Preparation method of an ultrathin asphalt mixture overlay composite test piece and evaluation method thereof

Abstract

This invention discloses a method for preparing ultra-thin asphalt mixture overlay composite specimens, comprising the following steps: determining the thickness of the upper and lower layers of the specimen mold based on the design thickness of the ultra-thin overlay, the actual thickness of the upper layer of the original pavement structure, and the gradation; determining the planar dimensions of the specimen mold based on various evaluation indicators of the ultra-thin overlay asphalt mixture; determining the aging time of the lower layer asphalt mixture based on the service time of the upper layer and performing aging treatment; preparing the lower layer of the shaped composite specimen using the aged asphalt mixture according to the upper layer thickness and the planar dimensions of the specimen mold; performing pretreatment of the shaped lower layer according to the type of upper layer defects, and uniformly coating the surface of the lower layer with an interlayer bonding material; laying the ultra-thin asphalt mixture overlay on the lower layer coated with the interlayer bonding material according to the determined upper layer thickness and the planar dimensions of the specimen mold to prepare the upper layer of the shaped composite specimen, thereby obtaining the composite specimen for testing.

Description

Technical Field

[0001] This invention belongs to the field of asphalt pavement technology, specifically relating to a method for preparing and evaluating ultrathin asphalt mixture overlay composite specimens. Background Technology

[0002] Ultra-thin overlay technology is a pavement technique that uses ultra-thin asphalt mixtures with a thickness of 10mm to 25mm, only 1 / 3 to 1 / 2 the thickness of the traditional 4cm asphalt concrete wearing course. Ultra-thin overlays primarily serve as functional wearing courses on road surfaces, offering advantages such as noise reduction, restoration of surface texture, improved surface aesthetics, rapid construction, and low resource consumption. Ultra-thin overlays are mainly used for preventative and routine maintenance of asphalt pavements, repairing minor rutting, cracks, aggregate loss, and insufficient skid resistance. They can also be used for converting cement pavements from white to black.

[0003] When evaluating the performance of ultra-thin overlays indoors, high-temperature stability, water resistance, and texture depth are typically assessed by molding 50mm thick single-layer rutting slabs; low-temperature stability is assessed by molding 50mm thick single-layer rutting slabs and cutting them into small beams; and interlayer pull-out strength is assessed by molding 50mm+50mm composite specimens. It is evident that current evaluation methods for ultra-thin overlay asphalt mixtures still follow those for thick-layer asphalt mixtures. However, these existing methods have the following problems:

[0004] (1) The cooling rate of a 25mm thick ultra-thin overlay is twice that of a 40mm thick asphalt mixture. Under the same mixing temperature and compaction work, the rolling state of the thin layer and the thick layer are different, resulting in performance differences.

[0005] (2) The performance of the mixture in the room and on the field is affected by the size of the specimen. The same material also exhibits different performance at different sizes.

[0006] Furthermore, when ultra-thin overlays are used as a maintenance method for asphalt pavements, their actual service performance is affected by the type of damage and service time of the underlying asphalt mixture, requiring consideration of factors such as cracking and aging of the underlying material. Therefore, due to these factors, existing evaluation methods for ultra-thin overlay mixtures cannot truly reflect the performance of ultra-thin overlays during actual service. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing and evaluating ultrathin asphalt mixture overlay composite specimens.

[0008] To achieve the above objectives, the present invention is implemented using the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing an ultrathin asphalt mixture overlay composite specimen, comprising the following steps:

[0010] Based on the design thickness of the ultra-thin overlay, the actual thickness and gradation of the upper layer of the original pavement structure, the thickness of the upper and lower layers of the specimen mold are determined.

[0011] The planar dimensions of the specimen mold were determined based on the various evaluation indicators of the ultra-thin overlay asphalt mixture.

[0012] The aging time of the lower asphalt mixture of the composite specimen is determined based on the service time of the upper layer of the original pavement structure, and aging treatment is carried out accordingly.

[0013] The lower layer of the composite specimen was prepared using aged asphalt mixture according to the thickness of the lower layer and the plane dimensions of the specimen mold.

[0014] Based on the type of defects in the upper layer of the original pavement structure, the formed lower layer is pretreated for defects, and after pretreatment, an interlayer bonding material is uniformly coated on the surface of the lower layer.

[0015] Based on the determined thickness of the top layer and the plane dimensions of the specimen mold, an ultra-thin asphalt mixture overlay is laid on the bottom layer of the coating interlayer adhesive material to prepare the top layer of the shaped composite specimen, thus obtaining the composite specimen for testing.

[0016] Furthermore, the evaluation indicators include high-temperature stability, water impermeability, anti-slip properties, interlayer bonding properties, low-temperature stability, and fatigue life.

[0017] Furthermore, when the evaluation indicators are high temperature stability, interlayer bonding performance, low temperature stability, water resistance, and anti-slip performance, the sample mold plane size is 300mm×300mm.

[0018] When the evaluation index is fatigue life, the test piece mold plane size is 400mm×300mm.

[0019] Furthermore, the thickness of the upper layer is 10mm to 25mm, and the thickness of the lower layer is 30mm to 80mm.

[0020] Furthermore, the lower layer of asphalt mixture is aged by heating in an oven at 85°C;

[0021] When the original pavement structure surface layer has been in service for no more than 3 years, the aging time shall not exceed 2 days.

[0022] When the original pavement structure surface layer has been in service for more than 3 years but not more than 5 years, the aging time is more than 2 days but not more than 4 days.

[0023] When the surface layer of the original road structure has been in service for more than 5 years, the aging time exceeds 4 days.

[0024] Furthermore, the disease pretreatment includes:

[0025] Rutting defects in the original pavement structure were achieved through rutting tests, with the rutting depth not exceeding 15mm.

[0026] The original pavement structure cracks are removed by cutting, with the crack depth not exceeding 80% of the thickness of the underlying layer and the crack width not exceeding 10mm.

[0027] Furthermore, the type of interlayer bonding material is one of emulsified asphalt, solvent-based asphalt, or epoxy materials.

[0028] Secondly, the present invention provides a method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens, comprising the following steps:

[0029] Ultra-thin asphalt mixture overlay composite specimens were prepared according to the preparation method described in the first aspect;

[0030] The composite specimens were processed according to the various evaluation indicators:

[0031] When evaluating the high-temperature stability, water resistance, and anti-slip properties of composite specimens, no treatment is required for the composite specimens.

[0032] When evaluating the low-temperature stability and fatigue life of composite specimens, the composite specimens need to be cut to obtain small-beam composite specimens:

[0033] When evaluating low-temperature stability, the length, height, and width of the beam composite specimen were 250 mm, 35 mm, and 30 mm, respectively, and the thickness of the upper layer of the beam composite specimen remained unchanged.

[0034] When evaluating fatigue life, the length, height and width of the beam composite specimen were 380 mm, 50 mm and 63 mm, respectively, and the thickness of the upper layer of the beam composite specimen remained unchanged.

[0035] When evaluating the interlayer bonding performance of composite specimens, core drilling is required. The core diameter is 50 mm and the core depth extends at least 10 mm to 20 mm beyond the top layer of the composite specimen.

[0036] The treated composite specimens were subjected to performance evaluation tests according to various evaluation indicators.

[0037] Furthermore, to evaluate the low-temperature stability of the composite specimen, a -10℃ low-temperature bending test was conducted to obtain the force-displacement curve. The fracture energy of the composite specimen was calculated using the force-displacement curve to evaluate its low-temperature stability. The formula for calculating the fracture energy is as follows:

[0038]

[0039] In the formula, x represents displacement, and the upper limit of displacement x is the displacement corresponding to the second peak value, F(x) represents load, and A represents fracture area.

[0040] For the three-point beam test of asphalt mixtures, the standard requires low-temperature flexural strain as the evaluation index, and fracture energy is obtained by integrating the force-displacement curve and calculating the area included with the coordinate axes. Fracture energy is used here instead of low-temperature flexural strain because the double-layer composite specimen exhibits two peak values ​​in the three-point beam specimen. The existing standard's calculation of the low-temperature flexural strain index only applies to the first peak value, making it unsuitable for evaluating composite specimens. Fracture energy, on the other hand, covers the entire process of both peaks, thus making it a more accurate and reliable evaluation index.

[0041] Furthermore, when evaluating the interlayer bond performance, the composite specimen is subjected to a pull-out strength test, which includes the following steps in sequence:

[0042] 1) Place the composite specimen in a 25℃ ambient chamber for at least 4 hours;

[0043] 2) Use two-component epoxy AB adhesive to bond and fix the pull-out head to the core sample on the surface of the composite specimen;

[0044] 3) Continue to place the composite specimen in a 25℃ environmental chamber for curing for at least 30 minutes;

[0045] 4) Take out the composite specimen, place the clamp on the drawing head and fix it, and test it with an automatic drawing machine with a test loading rate of 0.2MPa / s.

[0046] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0047] The present invention provides a method for preparing ultrathin asphalt mixture overlay composite specimens and a method for evaluating their performance. This method incorporates factors such as the actual thickness of the ultrathin overlay and the thickness of the underlying layer, the type of damage, and the degree of aging of the road structure under service. By molding composite specimens, the high-temperature stability, low-temperature stability, skid resistance, water resistance, interlayer bonding performance, and fatigue life of the ultrathin overlay are evaluated. The proposed preparation and evaluation methods are closer to the actual molding process and service conditions in engineering, and can better reflect the true performance of the ultrathin overlay. Detailed Implementation

[0048] The present invention will now be further described. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0049] Example 1

[0050] The design thickness of the ultra-thin overlay is 2cm, and the gradation type is dense skeleton interlocking high toughness asphalt mixture HTUC-10; the actual thickness of the top layer of the original pavement structure is 5cm, and the gradation type is suspended dense asphalt concrete AC-13; therefore, the thickness of the top layer and the bottom layer of the specimen mold are determined to be 2cm and 5cm, respectively.

[0051] In this embodiment, the high-temperature stability of asphalt mixtures, i.e., the dynamic stability index of asphalt mixtures, is evaluated. Therefore, the planar dimensions of the specimen mold are determined to be 300mm × 300mm.

[0052] The service life of the upper layer of the original pavement structure is 1 year, not exceeding 3 years. Therefore, the lower layer asphalt mixture of the ultra-thin asphalt mixture overlay composite specimen is treated by heating and aging in an oven at 85℃ for 16 hours.

[0053] The lower layer of the composite specimen was prepared using aged asphalt mixture with a bottom layer thickness of 5cm and a specimen mold plane size of 300mm×300mm.

[0054] The original pavement structure has no ruts or cracks in the upper layer, so there is no need to pre-treat the formed lower layer. Instead, an interlayer bonding material, which is non-stick emulsified asphalt, is directly and evenly applied to the surface of the lower layer.

[0055] On the lower layer of the specimen coated with interlayer bonding material, an ultra-thin asphalt mixture overlay is laid to prepare the upper layer of the shaped composite specimen, thus obtaining the composite specimen for testing.

[0056] According to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (T0719-2011), rutting tests were conducted on composite specimens to obtain the rutting depth and dynamic stability of the composite specimens.

[0057] To illustrate the advanced nature and inventiveness of the preparation method and evaluation method of the ultra-thin asphalt mixture overlay composite specimen proposed in this invention, in addition to the experimental results of the composite specimen, this embodiment also compares the rutting test results of 5cm suspended dense asphalt concrete AC13, 5cm dense skeleton interlocking high-toughness asphalt mixture HTUC-10, and 5cm suspended dense asphalt concrete AC13+5cm dense skeleton interlocking high-toughness asphalt mixture HTUC-10, as shown in Table 1.

[0058] Table 1 Comparison and evaluation of high-temperature rutting resistance performance of different specimen combinations

[0059]

[0060]

[0061] The results show that by forming a composite specimen combination that takes into account the actual thickness and service conditions, the rutting test results can better reflect the actual performance level of the pavement structure under the thickness of the overlay layer compared with single-layer specimens and the commonly used 5cm+5cm composite specimens.

[0062] Example 2

[0063] The design thickness of the ultra-thin overlay is 1.5cm, and the gradation type is dense skeleton interlocking high toughness asphalt mixture HTUC-5; the actual thickness of the top layer of the original pavement structure is 5cm, and the gradation type is skeleton dense asphalt mixture SMA-13; therefore, the thickness of the top layer and the bottom layer of the specimen mold are determined to be 1.5cm and 5cm, respectively.

[0064] In this embodiment, the fatigue life of asphalt mixture is evaluated, namely the 15℃ four-point bending fatigue life index of asphalt mixture. Therefore, the planar dimensions of the specimen mold are determined to be 400mm×300mm.

[0065] The service life of the upper layer of the original pavement structure is 4 years. Therefore, the lower layer asphalt mixture of the ultra-thin asphalt mixture overlay composite specimen was treated by heating and aging in an oven at 85℃ for 96 hours.

[0066] The lower layer of the composite specimen was prepared using aged asphalt mixture with a bottom layer thickness of 5cm and a specimen mold plane size of 400mm×300mm.

[0067] The original pavement structure has rutting and cracking defects in the upper layer. Therefore, the formed lower layer needs to be pretreated to remove these defects. The rutting depth is 13mm, the crack depth is 3.5cm, and the width is 9mm. After pretreatment, the surface of the lower layer is uniformly coated with an interlayer bonding material, which is high-viscosity and high-elasticity emulsified asphalt.

[0068] A 1.5cm ultrathin asphalt mixture overlay is laid on the lower layer of the specimen coated with interlayer bonding material to prepare the upper layer of the shaped composite specimen, thus obtaining the composite specimen for testing.

[0069] By cutting the composite specimen while keeping the thickness of the upper layer constant, composite beams with lengths of 380 mm, heights of 50 mm, and widths of 63 mm were obtained.

[0070] According to the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (T0739-2011), a four-point bending fatigue life test of asphalt mixture was conducted on the composite specimen to obtain the fatigue life number of the composite specimen.

[0071] In addition to the experimental results of the composite specimens, this embodiment also compared the four-point bending fatigue life test results of single-layer skeleton dense asphalt concrete SMA13 and single-layer dense skeleton interlocking high-toughness asphalt mixture HTUC-5. The test conditions were 15℃ and 400με, and the results are shown in Table 2.

[0072] Table 2 Comparison and evaluation of four-point bending fatigue life of different specimen combinations

[0073] Specimen combination type Fatigue life / cycle SMA-13+HTUC-5 421981 SMA-13 95814 HTUC-5 1000000

[0074] The results show that, compared with single-layer specimens, the four-point bending fatigue life test, which uses a composite specimen combination that takes into account the actual thickness and service conditions, can better reflect the actual performance level of the pavement structure under the thickness of the overlay layer.

[0075] Example 3

[0076] The design thickness of the ultra-thin overlay is 1cm, and the gradation type is dense skeleton interlocking high toughness asphalt mixture HTUC-5; the actual thickness of the top layer of the original pavement structure is 4cm, and the gradation type is skeleton dense asphalt mixture SMA-13; therefore, the thickness of the top layer and the bottom layer of the specimen mold are determined to be 1cm and 4cm, respectively.

[0077] In this embodiment, the interlayer bonding performance of asphalt mixture is evaluated, namely the interlayer pull-out strength index of asphalt mixture. Therefore, the planar dimensions of the specimen mold are determined to be 300mm×300mm.

[0078] The service life of the upper layer of the original pavement structure is 2 years. Therefore, the lower layer asphalt mixture of the ultra-thin asphalt mixture overlay composite specimen was treated by heating and aging in an oven at 85℃ for 16 hours.

[0079] The lower layer of the composite specimen was prepared using aged asphalt mixture with a bottom layer thickness of 4cm and a specimen mold plane size of 300mm×300mm.

[0080] The top layer of the original pavement structure has no obvious rutting or cracking defects, so there is no need to pre-treat the defects of the formed bottom layer. The bottom layer surface is uniformly coated with interlayer bonding material, which is water-based epoxy emulsified asphalt.

[0081] A 1cm ultrathin asphalt mixture overlay is laid on the lower layer of the specimen coated with interlayer bonding material to prepare the upper layer of the shaped composite specimen, thus obtaining the composite specimen for testing.

[0082] The composite specimen was subjected to core drilling, with a core diameter of 50 mm and a core drilling depth of at least 10 mm to 20 mm beyond the top layer of the composite specimen.

[0083] The tensile strength test of the composite specimen includes the following steps in sequence:

[0084] 1) Place the composite specimen in a 25℃ ambient chamber for at least 4 hours;

[0085] 2) Use two-component epoxy AB adhesive to bond and fix the pull-out head to the core sample on the surface of the composite specimen;

[0086] 3) Continue to place the composite specimen in a 25℃ environmental chamber for curing for at least 30 minutes;

[0087] 4) Take out the composite specimen, place the clamp on the drawing head and fix it, and test it with an automatic drawing machine with a test loading rate of 0.2MPa / s.

[0088] In addition to the experimental results of the composite specimens, this embodiment also compared the interlayer pull-out strength of the 5cm skeleton dense asphalt concrete SMA13 + 5cm dense skeleton interlocking high toughness asphalt mixture HTUC-5 double-layer composite specimens, as well as the adhesion pull-out strength between the interlayer bonding material and the skeleton dense asphalt concrete SMA13. The results are shown in Table 3.

[0089] Table 3 Comparison and evaluation of pull-out strength of different specimen combinations

[0090] Specimen combination type Pull-out strength / MPa 5cm SMA-13+5cm HTUC-5 0.94 5cm SMA-13+2cm HTUC-5 0.61 SMA13+ Epoxy Emulsified Asphalt 2.08

[0091] The results show that the interlayer bond strength test conducted by molding composite specimens that take into account the actual thickness and service conditions is more effective in reflecting the true performance level of the pavement structure under the thickness of the overlay layer than the adhesion strength test of the material and the commonly used 5cm+5cm composite specimen.

[0092] It should be noted that, according to the Highway Asphalt Pavement Design Specification (JTGD50-2017), the recommended thickness varies for different nominal maximum particle sizes in the various embodiments of the present invention. Considering factors such as compaction and paving, the thickness is generally 2 to 3 times the nominal maximum particle size. For example, for gradation type SMA-10 with a nominal maximum particle size of 13.2 mm, the recommended design thickness is 2 cm to 3 cm; for gradation type SMA13 with a nominal maximum particle size of 16 mm, the recommended design thickness is 3 to 5 cm.

[0093] Table 4 Thickness of Asphalt Mixture Layers with Different Aperture Sizes

[0094]

[0095] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens, characterized in that, Includes the following steps: Based on the design thickness of the ultra-thin overlay, the actual thickness and gradation of the upper layer of the original pavement structure, the thickness of the upper and lower layers of the specimen mold are determined. The planar dimensions of the specimen mold were determined based on the various evaluation indicators of the ultra-thin overlay asphalt mixture. The aging time of the lower asphalt mixture of the composite specimen is determined based on the service time of the upper layer of the original pavement structure, and aging treatment is carried out accordingly. The lower layer of the composite specimen was prepared using aged asphalt mixture according to the thickness of the lower layer and the plane dimensions of the specimen mold. Based on the type of defects in the upper layer of the original pavement structure, the formed lower layer is pretreated for defects, and after pretreatment, an interlayer bonding material is uniformly coated on the surface of the lower layer. Based on the determined thickness of the top layer and the plane dimensions of the specimen mold, an ultra-thin asphalt mixture overlay is laid on the bottom layer of the coating interlayer adhesive material to prepare the top layer of the shaped composite specimen, thus obtaining the composite specimen for testing. The composite specimens were processed according to the various evaluation indicators: When evaluating the high-temperature stability, water resistance, and anti-slip properties of composite specimens, no treatment is required for the composite specimens. When evaluating the low-temperature stability and fatigue life of composite specimens, the composite specimens need to be cut to obtain small-beam composite specimens: When evaluating low-temperature stability, the length, height, and width of the beam composite specimen were 250 mm, 35 mm, and 30 mm, respectively, and the thickness of the upper layer of the beam composite specimen remained unchanged. When evaluating fatigue life, the length, height and width of the beam composite specimen were 380 mm, 50 mm and 63 mm, respectively, and the thickness of the upper layer of the beam composite specimen remained unchanged. When evaluating the interlayer bonding performance of composite specimens, core drilling is required. The core diameter is 50 mm and the core depth is at least 10 mm to 20 mm beyond the top layer of the composite specimen. The treated composite specimens were subjected to performance evaluation tests according to each evaluation index. When evaluating the low-temperature stability of the composite specimen, a -10℃ low-temperature bending test is used to obtain the force-displacement curve. The fracture energy of the composite specimen is then calculated from the force-displacement curve to evaluate its low-temperature stability. The formula for calculating the fracture energy is as follows: ； In the formula, x represents displacement, and the upper limit of displacement x is the displacement corresponding to the second peak value. F (x) represents the load, and A represents the fracture area.

2. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to claim 1, characterized in that, When evaluating interlayer bond performance, tensile strength tests are performed on the composite specimens, and the following steps are performed in sequence: 1) Place the composite specimen in a 25℃ ambient chamber for at least 4 hours; 2) Use two-component epoxy AB adhesive to bond and fix the pull-out head to the core sample on the surface of the composite specimen; 3) Continue to place the composite specimen in the 25℃ environmental chamber and cure for at least 30 minutes; 4) Take out the composite specimen, place the clamp on the drawing head and fix it, and test it with an automatic drawing machine with a test loading rate of 0.2MPa / s.

3. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to claim 1, characterized in that, The evaluation indicators include high-temperature stability, water impermeability, anti-slip properties, interlayer bonding properties, low-temperature stability, and fatigue life.

4. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to claim 1, characterized in that, When the evaluation indicators are high temperature stability, interlayer bonding performance, low temperature stability, water resistance, and anti-slip performance, the sample mold plane size is 300mm×300mm. When the evaluation index is fatigue life, the test piece mold plane size is 400mm×300mm.

5. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to claim 4, characterized in that, The thickness of the upper layer is 10mm to 25mm, and the thickness of the lower layer is 30mm to 80mm.

6. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to any one of claims 1 to 5, characterized in that, The lower layer asphalt mixture is aged by heating in an oven at 85°C. When the original pavement structure surface layer has been in service for no more than 3 years, the aging time shall not exceed 2 days. When the original pavement structure surface layer has been in service for more than 3 years but not more than 5 years, the aging time is more than 2 days but not more than 4 days. When the surface layer of the original road structure has been in service for more than 5 years, the aging time exceeds 4 days.

7. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to claim 6, characterized in that, The disease pretreatment includes: Rutting defects in the original pavement structure were achieved through rutting tests, with the rutting depth not exceeding 15mm. The original pavement structure cracks are removed by cutting, with the crack depth not exceeding 80% of the thickness of the underlying layer and the crack width not exceeding 10mm.

8. The method for evaluating the performance of ultra-thin asphalt mixture overlay composite specimens according to claim 7, characterized in that, The type of interlayer bonding material is one of emulsified asphalt, solvent-based asphalt, or epoxy materials.

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