If the construction unit purchases finished aggregates, it shall assign special personnel to control on site to avoid shoddy and ensure that the whole process of quarrying, processing, transportation and receiving is controllable.
Discontinuous grading forms large pores on the surface, with large structural depth and good sliding resistance.
For major projects bearing heavy traffic such as expressways, especially hot in summer or cold in winter, modified asphalt should be used: (2) When modified asphalt binder is not used, the quality of asphalt must meet the “technical requirements for heavy traffic road asphalt”, and grade 5 or grade 2 asphalt slightly harder than the local common asphalt grade shall be used.
Fiber stabilizer is added to maintain high viscosity of asphalt binder, and its paving and compaction effect is good.
If the construction unit processes aggregates by itself and uses rubble for processing, rubble with complete, fresh, clean rock stratum, high strength and uniform material shall be selected.
However, external factors such as low temperature in winter, tight construction period and shortage of pavement materials have an adverse impact on the quality control of asphalt pavement construction.
In order to improve the rutting resistance of asphalt mixture, the softening point temperature of modified asphalt should be higher than the annual maximum pavement temperature.
Its composition features mainly include two aspects: ① coarse aggregates with large content are interlocked with each other to form a structural skeleton with high stability (strong deformation resistance); ② The asphalt mastic composed of fine aggregate mineral powder, asphalt and fiber stabilizer binds the skeleton together and fills the skeleton gap, so that the mixture has better flexibility and durability.
It will not deteriorate and brittle at the dry mixing temperature of 250 ℃.
The penetration grade after asphalt modification should be 40 ~ 60 in South and central China, 40 ~ 80 in North China and 60 ~ 100 in cold areas in Northeast China.
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The resulting discontinuous gradation rarely uses fine aggregate; ② In order to add more asphalt, on the one hand, increase the amount of mineral powder and use fiber as stabilizer; ③ There is a large amount of asphalt, up to 6.5% ~ 7%, with high adhesion requirements.
The dry mineral powder produced by limestone processing shall be strictly used as the mineral powder, and it is strictly prohibited to use the mixing plant to recover the powder and other wastes.
In order to ensure the construction quality of asphalt pavement, reduce the early damage of asphalt pavement and prolong the service life of asphalt pavement, the following work requirements are put forward for further strengthening the construction quality control of Expressway Asphalt Pavement: 1、 Strengthen the quality control of raw materials Various raw materials used for asphalt pavement shall be sampled for quality inspection in strict accordance with the specification requirements, so that the incoming materials must be inspected and qualified.
The SMA technical guide stipulates as follows: (1) Asphalt binder used for SMA must have high strength and good adhesion with aggregate to ensure sufficient high-temperature stability and low-temperature toughness.
At the same time, the gap of the mixture is very small, and the aging resistance and durability are very good, which comprehensively improves the pavement performance of asphalt mixture.
Due to the good embedment of coarse aggregate, the mixture has very good high-temperature rutting resistance.
Discontinuous grading forms large pores on the surface, with large structural depth and good sliding resistance.
（2） Bituminous materials.
The mixing tank equipped with mixing device shall be added accurately and shall not be added less or omitted.
Constituent organization: The structural composition of SMA can be summarized as “three more and less, that is, more coarse aggregate, more mineral powder, more asphalt and less fine aggregate”.
The proportion of coarse aggregate above 5mm is as high as 70% ~ 80%, and the amount of mineral powder is as high as 7% ~ 13% (the “powder binder ratio” exceeds the limit of 1.2).
At the same time, the gap of the mixture is very small, and the aging resistance and durability are very good, which comprehensively improves the pavement performance of asphalt mixture.
Due to the good embedment of coarse aggregate, the mixture has very good high-temperature rutting resistance.
Principle and features: Asphalt mastic macadam mixture (SMA) is a kind of asphalt mastic binder composed of asphalt, mineral powder and fiber stabilizer, which is filled in the discontinuous graded mineral aggregate skeleton.
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It is hoped to select asphalt with small penetration, high softening point and good temperature stability (modified asphalt is best).
The grade of base asphalt shall be determined by test.
The warm mix agent shall be the product with quality meeting the specification requirements, obvious cooling and road performance not lower than that of similar hot mix asphalt mixtures..
SMA features: Asphalt mastic macadam mixture is a kind of asphalt surface mixture with strong deformation resistance and good durability.
（3） Other materials.
（1） Aggregate.
Encourage centralized procurement and select reputable suppliers and supply brands.
The lignin fiber used in SMA asphalt mixture shall be processed from natural wood, and the fiber processed from waste paper and cotton wadding shall not be used.
Specifically: ① SMA is a discontinuous graded asphalt mixture.
2、 Industry requirements First, let’s take a look at the construction requirements and precautions of the competent department for SMA asphalt mastic! Notice on strengthening the quality control of asphalt pavement construction of expressway project opened to traffic in 2021 all relevant municipal (prefecture) transportation bureaus, relevant expressway project companies under construction and relevant units directly under the Department: at present, the expressway projects planned to be opened to traffic in 2021 in our province have successively entered the asphalt pavement construction stage.
The crusher must be equipped with dust suction and water washing equipment.
(4) The quality of polymer modified asphalt used for SMA shall meet the technical requirements specified in technical code for construction of highway modified asphalt (jtj036-2002).
The asphalt mixing plant shall be equipped with sufficient asphalt storage tanks to ensure continuous production of asphalt mixture.
Technical requirements for asphalt binder quality: SMA Mixture requires asphalt binder with higher viscosity (consistency) than conventional AC mixture.
It is strictly prohibited to mix weathered rock, soil and weak interlayer; When processing pebbles and gravels, the raw materials must be washed and screened; Aggregate processing must be specialized and centralized production, strictly graded, and no material channeling is allowed.
(5) Except for special circumstances, the reasonable dosage of various modified asphalt modifiers should be selected in the following range: for SBS and SBR modified asphalt, the dosage of modifier calculated by interpolation method should be 3.5% ~ 5%, and for EVA or PE modified asphalt, the dosage should be 4% ~ 6%.
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1、 What is SMA asphalt and mastic asphalt? Asphalt mastic macadam mixture (SMA) is a kind of asphalt mastic binder composed of asphalt, mineral powder and fiber stabilizer, which is filled in the discontinuous graded mineral aggregate skeleton.
At the same time, due to the bonding effect of asphalt mastic, the low-temperature deformation performance and water stability are also improved.
Asphalt mastic macadam mixture is a kind of asphalt surface mixture with strong deformation resistance and good durability.
Its composition features mainly include two aspects: ① coarse aggregates with large content are interlocked with each other to form a structural skeleton with high stability (strong deformation resistance); ② The asphalt mastic composed of fine aggregate mineral powder, asphalt and fiber stabilizer binds the skeleton together and fills the skeleton gap, so that the mixture has better flexibility and durability.
Fiber stabilizer is added to maintain high viscosity of asphalt binder, and its paving and compaction effect is good.
The anti stripping agent shall have excellent performance and good thermal stability.
Strengthen the sampling inspection of asphalt before delivery, and the asphalt can only be delivered to the construction site after passing the asphalt index test.
Generally, the grade equivalent to the grade of ordinary asphalt or slightly higher penetration shall be adopted.
(3) When modified asphalt is used, the base asphalt used for modified asphalt must meet the “technical requirements for heavy traffic road asphalt”.
At the same time, due to the bonding effect of asphalt mastic, the low-temperature deformation performance and water stability are also improved.
