Intermittent system strong base thin surface type pavement structure layer combination and construction method

Abstract

The application relates to an intermittent system strong-base thin-surface type pavement structure layer combination and a construction method, and belongs to the technical field of road engineering. The structure layer combination is composed of a base layer and a functional layer. The base layer comprises a semi-rigid bottom base layer and a plurality of semi-rigid base layers. The base layer is a bearing layer, adopts a skeleton dense type semi-rigid base layer, and the plurality of semi-rigid base layers are continuous. The functional layer comprises a waterproof seal layer, an intermittent layer and an asphalt pavement surface layer from bottom to top. The pavement structure layer combination can solve the problem that the asphalt pavement is prone to rutting in the strong-base thin-surface type inverted pavement structure layer combination.

Description

Technical Field

[0001] The invention belongs to the technical field of road engineering, and in particular relates to a discontinuous system strong base thin surface type pavement structure layer combination and a construction method. Background Art

[0002] As the asphalt pavement structural layer combination of inorganic binder stabilized granular semi-rigid base (semi-rigid base for short) has strong bearing capacity and low cost, it has been widely used for a long time and has made great contributions to my country's road engineering construction.

[0003] In the semi-rigid base asphalt pavement structure layer combination, the semi-rigid base has strong bearing capacity and is the main bearer of traffic loads, while the thickness of the asphalt pavement is relatively thin (no more than 18 cm), so this pavement structure is called a strong base and thin surface pavement structure layer combination.

[0004] The design of the strong-base thin-surface pavement structure layer combination is based on the theory of multi-layer elastic continuous system. The method adopted is to enhance the connection between layers and spread penetrating oil on the top of the semi-rigid base layer to increase the adhesion between the base layer and the asphalt pavement, so that the semi-rigid base layer and the asphalt surface layer can jointly bear the traffic load; in addition, the water immersion strength of the semi-rigid base layer will be reduced, so a waterproof seal layer is set on it.

[0005] Problems with strong-base, thin-surface pavement structural layer combinations include: The semi-rigid base layer is prone to cracking (these cracks develop early, typically within a year, and are numerous, an inherent characteristic of the semi-rigid base layer). This in turn drives cracks in the asphalt pavement, known as reflective cracks. (Although some asphalt crushed stone stress-absorbing layers are used, their effectiveness is limited and the results are less than ideal.) Reflective cracks in asphalt pavements act as pathways for surface water to penetrate into the pavement structure and even the subgrade, making it difficult to drain away. This results in premature road damage (manifested by reduced base strength and bearing capacity, mud pumping, cracking, potholes, etc.) and accelerated structural failure. The actual service life (the time from completion and opening to structural failure) typically falls short of the designed service life (10-15 years). These early-stage defects are common in semi-rigid base asphalt pavement structural layer combinations in my country, leading to frequent and expensive maintenance, high maintenance costs, and high lifecycle costs. They also hinder vehicle traffic, reduce road utilization, and incur high social costs.

[0006] In order to solve the above problems, the inverted pavement structure layer combination appears, which is to set the graded broken stone layer between the semi-rigid base and the asphalt pavement, and can block the reflection of the semi-rigid base crack to the asphalt pavement. Since the compressive resilience modulus of the graded broken stone layer (the average compressive resilience modulus of the graded broken stone is about 350 MPa) is less than that of the semi-rigid base, it is called the inverted pavement structure layer combination, which is also an intermittent system pavement structure layer combination. The problem is that the compressive resilience modulus of the graded broken stone layer is small, the shear strength is low, and the plastic deformation is large, which leads to the rutting of the asphalt pavement. SUMMARY

[0007] The purpose of the present application is to provide an intermittent system strong base thin surface type pavement structure layer combination and construction method, which solves the problem of rutting of the asphalt pavement in the strong base thin surface type inverted pavement structure layer combination.

[0008] An intermittent system strong base thin surface type pavement structure layer combination is composed of a base layer and a functional layer. The base layer includes a semi-rigid bottom base layer and several layers of semi-rigid base layers. The base layer is a load-bearing layer, adopts a skeleton dense type semi-rigid base layer, and the multiple layers of semi-rigid base layers are continuous. The functional layer includes a waterproof seal layer, an intermittent layer, and an asphalt pavement surface layer from bottom to top.

[0009] Further, the thickness of the base layer is ≥60 cm. In the current strong base thin surface type pavement structure layer combination in China, the thickness of the base layer is generally 40-50 cm, which meets the specification requirements, but research shows that this thickness is too thin and not strong enough. Fatigue cracks will occur in the middle of the pavement service period, inducing structural damage to the pavement. When the thickness of the base layer reaches 60 cm, the pavement deformation will be greatly reduced, and the time of fatigue crack occurrence will be greatly extended, ensuring that no fatigue cracks occur within the design service life.

[0010] Research shows that in the inverted strong base thin surface type pavement structure layer combination, when the road surface deflection value is <20 (0.01 mm), the semi-rigid base layer has the ability to bear the design load alone even without the asphalt surface layer. At this time, the pavement structure layer above the semi-rigid base layer is regarded as a functional layer, i.e. the load-bearing function of the functional layer is ignored.

[0011] Further, the waterproof seal layer adopts emulsified asphalt slurry seal or asphalt chip seal. The water immersion strength of the semi-rigid base layer will be reduced, so a waterproof seal layer is set above the semi-rigid base layer. The thickness of the waterproof seal layer is selected according to the provisions of "Technical Specification for Construction of Highway Asphalt Pavement" (JTG F40-2004).

[0012] Furthermore, the intermittent layer is a composite intermittent layer, 10 cm thick, constructed using sand, gravel, and emulsified asphalt, with the gravel particle size ranging from 3 cm to 7 cm. Penetrating emulsified asphalt is poured over the sand and gravel to form the composite intermittent layer. This serves two purposes: first, it consolidates loose surface materials, prevents dust, and facilitates temporary passage (temporary passage refers to the passage of construction machinery, vehicles, and equipment); second, research has shown that pouring a penetrating layer of emulsified asphalt over the sand and gravel layer can increase the compressive rebound modulus of this layer, thereby improving the rutting and fatigue resistance of the asphalt pavement.

[0013] Furthermore, the compressive rebound modulus of the composite fault layer is ≥700 MPa.

[0014] The main functions of the fault layer are: first, forming a discontinuous layer to block the upward reflection of cracks in the semi-rigid base layer; second, drainage. The fault layer makes the entire pavement structure a discontinuous system.

[0015] Furthermore, the asphalt pavement surface layer includes a lower layer, an upper layer, and a surface. The function of the asphalt pavement surface layer is to resist damage to the road surface caused by traffic and natural factors. The multiple layers of asphalt pavement are continuous.

[0016] 1. Bottom layer

[0017] The main function of the lower layer is to resist the driving load, and it adopts anti-rutting asphalt pavement. Anti-rutting asphalt pavement refers to asphalt pavement with excellent anti-rutting performance and dynamic stability ≥10,000 times / mm.

[0018] Studies have shown that in double / triple-layer asphalt pavements, the lower layer is prone to rutting. Therefore, the lower layer of the asphalt pavement adopts a cement-asphalt composite binder semi-rigid and semi-flexible pavement (referred to as semi-rigid and semi-flexible pavement). This pavement has the advantages of both flexible and rigid pavements, with a high compressive modulus and strong plate properties. It is known as a pavement that will not produce rutting.

[0019] The lower layer adopts cement emulsified asphalt mortar penetrating semi-rigid and semi-flexible pavement, which is a rutting-resistant asphalt pavement and also a type of semi-rigid and semi-flexible pavement. It has excellent rutting resistance and the dynamic stability can easily reach more than 10,000 times / mm.

[0020] The thickness of the lower layer is 5cm to 10cm, which is determined based on experience.

[0021] 2. Upper layer

[0022] The main function of the upper layer is to resist shrinkage cracks caused by low temperatures, and it adopts a crack-resistant asphalt pavement. Crack-resistant asphalt pavement refers to an asphalt pavement with excellent resistance to low-temperature shrinkage cracks, and the maximum bending tensile strain in the low-temperature bending test is ≥20,000με.

[0023] Research has shown that low-temperature shrinkage cracking is the primary hazard in the upper layer, so the upper layer should utilize an asphalt pavement with excellent resistance to low-temperature shrinkage cracking. Furthermore, as the stiffness of the lower layer increases, the layer where rutting occurs shifts upward. Since the lower layer of this invention utilizes a semi-rigid, semi-flexible pavement, the upper layer must exhibit excellent rutting resistance.

[0024] The upper layer utilizes mastic asphalt pavement, which utilizes modified asphalt containing 15% to 25% scrap tire rubber powder, also known as rubber asphalt. Asphalt mastic asphalt pavement using rubber asphalt as a binder is called rubber mastic asphalt pavement, or AR-SMA pavement. This type of asphalt pavement is crack-resistant and exhibits outstanding resistance to low-temperature shrinkage cracking. The maximum flexural strain at failure in a low-temperature bending test of the mixture easily exceeds 20,000 με. This type of asphalt pavement exhibits the following characteristics: first, few cracks; second, cracks develop later. Furthermore, it exhibits excellent rutting resistance, with dynamic stability easily exceeding 10,000 times / mm and a compressive rebound modulus exceeding 2,000 MPa.

[0025] The thickness of the upper layer is 3cm to 5cm, which is determined based on experience.

[0026] 3. Surface treatment

[0027] The surface is a protective layer with functions or properties such as water sealing, anti-slip and wear resistance.

[0028] The surface treatment adopts MS-3 type micro-surfacing with coarse aggregate as hard mineral material.

[0029] The thickness of MS-3 micro-surfacing is 0.95cm.

[0030] In the internal structure of the micro-surfacing, the maximum gravel particle size is equal to the thickness of the micro-surfacing, forming a "sky-to-sky" skeleton that will not produce rutting.

[0031] Asphalt pavement layers are continuous. Although the load-bearing capacity of the asphalt pavement is not considered when designing the pavement structure's thickness, continuity between layers can actually improve the overall load-bearing capacity of the pavement structure. When asphalt pavement layers are constructed continuously, the layers are firmly bonded and naturally continuous. When asphalt pavement layers are constructed discontinuously, bonding asphalt is applied between the layers to ensure a firm and continuous bond.

[0032] Studies have shown that the depth of low-temperature shrinkage cracks in asphalt pavements generally does not exceed 10 cm. After considering a certain insurance factor, the total thickness of the asphalt pavement is at least 12 cm.

[0033] The quality of the materials used in the present invention meets the requirements of (JTG / T F20-2015) "Technical Specifications for Highway Pavement Base Construction" and (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction".

[0034] The thickness of the pavement structure layer is determined according to the "Code for Design of Highway Asphalt Pavement" (JTG D50-2017).

[0035] In order to simplify the calculation, the upper layer, the lower layer, the intermittent layer and the base layer participate in the pavement structure layer thickness design.

[0036] A construction method of an intermittent system strong base thin surface type pavement structure layer combination, comprising the following steps:

[0037] I. Semi-rigid subbase, skeleton dense semi-rigid base construction

[0038] According to the "Technical Details for Highway Pavement Base Construction" (JTG / T F20-2015);

[0039] II. Functional layer construction

[0040] (I) Waterproof seal coat

[0041] According to the "Technical Code for Construction of Highway Asphalt Pavement" (JTG F40-2004);

[0042] (II) Intermittent layer

[0043] The construction method of the intermittent layer is as follows:

[0044] First step, paving gravel;

[0045] Second step, leveling and stabilizing gravel;

[0046] Third step, paving fine sand;

[0047] Fourth step, water compaction;

[0048] Fifth step, leveling;

[0049] Sixth step, spreading emulsified asphalt;

[0050] After the sand and gravel are paved and vibrated, emulsified asphalt is uniformly spread on them. The emulsified asphalt is spread in multiple times, and the penetration depth of emulsified asphalt is controlled within 7cm-8cm in each time of spreading, and the spreading amount is determined accordingly. The interval time of each time of spreading emulsified asphalt is greater than 4h;

[0051] Seventh step, maintenance;

[0052] Eighth step, rolling;

[0053] (III) Asphalt pavement surface layer

[0054] 1. Lower layer

[0055] The construction method of the cement emulsified asphalt mortar penetrating type semi-rigid semi-flexible pavement lower layer is as follows:

[0056] The first step is to spread the coarse aggregate gravel

[0057] Drive the gravel spreader to the construction site and spread the coarse aggregate gravel according to the layout and loose paving thickness;

[0058] The second step is to level and stabilize the coarse aggregate gravel

[0059] After the coarse aggregate gravel is spread, it is manually assisted to level it. The required effect is: the gravel is evenly distributed and the surface is flat. After the coarse aggregate gravel is leveled, it is statically compacted 1 to 2 times with a light double steel wheel roller to stabilize the gravel.

[0060] Step 3: Mix / spread / inject cement emulsion asphalt mortar

[0061] Drive the slurry mixing and spreading machine to the construction site, mix and spread the slurry mixture on the stabilized coarse aggregate gravel, and penetrate the cement emulsion asphalt mortar into the gaps between the coarse aggregate gravel;

[0062] Step 4: Vibration rolling

[0063] Use a roller with a vibrating device, turn on the vibration, and roll it; the purpose of vibration is to help the cement emulsion asphalt mortar penetrate; rolling can make the cement emulsion asphalt mortar evenly distributed;

[0064] Step 5: Scraping

[0065] After the vibration rolling is completed, use a hard rubber strip to scrape off the excess cement emulsion asphalt mortar on the surface;

[0066] Step 6: Crushing

[0067] Rolling is carried out immediately after scraping. The purpose of rolling is to make the skeleton of the coarse aggregate gravel dense; secondly, the surface of the coarse aggregate gravel will be uneven during the mixing, spreading and penetration of cement emulsified asphalt mortar, and rolling can restore the surface of the gravel to a flat state.

[0068] Step seven, maintenance.

[0069] Follow the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction";

[0070] 2. Upper layer

[0071] Follow the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction";

[0072] 3. Surface treatment

[0073] The construction method of MS-3 micro-surfacing is as follows:

[0074] The first step is to mix / spread the modified emulsified asphalt slurry mixture

[0075] Follow the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction";

[0076] The second step is vacuum water absorption

[0077] Start the vacuum pump, and the vacuum degree in the slurry mixture gradually increases, and the water is sucked out. When the water absorption is normal, the vacuum degree is controlled at 0.08MPa. When no water can be sucked out, the vacuum degree is gradually increased to continue absorbing water until the vacuum degree increases to 0.13MPa. When no water can be sucked out for 2 minutes, the water absorption is terminated. Research shows that at this time, more than 90% of the total water in the slurry mixture is sucked out.

[0078] The third step is maintenance

[0079] Maintenance is to spread the maintenance material, that is, stone chips, and the amount is 1.5 to 2m 3 / 1000m 2 The purpose of spreading curing material is to prevent asphalt from sticking to the wheels and open up traffic as soon as possible.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] 1. The average compressive resilience modulus of the composite fault layer in the present invention is increased by nearly 2 times, and the deformation resistance is significantly improved.

[0082] The present invention adopts composite discontinuity layer such as Figure 1 As shown in the figure, emulsified asphalt is penetrated into the upper 7cm to 8cm, and the compressive rebound modulus can reach more than 700MPa, which is beneficial to suppress rutting on the asphalt pavement.

[0083] In the prior art, the discontinuity layer is made of graded crushed stone, which has a compressive rebound modulus of 300 MPa to 450 MPa, and the asphalt pavement is prone to rutting.

[0084] In the composite intermittent layer, the upper 7-8 cm thick portion consists of asphalt mixture, which has a much greater compressive resilient modulus than graded crushed stone. This is because the asphalt mixture sits atop a large volume of 3-7 cm crushed stone, which has a higher compressive resilient modulus. This significantly increases the overall compressive resilient modulus of the composite intermittent layer. Because the stress generated by the upward reflection of cracks in the semi-rigid base is far less than the tensile strength of the crushed stone, the lower crushed stone is not pulled apart. Furthermore, the sand does not transmit tensile stress and strain, blocking the upward reflection of cracks in the semi-rigid base. Therefore, the composite intermittent layer not only maintains the function of existing graded crushed stone—blocking reflective cracks—but also overcomes its shortcomings, improving the compressive resilient modulus. It also adds a new function: the large-particle crushed stone spans the cracks in the semi-rigid base, acting as a bridge and improving the integrity and continuity of the semi-rigid base.

[0085] 2. The asphalt pavement in the present invention has greatly improved anti-rutting ability.

[0086] The lower layer in this invention adopts a semi-rigid and semi-flexible pavement, which has an average compressive rebound modulus of about 2500MPa, more than twice that of the commonly used asphalt pavement. It has high rigidity, good plate properties, strong ability to resist deformation, and will not produce rutting by itself; furthermore, the upper layer adopts AR-SMA pavement, which is a skeleton-dense structure. The high-viscosity rubber asphalt binder and the skeleton jointly improve the shear strength, resulting in a strong anti-rutting ability; in addition, the surface adopts MS-3 type micro-surfacing, and the maximum crushed stone particle size is equal to the thickness of the micro-surfacing, forming a strong skeleton structure that "stands up to the sky and the ground", which will not produce rutting.

[0087] The average compressive rebound modulus of the asphalt pavement in the prior art is about 1200 MPa, which is prone to rutting.

[0088] 3. The micro-surfacing vacuum absorption technology of the present invention can extend the construction season and shorten the time it is open to traffic. In addition, the micro-surfacing acts as a protective layer, which can delay the aging of the main structural layer of the asphalt pavement and improve its durability.

[0089] 4. In the slurry mixture, water first forms a water film on the surface of the aggregate, and then the emulsified asphalt breaks the emulsion, and then an asphalt film is gradually formed outside the water film, which greatly reduces the bonding strength between the asphalt and the aggregate. Under the condition of natural volatilization, the water wrapped by the asphalt film cannot be volatilized for a long time, resulting in a shortened service life of the micro-surfacing. The vacuum water absorption construction technology of the present invention can absorb most of the water wrapped by the asphalt film, significantly reducing the adverse effect of water on the bonding strength between asphalt and aggregate, which is beneficial to improving the service life of the micro-surfacing. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 Schematic diagram of the internal structure of the composite fault layer;

[0091] In the figure, 1. Gravel with particle size of 3cm to 7cm; 2. Sand; 3. Emulsified asphalt. DETAILED DESCRIPTION

[0092] The technical solutions and effects of the present invention are further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0093] Example 1

[0094] The design process of the discontinuous system strong base thin surface pavement structure layer combination of this embodiment is as follows:

[0095] 1. Design of pavement structure layer combination

[0096] (1) Project Overview and Traffic Load Parameters

[0097] The project is located in Pingdingshan City, Henan Province, and belongs to a first-class highway. The target reliability index is 1.28, the design service life is 15.0 years, the period from opening to the first rut maintenance is 15 years, according to the traffic OD survey analysis, the large passenger car and truck traffic volume of the section is 6036 vehicles / day, the traffic volume annual growth rate is 3.5%, the direction coefficient is 55.0%, the lane coefficient is 65.0%, the overall truck proportion is 34.3%, and the semi-trailer truck proportion is 43.7%. The vehicle type distribution coefficient is shown in Table 1.

[0098] Table 1 Vehicle type distribution coefficient

[0099] Vehicle type Category 2 Category 3 Category 4 5 categories 6 categories 7 categories 8 categories 9 categories 10 categories 11 categories Model distribution coefficient (%) 8 34.1 10 12 31 54 36 46 39 0

[0100] The initial year design lane large passenger car and truck average daily traffic volume is 2157 vehicles / day, the design lane cumulative large passenger car and truck traffic volume in the design service life is 1.519159E+07 vehicles, and the pavement design traffic load level is heavy traffic load level.

[0101] When checking the asphalt pavement fatigue cracking, the equivalent design axle load cumulative action frequency on the design lane in the design service life is 3.757447E+07.

[0102] When checking the semi-rigid base fatigue cracking, the equivalent design axle load cumulative action frequency on the design lane in the design service life is 2.461238E+09.

[0103] When checking the asphalt pavement permanent deformation, the equivalent design axle load cumulative action frequency on the design lane in the period from opening to the first rut maintenance is 3.757447E+07.

[0104] When checking the roadbed top surface vertical compressive strain, the equivalent design axle load cumulative action frequency on the design lane in the design service life is 6.330478E+07.

[0105] (2) Pavement structure layer combination design and checking

[0106] The number of pavement structure layer combinations: 11 (simplified to 9), design axle load: 100 kN, pavement design layer position: 8 (simplified to 6), and design layer initial thickness: 100 mm. The initial pavement structure layer combination and related parameters are shown in Table 2.

[0107] Table 2 Initial pavement structure layer combination and related parameters

[0108]

[0109]

[0110] In order to simplify the calculation, the micro-surfacing and slurry seal in the functional layer are omitted. The simplified preliminary pavement structure layer combination and related parameters are shown in Table 3.

[0111] Table 3 Simplified preliminary pavement structure layer combination and related parameters

[0112]

[0113] Research shows that when building multiple layers of base, increasing the thickness of each layer from bottom to top has different effects on improving the road's bearing capacity, with the effect gradually increasing from bottom to top. Therefore, increasing the thickness of the upper base layer has a greater effect, and when determining the thickness of the base layer, increasing the thickness of the upper base layer should be prioritized.

[0114] The calculation and verification of the pavement structure layer thickness is a mature technology and is carried out in accordance with the provisions of the (JTG D50-2017) "Highway Asphalt Pavement Design Specifications". I will not go into details here. The results are as follows:

[0115] 1) Fatigue cracking calculation of the 4th layer of semi-rigid base

[0116] The design layer thickness H(6) = 100 mm, the seasonal frozen soil area adjustment coefficient KA = 0.9, the temperature adjustment coefficient KT2 = 0.967, the on-site comprehensive correction coefficient KC = -0.491, the tensile stress at the bottom of the fourth layer σ = -0.006 MPa, the fatigue cracking life of the fourth layer semi-rigid base layer NF2 = 1.096848E+12 times, and the cumulative number of equivalent design axle load actions on the design lane within the design service life NZB2 = 2.461238E+09 axle times.

[0117] The fatigue cracking calculation of the 4th layer of semi-rigid base has met the design requirements.

[0118] 2) Fatigue cracking calculation of the 5th layer of semi-rigid base

[0119] The design layer thickness H(6) = 100 mm, the seasonal frozen soil area adjustment coefficient KA = 0.9, the temperature adjustment coefficient KT2 = 0.967, the on-site comprehensive correction coefficient KC = -1.324, the tensile stress at the bottom of the fifth layer σ = 0.036 MPa, the fatigue cracking life of the fifth layer semi-rigid base layer NF2 = 6.993455E+10 axle times, and the cumulative number of equivalent design axle load actions on the design lane within the design service life NZB2 = 2.461238E+09 axle times.

[0120] The fatigue cracking calculation of the 5th layer of semi-rigid base has met the design requirements.

[0121] 3) Fatigue cracking calculation of the 6th layer of semi-rigid base

[0122] The design layer thickness H(6) = 100 mm, the seasonal frozen soil area adjustment coefficient KA = 0.9, the temperature adjustment coefficient KT2 = 0.967, the on-site comprehensive correction coefficient KC = -1.324, the tensile stress at the bottom of the sixth layer σ = 0.046 MPa, the fatigue cracking life of the sixth layer semi-rigid base layer NF2 = 5.732538E+10 axle times, and the cumulative number of equivalent design axle load actions on the design lane within the design service life NZB2 = 2.461238E+09 axle times.

[0123] The fatigue cracking calculation of the 6th layer of semi-rigid base has met the design requirements.

[0124] 4) Calculation of fatigue cracking of the 7th cement soil layer

[0125] The design layer thickness H(6) = 100 mm, the seasonal frozen soil area adjustment coefficient KA = 0.9, the temperature adjustment coefficient KT2 = 0.967, the on-site comprehensive correction coefficient KC = -0.827, the tensile stress at the bottom of the 7th layer σ = 0.008 MPa, the fatigue cracking life of the 7th layer cement soil NF2 = 2.791946E+10 axle times, and the cumulative number of equivalent design axle load actions on the design lane within the design service life NZB2 = 2.461238E+09 axle times.

[0126] The fatigue cracking calculation of the 7th layer of cement soil has met the design requirements.

[0127] 5) Calculation of fatigue cracking of the 8th cement soil layer

[0128] The design layer thickness H(6) = 100 mm, the seasonal frozen soil area adjustment coefficient KA = 0.9, the temperature adjustment coefficient KT2 = 0.967, the on-site comprehensive correction coefficient KC = -0.827, the tensile stress at the bottom of the 8th layer σ = 0.014 MPa, the fatigue cracking life of the 8th layer cement soil NF2 = 2.169094E+10 axle times, and the cumulative number of equivalent design axle load actions on the design lane within the design service life NZB2 = 2.461238E+09 axle times.

[0129] The fatigue cracking calculation of the 8th layer of cement soil has met the design requirements.

[0130] 6) Fatigue cracking calculation of the 9th cement soil layer

[0131] The design layer thickness H(6) = 100 mm, the seasonal frozen soil area adjustment coefficient KA = 0.9, the temperature adjustment coefficient KT2 = 0.967, the on-site comprehensive correction coefficient KC = -0.827, the tensile stress at the bottom of the 9th layer σ = 0.023 MPa, the fatigue cracking life of the 9th layer cement soil NF2 = 1.485373E+10 axle times, and the cumulative number of equivalent design axle load actions on the design lane within the design service life NZB2 = 2.461238E+09 axle times.

[0132] The fatigue cracking calculation of the 9th layer cement soil has met the design requirements.

[0133] 7) Fatigue cracking calculation of asphalt pavement

[0134] The design layer thickness H(6) is 100 mm, the seasonal frozen soil area adjustment coefficient KA is 0.9, the fatigue loading mode coefficient KB is 0.916, the temperature adjustment coefficient KT1 is 0.665, the asphalt saturation of the asphalt mixture VFA is 75%, the bottom tensile strain of the asphalt pavement layer ε is 61x10-6, and the fatigue cracking life of the asphalt pavement NF1 is 9.895752E+07 axle times. The equivalent design axle load cumulative action times NZB1 on the design lane within the design service life is 3.757447E+07 axle times.

[0135] The fatigue cracking calculation of the asphalt pavement has met the design requirements.

[0136] 8) Permanent deformation calculation of asphalt pavement

[0137] The equivalent temperature of the permanent deformation of the asphalt pavement TPEF is 22.8℃, the equivalent design axle load cumulative action times NZB3 on the design lane within the period from the opening to the first rut maintenance is 3.757447E+07 axle times, and the permanent deformation calculation layer number N of the asphalt pavement is 5.

[0138] The permanent deformation of the first layer of asphalt pavement RAI(1) is 0.73 mm;

[0139] The permanent deformation of the second layer of asphalt pavement RAI(2) is 1.81 mm;

[0140] The permanent deformation of the third layer of asphalt pavement RAI(3) is 1.58 mm;

[0141] The permanent deformation of the fourth layer of asphalt pavement RAI(4) is 0.86 mm;

[0142] The permanent deformation of the fifth layer of asphalt pavement RAI(5) is 0.37 mm;

[0143] The permanent deformation of the asphalt pavement RAI is 5.35 mm.

[0144] The allowable permanent deformation of the asphalt pavement RAR is 15 mm.

[0145] The permanent deformation of the asphalt pavement meets the specification requirements.

[0146] The technical requirement of the dynamic stability of the first layer of asphalt mixture rut test is 5139 times / mm;

[0147] The technical requirement of the dynamic stability of the second layer of asphalt mixture rut test is 5139 times / mm.

[0148] By rounding the design layer thickness and further modifying the pavement thickness based on the pavement structure layer combination design experience in the region, the simplified pavement structure design results are finally obtained as shown in Table 4.

[0149] Table 4 Simplified pavement structure layer combination design results

[0150]

[0151] Calculate the acceptance deflection value of the designed pavement structure

[0152] The modulus reduction coefficient of subgrade soil under dry-wet cycle or freeze-thaw cycle conditions is KAT=0.95

[0153] The deflection value of the roadbed top surface acceptance LG=443.5(0.01mm)

[0154] The road surface acceptance deflection value LA=18 (0.01mm).

[0155] The pavement structure design results are shown in Table 5.

[0156] Table 5 Pavement structure layer combination design results

[0157]

[0158]

[0159] 2. Construction method of pavement structure layer

[0160] (1) Base construction method

[0161] It shall be implemented in accordance with the relevant provisions of (JTG / T F20-2015) "Technical Specifications for Highway Pavement Base Construction".

[0162] (2) Functional layer construction method

[0163] 1. Construction method of ES-2 type slurry seal waterproof layer

[0164] It shall be implemented in accordance with the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction".

[0165] 2. Composite fault construction method

[0166] (1) Composite intermittent layer mixture proportion design and compressive rebound modulus test

[0167] The composite fault layer includes the following volume components: 3cm to 7cm gravel 100 to 150m 3 / 1000m 2 , sand 10~30m 3 / 1000m 2 , emulsified asphalt 3~8m 3 / 1000m 2 . Among them: the volume of gravel and sand refers to the compacted pile volume.

[0168] When designing the mixture proportion, the amount of sand is calculated based on the compacted porosity of gravel and sand and the designed thickness; the amount of emulsified asphalt is determined based on experience, with the principle of ensuring the stability of the material 7cm to 8cm thick above the sand and gravel layer.

[0169] The thickness of the composite fault layer in this example is 10 cm. Figure 1 As shown, it includes crushed stone 1 with a particle size of 3cm to 7cm, sand 2, and emulsified asphalt 3. The known conditions are: the porosity of the crushed stone is 19.7%, and the loose paving coefficient of the crushed stone and sand is 1.1. Based on experience, the amount of emulsified asphalt is selected as 3m 3 / 1000m 2 The compressive rebound modulus of the sand and gravel fault layer can reach more than 700MPa.

[0170] 1000m 2 The material dosage of the sand and gravel interlayer is:

[0171] Compacted gravel accumulation volume = 1000m 2 ×10cm=100m 3

[0172] Compacted volume of fine sand = 100m 3 ×19.7%=19.7m 3

[0173] Emulsified asphalt volume = 1000m 2 ×3m 3 / 1000m 2 =3m 3

[0174] The compressive modulus of composite fault layers was tested according to the "Appendix D: Test Method for Rebound Modulus of Aggregate Materials" in the "Highway Asphalt Pavement Design Specification" (JTGD50-2017), with the following differences: First, the specimen height was changed to 100 mm, consistent with the designed thickness of the structural layer; second, emulsified asphalt was poured into the upper 7-8 cm of the specimen according to the designed mix ratio; and third, the specimen was allowed to stand indoors for at least 24 hours after fabrication before the compressive modulus test was conducted. The test results showed a compressive modulus of 755 MPa, meeting the requirements.

[0175] (2) Composite fault construction

[0176] The first step is to spread the gravel with a loose thickness of: 10cm×1.1=11cm.

[0177] The second step is to crush the gravel.

[0178] Use a ≥16t rubber-wheel roller to compact the spread gravel to make it dense.

[0179] The third step is to spread fine sand, 1000m 2 The amount of sand spread is: 19.7m 3 ×1.1=21.67m 3 .

[0180] The fourth step is to flush water to compact the sand.

[0181] Step 5: Leveling.

[0182] Finishing makes the surface smooth and the sand evenly distributed.

[0183] Step 6: Spread emulsified asphalt.

[0184] Emulsified asphalt is spread three times, with each spreading amount of 1m 3 / 1000m 2 .

[0185] Step seven, maintenance.

[0186] The purpose of maintenance is to prevent the inter-layer materials of sand and gravel from sticking to the wheel.

[0187] Step 8: Crush.

[0188] Use a ≥16t rubber wheel roller to roll 2 to 3 times.

[0189] 3. Construction method of the lower layer of cement emulsified asphalt mortar penetration semi-rigid and semi-flexible pavement

[0190] (1) Mixture proportion design of the lower layer of cement emulsion asphalt mortar penetration semi-rigid semi-flexible pavement

[0191] The first step is to configure optimized coarse aggregate and fine aggregate.

[0192] The gradation is selected according to the requirements of the dense asphalt pavement structure, and the mix ratio of various materials in the aggregate is determined; aggregates such as stones, stone chips, mineral powder, etc. ≤2.36mm are called fine aggregates, and ore aggregates >4.75mm are called coarse aggregates; after the gradation is selected, stones of 2.36mm~4.75mm are removed and replaced with aggregates of the adjacent grades of equal quality to form a discontinuous gradation. Its purpose is to increase the gaps between the coarse aggregate gravel to facilitate the penetration of cement emulsified asphalt mortar, that is, stones of 4.75mm~9.5mm of equal quality are used to replace stones of 2.36mm~4.75mm.

[0193] The second step is to configure the optimized binder.

[0194] The second binder uses fast-setting cement, and the cement-aggregate ratio (the weight percentage of cement to aggregate) is generally 3% to 6%. The cement dosage is calculated after the cement-aggregate ratio is determined; the cement is used by the internal admixture method, that is, the mineral powder in the fine aggregate is replaced by cement of equal mass, and the cement is used as part of the fine aggregate.

[0195] The first binder is slow-cracking and slow-setting SBR modified emulsified asphalt. The evaporation residue of the emulsified asphalt is taken and the oil-stone ratio is determined using the method of (T0709-2011) "Marshall Stability Test for Asphalt Mixtures". The oil-stone ratio refers to the mass percentage of the evaporation residue to the aggregate. The amount of emulsified asphalt is calculated based on the oil-stone ratio and the content of the evaporation residue in the emulsified asphalt.

[0196] The third step is to prepare cement emulsified asphalt mortar.

[0197] According to the dosage ratio determined above, take emulsified asphalt, cement-containing fine aggregate and different amounts of water, and use the method of (T0751-1993) "Emulsified Asphalt Slurry Sealing Mixture Consistency Test" to control the consistency value between 3cm and 5cm to determine the amount of additional water; whether to use admixtures, which admixtures to use and their dosage, such as retarders, water reducers or other additives, are determined through tests; the demulsification time of cement emulsified asphalt mortar is controlled to at least 15 minutes.

[0198] The mix ratio of cement emulsion asphalt mortar, i.e. fine aggregate: emulsified asphalt: added water: admixture, is determined based on Marshall test, consistency test, demulsification time test, etc.

[0199] During construction, the fine aggregate containing cement should be kept basically dry, and the test mix ratio of cement emulsion asphalt mortar can be regarded as the construction mix ratio, which is the basis for calibrating the slurry mixture mixing and spreading machine (also known as slurry sealing machine).

[0200] Step 4: Material matching

[0201] The materials before construction are mixed together according to the mix ratio design. First, the stone, stone chips, mineral powder aggregates ≤2.36mm are mixed with cement, and they should be used as soon as possible after mixing; second, the ore aggregates >4.75mm are mixed; third, various admixtures are mixed.

[0202] Step 5: Check and debug construction machinery and equipment

[0203] Check the integrity of mechanical equipment; debug and calibrate various material control systems according to the designed material dosage or mix ratio.

[0204] Step 6: Test section

[0205] The main purposes of building a test section are: to determine the thickness of the coarse aggregate gravel spreading, that is, to determine the loose paving coefficient; to determine the unit area usage of cement emulsion asphalt mortar, which is convenient for control during large-scale construction; to verify the conformity and rationality of the design, etc.

[0206] In this example, AC-20 type asphalt concrete graded gravel is selected to make an 8cm thick semi-rigid semi-flexible pavement. The specific method is as follows:

[0207] Taking 100kg of aggregate as an example, the design consists of 60kg of stone >4.75mm (10mm-20mm crushed stone: 4.75mm-9.5mm crushed stone = 40:20), 10kg of stone 2.36mm-4.75mm, and 30kg of material <2.36mm (rough stone: stone chips: mineral powder = 10:10:10), which meet the specification requirements. If 10kg of 4.75mm-9.5mm stone is used to replace the 2.36mm-4.75mm stone, the 100kg aggregate will contain 70kg of coarse aggregate and 30kg of fine aggregate. The coarse aggregate mix ratio then becomes: 10mm-20mm crushed stone: 4.75mm-9.5mm crushed stone = 40:30, while the fine aggregate mix ratio remains: rough stone: stone chips: mineral powder = 10:10:10.

[0208] If the cement-aggregate ratio is set at 3%, the cement consumption is: 100kg×3%=3kg.

[0209] If the internal admixture method is adopted to replace the mineral powder with cement of equal weight, the fine aggregate mix ratio becomes: rice stone: stone chips: mineral powder: cement = 10:10:7:3.

[0210] When the Marshall test is performed on emulsified asphalt evaporation residue and cement-containing aggregate, an asphalt-to-aggregate ratio of 5.4% meets the requirements. Therefore, the amount of evaporation residue required is: 100kg x 5.4% = 5.4kg.

[0211] If modified emulsified asphalt with an evaporation residue content of 60% is selected, the amount of modified emulsified asphalt used is: 5.4kg ÷ 60% = 9kg.

[0212] In a consistency test using cement-containing fine aggregate, modified emulsified asphalt, water, and a water reducer, the requirements were met when the added water content was 0.1% of the fine aggregate weight and the water reducer content was 3% of the cement weight. Therefore, the added water dosage is: 30kg x 0.1% = 3kg; the water reducer dosage is: 3kg x 3% = 0.09kg.

[0213] The mix ratio of cement emulsified asphalt mortar mixture is: modified emulsified asphalt: fine aggregate: added water: water reducer = 9:30:3:0.09.

[0214] Material preparation: Mix the materials according to the designed mix ratio. First, fine aggregate (<2.36mm)—rice stone, stone chips, and mineral powder—is mixed with cement in a ratio of 10:10:7:3. Use as soon as possible after mixing. Second, coarse aggregate (>4.75mm)—10mm-20mm crushed stone and 4.75mm-9.5mm crushed stone—is mixed in a ratio of 2:1. Third, various admixtures are mixed. In this example, only a water reducer is used, so no admixture is required.

[0215] (2) Construction of the lower layer of cement emulsion asphalt mortar penetration semi-rigid semi-flexible pavement

[0216] The first step is to spread the coarse aggregate crushed stone.

[0217] Drive the gravel spreader to the construction site and spread the coarse aggregate gravel according to the layout and loose laying thickness.

[0218] The second step is to level and stabilize the coarse aggregate gravel.

[0219] After the coarse aggregate gravel is spread, it is leveled and statically compacted 1 to 2 times with a light double steel wheel roller.

[0220] The third step is mixing and spreading.

[0221] Drive the slurry mixture mixer and paver onto the stabilized gravel to mix and spread.

[0222] The fourth step is vibration rolling.

[0223] Then, a roller with a vibrating device is used to turn on the vibration and roll to help the cement emulsion asphalt mortar penetrate; during this process, manual assistance is used to ensure that the cement emulsion asphalt mortar is evenly distributed.

[0224] Step 5: Scrape the slurry.

[0225] After the vibration rolling is completed, use a hard rubber strip to scrape off the excess cement emulsion asphalt mortar on the surface.

[0226] Step six, crush.

[0227] Use a light double steel wheel roller (or rubber wheel roller) to roll 1 to 2 times.

[0228] Step seven, maintain health.

[0229] Maintain health until the water is basically consumed.

[0230] 4. Construction method of AR-SMA pavement top layer

[0231] It shall be implemented in accordance with the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction".

[0232] 5. MS-3 micro-surfacing

[0233] (1) Design of the mix ratio of MS-3 modified emulsified asphalt slurry mixture

[0234] It shall be implemented in accordance with the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction".

[0235] (2) MS-3 micro-surfacing construction

[0236] The first step is to mix / spread the modified emulsified asphalt slurry mixture

[0237] It shall be implemented in accordance with the relevant provisions of (JTG F40-2004) "Technical Specifications for Highway Asphalt Pavement Construction".

[0238] The second step is vacuum water absorption

[0239] Vacuum dehydration begins 15 minutes after the slurry mixture is spread, that is, after the slurry mixture breaks.

[0240] Start the vacuum pump to gradually increase the vacuum degree in the slurry mixture to absorb water. When the water absorption is normal, the vacuum degree is controlled at 0.08MPa. When no water can be absorbed, the vacuum degree is gradually increased to absorb water until the vacuum degree increases to 0.13MPa. When no water can be absorbed for 2 minutes, the water absorption is terminated.

[0241] Vacuum water absorption equipment includes: vacuum water absorption filter cloth, vacuum water absorption pad, vacuum water absorption pipe and vacuum pump.

[0242] The vacuum filter cloth is laid over the paved slurry mixture, and a vacuum pad is placed on top. The pad is connected to a vacuum pump via a vacuum suction pipe. The vacuum pump is used to remove and drain the water produced by the emulsified asphalt demulsification. When the vacuum pad is laid, a 5mm thick and 30mm to 50mm wide layer of emulsified asphalt cement slurry is filled around the edges of the pad and sealed tightly against the road surface. The emulsified asphalt cement slurry is a mixture of cement and emulsified asphalt, with a required consistency of 0.5cm to 1cm, or 0.6cm in this example. The dimensions of the vacuum filter cloth are 3.1m x 20m, and the dimensions of the vacuum pad are 3.2m x 20.2m. The widths of the paving box, vacuum filter cloth, and vacuum pad, respectively, must be at least 10cm wide, and the lengths of the vacuum filter cloth and vacuum pad, respectively, must be at least 20cm. These lengths can be adjusted for ease of construction.

[0243] After vacuuming is completed, remove the emulsified asphalt cement slurry.

[0244] The third step is maintenance

[0245] Maintenance is to spread the maintenance material, that is, stone chips, and the amount is 1.5 to 2m 3 / 1000m 2The purpose of spreading curing material is to prevent asphalt from sticking to the wheels and open up traffic as soon as possible.

[0246] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A discontinuous system strong base thin surface type pavement structure layer combination, characterized in that: The structural layer combination consists of a base layer and a functional layer. The base layer includes a semi-rigid subbase layer and several layers of semi-rigid base layers. The base layer is a load-bearing layer and adopts a skeleton-dense semi-rigid base layer. The multiple layers of semi-rigid base layers are continuous. The functional layer includes a waterproof seal layer, a fault layer and an asphalt pavement surface layer from bottom to top. The thickness of the base layer is ≥60cm; The waterproof seal layer adopts emulsified asphalt slurry seal layer or asphalt chip seal layer; The fault layer is a composite fault layer with a thickness of 10 cm, and is paved with sand, crushed stone and emulsified asphalt, wherein the crushed stone particle size is 3 cm to 7 cm. Emulsified asphalt is poured on the sand and crushed stone, and the penetration depth of the emulsified asphalt is 7 cm to 8 cm to form a composite fault layer; The composite fault layer includes the following volume components: 3cm to 7cm gravel 100 to 150m 3 / 1000m 2 , sand 10~30m 3 / 1000m 2 , emulsified asphalt 3~8m 3 / 1000m 2 ; Among them: the volume of gravel and sand refers to the compacted volume; The compressive resilience modulus of the discontinuity layer is ≥700 MPa; The asphalt pavement surface layer includes a lower layer, an upper layer and a surface, and the layers are continuous; The lower layer adopts a cement emulsified asphalt mortar penetration type semi-rigid and semi-flexible pavement with a thickness of 5cm to 10cm. The gradation is selected according to the requirements of the dense asphalt pavement structure. Stone, stone chips, and mineral powder aggregates ≤ 2.36mm are called fine aggregates, and mineral aggregates > 4.75mm are called coarse aggregates. After the gradation is selected, stones of 2.36mm to 4.75mm are removed and replaced with aggregates of the same quality as those of the adjacent grades to form a discontinuous gradation. The purpose is to increase the gaps between the coarse aggregate gravel to facilitate the penetration of the cement emulsified asphalt mortar, that is, stones of 4.75mm to 9.5mm of the same quality are used to replace stones of 2.36mm to 4.75mm. The upper layer adopts asphalt mastic macadam pavement, wherein the asphalt adopts rubber asphalt, and the thickness of the upper layer is 3cm to 5cm; The surfacing adopts MS-3 type micro surfacing in which the coarse aggregate is hard mineral material, and the thickness of the MS-3 type micro surfacing is 0.95 cm.

2. The discontinuous system strong base thin surface type pavement structure layer combination according to claim 1, characterized in that: Construction method of the discontinuous system strong base thin surface type pavement structure layer combination The following steps are involved: The first step is the construction of semi-rigid subbase and skeleton dense semi-rigid base Follow JTG / T F20-2015 Technical Specifications for Highway Pavement Base Construction; Step 2: Functional layer construction S1. Waterproof seal Follow JTG F40-2004 Technical Specifications for Highway Asphalt Pavement Construction; S2, fault layer The intermittent layer construction method is as follows: S201, paving gravel; S202, leveling and stabilizing crushed stone; S203, spreading fine sand; S204, water town dense; S205, leveling; S206, spreading emulsified asphalt; After the sand and gravel are paved and compacted, emulsified asphalt is evenly spread on it. The emulsified asphalt is spread in multiple times. The penetration depth of the emulsified asphalt is controlled within the range of 7cm to 8cm each time and the amount of emulsified asphalt is determined accordingly. The interval between each emulsified asphalt spreading is greater than 4 hours. S207, maintenance; S208, rolling; S3, asphalt pavement surface layer S301, lower layer The construction method of the lower layer of cement emulsified asphalt mortar penetration semi-rigid and semi-flexible pavement is as follows: S301-1, Paving Coarse Aggregate Crushed Stone Drive the gravel spreader to the construction site and spread the coarse aggregate gravel according to the layout and loose paving thickness; S301-2, leveling and stabilizing coarse aggregate crushed stone After the coarse aggregate gravel is spread, it is manually assisted to level it. The required effect is: the gravel is evenly distributed and the surface is flat. After the coarse aggregate gravel is leveled, it is statically compacted 1 to 2 times with a light double steel wheel roller to stabilize the gravel. S301-3, Mixing / Spreading / Injecting Cement Emulsion Asphalt Mortar Drive the slurry mixing and spreading machine to the construction site, mix and spread the slurry mixture on the stabilized coarse aggregate gravel, and penetrate the cement emulsion asphalt mortar into the gaps between the coarse aggregate gravel; S301-4, vibration rolling Use a roller with a vibration device, turn on the vibration, and perform rolling; S301-5, scraping After the vibration rolling is completed, use a hard rubber strip to scrape off the excess cement emulsion asphalt mortar on the surface; S301-6, crushing Rolling is carried out immediately after scraping. The purpose of rolling is to make the skeleton of the coarse aggregate gravel dense; secondly, the surface of the coarse aggregate gravel will be uneven during the mixing, spreading and penetration of cement emulsified asphalt mortar, and rolling can restore the surface of the gravel to a flat state. S301-7, Maintenance Follow the relevant provisions of JTG F40-2004 Technical Specifications for Highway Asphalt Pavement Construction; S302, upper layer Follow the relevant provisions of JTG F40-2004 Technical Specifications for Highway Asphalt Pavement Construction; S303, surface treatment The construction method of MS-3 micro-surfacing is as follows: S303-1, Mixing / paving modified emulsified asphalt slurry mixture Follow the relevant provisions of JTG F40-2004 Technical Specifications for Highway Asphalt Pavement Construction; S303-2, vacuum water absorption Start the vacuum pump, the vacuum degree in the slurry mixture gradually increases, and the water is sucked out. When the water absorption is normal, the vacuum degree is controlled at 0.08MPa. When no water can be sucked out, the vacuum degree is gradually increased to absorb water until the vacuum degree increases to 0.13MPa. When no water can be sucked out for 2 minutes, the water absorption is terminated. S303-3, Maintenance Maintenance is to spread the maintenance material, that is, stone chips, and the amount is 1.5 to 2m 3 / 1000m 2 The purpose of spreading curing material is to prevent asphalt from sticking to the wheels and open up traffic as soon as possible.

Images