A modified asphalt mixture

Abstract

The present invention discloses a modified asphalt mixture, which comprises modified asphalt, aggregate and mineral powder; the control of the passing rate range of the aggregate for each sieve hole is shown in Table 1. By modifying the aggregate gradation, the asphalt mixture has the characteristics of good water tightness, uniform and not easy to segregate, outstanding anti-skid performance, high temperature resistance, long service life, convenient maintenance and low operation cost, and is applicable to the climate with high temperature and heavy rain.

Description

Technical Field

[0001] The present invention relates to a pavement construction material, and particularly to a modified asphalt mixture. Background Art

[0002] The climatic characteristics in the south are as follows: large rainfall, long rainy season, high summer temperature, and no negative temperature climate in most areas in winter. The pavement is prone to water damage and slippery driving accidents, so high requirements are imposed on the water tightness, uniformity, and anti-skid performance of the asphalt pavement. In summer in the south, the pavement temperature often exceeds 65°C, so high requirements are imposed on the high-temperature performance of the pavement mixture, while pavement diseases related to freezing do not exist. In addition, the traffic volume of many expressways is extremely heavy, thus imposing particularly stringent requirements on the pavement. Therefore, there are special requirements for the asphalt mixture gradation design and the selection of mix design methods, and these characteristics should be fully considered to meet the actual needs of asphalt pavements in high-temperature and water-rich climates.

[0003] In the prior art, in accordance with the JTJO32-94 specification, the mixture has always been designed into a suspended dense structure based on the median line of the gradation. This type of mixture has good water tightness and uniformity, but its high-temperature stability is relatively low, and serious rutting will occur on the pavement. Therefore, there is an urgent need to find a method for designing the middle and lower layer mixtures into a framework dense structure. For example, the following two are the most common solutions.

[0004] The first solution is to directly use the Superpave method to design the middle and lower layer mixtures. Using AH-70 asphalt, the asphalt-aggregate ratio is 4.5%, and the void ratio is 4.0%. The Super20 of the middle layer paved has a dynamic stability of 1279 times / mm; the Super25 of the lower layer paved with an asphalt-aggregate ratio of 4.4% and a void ratio of 4.0% has a dynamic stability of 1800 times / mm. It has achieved certain effects in improving high-temperature stability compared with the suspended dense structure extended until then. However, according to the rotational compaction method to determine the standard density, it is necessary to improve the construction rolling level, thereby increasing the construction investment. Under the condition that the budget does not increase, it is difficult for the construction unit to construct according to the Superpave ratio and accept the compaction degree according to the standard density of rotational compaction.

[0005] The second solution is to use the Marshall method for mix proportion design according to the S-shaped mixture gradation curve of the Superpave method. The results show that for the middle and lower layer mixtures whose S-shaped curves fully comply with the Superpave restricted zone regulations, when the mix proportion determined by the Marshall compaction method is used, the void ratio increases significantly. At this time, if the void ratio is controlled at about 4% to meet the water-tightness requirement, the asphalt-aggregate ratio needs to be increased significantly. For example, for the Super25 lower layer of a certain section of the Kaiyang Expressway, the mixture with an S-shaped curve that complies with the restricted zone regulations has an asphalt-aggregate ratio of 4.4% at a void ratio of 4% (rotary compaction method). For this mixture with this mix proportion, when the Marshall compaction method is used instead, it is found that at an asphalt-aggregate ratio of 4.4%, the void ratio of the mixture is 5.6%. This means that at a compaction degree of 97%, the in-situ void ratio reaches 8.6% and is in a permeable state. Therefore, when the construction compaction is controlled by the Marshall density, for the S-shaped curves of the middle and lower layer mixtures that fully comply with the Superpave restricted zone regulations, the water-tightness acceptance requirements cannot be met.

[0006] However, neither of the above two solutions can balance the relationship among the water-tightness, uniformity, and durability of the pavement paving materials. Therefore, a mixture for pavement paving is needed that can improve the high-temperature stability on the premise of ensuring that the water-tightness and uniformity (non-segregation) of the pavement meet the requirements. Summary of the Invention

[0007] Object of the Invention: The object of the present invention is to provide a modified asphalt mixture that can improve the high-temperature stability on the premise of ensuring good water-tightness and uniformity of the pavement paving materials.

[0008] Technical Solution: A modified asphalt mixture according to the present invention; includes modified asphalt, aggregate, and mineral powder; the control of the passing rate range of the aggregate for each sieve hole is shown in Table 1:

[0009] Table 1

[0010]

[0011] Further, the aggregate is divided into four groups according to the particle size: the particle size range of the first group of aggregate is 0 - 2.36 mm; the particle size range of the second group of aggregate is 2.36 - 4.75 mm; the particle size range of the third group of aggregate is 4.75 - 9.5 mm; the particle size range of the fourth group of aggregate is 9.5 - 16.0 mm.

[0012] Further, the first group of aggregate accounts for 21 - 25% of the mixture mass; the third group of aggregate accounts for 37 - 40% of the mixture mass; the fourth group of aggregate accounts for 30 - 37% of the mixture mass; the modified asphalt accounts for 5% of the asphalt mixture mass; the mineral powder accounts for 5% of the mixture mass.

[0013] Furthermore, the passing rate of each sieve hole with an aperture of 1.18 - 0.075 mm is adjusted downward by 1% based on its median value, while its upper and lower limits remain unchanged. A relatively low median value is set based on the median value within the upper and lower limit range to improve the durability of the asphalt mixture.

[0014] Furthermore, the Marshall stability of the mixture is not less than 13 KN and the dynamic stability at 60 °C is not less than 10,000 times / mm.

[0015] Furthermore, the maximum flexural tensile strain value of the mixture when damaged at a temperature of -10 °C is not less than 2890 με.

[0016] Furthermore, the four-point bending fatigue life of the mixture is not less than 1.17 million times.

[0017] Furthermore, the Marshall residue stability ratio of the mixture is not less than 88% and the freeze-thaw splitting strength ratio is not less than 84%.

[0018] Furthermore, the aggregate is basalt and the mineral powder is limestone powder.

[0019] Furthermore, the modified asphalt is SBS modified asphalt.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0021] This asphalt mixture has the characteristics of good water tightness, uniform and not easy to segregate, outstanding anti-skid performance, high temperature resistance, long service life, convenient maintenance and low operation cost, and is suitable for climates with high temperature and abundant rain. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the discontinuous grading curve graph of the modified asphalt mixture of the present invention;

[0023] Figure 2 It is the continuous grading curve graph of the hot mix asphalt mixture AC-13 in Comparative Example 1;

[0024] Figure 3 It is the framework dense structure diagram of the modified asphalt mixture of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The technical solution of the invention will be further described below in conjunction with the embodiments.

[0026] Embodiment of the laboratory test: The aggregate used in the test is basalt. The particle size of the first group of aggregate is 0 - 2.36 mm; the particle size of the second group of aggregate is 2.36 - 4.75 mm; the particle size of the third group of aggregate is 4.75 - 9.5 mm; the particle size of the fourth group of aggregate is 9.5 - 16.0 mm. The sieving test is carried out on the used aggregate, and the results are shown in Table 2.

[0027] Table 2

[0028]

[0029] Relative density tests were carried out on four groups of aggregates, and the results are shown in Table 3.

[0030] Table 3

[0031] Particle size Fourth group Third group Second group First group Bulk relative density 2.890 2.876 2.861 2.732 Apparent relative density 2.952 2.941 2.936 2.815

[0032] Sieving tests were carried out on the used mineral powder, and the results are shown in Table 4.

[0033] Table 4

[0034]

[0035] Tests were carried out on the Shuangnuo brand SBS (I-D) modified asphalt produced by Guangdong Tiannuo Highway Engineering Materials Co., Ltd., and the results are shown in Table 5.

[0036] Table 5

[0037]

[0038] Example 1

[0039] Take the gradation of Example 1 in Table 6 to prepare the modified asphalt mixture. Among them, for the synthetic gradation of Example 1, raw materials are selected according to the upper and lower limits of the gradation required in Table 1, and raw material sieving and density tests are carried out. According to the test results of single-grade material sieving in Table 2 and Table 4, the proportion distribution of materials with different particle sizes is carried out to make the combined gradation meet the upper and lower limit requirements of Table 1 and be as close to the median value as possible.

[0040] The proportion of mixture components is: 25.0% of the first group of aggregates; 0.0% of the second group of aggregates; 40.0% of the third group of aggregates; 30.0% of the fourth group of aggregates; 5.0% of the mineral powder; 5.0% of the asphalt, and its discontinuous gradation curve is as Figure 1 shown in Sample 1.

[0041] Prepare the modified asphalt mixture according to the production method of hot mix asphalt mixture required in the "Test Procedures for Asphalt and Asphalt Mixtures in Highway Engineering" (JTG E20-2011). Mix the above-mentioned aggregates, mineral powder, and asphalt respectively, and the steps are as follows:

[0042] (1) Place aggregates of various specifications in an oven at 105°C ± 5°C and dry them to a constant weight (generally not less than 4h to 6h).

[0043] (2) Weigh the mass of the dried and graded coarse and fine aggregates according to the design grading requirements of each specimen, mix them evenly in a metal tray, put the mineral powder in a small basin separately, and then heat them in an oven to about 15°C above the asphalt mixing temperature (usually 163°C when using petroleum asphalt; usually 180°C when using modified asphalt) for use. Generally, materials are prepared according to a group of specimens (4 to 6 per group), but it is advisable to prepare materials for each specimen separately when designing the mix ratio. Aggregates of room temperature asphalt mixtures should not be heated.

[0044] (3) The asphalt sample taken in accordance with this Regulation T 0601 shall be heated in an oven to the specified asphalt mixture mixing temperature, but shall not exceed 175°C. When direct heating in a gas furnace or electric furnace is unavoidable for dehydration, asbestos pads must be used for separation.

[0045] (4) Preheat the asphalt mixture mixer to a mixing temperature of about 10°C.

[0046] (5) Place the heated coarse and fine aggregates in a mixer, mix them properly with a small shovel, then add the required amount of asphalt (if the asphalt has been weighed in a special container, you can use some hot mineral powder to wipe the asphalt on the container wall after pouring out the asphalt and pour it into the mixing pot together), start the mixer and insert the mixing blade into the mixture while stirring for 1min to 1.5min, then stop stirring, add the heated mineral powder, continue stirring until it is uniform, and keep the asphalt mixture within the required mixing temperature range. The standard total mixing time is 3min.

[0047] (6) The sample obtained in step (5) is taken out of the oven at 170° C. to form an asphalt mixture specimen, which is recorded as sample 1. The road performance of sample 1 is then measured.

[0048] Example 2

[0049] The preparation method of asphalt mixture is basically the same as that of Example 1, except that the mixture is prepared by taking the synthetic gradation of Example 2 in the gradation of Table 6, the gradation of Example 2 is in accordance with the gradation upper and lower limits required by Table 1, the raw materials are selected and the raw material screening and density test are carried out, and the proportion of materials of different particle sizes is allocated according to the test results of single-stage material screening in Table 2 and Table 4, so that its combined gradation meets the upper and lower limit requirements of Table 1 and is as close to the lower limit as possible.

[0050] The composition of the mixture is: 21.0% of the first group of aggregates; 0.0% of the second group of aggregates; 37.0% of the third group of aggregates; 37.0% of the fourth group of aggregates; 5.0% of mineral powder; 5.0% of asphalt; the discontinuous grading curve is as follows Figure 1 Sample 2 is shown.

[0051] The formed asphalt mixture specimens prepared in Example 2 are denoted as Sample 2, and then the pavement performance of Sample 2 is measured.

[0052] Example 3

[0053] The preparation method of the asphalt mixture is basically the same as that of Example 1, except that the synthetic gradation of Example 3 in Table 6 is used to prepare the mixture. For the gradation of Example 3, raw materials are selected according to the upper and lower limits of the gradation required in Table 1, and raw material screening and density test are carried out. According to the test results of single - grade material screening in Table 2 and Table 4, the proportion distribution of materials with different particle sizes is carried out to make the combined gradation meet the upper and lower limit requirements of Table 1 and be as close to the upper limit as possible.

[0054] The proportion of mixture components is: 21.0% of the first group of aggregates; 0.0% of the second group of aggregates; 37.0% of the third group of aggregates; 37.0% of the fourth group of aggregates; 5.0% of mineral powder; 5.0% of asphalt; its discontinuous gradation curve is as Figure 1 shown in Sample 3.

[0055] The formed asphalt mixture specimens prepared in Example 3 are denoted as Sample 3, and then the pavement performance of Sample 3 is measured.

[0056] Comparative Example 1

[0057] The preparation method of the asphalt mixture is basically the same as that of Example 1, except that the aggregates are prepared according to the gradation requirements of AC - 13 type asphalt mixture (JTG F40 - 2004), and the specific requirements are shown in Table 6. According to the upper and lower limits of the gradation required in Table 6, raw materials are selected and raw material screening and density test are carried out. According to the test results of single - grade material screening in Table 2 and Table 4, the proportion distribution of materials with different particle sizes is carried out to make the combined gradation meet the upper and lower limit requirements of Table 7 and be as close to the median as possible; specifically, the synthetic gradation of Comparative Example 1 in Table 6 is used to prepare the mixture, and the proportion of mixture components is: 21.0% of the first group of aggregates; 0.0% of the second group of aggregates; 37.0% of the third group of aggregates; 37.0% of the fourth group of aggregates; 5.0% of mineral powder; 5.0% of asphalt; its discontinuous gradation curve is as Figure 2 shown; the formed asphalt mixture specimens are denoted as Sample 4, and then the pavement performance of Sample 4 is measured.

[0058] Table 6

[0059]

[0060] The median value of the gradation in Table 6=(upper limit of gradation + lower limit of gradation) / 2.

[0061] For samples 1 - 4 of the modified asphalt mixtures prepared in Examples 1 - 3 and Comparative Example 1, after forming specimens indoors, performance tests were carried out. The specific test results are as follows: The test results of high - temperature performance (Marshall stability test, dynamic stability test) are shown in Table 7; the test results of low - temperature performance (low - temperature bending test) are shown in Table 8; the test results of water stability (Marshall residual stability test, freeze - thaw splitting test) are shown in Table 9; the test results of fatigue life (four - point bending beam fatigue life test) are shown in Table 10.

[0062] Table 7

[0063]

[0064] Note: The "Technical Specifications for Construction of Highway Asphalt Pavements" JTG F40 - 2004 (hereinafter referred to as the specification) requires that the Marshall stability is not less than 8 kN and the dynamic stability at 60 °C is not less than 2800 times / mm.

[0065] Table 8

[0066]

[0067] Note: The test temperature is - 10 °C, and the specification requires not less than 2500 με.

[0068] Table 9

[0069]

[0070] Note: The specification requires that the ratio of Marshall residual stability is not less than 85% and the freeze - thaw splitting strength ratio is not less than 80%.

[0071] Table 10

[0072]

[0073] Note: The test temperature is 15 °C, the target strain is 130 με, the loading frequency is 10 HZ, and the test termination condition is 50%.

[0074] By evaluating and comparing the high temperature performance (Marshall stability test, dynamic stability test), low temperature performance (low temperature bending test), water stability (Marshall residual stability test, freeze-thaw splitting test) and fatigue life (four-point bending beam fatigue life test) of the test pieces formed indoors, it was found that the asphalt mixture of the present invention is superior to the AC-13 continuous dense gradation in all aspects, and 70°C is added as the rutting test temperature condition in Table 7 because the road surface temperature in summer is as high as 65°C or above. It can be seen from Tables 7-10 that the modified asphalt mixture of the present invention is superior to the conventional AC-13 continuous dense gradation (i.e., sample 4) in terms of low temperature performance and water stability, and its high temperature anti-rutting performance is much higher than that of the conventional AC-13 continuous dense gradation under the same conditions; and the fatigue life is also much higher than that of sample 4 in the prior art.

[0075] Figure 3 This is the structural diagram of the modified asphalt mixture of Example 1. It can be seen that the modified asphalt mixture is nearly a skeleton-dense mixture. The coarse aggregates can move closer to each other and are not pushed apart by the fine aggregates, forming a skeleton, thereby increasing the embedding force and increasing the frictional resistance between the aggregates. The fine aggregates still maintain a dense structure according to the continuous grading and have a higher cohesive force. The entire structure can form a higher strength and is a more ideal composition structure than the continuous grading. It improves rutting resistance and increases the thickness of the asphalt film under the same effective asphalt content, which is beneficial to improving fatigue performance and aging resistance. For the anti-skid wear layer, the thickening of the asphalt film also extends the wear life; reducing the 4.75mm sieve hole pass rate means increasing the surface structure depth that characterizes the anti-skid performance; increasing the nominal maximum particle sieve hole pass rate to 97.5% is beneficial to improving uniformity.

Claims

1. A modified asphalt mixture, characterized in that, It is composed of modified asphalt, aggregate and mineral powder; the control of the passing rate range of each sieve hole of the aggregate is shown in Table 1: Table 1 The aggregate is divided into four groups according to particle size: the particle size range of the first group of aggregate is 0 - 2.36 mm; the particle size range of the second group of aggregate is 2.36 - 4.75 mm; the particle size range of the third group of aggregate is 4.75 - 9.5 mm; the particle size range of the fourth group of aggregate is 9.5 - 16.0 mm; The first group of aggregate accounts for 21 - 25% of the mixture mass; the third group of aggregate accounts for 37 - 40% of the mixture mass; the fourth group of aggregate accounts for 30 - 37% of the mixture mass; the modified asphalt accounts for 5% of the mixture mass; the mineral powder accounts for 5% of the mixture mass.

2. The modified asphalt mixture according to claim 1, characterized in that, The passing rate of each sieve hole with a pore size of 1.18 - 0.075 mm is adjusted down by 1% based on its median value.

3. The modified asphalt mixture according to claim 1, characterized in that, The Marshall stability of the mixture is not less than 13 KN and the dynamic stability at 60 °C is not less than 10000 times / mm.

4. The modified asphalt mixture according to claim 1, characterized in that, When the mixture is damaged at a temperature of -10 °C, the maximum flexural tensile strain value is not less than 2890 με.

5. The modified asphalt mixture according to claim 3, characterized in that, The four-point bending fatigue life of the mixture is not less than 1.17 million times.

6. The modified asphalt mixture according to claim 3, characterized in that, The Marshall residual stability ratio of the mixture is not less than 88% and the freeze-thaw splitting strength ratio is not less than 84%.

7. The modified asphalt mixture according to claim 1, characterized in that, The aggregate is basalt and the mineral powder is limestone powder.

8. The modified asphalt mixture according to claim 1, characterized in that, The modified asphalt is SBS modified asphalt.

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