Asphalt pavement paving thickness is the core control index of road engineering construction, which directly determines road bearing capacity, flatness, durability and driving comfort, and is the key factor to prevent pavement cracking, rutting, settlement, seepage and other diseases.Asphalt paving thickness shall strictly comply with the current national specifications and standards, accurately control in combination with road grade, traffic load grade and mixture type, and match scientific construction compaction technology to ensure the stability and service life of pavement structure.According to the Code for Design of Highway Asphalt Pavement (JTG D50-2017) and the general technical requirements for municipal road construction, this paper systematically combs the asphalt pavement thickness standard, layered construction requirements, control principles and acceptance specifications, and provides technical reference for engineering construction and quality control.
Core control principle of asphalt paving thickness
The paving thickness of asphalt pavement is not a single fixed value, and it is necessary to follow three core principles of structural adaptation, material type matching and compaction control, which are the basis of standard construction:
1. Aggregate particle size matching principle: the industry's common core technical criteria, asphalt single layer paving compaction thickness shall not be less than 4 times of the maximum nominal particle size of the mixture, to avoid uneven compaction of aggregates due to too thin thickness, excessive porosity, loose pavement falling off, and at the same time to prevent excessive thickness caused by compaction, late settlement deformation problems.
2. Layered structure adaptation principle: high-grade roads shall adopt multi-layer paving structure (upper layer + middle layer + lower layer), different layers shall bear different functions of waterproof, wear-resistant, load-bearing and stress diffusion, thickness standard shall be set differently, and one-time super-thick paving is prohibited.
3. Load grade adaptation principle: extra heavy and heavy traffic roads shall be paved with appropriate thickness; light load municipal branch roads and community roads shall be selected according to the lowest standard, giving consideration to project quality and economy.
Standard for layer thickness of asphalt paving for different grades of roads
In combination with national standards and national general municipal and highway engineering construction standards, the conventional paving compaction thickness (all formed thickness after compaction, non-paving virtual thickness) is divided according to road grade, layer position and mixture type. The specific standards are as follows:
(I) Expressway, Class I highway (high-grade heavy-duty road)
This kind of road has large traffic flow and many heavy vehicles. It adopts three-layer asphalt structure. The total asphalt layer thickness is normally controlled at 120-180 mm. The standards of each layer are as follows:
1. Upper layer (wear-resistant waterproof layer): fine particle AC, SMA modified asphalt mixture, standard thickness 40-50 mm.The core function is anti-wear, waterproof, ensure the smoothness of driving, thickness deviation should be strictly controlled, to avoid uneven thickness caused by road cracking.
2. Medium surface layer (main load-bearing layer): medium grain AC asphalt mixture with standard thickness of 50-60 mm.As the core stress structure of pavement, bearing the main vehicle load, thickness must meet the standard, is the key layer to prevent rutting disease.
3. Lower layer (stress diffusion layer): coarse grained AC asphalt mixture, standard thickness 60-80 mm.It mainly diffuses pavement load, buffers base stress, improves overall structural stability, and can take upper limit thickness for heavy load sections.
(II) Class II highway (medium-class general road)
Class II roads mostly adopt double-layer asphalt structure with a total thickness of 60-120mm, which is suitable for medium traffic load scenarios:
1. Upper layer: fine grained asphalt mixture, thickness 40mm;
2. Lower layer: medium-grained asphalt mixture, coarse grained asphalt mixture, thickness 50-80mm;
Heavy traffic sections can be added with middle layer, which shall be implemented according to Class I highway standards to improve road bearing performance.
(3) Class III and Class IV highways and municipal branch roads (light-load roads)
Low-grade highway, municipal community road, park branch road and other light-load pavement, traffic load is small, can adopt single-layer or double-layer simple structure:
1. Double layer structure: upper layer 30-40mm fine grain asphalt, lower layer 40-50mm medium grain asphalt, total thickness 70-90mm;
2. Single-layer structure: direct paving fine grain or medium grain asphalt mixture, compaction thickness is not less than 40mm, and it is forbidden to be less than 30mm (limit construction thickness).
III. Special Standards for Paving Thickness in Special Scenes
(1) SMA modified asphalt pavement
SMA asphalt mixture skeleton dense, wear-resistant and anti-skid, mostly used in high-speed, urban trunk road upper layer, standard paving thickness 40-50mm, and must meet the "particle size 4 times principle"(commonly used 13.2 mm particle size SMA mixture, minimum compaction thickness is not less than 40mm), thin paving construction is prohibited, to prevent skeleton structure damage, pavement seepage.
(II) Bituminous macadam flexible base
As the transition layer of pavement base, the paving and compaction thickness of asphalt macadam is usually 80-120mm, and the maximum paving thickness of single layer shall not exceed 150 mm. If the thickness is too large, it shall be paved and compacted layer by layer to ensure that the base is dense and uniform.
(III) Milling and paving of old roads
In the repair and reconstruction of old pavement diseases, the overlay thickness of thin layer shall not be less than 30mm, and the conventional overlay thickness shall be 40- 60mm; if the overlay thickness is less than 4 times of aggregate particle size, the fine particle mixture shall be replaced to avoid substandard compaction quality.
IV. Conversion standard of virtual paving thickness and compaction thickness
There is a difference between the virtual paving thickness controlled on the construction site and the compaction thickness finally accepted, which needs to be accurately converted through compaction coefficient, which is the key practical operation point of thickness control:
1. Conventional coefficient: compaction coefficient of ordinary AC asphalt mixture 1.15-1.25, compaction coefficient of SMA modified asphalt mixture 1.20-1.30;
2. Conversion formula: virtual paving thickness = design compaction thickness × compaction coefficient;
3. Construction requirements: test section must be made before formal paving, accurate compaction coefficient shall be determined through field compaction test, uniform application of fixed value shall be avoided, and forming thickness shall meet design standard.
V. Thickness construction acceptance deviation standard (compulsory requirements of national standard)
According to the highway and municipal engineering quality acceptance specifications, asphalt pavement paving thickness acceptance is divided into single point deviation and total thickness deviation, the specific limits are as follows:
1. Acceptance of total thickness: the allowable deviation of total thickness of expressway and Class I highway shall be-5mm (only negative deviation, no positive deviation), and the qualified rate shall be ≥95%; the allowable deviation of total thickness of Class II highway and below shall be-8mm, and the qualified rate shall be ≥90%;
2. Layer thickness acceptance: The single-point deviation of the paving thickness of each structural layer shall not exceed ±5 mm. The construction thickness in large areas shall be uniform and consistent, and there shall be no local over-thickness or under-thickness;
3. Inspection method: random sampling shall be conducted by means of core drilling sampling and nondestructive thickness inspection. The inspection points per kilometer shall not be less than the specification requirements, and the data shall be retained and archived as the acceptance basis.
Six, the thickness is not up to standard common diseases and prevention and control measures (a) insufficient thickness of the harm paving thickness will lead to pavement aggregate compaction is not dense, porosity is too large, late easy to appear seepage, loose, falling particles, cracks and other diseases; insufficient bearing layer thickness will directly reduce the road bearing capacity, causing rutting, road subsidence, base damage, greatly shorten the service life of the road.
(II) Excessive thickness harms single-layer paving, which will increase the compaction difficulty, insufficient compaction degree inside the mixture, hidden voids, uneven settlement and displacement deformation of the pavement in the later stage, and increase the cost of engineering materials, resulting in waste of resources.
(III) Core prevention and control measures 1. Strictly layer construction, avoid over-thick one-time paving, strictly match mixture particle size and paving thickness;
2. Calibrate paver thickness gauge and balance beam before construction, and determine accurate virtual paving thickness through test section;
3. Track and detect paving thickness and compaction in the whole process, adjust paving parameters in time, and strictly control construction deviation;
4. For special points such as connection between old and new pavement, intersection, curve and ramp, the frequency of thickness inspection shall be increased to ensure uniform construction quality.
VII. Measures to ensure uniformity of asphalt pavement thickness
Uneven asphalt pavement thickness is the core cause of poor pavement flatness, local rutting, water seepage and early damage. Thickness uniformity control shall run through the whole process of pre-construction preparation, paving process, compaction molding and special part treatment, relying on equipment calibration, process standardization, dynamic detection and fine control to realize unified overall thickness. Specific guarantee measures are as follows:
(I) Accurate pre-construction control to eliminate basic deviations
The flatness and standard height accuracy of base and lower bearing layer directly determine the uniformity of asphalt paving thickness, which is the core of early control.Before construction, it is necessary to comprehensively clean up the sundries and floating ash of the lower bearing layer, repair and level the pits, subsidence and loose diseases of the base layer in advance, and eliminate the uneven thickness of the asphalt layer caused by the height difference of the base layer.The pavement elevation shall be re-measured along the whole line in strict accordance with the leveling control points, and the reference points shall be accurately hung. The automatic leveling system of balance beam shall be preferred for high speed and main roads, and the steel line reference shall be adopted for municipal branch roads to ensure that the reference system is flat, accurate and free of deviation.At the same time, complete equipment calibration of paver and road roller before construction, correct paver thickness scale, material door opening and walking speed, and eliminate local thickness deviation caused by equipment error; accurately determine compaction coefficient and virtual paving thickness of different mixtures through test section, unify construction parameters of the whole line, and avoid different construction standards.
(II) Standardized operation in paving process and strict control of dynamic thickness
Standardization and continuous paving is the core process to ensure uniform thickness.During construction, the paver must be kept operating at a constant, continuous and uninterrupted speed, and the driving speed must be stably controlled at 2-6m/min. The speed must be fixed according to the type of mixture and paving thickness. It is strictly prohibited to change speed suddenly, stop midway, or change speed at will. Prevent thickness accumulation and thin layer defects at the stop position.Strictly control the feeding speed of paver hopper, keep the material level of screed stable, ensure uniform distribution of mixture, and avoid uneven thickness caused by local material shortage and accumulation.Assign special personnel to track and detect the whole process during paving. Use thickness gauge to spot check the paving thickness in real time. Set a detection point every 5- 10m to cover both sides and the center of the pavement horizontally. If deviation is found, adjust the paver parameters in time to prevent deviation accumulation.At the same time, the principle of layered paving shall be strictly followed, and the single-layer super-thick paving shall be avoided. The thickness of each structural layer shall be uniformly transited to ensure the consistency of the overall pavement thickness.
(III) Standardization of compaction process to avoid deviation of forming thickness
Non-standard compaction operation will lead to inconsistent mixture compression, indirectly resulting in uneven molding thickness.The compaction process determined by the test section shall be strictly followed, and the principle of "light first, then heavy, slow first, then fast, edge first, then middle, and adjacent compaction overlapping" shall be followed. The compaction speed, compaction times and compaction temperature shall be unified to prevent local overpressure, pressure leakage and underpressure problems.Over-compression and thin thickness of mixture will occur in overpressure area, insufficient compaction in leakage area, late settlement deformation and thickness deviation exceeding standard.During compaction, the overlapping width of adjacent compaction belts shall be controlled at 1/3 wheel width to eliminate compaction dead corners; the compaction temperature of asphalt mixture shall be strictly controlled. If the temperature is too high, it is easy to move, the thickness deformation, the compaction is difficult when the temperature is too low, and the porosity exceeds the standard, so as to ensure uniform compaction along the whole line, uniform compression amount and uniform pavement thickness after molding.
(IV) Fine treatment of special parts to eliminate deviation of weak points
Special road nodes are high incidence areas with uneven thickness, which need targeted fine construction.For intersections, curves, ramps, expansion joints and overlapping places of new and old pavements, it is necessary to optimize the paving scheme in advance, reduce the driving speed of pavers, increase the frequency of thickness detection, and focus on controlling the elevation and virtual paving thickness.The corners, kerbs and well periphery areas that cannot be covered by pavers shall be manually leveled and paved in strict accordance with the design thickness control, so as to eliminate the problems of random thickness and excessive deviation of manual paving.The construction joints are located at the high incidence points of thickness deviation. The horizontal joints shall be vertically cut. The joint thickness shall be accurately butted when paving new materials. The joint height difference and thickness difference shall be eliminated when rolling. The longitudinal joints shall be paved in a staggered manner and rolled in echelon to ensure that the thickness of the joints is consistent with the overall pavement.
(V) Dynamic detection and closed-loop rectification of the whole process
Establish the whole process dynamic detection mechanism to realize the early detection and early rectification of thickness deviation.After paving and compaction, comprehensive spot check shall be carried out on the transverse and longitudinal thickness of pavement by combining nondestructive thickness inspection and core drilling sampling, focusing on covering construction joints, special points and paragraph connection positions, and accurately counting thickness deviation data.Strictly implement the national standard acceptance deviation standard, timely formulate rectification plan for areas exceeding ±5mm delamination deviation and total thickness negative deviation, and conduct closed-loop treatment through thin layer repair, milling and repaving.At the same time, record daily construction parameters and inspection data, form construction accounts, summarize deviation rules, continuously optimize paving and rolling technology, and ensure uniform and stable asphalt paving thickness along the whole line from management level.
VIII. Summary
The core of asphalt paving thickness standard is grading adaptation, layer accuracy, particle size matching and strict control deviation.High-grade heavy-duty roads adopt multi-layer structure and thick-layer load-bearing design, light-load roads simplify structure and reasonably control thickness. All construction links must strictly comply with JTG D50-2017 specification requirements, and accurately control virtual paving thickness and compaction thickness in combination with test section parameters.Accurate thickness control is the basis of asphalt pavement flatness, compactness and durability, which can avoid all kinds of pavement diseases from the source and ensure long-term safe and stable passage of roads.At the same time, thickness uniformity shall rely on fine control of the whole process, from pre-foundation treatment, standardized paving, standardized rolling, special point treatment to dynamic detection and rectification, so as to form a complete quality control system, thoroughly solve the problem of uneven pavement thickness, and greatly improve the construction quality and service life of asphalt pavement.