Environment-friendly recycled asphalt concrete and preparation method thereof

Abstract

The invention belongs to the technical field of concrete, and particularly relates to environment-friendly recycled asphalt concrete and a preparation method thereof. The invention provides environment-friendly recycled asphalt concrete. The environment-friendly recycled asphalt concrete is prepared from the following raw materials in parts by weight: 100 parts of recycled asphalt mixture RAP; 15 to 20 parts of asphalt; 4 to 8 parts of sodium stearate modified basalt fiber; 5 to 15 parts of vermiculite nanosheets modified by HY-102 and octane diamine; and 9-15 parts of a polyolefin modifier. By adopting the recycled asphalt mixture, the cost can be saved, and the dispersity of the basalt fiber in the concrete can be improved by modifying the basalt fiber through the sodium stearate, so that the mechanical property of the asphalt concrete is improved; the vermiculite nanosheets modified by HY-102 and octane diamine can improve the dispersibility of the vermiculite nanosheets in the asphalt concrete, enhance the bonding strength of the vermiculite nanosheets and a base material and enhance the mechanical properties of the asphalt concrete, and the polyolefin modifier can improve the interfacial properties of asphalt and aggregate, so that the mechanical properties of the asphalt concrete are improved. Therefore, the overall performance of the mixture is improved.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology. More specifically, it relates to an environmentally friendly recycled asphalt concrete and its preparation method. Background Technology

[0002] With the rapid development of highway transportation in my country, asphalt concrete pavement has become the main pavement structure. However, the ever-increasing traffic volume and heavy-load transportation demands have led to varying degrees of damage to many highways shortly after they are put into use. Although using new, high-quality asphalt concrete can ensure pavement performance, it significantly increases construction costs and adds to the economic burden of highway maintenance. Therefore, exploring the recycling of waste asphalt concrete can not only effectively reduce maintenance costs and improve maintenance efficiency, but also reduce dependence on natural resources, resulting in significant social and economic benefits.

[0003] To address these issues, researchers have developed recycled asphalt concrete technology. This technology involves optimizing the composition of recycled asphalt concrete with new aggregates and asphalt. When the content of waste asphalt concrete exceeds 30%, a certain amount of recycling agent can be added to improve the mixture's performance, thus producing recycled asphalt concrete materials that meet usage requirements.

[0004] Polyolefins, as a type of polymer material, are widely used in asphalt modification due to their excellent oxidation resistance, heat resistance, and good mechanical properties. Polyolefin modifiers can effectively improve the interfacial properties between asphalt and aggregates, thereby enhancing the overall performance of the mixture.

[0005] CN118993618A discloses a recycled asphalt concrete, its preparation method, and its application. The recycled asphalt concrete raw materials include SBS modified asphalt, recycled asphalt mixture, aggregates, modified microporous silica, waste mineral oil, guaiac oil, dioctyl phthalate, a curing agent, and an anti-aging agent. Modified microporous silica, waste mineral oil, guaiac oil, dioctyl phthalate, a curing agent, and an anti-aging agent are used to regenerate aged asphalt in the recycled asphalt mixture. Combined with aggregates and SBS modified asphalt, a recycled asphalt concrete is prepared. In this recycled asphalt concrete, the proportion of recycled asphalt mixture is increased to over 50%. This recycled asphalt concrete exhibits good high-temperature rutting resistance and low-temperature crack resistance, and also has high flexural tensile strength.

[0006] CN114956671A discloses a method for preparing recycled asphalt concrete, including the following steps: S1: Asphalt concrete collection: old material on the road surface where recycled asphalt concrete is needed is excavated, and then the excavated old material is transported to the inside of the collection device through a conveying device; S2: Asphalt concrete preheating: The provided method for preparing recycled asphalt concrete preheats the old material through a preheating cylinder, and then mixes the recycling agent with the preheated old material to soften the old material asphalt. After softening, the new asphalt and old material asphalt are heated and stirred to ensure that the processed old material asphalt and new material asphalt can be fully mixed, so that the asphalt in the old material is fully regenerated, restoring its original properties and ensuring the quality of the recycled asphalt mixture. This avoids the problem in existing preparation methods where the new asphalt and old material asphalt cannot be fully mixed, resulting in poor asphalt quality.

[0007] CN105837105A discloses a fiber-reinforced composite recycled asphalt concrete, which is prepared from the following components by weight: 30 parts of 0-5mm recycled asphalt concrete RAP, 25 parts of 5-10mm recycled asphalt concrete RAP, 28 parts of 10-30mm recycled asphalt concrete RAP, 15 parts of 10-30mm new aggregate, 2 parts of mineral powder, 1.5 parts of cement, 4 parts of emulsified asphalt, 1 part of recycling agent, and 1.2 parts of glass fiber. By adding glass fiber with a length of 6mm, the material properties of the cold recycled mixture are significantly improved compared to other fibers. The dispersion effect of the special fiber in the cold recycled mixture is significantly better than other fibers, resulting in smoother discharge of the recycled mixture. The fiber-reinforced composite recycled concrete material provided by this invention has significantly better performance than the specifications, with improved tensile strength (split tensile strength), superior crack resistance, stronger resistance to reflective cracking, denser material, stronger resistance to water loss, and better durability.

[0008] As can be seen from the above, recycling asphalt concrete can effectively reduce costs. However, how to recycle asphalt concrete while ensuring that the resulting material has excellent low-temperature crack resistance and meets the needs of actual conditions is an urgent problem to be solved. Summary of the Invention

[0009] The technical problem this invention aims to solve is to overcome the defects and shortcomings of existing technologies and provide an environmentally friendly recycled asphalt concrete and its preparation method. The environmentally friendly recycled asphalt concrete provided by this invention comprises, by weight, the following raw materials: 100 parts recycled asphalt mixture (RAP); 15-20 parts asphalt; 4-8 parts sodium stearate-modified basalt fiber; 5-15 parts HY-102 and octyldiamine-modified vermiculite nanosheets; and 9-15 parts polyolefin modifier. Using recycled asphalt mixture can save costs. Furthermore, sodium stearate-modified basalt fiber improves the dispersibility of basalt fiber in concrete, thereby improving the mechanical properties of asphalt concrete. HY-102 and octyldiamine-modified vermiculite nanosheets improve the dispersibility of vermiculite nanosheets in asphalt concrete while enhancing the bonding strength between vermiculite nanosheets and the base material, thus enhancing the mechanical properties of asphalt concrete. The polyolefin modifier improves the interfacial properties between asphalt and aggregates, thereby improving the overall performance of the mixture.

[0010] The purpose of this invention is to provide an environmentally friendly recycled asphalt concrete.

[0011] Another objective of this invention is to provide a method for preparing environmentally friendly recycled asphalt concrete.

[0012] The above-mentioned objective of this invention is achieved through the following technical solution:

[0013] An environmentally friendly recycled asphalt concrete, by weight, comprises the following raw materials:

[0014] 100 parts of recycled asphalt mixture RAP;

[0015] 15-20 parts asphalt;

[0016] 4-8 parts of sodium stearate-modified basalt fiber;

[0017] 5-15 parts of HY-102 and octanediamine-modified vermiculite nanosheets;

[0018] 9-15 parts of polyolefin modifier.

[0019] In this invention, a preferred technical solution is provided, wherein the preparation method of the sodium stearate modified basalt fiber includes the following steps:

[0020] Sodium stearate and basalt fiber were added to deionized water, stirred, filtered, and then vacuum dried to constant weight to obtain modified basalt fiber.

[0021] Preferably, the mass ratio of basalt fiber to sodium stearate is 100:3-7; the length of the basalt fiber is 6-10 mm, and the aspect ratio is 30-50:1.

[0022] Preferably, the stirring conditions are stirring at 55℃-65℃ for 2-4 hours; the vacuum drying temperature is 50-70℃.

[0023] 5. The environmentally friendly recycled asphalt concrete according to claim 1, characterized in that: the preparation method of the HY-102 and octanediamine-modified vermiculite nanosheets includes the following steps:

[0024] (1) Crush the raw vermiculite ore, sieve it, and then place the vermiculite powder in a muffle furnace for heat treatment to obtain expanded vermiculite;

[0025] (2) Add the expanded vermiculite obtained in step (1) to deionized water, then rotate the machine, then perform ultrasonic treatment, let it stand, take the upper suspension for solid-liquid separation, and dry it to constant weight to obtain vermiculite nanosheets.

[0026] (3) The vermiculite nanosheets obtained in step (2) and titanate coupling agent HY-102 were dispersed in anhydrous ethanol, ultrasonically treated, filtered, washed, and dried to constant weight. Then, they were dispersed with octanediamine in deionized water, stirred and reacted, filtered, washed, and dried to constant weight to obtain modified vermiculite nanosheets.

[0027] Preferably, the sieved vermiculite powder has a particle size of 1-3 mm; the heat treatment conditions are heat treatment at 650-750℃ for 4-6 minutes.

[0028] Preferably, the stirring conditions are: stirring at 2000-3000 rpm for 5-15 minutes; the ultrasonic treatment conditions are: ultrasonic power of 200-400W and ultrasonic treatment time of 40-60 minutes; the standing time is 10-14 hours; and the drying temperature is 70-90℃.

[0029] Preferably, the ultrasonic treatment conditions are: ultrasonic treatment at 35~45℃ for 10~20 min; the mass ratio of vermiculite nanosheets, titanate coupling agent HY-102 and octanediamine is 10:0.5~0.7:0.1~0.3.

[0030] Preferably, the drying is carried out at 60~80℃; the stirring reaction conditions are: stirring reaction at 45~55℃ for 30~50 min.

[0031] The preparation method of environmentally friendly recycled asphalt concrete described above includes the following steps:

[0032] (1) Preheat the waste asphalt mixture at 130-140℃ for 10-20 minutes to obtain preheated waste asphalt mixture;

[0033] (2) Preheat the asphalt at 150-170℃ for 5-10 minutes, then add polyolefin modifier, modified basalt fiber and modified vermiculite nanosheets, stir for 3-5 minutes, and then mix with the preheated waste asphalt mixture obtained in step (1) to obtain environmentally friendly recycled asphalt concrete.

[0034] The present invention has the following beneficial effects:

[0035] (1) The present invention uses recycled asphalt mixture as raw material, which can effectively reduce maintenance costs and improve maintenance efficiency, and has significant economic benefits.

[0036] (2) The present invention improves the dispersibility of basalt fibers in concrete by modifying basalt fibers with sodium stearate, thereby improving the mechanical properties of asphalt concrete.

[0037] (3) Vermiculite nanosheets modified by HY-102 and octanediamine can improve the dispersibility of vermiculite nanosheets in asphalt concrete and enhance the bonding strength between vermiculite nanosheets and base materials, thereby improving the mechanical properties of asphalt concrete. By combining with sodium stearate modified basalt fiber, the mechanical properties of asphalt concrete are further improved.

[0038] (4) By using polyolefin modifiers, the interfacial properties between asphalt and aggregates can be improved, thereby improving the overall performance of the mixture. Detailed Implementation

[0039] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0040] The recycled asphalt mixture was measured according to JTG E20-2011, with the following performance indicators: softening point 84.7℃, penetration 39 (0.1mm), ductility at 15℃ 43 cm, and viscosity at 135℃ 19.5 Pa·s (RAP recycled from a highway in a certain location after milling). The asphalt used was 70# base asphalt. The polyolefin modifier was Honeywell Titan 7686. The vermiculite ore was purchased from Hebei Yanxi Mining Co., Ltd.

[0041] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0042] Example 1

[0043] An environmentally friendly recycled asphalt concrete, by weight, comprises the following raw materials:

[0044] 100 parts of recycled asphalt mixture RAP;

[0045] 20 parts asphalt;

[0046] Four parts of sodium stearate modified basalt fiber;

[0047] 15 parts of HY-102 and octyldiamine-modified vermiculite nanosheets;

[0048] Nine parts of polyolefin modifier.

[0049] The preparation method of sodium stearate modified basalt fiber includes the following steps:

[0050] 7g of sodium stearate and 100g of basalt fiber were added to 150mL of deionized water, stirred at 65℃ for 2h, filtered, and then vacuum dried at 70℃ to constant weight to obtain modified basalt fiber. The basalt fiber had a length of 10mm and an aspect ratio of 50:1.

[0051] The preparation method of HY-102 and octanediamine modified vermiculite nanosheets includes the following steps:

[0052] (1) 100g of vermiculite ore was crushed and sieved to obtain vermiculite powder with a particle size of 3mm. Then the vermiculite powder was placed in a muffle furnace and heat-treated at 750℃ for 4min to obtain expanded vermiculite.

[0053] (2) Add 100g of expanded vermiculite obtained in step (1) to 150mL of deionized water, stir at 3000rpm for 5min, then sonicate at 400W for 40min, let stand for 14h, take the upper suspension for solid-liquid separation, and dry at 80℃ to constant weight to obtain vermiculite nanosheets.

[0054] (3) Disperse 100g of vermiculite nanosheets obtained in step (2) and 7g of titanate coupling agent HY-102 into 150mL of anhydrous ethanol, sonicate at 45℃ for 10min, filter, wash, dry at 80℃ to constant weight, then disperse with 1g of octanediamine into 100mL of deionized water, stir and react at 55℃ for 30min, filter, wash, dry at 80℃ to constant weight to obtain modified vermiculite nanosheets.

[0055] A method for preparing environmentally friendly recycled asphalt concrete includes the following steps:

[0056] (1) Preheat the waste asphalt mixture at 135℃ for 15 minutes to obtain preheated waste asphalt mixture;

[0057] (2) Preheat the asphalt at 160°C for 8 minutes, then add polyolefin modifier, modified basalt fiber and modified vermiculite nanosheets, stir for 4 minutes, and then mix with the preheated waste asphalt mixture obtained in step (1) to obtain environmentally friendly recycled asphalt concrete.

[0058] Example 2

[0059] An environmentally friendly recycled asphalt concrete, by weight, comprises the following raw materials:

[0060] 100 parts of recycled asphalt mixture RAP;

[0061] 15 parts asphalt;

[0062] Eight parts of sodium stearate-modified basalt fiber;

[0063] Five parts of HY-102 and octanediamine-modified vermiculite nanosheets;

[0064] 15 parts of polyolefin modifier.

[0065] The preparation method of sodium stearate modified basalt fiber includes the following steps:

[0066] 3g of sodium stearate and 100g of basalt fiber were added to 150mL of deionized water, stirred at 55℃ for 4h, filtered, and then vacuum dried at 50℃ to constant weight to obtain modified basalt fiber. The basalt fiber had a length of 6mm and an aspect ratio of 30:1.

[0067] The preparation method of HY-102 and octanediamine modified vermiculite nanosheets includes the following steps:

[0068] (1) 100g of vermiculite ore was crushed and sieved to obtain vermiculite powder with a particle size of 1mm. Then the vermiculite powder was placed in a muffle furnace and heat-treated at 650℃ for 6min to obtain expanded vermiculite.

[0069] (2) Add 100g of expanded vermiculite obtained in step (1) to 150mL of deionized water, stir at 2000rpm for 15min, then sonicate at 400W for 40min, let stand for 10h, take the upper suspension for solid-liquid separation, and dry at 80℃ to constant weight to obtain vermiculite nanosheets.

[0070] (3) Disperse 100g of vermiculite nanosheets obtained in step (2) and 5g of titanate coupling agent HY-102 into 150mL of anhydrous ethanol, sonicate at 35℃ for 20min, filter, wash, dry at 60℃ to constant weight, then disperse with 3g of octanediamine into 100mL of deionized water, stir at 45℃ for 50min, filter, wash, dry at 60℃ to constant weight to obtain modified vermiculite nanosheets.

[0071] The preparation method of an environmentally friendly recycled asphalt concrete is the same as that in Example 1.

[0072] Example 3

[0073] An environmentally friendly recycled asphalt concrete, by weight, comprises the following raw materials:

[0074] 100 parts of recycled asphalt mixture RAP;

[0075] 18 parts asphalt;

[0076] Six parts of sodium stearate-modified basalt fiber;

[0077] 10 parts of HY-102 and octyldiamine-modified vermiculite nanosheets;

[0078] 12 parts of polyolefin modifier.

[0079] The preparation method of sodium stearate modified basalt fiber includes the following steps:

[0080] 5g of sodium stearate and 100g of basalt fiber were added to 150mL of deionized water, stirred at 60℃ for 3h, filtered, and then vacuum dried at 60℃ to constant weight to obtain modified basalt fiber. The basalt fiber had a length of 8mm and an aspect ratio of 40:1.

[0081] The preparation method of HY-102 and octanediamine modified vermiculite nanosheets includes the following steps:

[0082] (1) 100g of vermiculite ore was crushed and sieved to obtain vermiculite powder with a particle size of 2mm. Then the vermiculite powder was placed in a muffle furnace and heat-treated at 700℃ for 5min to obtain expanded vermiculite.

[0083] (2) Add 100g of expanded vermiculite obtained in step (1) to 150mL of deionized water, stir at 2500rpm for 10min, then sonicate for 50min under ultrasonic power of 300W, let stand for 12h, take the upper suspension for solid-liquid separation, and dry at 80℃ to constant weight to obtain vermiculite nanosheets.

[0084] (3) Disperse 100g of vermiculite nanosheets obtained in step (2) and 6g of titanate coupling agent HY-102 into 150mL of anhydrous ethanol, sonicate at 40℃ for 15min, filter, wash, dry at 70℃ to constant weight, then disperse with 2g of octanediamine into 100mL of deionized water, stir at 50℃ for 40min, filter, wash, dry at 70℃ to constant weight to obtain modified vermiculite nanosheets.

[0085] The preparation method of an environmentally friendly recycled asphalt concrete is the same as that in Example 1.

[0086] Comparative Example 1

[0087] Except for the differences, Comparative Example 1 is exactly the same as Example 3, except that no polyolefin modifier is added.

[0088] Comparative Example 2

[0089] Except for the differences, Comparative Example 2 is exactly the same as Example 3, except that basalt fiber of equal mass is used to replace sodium stearate modified basalt fiber.

[0090] Comparative Example 3

[0091] Except for the differences, Comparative Example 3 is identical to Example 3, except that HY-102 modified vermiculite nanosheets are used instead of HY-102 and octanediamine modified vermiculite nanosheets. The preparation method of the HY-102 modified vermiculite nanosheets includes the following steps:

[0092] (1) 100g of vermiculite ore was crushed and sieved to obtain vermiculite powder with a particle size of 2mm. Then the vermiculite powder was placed in a muffle furnace and heat-treated at 700℃ for 5min to obtain expanded vermiculite.

[0093] (2) Add 100g of expanded vermiculite obtained in step (1) to 150mL of deionized water, stir at 2500rpm for 10min, then sonicate for 50min under ultrasonic power of 300W, let stand for 12h, take the upper suspension for solid-liquid separation, and dry at 80℃ to constant weight to obtain vermiculite nanosheets.

[0094] (3) Disperse 100g of vermiculite nanosheets obtained in step (2) and 8g of titanate coupling agent HY-102 into 150mL of anhydrous ethanol, sonicate at 40℃ for 15min, filter, wash, and dry at 70℃ to constant weight to obtain modified vermiculite nanosheets.

[0095] Comparative Example 4

[0096] Except for the differences, Comparative Example 2 is exactly the same as Example 3. The difference is that sodium stearate modified basalt fiber of equal mass is used to replace HY-102 and octanediamine modified vermiculite nanosheets.

[0097] Performance testing

[0098] The environmentally friendly recycled asphalt concrete prepared in Examples 1-3 and Comparative Examples 1-3 was tested according to the method in T0729-2000 of JTJ052-2000 "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" to determine its low-temperature crack resistance by measuring the freeze-thaw splitting strength ratio (%). The test results are shown in Table 1 below.

[0099] Table 1

[0100]

[0101] Referring to the test results in Table 1 above, it can be seen that the environmentally friendly recycled asphalt concrete prepared in the embodiments of the present invention has excellent low-temperature crack resistance. A comparison of Examples 1-3 and Comparative Examples 1-4 shows that the present invention can improve the interfacial properties between asphalt and aggregates through the polyolefin modifier, thereby improving the mechanical properties of the mixture; the sodium stearate-modified basalt fiber can improve the dispersibility of basalt fiber in concrete, thus improving the mechanical properties of asphalt concrete; the HY-102 and octyldiamine-modified vermiculite nanosheets can improve the dispersibility of vermiculite nanosheets in asphalt concrete while enhancing the bonding strength between vermiculite nanosheets and the base material, thus enhancing the mechanical properties of asphalt concrete. Furthermore, the synergistic effect of these modifications with the sodium stearate-modified basalt fiber further improves the low-temperature crack resistance of the environmentally friendly recycled asphalt concrete.

[0102] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An environmentally friendly recycled asphalt concrete, characterized in that: By weight: Including the following raw materials: 100 parts of recycled asphalt mixture RAP; 15-20 parts asphalt; 4-8 parts of sodium stearate-modified basalt fiber; 5-15 parts of HY-102 and octanediamine-modified vermiculite nanosheets; 9-15 parts of polyolefin modifier.

2. The environmentally friendly recycled asphalt concrete according to claim 1, characterized in that: The preparation method of the sodium stearate modified basalt fiber includes the following steps: Sodium stearate and basalt fiber were added to deionized water, stirred, filtered, and then vacuum dried to constant weight to obtain modified basalt fiber.

3. The environmentally friendly recycled asphalt concrete according to claim 1 as described in claim 2, characterized in that: The mass ratio of basalt fiber to sodium stearate is 100:3~7; the length of the basalt fiber is 6~10mm and the aspect ratio is 30~50:

1.

4. The environmentally friendly recycled asphalt concrete according to claim 2, characterized in that: The stirring conditions are 55℃-65℃ for 2-4 hours; the vacuum drying temperature is 50-70℃.

5. The environmentally friendly recycled asphalt concrete according to claim 1, characterized in that: The preparation method of the HY-102 and octanediamine-modified vermiculite nanosheets includes the following steps: (1) Crush the raw vermiculite ore, sieve it, and then place the vermiculite powder in a muffle furnace for heat treatment to obtain expanded vermiculite; (2) Add the expanded vermiculite obtained in step (1) to deionized water, then rotate the spindle, then perform ultrasonic treatment, let stand, take the upper suspension for solid-liquid separation, and dry to obtain vermiculite nanosheets; (3) The vermiculite nanosheets obtained in step (2) and titanate coupling agent HY-102 were dispersed in anhydrous ethanol, ultrasonically treated, filtered, washed, and dried to constant weight. Then, they were dispersed with octanediamine in deionized water, stirred and reacted, filtered, washed, and dried to constant weight to obtain modified vermiculite nanosheets.

6. The environmentally friendly recycled asphalt concrete according to claim 5, characterized in that: In step (1), the sieved vermiculite powder is 1~3mm; the heat treatment conditions are 650~750℃ for 4~6min.

7. The environmentally friendly recycled asphalt concrete according to claim 5, characterized in that: In step (2), the stirring conditions are stirring at a speed of 2000~3000 rpm for 5~15 min; the ultrasonic treatment conditions are ultrasonic power of 200~400W and ultrasonic treatment time of 40~60 min; the standing time is 10~14 h; and the drying temperature is 70~90℃.

8. The environmentally friendly recycled asphalt concrete according to claim 5, characterized in that: In step (3), the ultrasonic treatment conditions are: ultrasonic treatment at 35~45℃ for 10~20min; the mass ratio of vermiculite nanosheets, titanate coupling agent HY-102 and octanediamine is 10:0.5~0.7:0.1~0.

3.

9. The environmentally friendly recycled asphalt concrete according to claim 5, characterized in that: In step (3), the drying is carried out at 60~80℃; the stirring reaction conditions are stirred at 45~55℃ for 30~50 min.

10. A method for preparing environmentally friendly recycled asphalt concrete according to any one of claims 1-9, characterized in that: The preparation method includes the following steps: (1) Preheat the waste asphalt mixture at 130~140℃ for 10~20min to obtain preheated waste asphalt mixture; (2) Preheat the asphalt at 150~170℃ for 5~10min, then add polyolefin modifier, modified basalt fiber and modified vermiculite nanosheets, stir for 3~5min, and then mix with the preheated waste asphalt mixture obtained in step (1) to obtain environmentally friendly recycled asphalt concrete.

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