineral materials in the hot recycled asphalt mixture (g); 1 ,ω 2 ,ω 3 They are respectively the mass percentage (%) of recycled RAP fine aggregate of 0-4.75mm, steel slag coarse aggregate of 4.75mm-9.5mm, and steel slag coarse aggregate of 9.5mm-16mm in hot recycled asphalt mixture; α is the mass percentage (%) of aged asphalt in RAP fine aggregate; γ is the oil-stone ratio of asphalt mixture (%).

[0014] Preferably, in the method for preparing the small-size RAP-steel slag hot-regenerated asphalt mixture, the mineral powder is added according to the following calculation:

[0015] m b =A·(ω 4 -ω 1 β);

[0016] Where A is the total design mass of all mineral materials in the hot recycled asphalt mixture (g), ω 4 is the mass percentage (%) of mineral powder designed for hot recycled asphalt mixture, and β is the mass percentage (%) of original mineral powder in RAP fine aggregate.

[0017] Preferably, the method for preparing the small-particle RAP-steel slag hot-regenerated asphalt mixture prepares AC type hot-regenerated asphalt mixture, the recycled RAP fine aggregate accounts for 30wt% to 40wt% of the total aggregate, the 4.75mm to 9.5mm steel slag coarse aggregate accounts for 30wt% to 35wt% of the total aggregate, and the 9.5mm to 16mm steel slag coarse aggregate accounts for 30wt% to 40wt% of the total aggregate.

[0018] Preferably, the method for preparing the small-particle RAP-steel slag hot-regenerated asphalt mixture prepares SMA type hot-regenerated asphalt mixture, the recycled RAP fine aggregate accounts for 35wt% to 45wt% of the total aggregate, the 4.75mm to 9.5mm steel slag coarse aggregate accounts for 30wt% to 45wt% of the total aggregate, and the 9.5mm to 16mm steel slag coarse aggregate accounts for 10wt% to 30wt% of the total aggregate.

[0019] Preferably, in the method for preparing small-particle RAP-steel slag hot-regenerated asphalt mixture, the asphalt regeneration agent includes one or more combinations of RA-1, RA-5, RA-25, RA-75, RA-250, and RA-500 asphalt regeneration agents, which are added at 5% to 15% of the mass of aged asphalt in the RAP fine aggregate.

[0020] Preferably, in the method for preparing the small-size RAP-steel slag hot-regenerated asphalt mixture, in the primary regeneration, the RAP fine aggregate and the asphalt regeneration agent are mixed and then left to stand at room temperature for 24-48 hours.

[0021] In addition, according to another aspect of the present invention, a small-particle RAP-steel slag thermally regenerated asphalt mixture is provided, which is prepared according to the preparation method described in the present invention.

[0022] In addition, according to another aspect of the present invention, there is also provided a use of the small-size RAP-steel slag hot-regenerated asphalt mixture as described in the present invention in asphalt pavement repair.

[0023] In general, compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects due to the RAP-steel slag hot recycled asphalt mixture and its preparation method and application provided by the present invention:

[0024] The preparation method of the small-size RAP-steel slag hot-regenerated asphalt mixture provided by the present invention uses the recycled RAP fine aggregate as the fine aggregate and the steel slag as the coarse aggregate, and adopts two regeneration processes, wherein the RAP fine aggregate is first mixed with the asphalt regeneration agent and allowed to stand for one regeneration, so that the performance of the aged asphalt is restored to a certain extent, and then the RAP fine aggregate is heated and regenerated at a medium-low temperature of 130°C to 150°C, which can avoid the secondary aging problem of asphalt caused by high temperature (170 to 180°C), thereby improving the utilization rate of the RAP fine aggregate. Compared with the existing regeneration prepared by recycling old asphalt mixtures, Asphalt mixture, in the present invention, the amount of RAP fine aggregate can reach more than 30wt% and has good road performance; in addition, steel slag is used as coarse aggregate and the steel slag coarse aggregate is heated at a high temperature of 200℃~220℃, which can reduce the free calcium oxide content in the steel slag and improve the stability of the steel slag, so that the RAP fine aggregate and the steel slag coarse aggregate can completely replace the natural aggregate, and realize the full resource utilization of the two solid wastes of RAP and steel slag in the asphalt mixture, which is beneficial to reduce the mining of natural aggregates, and also reduces the production cost of thermally recycled asphalt mixture, and has broad market application prospects. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] In the existing research on hot-regenerated asphalt mixtures, recycled old asphalt mixtures are generally used directly, but the used asphalt mixtures used include coarse aggregate and fine aggregate. The proportions of coarse aggregate and fine aggregate in the old asphalt mixtures from different regions or different batches are different, which easily leads to performance differences between the prepared hot-regenerated asphalt mixtures. Generally, scientific mix design is required, such as patents CN 114580959A and CN111548057B, but the design method is complicated and may require multiple adjustments. A large amount of fine aggregate will be generated in the recycled old asphalt mixture, which can account for up to 60wt% of the RAP recycled material, and the asphalt binder is generally wrapped in the RAP fine aggregate. In order to improve the utilization rate of aged asphalt in the old asphalt mixture, in the present invention, RAP with a particle size of less than 4.75mm is used as fine aggregate to improve the reuse rate of aged asphalt in the old asphalt mixture. At the same time, it can also avoid the differences in the old asphalt mixtures from different regions or different batches. In addition, using steel slag as coarse aggregate can further reduce solid waste accumulation, and it is also beneficial to reduce the production cost of hot-regenerated asphalt mixtures.

[0027] However, the use of old asphalt mixture will reduce the anti-skid performance of the road surface, especially when a large amount of RAP fine aggregate is used. Although adding steel slag aggregate is beneficial to increase the anti-skid performance of the road surface, the ratio of the two needs to be controlled within an appropriate range. Moreover, when steel slag is used as aggregate, it has a high content of harmful components such as free calcium oxide.

[0028] The safety is poor. Generally, it will undergo heat stewing, aging, modification and other treatments before use. The aging treatment usually takes more than 6 months. It is difficult to directly use the newly produced steel slag as aggregate, or it needs to be used in combination with other natural aggregates such as basalt, which greatly limits the application of steel slag in asphalt concrete.

[0029] In the preparation of hot-regenerated asphalt mixture, the RAP fine aggregate is first mixed with the asphalt regeneration agent and subjected to a first regeneration treatment below 60°C, so that the softening point of the aged asphalt in the RAP fine aggregate is reduced by more than 15%, that is, the performance of the aged asphalt is restored to a certain extent, and then a high-temperature heating of 130-150°C is used for a second regeneration, so that the performance of the aged asphalt is further restored, and can even be restored to a performance close to that of new asphalt, while avoiding the secondary aging of asphalt caused by the high existing thermal regeneration temperature (150-180°C), which is beneficial to improving the utilization rate of the RAP fine aggregate; and the steel slag coarse aggregate is heated at a high temperature of 200°C to 220°C, which is beneficial to reducing the content of free calcium oxide, a harmful component, in the steel slag coarse aggregate, and improving the stability of the steel slag powder, so that it complies with the existing regulations (JT / T 1086-2016 "Steel Slag for Asphalt Mixture"

[0030] The requirement for free calcium oxide can be met in the process. At the same time, the high temperature of the steel slag coarse aggregate can be used to quickly heat the recycled RAP fine aggregate, new asphalt and mineral powder, so that the temperature of all mineral materials reaches the mixing temperature requirement of hot regeneration (above 150°C) during mixing.

[0031] The experiment found that 15wt% to 45wt% of recycled RAP fine material (0 to 4.75mm) and 55wt% to 85wt% of steel slag coarse aggregate can completely replace natural aggregate. The performance of the steel slag coarse aggregate meets the relevant specifications, such as the existing regulations (JT / T 1086-2016 "Steel Slag for Asphalt Mixture" performance requirements, the steel slag coarse aggregate includes steel slag coarse aggregate with two particle sizes of 4.75mm to 9.5mm and 9.5mm to 16mm. Furthermore, in the preparation of AC type hot regenerated asphalt mixture, 30wt% to 40wt% of recycled RAP fine aggregate, 30wt% to 35wt% of 4.75mm to 9.5mm steel slag coarse aggregate and 30wt% to 40wt% of 9.5mm to 16mm When the AC type hot recycled asphalt mixture is completely replaced by natural aggregate with steel slag coarse aggregate of m, the road performance of the AC type hot recycled asphalt mixture is good; when in the preparation of SMA type hot recycled asphalt mixture, 35wt%~45wt% of recycled RAP fine aggregate, 30wt%~45wt% of 4.75mm~9.5mm steel slag coarse aggregate and 10wt%~30wt% of 9.5mm~16mm steel slag coarse aggregate are used to completely replace natural aggregate, the SMA type hot recycled asphalt mixture has good road performance.

[0032] Based on this, the present invention provides a method for preparing a small-size RAP-steel slag hot-regenerated asphalt mixture, wherein the hot-regenerated asphalt mixture comprises recycled RAP fine aggregate, steel slag coarse aggregate, asphalt and mineral powder, and specifically comprises the following steps:

[0033] (1) Determine the mass percentage α of aged asphalt in the RAP fine aggregate obtained by recycling and screening, where the particle size of the RAP fine aggregate is within 4.75 mm;

[0034] (2) One-time regeneration to prepare recycled RAP fine aggregate: the obtained RAP fine aggregate is mixed with an asphalt regeneration agent and regenerated at a temperature not exceeding 60° C., so that the softening point of aged asphalt in the RAP fine aggregate is reduced by more than 15%, thereby obtaining recycled RAP fine aggregate;

[0035] The asphalt regeneration agent includes one or more combinations of RA-1, RA-5, RA-25, RA-75, RA-250, and RA-500 asphalt regeneration agents, and is preferably added at 5% to 15% of the mass of aged asphalt in RAP fine aggregate.

[0036] If too little asphalt regeneration agent is added, the performance of aged asphalt in RAP fine aggregate will not be fully restored; if too much asphalt regeneration agent is added, the high temperature performance of the final asphalt mixture will be reduced. The amount of asphalt regeneration agent added should be adjusted according to the type and aging degree of asphalt in RAP, so as to restore the performance of aged asphalt in RAP fine aggregate to the target range.

[0037] In some embodiments, the one-time regeneration has a standing time at room temperature of less than or equal to 48 hours.

[0038] (3) Preparation of asphalt mixture by secondary thermal regeneration: The recycled RAP fine aggregate obtained in step (2) is heated to 130°C to 150°C, the steel slag coarse aggregate is heated to 200°C to 220°C, and new asphalt and mineral powder are added while hot, and mixed to obtain a small-particle RAP-steel slag thermally recycled asphalt mixture; the asphalt includes any one of 70# base asphalt, 90# base asphalt, SBS modified asphalt or rubber asphalt.

[0039] The heating temperatures of the recycled RAP fine aggregate and the steel slag coarse aggregate need to be coordinated to avoid the aggregate temperature being too low or too high after mixing, which would affect the thermal regeneration effect. The experimental results show that the road performance of the hot-regenerated asphalt mixture prepared by first regeneration (asphalt regeneration agent) and then secondary thermal regeneration is significantly improved. Among them, the use of 130℃~150℃ heating treatment of recycled RAP fine aggregate can avoid the secondary aging of asphalt in RAP fine aggregate caused by high temperature, which is conducive to increasing the amount of RAP fine aggregate. However, it is difficult to activate the aged asphalt in RAP fine aggregate when the temperature is below 130℃. The aged asphalt has almost no fluidity. It is impossible to evenly disperse the aged asphalt in RAP fine aggregate during mixing, and the working performance of the mixed asphalt mixture is poor (that is, when paving and compacting, the asphalt viscosity is high and the asphalt mixture has poor fluidity, which is not conducive to construction operation). The difficulty of paving and compaction increases, and it is difficult to ensure the flatness and compaction of the final road surface.

[0040] The high temperature of 200℃~220℃ for heating steel slag coarse aggregate is beneficial to reduce the free calcium oxide content of harmful components in the steel slag coarse aggregate, so that it meets the requirements of free calcium oxide specified in the existing (JT / T 1086-2016 "Steel Slag for Asphalt Mixture"). At the same time, the high temperature of steel slag coarse aggregate can be used to quickly heat asphalt and mineral materials, so that all mineral materials can reach the hot regeneration mixing temperature requirements (mixing at above 150℃) during mixing, which is beneficial to ensure the hot regeneration effect.

[0041] Preferably, the steel slag coarse aggregate includes 40wt% to 50wt% of 4.75mm to 9.5mm steel slag and 50wt% to 60wt% of 9.5mm to 16mm steel slag. The steel slag coarse aggregate with this ratio can completely replace natural coarse aggregate such as basalt aggregate.

[0042] In the present invention, RAP fine aggregate accounts for 15wt% to 45wt% of the total aggregate, preferably 30wt% to 45wt%. According to the preparation method of the present invention, the hot-regenerated asphalt mixture prepared with RAP fine aggregate content exceeding 30wt% still has good road performance.

[0043] In some embodiments, the recycled RAP fine aggregate is kept at 130°C to 150°C for 4h to 5h, the steel slag coarse aggregate and mineral powder are kept at 200°C to 220°C for 4h to 5h, and the new asphalt is kept at 170°C to 180°C for 4h to 5h. The road performance improvement effect of the hot-recycled asphalt mixture is more significant.

[0044] Further, in some embodiments, the performance of aged asphalt in RAP fine aggregate is restored to be close to that of new asphalt after one regeneration, and the amount of asphalt added is calculated as follows:

[0045] m a =A·[(ω 1 +ω 2 +ω 3 )·γ-ω 1 α];

[0046] Where A is the total design mass of all mineral materials in the asphalt mixture (g); 1 ,ω 2 ,ω 3 They are respectively the mass percentage (%) of recycled RAP fine aggregate of 0-4.75mm, steel slag coarse aggregate of 4.75mm-9.5mm, and steel slag coarse aggregate of 9.5mm-16mm in asphalt mixture; α is the mass percentage (%) of aged asphalt in RAP fine aggregate; γ is the oil-stone ratio of asphalt mixture (%).

[0047] Preferably, in step (1), the mass percentage β of the mineral powder in the RAP fine aggregate obtained by the recovery and screening is also determined, and the mineral powder is added according to the following calculation:

[0048] m b =A·(ω 4 -ω 1 β);

[0049] Where A is the total design mass of all mineral materials in the hot recycled asphalt mixture (g), ω 4 is the mass percentage (%) of mineral powder designed for hot recycled asphalt mixture, and β is the mass percentage (%) of original mineral powder in RAP fine aggregate.

[0050] In some embodiments of preparing AC type hot-regenerated asphalt mixture, it is preferred that the recycled RAP fine aggregate accounts for 30wt% to 40wt% of the total aggregate, the 4.75mm to 9.5mm steel slag coarse aggregate accounts for 30wt% to 35wt% of the total aggregate, and the 9.5mm to 16mm steel slag coarse aggregate accounts for 30wt% to 40wt% of the total aggregate.

[0051] In some embodiments of preparing SMA type hot-regenerated asphalt mixture, it is preferred that the recycled RAP fine aggregate accounts for 35wt% to 45wt% of the total aggregate, the 4.75mm to 9.5mm steel slag coarse aggregate accounts for 30wt% to 45wt% of the total aggregate, and the 9.5mm to 16mm steel slag coarse aggregate accounts for 10wt% to 30wt% of the total aggregate.

[0052] In addition, the present invention also provides a small-particle RAP-steel slag hot-regenerated asphalt mixture obtained according to the preparation method of the present invention, which includes 15wt% to 45wt% of recycled RAP fine aggregate, 55wt% to 85wt% of steel slag coarse aggregate, asphalt and mineral powder; the steel slag coarse aggregate includes 40wt% to 50wt% of 4.75mm to 9.5mm and 50wt% to 60wt% of 9.5mm to 16mm steel slag coarse aggregate.

[0053] In addition, the present invention also provides an application of the small-size RAP-steel slag hot-regenerated asphalt mixture as described in the present invention in asphalt pavement repair.

[0054] The following are examples:

[0055] Example 1 Recycled RAP fine aggregate 1

[0056] The regenerated RAP fine aggregate 1 includes RAP fine aggregate of 0 to 4.75 mm and RA-1 type asphalt regeneration agent, which is prepared according to the following preparation method:

[0057] (1) Determination of the aged asphalt content in RAP fine aggregate: After the asphalt is extracted from the RAP fine aggregate according to the Test Procedure for Asphalt and Asphalt Mixtures for Highway Engineering (JTG E20-2011), the particle size of the remaining aggregate ranges from 0 to 4.75 mm, and its performance indicators meet the requirements of the Technical Specification for Regeneration of Highway Asphalt Pavement (JTG / T 5521-2019).

[0058] According to the "Testing Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the asphalt content in RAP fine aggregate was tested, and the mass percentage α of aged asphalt in RAP fine aggregate was found to be 8%.

[0059] (2) Accurately weigh 1 kg of RAP fine aggregate, and weigh 10% of the mass of aged asphalt in the RAP fine aggregate, i.e., weigh 8 g of asphalt rejuvenator; in this embodiment, the asphalt rejuvenator is RA-1 type rejuvenator.

[0060] (3) The weighed RAP fine aggregate and asphalt regeneration agent are mixed and stirred evenly, and stored at room temperature for 24 hours to obtain recycled RAP fine aggregate.

[0061] Example 2 Recycled RAP fine aggregate 2

[0062] The regenerated RAP fine aggregate 2 includes RAP fine aggregate of 0 to 4.75 mm and RA-1 type asphalt regeneration agent, which is prepared according to the following preparation method:

[0063] (1) Determination of the aged asphalt content in RAP fine aggregate: After the asphalt is extracted from the RAP fine aggregate according to the "Test Procedure for Asphalt and Asphalt Mixtures for Highway Engineering" (JTG E20-2011), the particle size range of the remaining aggregate is 0 to 4.75 mm, and its performance indicators meet the requirements of the "Technical Specification for Regeneration of Highway Asphalt Pavement" (JTG / T 5521-2019).

[0064] According to the "Testing Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), the asphalt content in RAP fine aggregate was tested, and the mass percentage α of aged asphalt in RAP fine aggregate was found to be 8%.

[0065] (2) Accurately weigh 1 kg of RAP fine aggregate and weigh 4.8 g of RA-1 asphalt regeneration agent according to 6% of the mass of aged asphalt in the RAP fine aggregate.

[0066] (3) The weighed RAP fine aggregate and asphalt regeneration agent are mixed and stirred evenly, and stored at room temperature for 24 hours to obtain recycled RAP fine aggregate.

[0067] Comparative Example 1

[0068] The RAP fine aggregate is the same as in Example 1. 1 kg of RAP fine aggregate is accurately weighed, and 1.6 g of RA-1 type asphalt regeneration agent is weighed according to 2% of the mass of aged asphalt in the RAP fine aggregate. Regenerated RAP fine aggregate is prepared according to the method in Example 1.

[0069] Example 3 Performance test of recycled RAP fine aggregate

[0070] The recycled RAP fine aggregates obtained in Example 1, Example 2 and Comparative Example 1 were subjected to physical property tests on the recovered asphalt in RAP and the recovered asphalt in the recycled RAP fine aggregates in accordance with the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), and the aged asphalt in the recycled RAP fine aggregates was used as a control. The test results are shown in Table 1 below.

[0071] Table 1 Test results of physical properties of recycled asphalt binder

[0072]

[0073] The higher the asphalt softening point, the harder the asphalt is, and it will soften at a higher temperature. The higher the ductility and penetration, the softer the asphalt is at a lower temperature, and the better the low-temperature performance of the asphalt. Studies have shown that the asphalt in the old asphalt mixture RAP will become harder and more brittle due to aging during service, and the softening point will increase, but the low-temperature performance will decrease significantly. Therefore, the recovery effect of asphalt performance after using the regeneration agent can be evaluated by indicators such as penetration, softening point and ductility.

[0074] However, since RAP is milled from the road surface, it has basically been in service for more than 10 years, and the asphalt was constructed many years ago. Now there is almost no way to know the original performance of the asphalt used at that time, that is, the performance indicators of the asphalt before aging are unknown, and it is difficult to evaluate the performance recovery degree. Generally, compared with the aged asphalt, the performance of the asphalt after adding the regeneration agent is improved. For example, by measuring the softening point of the aged asphalt and the regenerated asphalt, the degree of reduction of the asphalt softening point can be known, or the ductility of the aged asphalt and the regenerated asphalt can be measured to know the increase in ductility after adding the regeneration agent.

[0075] It can be seen from Table 1 that the softening point of asphalt decreases with the increase of the amount of asphalt regeneration agent added. However, compared with the aged asphalt, the asphalt softening point in the recycled RAP fine aggregate in Example 1, Example 2 and Comparative Example 1 decreased by 34%, 20% and 6% respectively, while the penetration increased by 75%, 48% and 16% respectively; the ductility increased by 142%, 80% and 41% respectively. It can be seen that compared with the recycled RAP fine aggregate, the penetration and ductility of asphalt in the recycled RAP fine aggregate are significantly improved, and the softening point is significantly reduced, indicating that adding the asphalt regeneration agent for one regeneration can significantly restore the low-temperature performance of the aged asphalt in the recycled RAP fine aggregate.

[0076] Example 4 Performance test of steel slag coarse aggregate with different pretreatments

[0077] The steel slag coarse aggregate 1, calculated by mass percentage, includes 47wt% of 4.75mm-9.5mm steel slag coarse aggregate and 53wt% of 9.5mm-16mm steel slag coarse aggregate. The two kinds of steel slag coarse aggregate are placed in an oven and heated and kept warm at 210°C for 4 hours. The two kinds of steel slag coarse aggregate after insulation treatment are poured into a 180°C mixer and stirred for 90 seconds to mix evenly. The pretreated steel slag coarse aggregate 1 is obtained by cooling to room temperature in a natural state.

[0078] Steel slag coarse aggregate 2 is obtained after aging steel slag from the same batch as steel slag coarse aggregate 1 for 6 months, including 47wt% of 4.75mm-9.5mm and 53wt% of 9.5mm-16mm steel slag coarse aggregate, which are placed in an oven and heated at 180°C for 4h. The two types of steel slag coarse aggregates after insulation treatment are poured into a 180°C mixer and stirred for 90s to mix evenly, and cooled to room temperature in a natural state to obtain pre-treated steel slag coarse aggregate 2;

[0079] The steel slag coarse aggregate 3 is obtained after aging the steel slag from the same batch as the steel slag coarse aggregate 1 for 6 months, including 47wt% of two grades of steel slag coarse aggregates of 4.75mm-9.5mm and 53wt% of 9.5mm-16mm. The steel slag coarse aggregate is placed in a mixer and stirred at 180°C for 90s to mix evenly, which is the pretreated steel slag coarse aggregate 3.

[0080] The steel slag coarse aggregate obtained after the above-mentioned pretreatments was used as the test object. According to the "Ferrous Metallurgical Industry Standard of the People's Republic of China" (YB / T 5051-2016), the free calcium oxide content of the cooled steel slag coarse aggregate was determined; according to the "Highway Engineering Aggregate Test Code" (JTG E42-2005), the cooled steel slag coarse aggregate was sampled by quartering method, and then the steel slag activity and expansion test were carried out. The free calcium oxide content of the steel slag coarse aggregate and the test results of the steel slag activity and expansion are shown in Table 2.

[0081] Table 2 Test results of slag activity and expansion properties

[0082]

[0083]

[0084] It can be seen from Table 2 that the samples of the three types of steel slag coarse aggregate all meet the requirements of the specification, but the lower the f-CaO content and water expansion rate, the better the stability of the steel slag. Although heating of steel slag may reduce the f-CaO content and water expansion rate, it can be seen from the pretreatment of steel slag coarse aggregates 2 and 3 that after the steel slag coarse aggregate aged for 6 months was heated at 180°C (lower than 200°C) for 4 hours, the content of free calcium oxide in the steel slag was only reduced by 0.3%, and the water expansion rate was only reduced by 0.57%, with almost no obvious change; while in Example 4, the steel slag coarse aggregate was treated at 210°C for 4 hours (the steel slag temperature was heated to 210°C), and the content of free calcium oxide in the steel slag was reduced by 9% compared with the steel slag aged for 6 months, and the water expansion rate was reduced by 5%. It can be seen that heating the steel slag coarse aggregate to 200-220°C in the present invention can significantly reduce the content of free calcium oxide and the water expansion rate of the steel slag, thereby greatly improving the stability of the steel slag, and the steel slag can even be directly used as coarse aggregate.

[0085] Example 5: Small-size RAP-steel slag hot-regenerated asphalt mixture

[0086] In this embodiment, the asphalt mixture is an AC graded mixture, the small-size RAP-steel slag hot recycled asphalt mixture includes recycled RAP fine aggregate, steel slag coarse aggregate, SBS modified asphalt, and limestone powder, the recycled RAP fine aggregate has a particle size of less than 4.75 mm, and the steel slag coarse aggregate includes two grades of steel slag coarse aggregate with particle sizes of 4.75 mm to 9.5 mm and 9.5 mm to 16 mm;

[0087] Specifically, it is prepared according to the following preparation method:

[0088] (1) Determination of the content of aged asphalt in RAP fine aggregate: Same as Example 1;

[0089] (2) Primary regeneration: RA-1 asphalt regeneration agent was weighed according to 10% of the mass of aged asphalt in RAP fine aggregate of 0-4.75 mm, added to the RAP fine aggregate, stirred evenly and stored at room temperature for 24 h to obtain regenerated RAP fine aggregate. The softening point of asphalt in the regenerated RAP fine aggregate was 48°C, which was 35% lower than that of aged asphalt. The asphalt performance test was the same as in Example 3.

[0090] (3) Secondary regeneration: Weigh 16 parts of the recycled RAP fine aggregate obtained in step (2) and heat them at 140°C for 4 h; place 35 parts of 4.75 mm to 9.5 mm steel slag coarse aggregate and 40 parts of 9.5 mm to 16 mm steel slag coarse aggregate and 4 parts of mineral powder and limestone mineral powder in an oven and heat them at 210°C for 4 h; place 9 parts of SBS modified asphalt (oil-to-stone ratio 6%) in an oven and heat them at 165°C for 4 h; the SBS modified asphalt can also be added according to the following calculation:

[0091] m a =A·[(ω 1 +ω 2 +ω 3 )·γ-ω 1 α];

[0092] Where A is the total design mass of all mineral materials in the hot recycled asphalt mixture (g); 1 ,ω 2 ,ω 3 They are respectively the mass percentage (%) of recycled RAP fine aggregate of 0-4.75mm, steel slag coarse aggregate of 4.75mm-9.5mm, and steel slag coarse aggregate of 9.5mm-16mm in hot recycled asphalt mixture; α is the mass percentage (%) of aged asphalt in RAP fine aggregate; γ is the oil-stone ratio of asphalt mixture (%).

[0093] The recycled RAP fine aggregate after insulation treatment and two kinds of steel slag coarse aggregates were poured into a mixer at 180°C and stirred for 90 seconds, SBS modified asphalt was added and stirred for 90 seconds, and finally limestone powder was added and stirred for 90 seconds to obtain a small-particle RAP-steel slag hot recycled asphalt mixture.

[0094] In addition, lignin fiber needs to be added in the preparation of SMA-graded asphalt mixture. Lignin fiber is added according to the mass of the external admixture mineral powder 3wt‰ and stirred for 90s, and then SBS modified asphalt (oil-stone ratio 6%) is added and stirred for 90s, and finally limestone mineral powder is added and stirred for 90s to obtain a small-particle RAP-steel slag composite asphalt mixture.

[0095] According to the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), Marshall specimens and rutting plate specimens of asphalt mixtures were formed, and their volume properties and road performance were tested. The test results are shown in Table 3 below.

[0096] Table 3 Test results of volumetric properties and road performance of asphalt mixture

[0097]

[0098]

[0099] The test results in Table 3 show that the various properties of the small-particle RAP-steel slag hot-recycled asphalt mixture meet the technical specifications, indicating that the preparation method provided by the present invention can fully resource-efficiently utilize two solid wastes, 0-4.75 mm RAP fine aggregate and 4.75 mm-16 mm steel slag coarse aggregate, as raw materials for the preparation of asphalt mixture, and obtain small-particle RAP-steel slag hot-recycled asphalt mixture with qualified volume performance and excellent road performance.

[0100] Comparative Example 2

[0101] In the RAP-steel slag hot recycled asphalt mixture prepared in this comparative example, the RAP recycled material was not subjected to a regeneration pretreatment during the preparation process, and the asphalt regeneration agent and the RAP recycled material were directly heated at 140°C after being mixed, as follows:

[0102] (1) Determination of the content of aged asphalt in RAP fine aggregate: Same as Example 1;

[0103] (2) Preparation of asphalt mixture by thermal regeneration: RA-1 asphalt regeneration agent is weighed according to 10% of the mass of aged asphalt in RAP fine aggregate of 0 to 4.75 mm, added to the RAP fine aggregate, and directly heated at 140° C. for 4 h. The other steps are the same as those in Example 5 to obtain RAP-steel slag thermally regenerated asphalt mixture.

[0104] The RAP-steel slag recycled asphalt mixture obtained in Example 5 and Comparative Example 2 was molded into asphalt mixture Marshall specimens and rutting plate specimens according to the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011); the road performance test was carried out according to the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), and the test results are shown in Table 4 below.

[0105] Table 4 Asphalt mixture performance test results

[0106]

[0107]

[0108] It can be seen from Table 4 that the rutting dynamic stability, water immersion residual stability and freeze-thaw splitting residual strength ratio of the RAP-steel slag thermally regenerated asphalt mixture provided by the present invention are all higher than those of the control sample, indicating that the preparation method provided by the present invention, compared with direct thermal regeneration treatment, first regenerating once and then thermally regenerating, can significantly improve the high temperature performance and water stability of the RAP-steel slag thermally regenerated asphalt mixture.

[0109] Example 6 Small-size RAP-steel slag asphalt mixture

[0110] In this embodiment, the asphalt mixture is an AC graded mixture, the small-size RAP-steel slag hot recycled asphalt mixture includes recycled RAP fine aggregate, steel slag coarse aggregate, SBS modified asphalt, and limestone powder, the recycled RAP fine aggregate has a particle size of less than 4.75 mm, and the steel slag coarse aggregate includes two grades of steel slag coarse aggregate with particle sizes of 4.75 mm to 9.5 mm and 9.5 mm to 16 mm;

[0111] Specifically, it is prepared according to the following preparation method:

[0112] (1) Determination of the content of aged asphalt in RAP fine aggregate: Same as Example 1;

[0113] (2) Primary regeneration: RA-5 asphalt regeneration agent was weighed according to 5% of the mass of aged asphalt in RAP fine aggregate of 0-4.75 mm, added to the RAP fine aggregate, stirred evenly and stored at room temperature for 24 h to obtain regenerated RAP fine aggregate. The softening point of asphalt in the regenerated RAP fine aggregate was 60°C, which was 18% lower than that of aged asphalt. The asphalt performance test was the same as in Example 3.

[0114] (3) Secondary regeneration: Weigh 38 parts of the regenerated RAP fine aggregate obtained in step (2) and heat them at 140°C for 4 h; place 30 parts of 4.75 mm to 9.5 mm steel slag coarse aggregate and 30 parts of 9.5 mm to 16 mm steel slag coarse aggregate and 4 parts of limestone powder in an oven and heat them at 210°C for 4 h; place 9 parts of SBS modified asphalt (oil-to-stone ratio 5%) in an oven and heat them at 165°C for 4 h; limestone powder can also be added according to the following calculation:

[0115] m b =A·(ω 4 -ω 1 β);

[0116] Where A is the total design mass of all mineral materials in the hot recycled asphalt mixture (g), ω 1 ,ω 2 ,ω 3 are the mass percentage (%) of recycled RAP fine aggregate with a size of 0-4.75 mm in hot recycled asphalt mixture, ω 4 The mass percentage (%) of mineral powder designed for hot recycled asphalt mixture. Generally, the designed addition amount of mineral powder is 3-5wt% of the total mass of aggregate. β is the mass percentage (%) of original mineral powder in RAP fine aggregate.

[0117] The recycled RAP fine aggregate after insulation treatment and two kinds of steel slag coarse aggregates were poured into a mixer at 180°C and stirred for 90 seconds, SBS modified asphalt was added and stirred for 90 seconds, and finally limestone powder was added and stirred for 90 seconds to obtain a small-particle RAP-steel slag hot recycled asphalt mixture.

[0118] Comparative Example 3 RAP-Steel Slag Hot Recycled Asphalt Mixture

[0119] In the RAP-steel slag hot recycled asphalt mixture prepared in this comparative example, the RAP recycled material was not subjected to a regeneration pretreatment during the preparation process, and the asphalt regeneration agent was directly heated at 170°C after mixing with the RAP recycled material. The details are as follows:

[0120] (1) Determination of the content of aged asphalt in RAP fine aggregate: Same as Example 1;

[0121] (2) Preparation of asphalt mixture by thermal regeneration: RA-5 asphalt regeneration agent is weighed according to 10% of the mass of aged asphalt in RAP fine aggregate of 0 to 4.75 mm, added to the RAP fine aggregate, and directly heated at 170° C. for 4 h. The other steps are the same as those in Example 6 to obtain RAP-steel slag thermally regenerated asphalt mixture.

[0122] Comparative Example 4

[0123] In the comparative sample preparation process in this comparative example, the heating and insulation temperature of the steel slag coarse aggregate and the mineral powder is 170° C., and the other steps are the same as those in Example 6.

[0124] The RAP-steel slag recycled asphalt mixture obtained in Example 6, Comparative Example 3 and Comparative Example 4 was molded into asphalt mixture Marshall specimens and rutting plate specimens according to the "Test Procedure for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011), and its volume performance and road performance were tested. The test results are shown in Table 5.

[0125] Table 5 Asphalt mixture road performance test results

[0126]

[0127] It can be seen from Table 5 that the rutting dynamic stability, water immersion residual stability, freeze-thaw splitting residual strength ratio, swing value and structural depth of the small-particle RAP-steel slag asphalt mixture provided in Example 6 are higher than those of Comparative Example 3 and Comparative Example 4, indicating that the road performance of the small-particle RAP-steel slag asphalt mixture provided by the present invention is better.

[0128] Comparing Example 6 with Comparative Example 3, the two regeneration treatments in the present invention have a lower temperature than the existing thermal regeneration treatment, and the regenerated asphalt mixture achieves better road performance, indicating that the preparation method provided by the present invention can significantly improve the road performance of the regenerated asphalt mixture.

[0129] Comparing Example 6 and Comparative Example 4, two regeneration treatments were adopted, but the steel slag treatment temperatures were different. It can be seen from the results of Example 6 and Comparative Example 4 that increasing the steel slag treatment temperature is beneficial to improving the performance of the recycled asphalt mixture. This may be because the steel slag heating temperature is between 200 and 230°C, the free calcium oxide content in the steel slag is significantly reduced, and its stability is significantly improved, which is more conducive to enhancing the high temperature performance, water stability and anti-skid performance of the RAP-steel slag hot-regenerated asphalt mixture.

[0130] In addition, the experiment also found that the aged asphalt in RAP was kept warm below 130°C, making it difficult to activate the aged asphalt. The aged asphalt has almost no fluidity, and this part of the asphalt cannot be evenly dispersed during mixing. Moreover, the working performance of the mixed asphalt mixture is poor, that is, when paving and compacting, the asphalt viscosity is high and the asphalt mixture has poor fluidity, which is not conducive to construction operations. The difficulty of paving and compaction increases, and it is difficult to ensure the flatness and compaction of the final road surface.

[0131] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture, It is characterized in that The following steps are involved: (1) Preparation of recycled RAP fine aggregate by one-time regeneration: The RAP fine aggregate obtained by recycling and screening is mixed with an asphalt regeneration agent and regenerated at a temperature not exceeding 60°C, so that the softening point of the aged asphalt in the RAP fine aggregate is reduced by more than 15%, the needle penetration is increased by more than 30%, or the ductility is increased by more than 50%, thereby obtaining recycled RAP fine aggregate; (2) Preparation of asphalt mixture by secondary thermal regeneration: the recycled RAP fine aggregate obtained in step (1) is heated to 130°C to 150°C, the steel slag coarse aggregate is heated to 200°C to 220°C, and new asphalt and mineral powder are added while hot, and mixed to obtain a small-particle RAP-steel slag thermally recycled asphalt mixture; The recycled RAP fine aggregate accounts for 15wt% to 45wt% of the total aggregate, and the steel slag coarse aggregate accounts for 55wt% to 85wt% of the total aggregate.

2. The method for preparing the small-size RAP-steel slag hot-regenerated asphalt mixture according to claim 1, It is characterized in that The steel slag coarse aggregate comprises 40wt% to 50wt% of coarse aggregate of 4.75mm to 9.5mm and 50wt% to 60wt% of coarse aggregate of 9.5mm to 16mm.

3. The method for preparing the small-size RAP-steel slag hot-regenerated asphalt mixture according to claim 2, It is characterized in that When the performance of the aged asphalt in the recycled RAP fine aggregate is restored to a level close to that of new asphalt, the new asphalt is added according to the following calculation: m a =A·[(ω 1 +oh 2 +oh 3 )·g-w 1 ·a]; Where A is the total designed mass of all mineral materials in the hot recycled asphalt mixture; 1 ,ω 2 ,ω 3 They are respectively the mass percentage of recycled RAP fine aggregate of 0-4.75mm, steel slag coarse aggregate of 4.75mm-9.5mm, and steel slag coarse aggregate of 9.5mm-16mm in hot recycled asphalt mixture, measured in %; α is the mass percentage of aged asphalt in RAP fine aggregate, measured in %; γ is the oil-stone ratio of asphalt mixture, measured in %.

4. The method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture according to claim 2, It is characterized in that The mineral powder is added according to the following calculation: m b =A·(ω 4 -oh 1 ·b); Where A is the total design mass of all mineral materials in the hot recycled asphalt mixture, ω 4 β is the mass percentage of mineral powder designed for hot recycled asphalt mixture, in %, and β is the mass percentage of original mineral powder in RAP fine aggregate, in %.

5. The method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture according to any one of claims 2 to 4, It is characterized in that When preparing AC type hot-regenerated asphalt mixture, the recycled RAP fine aggregate accounts for 30wt% to 40wt% of the total aggregate, the 4.75mm to 9.5mm steel slag coarse aggregate accounts for 30wt% to 35wt% of the total aggregate, and the 9.5mm to 16mm steel slag coarse aggregate accounts for 30wt% to 40wt% of the total aggregate.

6. The method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture according to any one of claims 2 to 4, It is characterized in that When preparing SMA type hot-regenerated asphalt mixture, the recycled RAP fine aggregate accounts for 35wt% to 45wt% of the total aggregate, the 4.75mm to 9.5mm steel slag coarse aggregate accounts for 30wt% to 45wt% of the total aggregate, and the 9.5mm to 16mm steel slag coarse aggregate accounts for 10wt% to 30wt% of the total aggregate.

7. The method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture according to claim 1, It is characterized in that The asphalt regeneration agent includes one or more combinations of RA-1, RA-5, RA-25, RA-75, RA-250, and RA-500 asphalt regeneration agents, which are added according to 5% to 15% of the mass of aged asphalt in RAP fine aggregate.

8. The method for preparing small-size RAP-steel slag hot-regenerated asphalt mixture according to claim 7, It is characterized in that In the primary regeneration, the RAP fine aggregate and the asphalt regeneration agent are mixed and left to stand at room temperature for 24-48 hours.

9. A small-size RAP-steel slag hot recycled asphalt mixture, It is characterized in that Prepared according to the preparation method according to any one of claims 1 to 8.

10. Use of the small-size RAP-steel slag hot-regenerated asphalt mixture as claimed in claim 9 in asphalt pavement repair.

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