Preparation method of secondary remelting pouring type asphalt mixture

Abstract

The invention provides a preparation method of a secondary remelting pouring type asphalt mixture. The preparation method comprises the following steps: preparing a precast block of the pouring type asphalt mixture; the precast blocks are put into mixing equipment in batches to be subjected to hot melting mixing, a compensating agent is put in the hot melting mixing process, and the pouring type asphalt mixture is obtained after hot melting mixing is finished. The problems that in the prior art, due to thermo-oxidative aging, the performance of the pouring type asphalt mixture subjected to secondary hot melting is affected, the performance of the pouring type asphalt mixture cannot reach the performance of the pouring type asphalt mixture when the pouring type asphalt mixture is just produced, the road maintenance effect is poor, and the expected maintenance effect cannot be achieved are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of road maintenance, and particularly relates to a preparation method of secondary remelted cast asphalt mixture. BACKGROUND

[0002] For the pit and groove repair of asphalt pavement, the traditional maintenance materials such as SMA, AC and the like are faced with the dilemma of construction process and performance limitation. The SMA, AC and the like need to be formed by rolling when newly paved to ensure the compactness, but due to the small repair area, poor rolling conditions or rolling equipment and the like, the material compactness in daily maintenance engineering is difficult to reach the standard, and generally can only reach about 80%. The lower compactness causes more voids in the material, which can cause the repaired area to be damaged again and fall into a vicious cycle of repeated repair.

[0003] In comparison, the cast asphalt mixture has a void ratio of almost 0, and does not need to be rolled to realize self-compaction, thereby eliminating the risk of water penetration from the root; the asphalt mastic formed by high content of asphalt and mineral powder has extremely high toughness and anti-deformation ability, and can adapt to the deformation demand of traffic load and temperature action; the self-leveling property can closely adhere to the surface of the pit and groove, and can be bonded with the original pavement to form a whole and co-deform; in addition, the cast asphalt mixture has outstanding road performance, and can guarantee that the repaired pavement maintains the long-term effectiveness of asphalt pavement repair under long-term vehicle load action. As can be seen, the cast asphalt mixture is an ideal repair material in daily maintenance and repair.

[0004] However, for the small-scale material demand of daily maintenance engineering, it is obviously not economical and reasonable to purchase preparation raw materials and use large-scale mixing equipment to prepare a small amount of cast asphalt mixture on site, and therefore, in order to meet the demand of road maintenance, the cast asphalt mixture prepared by the mixing station is used for secondary hot melting, but the performance of the cast asphalt mixture is affected by thermal oxidation aging after the secondary hot melting, and generally cannot reach the performance when it is just produced, thereby causing poor road maintenance effect and failing to achieve the expected maintenance effect. SUMMARY

[0005] In view of the deficiencies in the prior art, the present application provides a preparation method of secondary remelted cast asphalt mixture, which solves the problem that the performance of the cast asphalt mixture after secondary hot melting is affected by thermal oxidation aging in the prior art, and generally cannot reach the performance when it is just produced, thereby causing poor road maintenance effect and failing to achieve the expected maintenance effect.

[0006] According to an embodiment of the present application, a preparation method of secondary remelted cast asphalt mixture comprises the following steps: preparing a precast block of cast asphalt mixture; The precast blocks are put into the mixing device in batches for hot-melt mixing, and the compensating agent is put into the hot-melt mixing process, and the hot-melt mixing is completed to obtain the paving asphalt mixture.

[0007] Preferably, the method for preparing the precast blocks of the paving asphalt mixture comprises: A site with good flatness is selected, and qualified paving asphalt mixture produced in the mixing station is used to form a paving layer with a required thickness by using a special paving device; A cutting device is used to cut a plurality of test blocks with different sizes from the paving layer according to a preset size range; The hot-melt efficiency of each test block is tested, and the size corresponding to the test block with the required hot-melt efficiency is selected as the cutting size; The paving layer is cut according to the cutting size to obtain a plurality of precast blocks.

[0008] Preferably, if the time for completing the process of agglomeration to uniform mixing in the mixing device at a temperature of 220-240℃ is also within 60 minutes, the hot-melt efficiency of the test block meets the requirements.

[0009] Preferably, the method for preparing the precast blocks of the paving asphalt mixture comprises: The temperature of the mixing device is heated to 200℃, a first weight of precast blocks and the compensating agent are put into the mixing device, and hot-melt is performed until the pressure of the mixing device is stable; The temperature of the mixing device is heated to 220℃, a second weight of precast blocks and the compensating agent are put into the mixing device, and hot-melt is performed until the pressure of the mixing device is stable; A third weight of precast blocks and the compensating agent are put into the mixing device, and hot-melt is performed until the pressure of the mixing device is stable, and then the step is repeated until all the precast blocks are put into the mixing device; The temperature of the mixing device is heated to 240℃, and the material is discharged after the pressure of the mixing device is stable to obtain the paving asphalt mixture.

[0010] Preferably, the precast blocks comprise paving asphalt and mineral aggregates, and the mass ratio of the compensating agent put into the precast blocks to the paving asphalt contained in the precast blocks is 6-10:100.

[0011] Preferably, the compensating agent comprises one or more of hyperbranched polymers, comb-shaped polymers, and multi-block polymers.

[0012] Preferably, the hyperbranched polymer is hyperbranched polyethylene, the comb-shaped polymer is a comb-shaped polyolefin thermoplastic elastomer, and the multiblock polymer is one or more of polyolefin multiblock polymers and styrene multiblock polymers.

[0013] Compared with the prior art, the present invention has the following beneficial effects: This invention involves cutting cast-in-place asphalt mixtures produced centrally at a mixing plant into precast blocks with sufficient hot-melt efficiency. After these precast blocks undergo secondary hot-melting, a compensating agent is added to the asphalt mixtures subjected to heat and oxygen aging to compensate for their performance, thereby improving the performance of the asphalt mixtures and enabling them to meet the requirements of road maintenance. Attached Figure Description

[0014] Figure 1 This diagram illustrates a secondary hot-melt preparation method for cast-in-place asphalt mixtures according to an embodiment of the present invention. Detailed Implementation

[0015] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0016] like Figure 1 As shown in the figure, this invention proposes a method for preparing cast-in-place asphalt mixtures with secondary remelting, comprising: Precast blocks for cast-in-place asphalt mixtures; Since the amount of cast-in-place asphalt mixture required for on-site maintenance is relatively small, it is clearly uneconomical and unreasonable to use a mixing plant for small-batch production of cast-in-place asphalt mixture. To solve the problem of material shortage for small-batch production, a site with good flatness is selected, and qualified cast-in-place asphalt mixture produced centrally at the mixing plant is laid to the required thickness using specialized cast-in-place paving equipment. After being shaped, it is then cut into precast blocks of cast-in-place asphalt mixture and transported to the construction site for storage.

[0017] After paving, the asphalt mixture is cut into multiple test blocks of different sizes according to a preset size range using a cutting device. The size range is length (10cm~40cm) × width (5cm~20cm) × height (5cm~10cm). In this invention, three sizes are used for illustration: size 1 (10cm×5cm×5cm), size 2 (40cm×20cm×5cm), and size 3 (80cm×20cm×5cm).

[0018] Since the cutting process will affect the gradation and performance of the paving asphalt mixture, after cutting out the test block, the gradation and performance of each test block need to be tested, as shown in Table 1 and Table 2, according to Table 1 and Table 2, the cutting affects the passing rate of the key sieve (2.36mm / 4.75mm) of the paving asphalt mixture within 5%, and the influence of the paving asphalt mixture gradation and performance can be basically ignored, so the cutting process will not affect the performance of the paving asphalt mixture.

[0019] Table 1: Influence of cutting process on paving asphalt mixture gradation Table 2: Influence of cutting preparation of precast block on mixture performance Then test the hot melt efficiency of each test block, for the hot melt efficiency of the paving asphalt mixture, it should meet the requirements: Under the temperature condition of 220~240℃, the mixture experiences the process of "agglomeration-dispersion-uniform mixing" in the mixing equipment, and the required mixing time is within 60min.

[0020] Through testing, the hot melt efficiency of the test block of three sizes is shown in Table 3, from Table 3, it can be seen that only the hot melt efficiency of size 1 and size 2 meets the requirements, but using size 1 to cut will result in too many and too small precast blocks, which makes the cutting and transportation operation more complicated, therefore, if the sizes that meet the hot melt efficiency requirements are multiple, the larger size should be selected as the cutting size, in the present application, size 2 is selected as the cutting size.

[0021] Table 3: Hot melt time of test block According to size 2, the paving asphalt paving asphalt mixture formed by paving is cut to obtain precast blocks of corresponding size, since the paving asphalt mixture contains paving asphalt and mineral aggregate, the precast block also contains paving asphalt and mineral aggregate.

[0022] The precast blocks are put into the mixing equipment in batches for hot melt mixing, and the compensating agent is put into the hot melt mixing process, and the paving asphalt mixture is obtained after the hot melt mixing is completed.

[0023] Precast blocks are transported from the mixing plant to the construction site for secondary remelting. During the remelting process, if too many precast blocks are added to the mixing equipment at once, two problems arise: First, because the precast blocks are solid in their unmelted state, the irregular accumulation, embedding, and tumbling of these solid blocks during mixing can overload the equipment. Second, the melting time of too many precast blocks will far exceed the normal time. This prolonged hot-melting process can lead to excessive thermo-oxidative aging of the mixture within the mixing equipment, resulting in a decline in the mixture's performance. Therefore, when hot-melting and mixing precast blocks, they must be added to the mixing equipment in batches and in small quantities, as detailed below: (1) Preheat the temperature of the mixing equipment to 200°C, then add the first weight of precast blocks and compensating agent to the mixing equipment and heat them fully until the pressure of the mixing equipment stabilizes. Stable pressure indicates that the solid precast blocks have been heat-melted and a uniform fluid mixture has been formed.

[0024] In this step, since it is the first addition, a larger amount of precast blocks should be added because: ① there is less material in the pot, and the equipment load can generally meet the power requirements; ② if there is too little material, the material will be piled up at the bottom of the pot (where the heating position is), which is prone to heat aging; ③ the first batch of material melts quickly, which can lubricate the pot wall and reduce the stirring load. Therefore, depending on the power of the selected mixing equipment, the amount of precast blocks is generally 300~500 kg.

[0025] (2) Heat the temperature of the mixing equipment to 220°C, add the second weight of precast blocks and compensating agent into the mixing equipment, and heat them thoroughly until the pressure of the mixing equipment stabilizes.

[0026] (3) Add the third weight of precast blocks and compensating agent and heat-melt them fully until the pressure of the mixing equipment stabilizes. Then repeat this step until all the precast blocks are added to the mixing equipment.

[0027] (4) Heat the temperature of the mixing equipment to about 240°C, and discharge the material after the pressure of the mixing equipment stabilizes to obtain cast-in-place asphalt mixture.

[0028] The mixing equipment used in the above steps is a mobile mixing equipment suitable for small-area repairs of highway asphalt pavement. The equipment has an automatic ignition and temperature control function, a temperature control range of 150~300℃, a heating efficiency of more than 1.6℃ / min, and a mixing power of more than 6kW.

[0029] In addition, after the precast blocks are transported to the construction site, they can be hot-melted according to the above steps without adding compensating agent, and the performance of the hot-melted cast-in-place asphalt mixture can be evaluated. If the performance meets the requirements of the repair material, the cast-in-place asphalt mixture produced at this time can be used as a pothole repair material. If it does not meet the requirements, it can be cooled again and compensating agent can be added according to the above steps to compensate for the performance.

[0030] The performance of cast-in-place asphalt mixtures produced centrally at mixing plants is affected after multiple hot-melting processes. A single hot-melting process is defined as the complete hot-melting of precast cast-in-place asphalt mixture blocks at 240℃. This process is repeated 1-3 times to obtain cast-in-place asphalt mixtures after 1-3 hot-melting cycles. The original cast-in-place asphalt mixture is labeled GA-R0, and the asphalt samples after one, two, and three hot-melting cycles are labeled GA-R1, GA-R2, and GA-R3, respectively. The properties of the asphalt and the mixture are shown in Tables 4 and 5, respectively.

[0031] Table 4: Effect of hot melt cycles on asphalt properties Table 5: Effect of the number of hot-melting cycles on the properties of the mixture As can be seen from Tables 4 and 5, the rate of performance degradation of cast-in-place asphalt mixtures gradually increases with the number of hot-melt cycles. After three hot-melt cycles, some properties under normal conditions reach their lowest point.

[0032] In this invention, the compensating agent for cast-in-place asphalt mixtures can be a composite material made of one or more of hyperbranched polymers, comb-shaped polymers, and multi-block polymers.

[0033] Among them, hyperbranched polymers can be hyperbranched polyethylene. The branching degree of hyperbranched polyethylene matches the polar components of asphalt (such as resins and asphaltenes), which can promote their uniform dispersion in asphalt and avoid segregation. At the same time, its elastic modulus (such as LDPE about 13MPa) works synergistically with the asphalt mixture to form a "rigid and flexible" skeleton, which inhibits high-temperature rutting and low-temperature cracking.

[0034] The comb-shaped polymer is a comb-shaped polyolefin thermoplastic elastomer (such as TPO, TPV, POE, etc.). Fully cross-linked rubber microparticles (1-2μm) are uniformly dispersed in the polyolefin matrix to form an "island structure". It retains the elasticity of rubber and has thermoplastic processability, achieving a balance between the dual properties of rubber and plastic. At the same time, its elastic modulus can give the mixture elastic recovery ability, reduce plastic deformation under repeated loads, and inhibit the propagation of low-temperature cracks.

[0035] The multi-block polymer is one or all of polyolefin multi-block polymers and styrene multi-block polymers. When the multi-block polymer is used as a compensator, its hard segments restrict the high-temperature flow of asphalt molecular chains (such as reducing penetration and increasing softening point), while the soft segments absorb stress through chain segment movement and inhibit low-temperature cracking (such as increasing failure strain by 20%-50%). This synergistic effect enables the mixture to maintain excellent viscoelastic response over a wide temperature range.

[0036] During the hot-melt mixing process of precast blocks, one or more of the above-mentioned substances are added as compensating agents, and the mass ratio of the added compensating agent to the cast-in-place asphalt in the precast blocks is 6~10:100.

[0037] The cast-in-place asphalt mixture precast blocks were hot-melted two or three times. Using the above-mentioned hot-melt compensation method, external compensating agents were added in proportion. The compensation effect on the cast-in-place asphalt mixture is shown in Table 6. Among them, GA10-R0 is the original cast-in-place asphalt mixture, and GA10-R1, GA10-R2, and GA10-R3 are the cast-in-place asphalt mixtures after one, two, and three hot-melt processes, respectively.

[0038] Table 6: Results of the improvement of performance of cast-in-place asphalt mixtures by compensating agents Based on the test data from the above examples, using the block size and molding method described above, the hot-melt mixing efficiency of the precast blocks can meet the on-site construction time requirements, while the impact on the material's own properties is negligible. Using the above hot-melt preparation method, the material properties of the cast-in-place asphalt mixture can be guaranteed to meet the repair material requirements after a single hot-melt process; for subsequent processes, a performance compensation method should be used. Using the above performance compensation method, with a certain proportion of compensating agent, can effectively compensate for the material performance loss caused by thermo-oxidative aging.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing castable asphalt mixture with secondary remelting, characterized in that: include: Precast blocks for cast-in-place asphalt mixtures; Precast blocks are fed into a mixing plant in batches for hot-melt mixing, and a compensating agent is added during the hot-melt mixing process. After the hot-melt mixing is completed, a castable asphalt mixture is obtained.

2. The method for preparing a castable asphalt mixture by secondary remelting as described in claim 1, characterized in that: Methods for preparing precast blocks of cast-in-place asphalt mixtures include: Select a site with good flatness, and use a special cast-in-place paving equipment to pave the qualified cast-in-place asphalt mixture produced centrally at the mixing plant to the required thickness. Using cutting equipment, multiple test blocks of different sizes are cut from the paved cast-in-place asphalt mixture according to a preset size range; Test the heat-melting efficiency of each test block, and select the size corresponding to the test block with the required heat-melting efficiency as the cutting size; The paved cast-in-place asphalt mixture is cut according to the cutting dimensions to obtain multiple precast blocks.

3. The method for preparing a castable asphalt mixture with secondary remelting as described in claim 2, characterized in that: If the time required to complete the agglomeration to uniform mixing process in the mixing equipment at a temperature of 220~240℃ is also within 60 minutes, then the hot melting efficiency of the test block meets the requirements.

4. The method for preparing a castable asphalt mixture with secondary remelting as described in claim 1, characterized in that: The method of feeding precast blocks into a mixing plant in batches for hot-melt mixing, adding a compensating agent during the hot-melt mixing process, and obtaining a castable asphalt mixture after the hot-melt mixing is completed includes: Heat the mixing equipment to 200°C, add the first weight of precast blocks and compensating agent into the mixing equipment, and heat them thoroughly until the pressure of the mixing equipment stabilizes. Heat the mixing equipment to 220°C, add the second weight of precast blocks and compensating agent into the mixing equipment, and heat them thoroughly until the pressure of the mixing equipment stabilizes. Add the third weight of precast blocks and compensating agent, and heat-melt them thoroughly until the pressure of the mixing equipment stabilizes. Then repeat this step until all the precast blocks are added to the mixing equipment. The temperature of the mixing equipment is heated to 240℃, and the material is discharged after the pressure of the mixing equipment stabilizes, resulting in castable asphalt mixture.

5. The method for preparing a castable asphalt mixture with secondary remelting as described in claim 4, characterized in that: The precast blocks consist of castable asphalt and aggregate. When adding the compensating agent, the mass ratio of the compensating agent to the castable asphalt contained in the precast blocks is 6~10:

100.

6. The method for preparing a castable asphalt mixture with secondary remelting as described in claim 4, characterized in that: The compensator includes one or more of hyperbranched polymers, comb-shaped polymers, and multiblock polymers.

7. The method for preparing a castable asphalt mixture with secondary remelting as described in claim 6, characterized in that: The hyperbranched polymer is hyperbranched polyethylene, the comb-shaped polymer is comb-shaped polyolefin thermoplastic elastomer, and the multiblock polymer is one or more of polyolefin multiblock polymers and styrene multiblock polymers.

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