The present invention relates generally to a method for continuous on-site repaving of an asphalt mixture layer of road pavement and a motor-driven vehicle system therefor, and, more particularly, to a method comprising steps of: applying heat to a surface of an asphalt mixture layer so as to allow the heat to reach to a depth exceeding the boundary surface between the base layer and the surface layer of the asphalt mixture layer or to a depth within the asphalt mixture layer, equivalent to that depth exceeding the boundary, whereby obtaining an asphalt mixture derived from existing road pavement (old asphalt mixture); adding and mixing either one of new materials of a coarse aggregate, or an aggregate covered with an asphalt or an asphalt mixture having a particle size distribution including coarse aggregates mixed therein, to produce a reinforcing asphalt mixture; spreading the reinforcing asphalt mixture onto the remaining layer of the existing asphalt mixture layer to form a coarse graded reinforcing layer as a middle layer having an elastic modulus greater than the remaining layer of the existing asphalt mixture; adding an asphalt mixture onto the coarse graded reinforcing layer to form a new layer; compacting the coarse graded reinforcing layer and the new layer together while heat still being stored, for, continuous on-site repaving of an asphalt mixture layer of road pavement, and a motor-driven vehicle system used with the method.
Road pavement is prone to often experiencing cracking such as rutting and subsidence due to compressive and tensile strain in both vertical and horizontal direction caused by heavy traffic volume. To address this, the road pavement is formed with three layers including a roadbed, a sub-base and an asphalt mixture layer, as shown in
In general, the term pavement is used to designate the four layers in “a sub-base and an asphalt mixture layer,” and the asphalt mixture layer includes a base layer and a surface layer, each having a thickness of about 40 to 50 mm to provide a required strength for a traffic volume. This is because that the thickness of a pavement is determined by the strength of the roadbed (California Bearing Ratio (CBR) value) and the traffic volume (N value) from the durability point of view, but, the thickness of each layer of a sub-base and an asphalt mixture layer is usually designed to be about two to three times in length of the maximum diameter of aggregates mixed therein. The maximum diameter of aggregates mixed into an asphalt mixture layer is usually around 20 mm, thus each thickness of the base layer and the surface layer comprising the asphalt mixture layer is designed to be around 40 to 50 mm, consequently the total thickness of the asphalt mixture layer may be around 80 to 100 mm.
However, depending on a required property, there are cases where an aggregate having the maximum particle size in a particle size distribution included in the surface layer with a thickness of about 40 to 50 mm is used in a dense graded layer having a thickness of about 13 mm and an, aggregate having the maximum particle size in a particle size distribution included in the base layer with the same thickness of about 40 to 50 mm is used in a coarse graded layer of about 20 mm. The thickness of the base layer is flexibly determined depending on a traffic volume. Thus, there are cases where a thickness of a base layer is determined to be about 40 to 350 mm.
Repaving of an asphalt mixture layer is explained as follows.
Each of a base layer and a surface layer of an asphalt mixture layer includes an asphalt which serves as a binder, particles of aggregate such as sand and crushed rocks and stone powder (filler) comprised of limestone powder adapted to fill spaces among the particles of the aggregate. In the composition ratio, in general, aggregate accounts for about 90%, asphalt (binder) for about 5 to 8%, and filler accounts for the rest.
The size of aggregate is referred as a particle size, and the mixture condition of these particles of aggregate which can be classified using screening device having a variety of screen meshes is referred as a particle size distribution.
There are two kinds of asphalt (binder) used as an aggregates binder, one is crude asphalt called as strait asphalt which is unmodified, the other is modified asphalt which modifying agent such as rubber or resin has been added to improve viscosity. As seen in the relation between temperature and viscosity shown in
It has been known that paved roads which are subjected to heavy traffic due to busy vehicle transportation have problems such as road surface deformation due to compressive and tensile strain in both vertical and horizontal direction and/or “rutting” as well as cracking due to softening and fluidizing of asphalt (binder) caused by being subjected to serious weather conditions for a prolonged time. These problems make a road surface uneven and cause further deterioration, as shown in
Specifically, there are two construction methods used for the purpose. One of the methods is a remixing method shown in
The other method is a repaving method shown in
However, as described above, there are many cases where cracks and deformation occurred on road pavement reach to a depth exceeding a boundary between a surface layer and a base layer which is generally at about 60 to 100 mm from a road surface or to a depth within an asphalt mixture layer equivalent to that depth exceeding the boundary. In road surface heating methods conventionally used for known on-site recycling pavement construction, such as the above described remixing method and repaving method, there was a limit to a depth from road surface to which heat can reach in a short period of time without causing asphalt to catch fire. Thus, the methods were applied to only a surface layer or a part of a surface layer. Therefore, when such on-site recycling pavement construction is performed for regenerating a surface layer of an asphalt mixture, some of cracks or deformations at the depth of 60 to 100 mm from the road surface, i.e. the depth equivalent to the base layer of an asphalt mixture layer or the equivalent depth in the asphalt mixture layer, had to be left behind.
U.S. Pat. No. 4,534,674 describes a method in which a remixing method is applied to a repaving method and repairing cracks and deformations in road pavement are also considered, more specifically, a method wherein a new surface layer is formed on a layer generated by adding a rejuvenating agent and heated fresh asphalt mixture to a scarified asphalt mixture, mixing them together, spreading and compacting. However, this method also has a limit to a depth of existing asphalt mixture layer being repaired as to 50 to 60 mm from road surface. In the above described cases, a life span of the recycled road pavement was short, because it was difficult to continuously recycle pavement on site to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth, i.e. 60 to 100 mm from road surface, to fundamentally improve a life span of the recycled road pavement. Road pavement damaged to such depth had to be, for example, reconstructed.
The applicant has, in a patent literature of Japanese Patent NO. 402-4293, already developed a heating method and device for on-site continuous recycling of an asphalt mixture layer, which enables materials in a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth to be heated in a short period of time without causing asphalt to catch fire while keeping the surface temperature of the existing asphalt mixture layer at around 250 degrees Centigrade, by using a heating means for spraying and circulating a blast of hot air at around 600 to 700 degrees Centigrade to a road surface of an asphalt mixture layer. The applicant has been committed to developing a repaving method that enables repairing damages and deterioration in road pavement to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth and that enables significantly improving the life span of the road pavement by using the above mentioned heating method and device.
(Nonpatent literature 1): “Pavement Recycling Handbook” (Japan Road Association)
(Patent literature 1): Japanese Patent NO. 402-4293
(Patent literature 2): U.S. Pat. No. 4,534,674
Asphalt is comprised of particulate ingredient called as asphaltene, and oil ingredient called as maltene, and the content of methane tends to be decreases as the pavement is aged with the result that the asphalt is made harder and less viscous due to an increase in relative amount of asphaltene to maltene. This could occur to both a surface layer and a base layer more or less to a same degree. Furthermore, aggregates mixed in the asphalt mixture layer may be subjected to abrasion and breakage. Therefore, when an asphalt mixture derived from existing road pavement is reused as old asphalt mixture, it may be preferably used for a whole asphalt mixture layer including a surface layer and a base layer.
The present invention proposes a method for repaving of an asphalt mixture layer of road pavement and a motor-driven vehicle system therefor, wherein the method comprising steps of; by using the above described heating method and device which enables heat to reach in a short period of time to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth to be heated without causing asphalt to catch fire, applying heat so as to reach to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to about 60 to 100 mm within the asphalt mixture layer which is equivalent to that depth and thereby softening materials within the depth; adding and mixing not only a rejuvenating agent but either one of new materials of a coarse aggregate or an aggregate covered with an asphalt or an asphalt mixture having a particle size distribution including coarse aggregates mixed therein, with the asphalt mixture scarified to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth, to produce a reinforcing asphalt mixture, as shown in
A solution of the above described problem will be accomplished by the present invention based on a knowledge that an asphalt mixture layer of road pavement can be continuously repaved on site by performing steps of applying heat to a surface of an asphalt mixture layer so as to allow the heat to reach to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth using a motor-driven vehicle system, whereby the materials in a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to that depth are softened and scarified to obtain an old asphalt mixture; adding and mixing a first new material, being heated to a temperature preventing re-aggregation, either one of a coarse aggregate or an aggregate covered with an asphalt or an asphalt mixture having a particle size distribution including coarse aggregate mixed therein, to produce a reinforcing asphalt mixture; spreading the reinforcing asphalt mixture on the remaining layer of the existing asphalt mixture layer to form a coarse graded reinforcing layer having an elastic modulus greater than the remaining layer of the remaining asphalt mixture; and adding and spreading a second new material for a new layer, being stored at a temperature preventing re-aggregation, onto the coarse graded reinforcing layer and compacting them together while heat still being stored to form a new surface layer. The present invention has the following characteristics.
The invention defined in claim 1 is a method for continuous on-site repaving of an asphalt mixture layer of a road pavement with a motor-driven vehicle system, comprising the steps of;
The invention defined in claim 2 is a method, in addition to the characteristics of the invention defined in claim 1, further comprising a step of carrying in, prior to said step (b), the first new material and the second new material at different timings conveyed from outside the motor-driven vehicle system to respective one of the storing apparatus coincidentally with the different timings.
The invention defined in claim 3 is a method, in addition to the characteristics of the invention defined in any of claim 1 or 2, wherein the first new material is any one of an aggregate or aggregate covered with asphalt having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer or an asphalt mixture having a particle size distribution including coarse aggregate mixed therein having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer.
The invention defined in claim 4 is a method, in addition to the characteristics of the invention defined in any of claims 1 to 3, wherein the reinforcing asphalt mixture includes an aggregate having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer for about 5 to 35 weight % to the total weight.
The invention defined in claim 5 is a method, in addition to the characteristics of the invention defined in any of claims 1 to 4, wherein said step (d) further comprises a step of adding an asphalt rejuvenating agent when mixing the old asphalt mixture with the first new material added therein.
The invention defined in claim 6 is a method, in addition to the characteristics of the invention defined in any of claims 1 to 5, wherein the second new material is an asphalt mixture including an aggregate having a substantially same particle size distribution as that of an aggregate included in the asphalt mixture layer.
The invention defined in claim 7 is a method, in addition to the characteristics of the invention defined in any of claims 1 to 6, wherein said step (e) further comprises a step of spreading an asphalt emulsion or a material for enhancing water proof property and bonding property over the remaining layer to bond the remaining layer and the coarse graded reinforcing layer.
The invention defined in claim 8 is a motor-driven vehicle system for continuous on-site repaving of an asphalt mixture layer of road pavement comprising a pre-heater vehicle (A) for applying heat to a surface of the asphalt mixture layer of road pavement so as to allow the heat to reach to a depth exceeding a boundary surface between a base layer and a surface layer of the asphalt mixture layer or to a depth within the asphalt mixture layer equivalent to the depth exceeding the boundary surface and thereby to soften the asphalt mixture layer; a miller vehicle (B) including a first tank for storing a first new material at a temperature preventing re-aggregation, the first new material being any one of a coarse aggregate, a coarse aggregate covered with asphalt or an asphalt mixture having a particle distribution including a coarse aggregate, a scarifying means for scarifying the heated and softened asphalt mixture layer to the depth exceeding the boundary surface or to the depth within the asphalt mixture layer equivalent to that depth exceeding the boundary surface to obtain an old asphalt mixture, and a first adding means for adding the first new material stored at a temperature preventing re-aggregation and discharged out of the first tank to the old asphalt mixture; and a mixer vehicle (C) including a second tank for storing a second new material at a temperature preventing re-aggregation, the second new material being a fresh asphalt mixture for a new surface layer, a mixing means for receiving the old asphalt mixture which the first new material is added therein and mixing the first new material with the old asphalt mixture to obtain a reinforcing asphalt mixture, a first screed for spreading the reinforcing asphalt mixture over a remaining layer of the asphalt mixture layer left un-scarified by the scarifying means to form a coarse graded reinforcing layer having an elastic modulus greater than that of the remaining layer, a second adding means for adding the second new material stored at a temperature preventing re-aggregation and discharged out of the second tank over the coarse graded reinforcing layer, and a second screed for spreading the added second new material to form a new surface layer, an operation of the second screed being linked with an operation of the first screed.
The invention defined in claim 9 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in claim 8, further comprising a compacting means for compacting the coarse graded reinforcing layer formed over the remaining layer and the new surface layer formed over the coarse graded reinforcing layer together while heat still being stored.
The invention defined in claim 10 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claim 8 or 9, wherein the miller vehicle (B) further comprises a relaying receiving-discharging apparatus for receiving and discharging the first and the second new material carried in at different timings from outside the motor-driven vehicle system, and a new material conveying apparatus including at least 2 continuous conveying paths and having a switching apparatus for carrying the first and the second new material discharged from the relaying receiving-discharging apparatus respectively into the first and the second tank coincidentally with the different timings, wherein, when the first new material is carried from the relaying receiving-discharging apparatus to the first tank, the switching apparatus therein disconnects the at least 2 continuous conveying paths of the new material conveying apparatus to form a carry-in opening, and the first new material is carried into the first tank via the carry-in opening, wherein, when the second new material is carried from the relaying receiving-discharging apparatus into the second tank, the switching apparatus closes the carry-in opening formed in the new material conveying apparatus to form 1 conveying path by connecting the at least 2 conveying paths and the second new material is carried from the relaying receiving-discharging apparatus into the second tank via the 1 conveying path.
The invention defined in claim 11 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 10, wherein the first new material is any one of an aggregate or aggregate covered with asphalt having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer or an asphalt mixture having a particle size distribution including coarse aggregate mixed therein having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer.
The invention defined in claim 12 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 11, wherein the reinforcing asphalt mixture includes an aggregate having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer for about 5 to 35 weight % to the total weight.
The invention defined in claim 13 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 12, wherein the second new material is an asphalt mixture including an aggregate having a substantially same particle size distribution as that of an aggregate included in the asphalt mixture layer.
The invention defined in claim 14 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 13, wherein the mixer vehicle (C) further comprises a rejuvenating agent adding means for adding an asphalt rejuvenating agent when mixing the old asphalt mixture with the first new material added therein.
The invention defined in claim 15 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 14, wherein the mixer vehicle (C) further comprises a third tank for storing an asphalt emulsion for bonding the remaining layer and the coarse graded reinforcing layer or a material for enhancing water proof property and bonding property.
The invention defined in claim 16 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 15, wherein the mixer vehicle (C) further comprises a storing space, arranged between the mixing means and the first screed, for adjusting a supply volume of the reinforcing asphalt mixture onto the remaining layer.
The invention defined in claim 17 is a motor-driven vehicle system, in addition to the characteristics of the invention defined in any of claims 8 to 16, wherein the mixer vehicle (C) further comprises a storing space, arranged between the first screed and the second screed, for adjusting a supply volume of the second material onto the coarse graded reinforcing layer.
With reference to
The method can further comprise a step, prior to the scarifying step, for conveying the first new material and the second new material carried in at different timings from outside the motor-driven vehicle system to respective one of the storing apparatus coincidentally with the different timings (referred a new material carry-in step), a step for adding for adding an asphalt rejuvenating agent when mixing the old asphalt mixture with the first new material added therein (referred as a rejuvenating agent adding step), and a step for spreading an asphalt emulsion or a material for enhancing water proof property and bonding property onto the remaining layer to bond the remaining layer and the coarse graded reinforcing layer (referred as an inter-layer bonding step).
The pre-heater vehicle (A) is an apparatus operated by a driver controlling the vehicle, and its heating means is located between front wheels and rear wheels of the vehicle and faced against a road surface.
Thus, the pre-heater vehicle (A) can form a high-temperature combustion gas layer of about 550 to 750 degrees Celsius on a surface of road pavement as moving at a speed of about 2 to 5 m/min, keep a temperature at the surface of the pavement at about 230 to 260 degrees Celsius, allow heat to reach to a depth exceeding a boundary surface between a base layer and a surface layer of an asphalt mixture layer or to a depth of about 60 to 100 mm within the asphalt mixture layer which is equivalent to that depth and heat up the deepest portion to about 50 to 60 degrees Celsius without causing asphalt to catch fire. The heating and softening step of the present invention is thereby achieved to allow a scarifying means 340 of the later-described miller vehicle (B) scarify without damaging aggregates of the asphalt mixture layer and obtain an old asphalt mixture and achieve the scarifying step. The heating means is not limited to the one described above but can be any one having a similar feature.
The miller vehicle (B) is also an apparatus operated by a driver controlling the vehicle as shown in
Specific elements of the miller vehicle (B) will now be described with referring to
The scarifying means 340 comprises a set of rotary scarifyer (claw for scarifying pavement) including 2 grinding apparatuses 341 and 342 wherein at least 2 rotating axes rotates inwardly to each other driven by generally a hydraulic power and claws thereon are arranged spirally in a direction from the edges to the center with respect to the transverse direction of a paved road. The scarifying means 340 scarifies the heated and softened asphalt mixture layer 330 to a depth exceeding a boundary surface between a base layer and a surface layer or to a depth within the asphalt mixture layer 330 equivalent to that depth for obtaining the old asphalt mixture 331 formed like a ridge along a central part of the apparatus in the transverse direction with respect to the moving direction. The scarifying means 340 comprising 2 grinding apparatuses 341 and 342 may also be arranged in a vehicle in front (B1) of a combination of 2 vehicles (B1+B2) as illustrated in
Preferably, a heat insulating apparatus is provided with the first tank 320 for storing the first new material 310. The stored and pre-heated first new material 310 is conveyed from a discharging opening 322 of the first tank 320 by a fourth conveying apparatus 351 of the first adding means 350 which end is placed inside the first tank 320, and added to the old asphalt mixture 331.
Each of elements of the miller vehicle (B) when a later-described second new material 510 is carried in by another heavy truck 400B will now be described with referring to
The second new material 510 is thus carried through the conveying apparatus 450 into the second tank 520 provided on the mixer vehicle (C). As will be understood from
The mixer vehicle (C) is also an apparatus operated by a driver controlling the vehicle as shown in
The mixer vehicle (C) further comprises; a rejuvenating agent adding means 620 for adding an asphalt rejuvenating agent when mixing the old asphalt mixture 331 with the first new material 310 added therein, a third tank 630 for storing an asphalt emulsion for bonding the remaining layer 560 and the coarse graded reinforcing layer 570 or a material for enhancing water proof property and bonding property, a storing space 640 for adjusting a supply volume of the reinforcing asphalt mixture 540 onto the remaining layer 560, formed by walls provided on both sides between the mixing means 550 and the first screed 580, and a storing space 650 for adjusting a supply volume of the second new material 510 onto the coarse graded reinforcing layer 570, formed by walls provided on both sides between the first screed 580 and the second screed 610.
The first screed 580 and the second screed 610 of the mixer vehicle (C) generally not only spread respective one of the reinforcing asphalt mixture 540 and the second new material 510 as well as compact the materials. Thus, the compacting roller (D) may be used when necessary to compact more rigidly.
By linking the miller vehicle (B) and the mixer vehicle (C) each storing respective one of the first new material 310 and the second new material 510 with the pre-heater vehicle (A) and moving them together at a speed of about 2 to 5 m/min, heat is reached to a depth of about 60 to 100 mm within the asphalt mixture layer 330 and the deepest portion of the asphalt mixture layer 330 is heated up to about 50 to 60 degrees Celsius for accomplishing the heating and softening step of the present invention. And, by scarifying the asphalt mixture layer 330 by the scarifying means 340 without damaging or breaking aggregates mixed in the asphalt mixture layer 330 to obtain the old asphalt mixture 331, the scarifying step of the present invention is accomplished. The steps following the above steps of the present invention will be described below.
In the first adding step, the first new material 310 is added to the scarified old asphalt mixture. The first new material 310 needs to be any one of an aggregate or aggregate covered with asphalt having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer 330, or an asphalt mixture having a particle size distribution including coarse aggregate mixed therein having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer 330. The reinforcing asphalt mixture 540 created in the next mixing step needs to contain about 5 to 35 weight % of an aggregate having a greater diameter than the greatest diameter of an aggregate included in the asphalt mixture layer 330 to the total weight. Where a content of a coarse graded aggregate is less than 5 weight %, a load bearing capacity of a pavement greater than that obtainable by increasing a thickness of a pavement cannot be achieved. On the other hand, where a content of a coarse graded aggregate is more than 35 weight %, a particle size distribution of an asphalt mixture is deteriorated which makes forming a dense asphalt mixture layer difficult. Therefore, in the coarse graded reinforcing layer forming step which follows, spreading and compacting a reinforcing asphalt mixture over the remaining layer 560 of the asphalt mixture layer 330 allows forming a coarse graded reinforcing layer having an elastic modulus greater than that of the remaining layer 560 as described later, though the thickness of the layer is increased as the asphalt mixture layer 330 is reused. A repaved structure which a new surface layer is formed thereon is intended at Hot In-place Strengthening of pavement structure by forming a coarse graded reinforcing layer.
The above expected life span of the surface layer is a value obtained by dividing a number of wheel loads to fatigue failure (Nf) of the asphalt mixture by the yearly traffic volume, calculated as 3,000 vehicles/day·direction×365 days in this case of C-class traffic volume. A number of wheel loads to fatigue failure (Nf) can be calculated using a standard equation for calculating number of wheel loads to fatigue failure (Manual for Asphalt Pavement, Japan Road Association, December, 1992) as follows.
N
f=8.108×10(M-3)/εt3.291×E0.854 (Equation 1)
where, εt: tensile strain at the lower surface of an asphalt mixture layer, E: elastic modulus of an asphalt mixture (kgf/cm2), M: a function of porosity (Vv) and an amount of asphalt (Vb) of an asphalt mixture calculated as M=4.84×{[Vb/(Vv−Vb)]−0.69}.
Comparing the case in
The data obtained in experiments shown in
σb=M/Z=(PI/6)/(bd2/6)=PI/bd2[N/mm2] (Equation 2)
where; M: the maximum bending moment in a specimen, Z: a section modulus [mm3], p: the maximum load [N], I: a distance between lower supporting points [mm] (300 mm in the test), b: a section width of a specimen [mm] (100 mm in the test), d: a section height a specimen [mm] 100 mm in the test)
The test result confirmed that the elastic modulus used for the numerical analysis of the material characteristics and that obtained from the bending capacity test were similar. The “combined elastic modulus” was 3.395 N/mm2 for the conventional 2-layer model, whereas that for the 3-layer model including the coarse graded reinforcing layer was improved by 1.41 times to 4.796 N/mm2. The bending capacity of 2-layer model was 6.41 N/mm2 whereas that of 3-layer model was improved to 8.1 N/mm2 showing about 1.3 times reinforcing effect. Even when considering a reinforcing effect provided by a thickness increase, the test result still clearly shows the reinforcing effect of the method of the present invention.
The test was performed with the following protocol. The purpose is to confirm a reinforcing effect of a pavement structure constructed with the method of the present invention through laboratory experiments. A compressive strain and a tensile strain at a lower surface of an asphalt pavement under load before and after reinforcing were measured.
A mixture used for a test is a general mixture satisfying the standard values determined in “Handbook for road pavement construction” and “Marshall procedures for optimum asphalt content of dense graded paving mixtures,” a technical material of National Asphalt Pavement Association (NAPA). The table 1 shows the references.
In a test, load was applied with 3-point uniform loading by a test machine stipulated in the “JIS A 1106 Method of test for flexural strength of concrete,” and a compressive strain and a tensile strain were measured (refer to
A conventional pavement construction method and the method of the present invention were compared by comparing the maximum load at the moment of bending failure of asphalt pavements.
Elastic modulus of each layer was calculated by a reverse analysis of the GAMES using strain occurred at an upper surface and a lower surface of an asphalt pavement to confirm a difference in reinforcing effect of the conventional method and the method of the present invention.
Since the method of the present invention further includes a rejuvenating agent adding step wherein an asphalt rejuvenating agent is added when mixing the old asphalt mixture with the first new material added therein, and an inter-layer bonding step wherein the remaining layer and the coarse graded reinforcing layer are bonded using an asphalt emulsion or a material for enhancing water-proof property or a bonding property spread over the remaining layer in the coarse graded reinforcing layer forming step, the method can efficiently regenerate a deteriorated asphalt mixture and can minimize influence of damages or deterioration such as cracks in a depth exceeding the boundary surface between the base layer and the surface layer or in the remaining layer by applying the bonding agent between the remaining layer and the coarse graded reinforcing layer.
Also, since the coarse graded reinforcing layer and the new surface layer were compacted together while heat still being stored, the method can also engage the lower surface of the new surface layer and the upper surface of the coarse graded reinforcing layer together including the aggregates mixed in those layers without applying any bonding agent between the new surface layer and the coarse graded reinforcing layer, and can prevent an inter-layer displacement often caused by layer slippage due to a vertical strain.
The pavement specimens No. 1 to 4 in
A pavement reinforcing effect can be evaluated by a number of wheel loads to fatigue failure of a pavement specimen (also referred to as a number of permissible driving wheels). The number of wheel loads to fatigue failure of pavement specimen is a number of wheels necessary to a moment of a crack occurring on the specimen under a repeated application of wheel loads to the pavement surface, and is calculated using values of a tensile strain at a lower surface and a compressive strain at an upper surface of roadbed of an asphalt mixture of a pavement specimen under a 5-ton wheel loading as shown in
(1) A structural difference between the specimen No. 1 and No. 2 is that No. 2 had a coarse graded reinforcing layer that replaced a top portion of a base layer of No. 1. Since a displacement measured for No. 2 was smaller than that for No. 1, a coarse graded reinforcing layer improved a bearing capacity of a pavement when bearing capacity of roadbed and sub-base are same.
(2) The specimen No. 3 and No. 4 had a sub-base in half a thickness of respective one of the specimen No. 1 and No. 2. The purpose of reducing the thickness of the sub-base was to change bearing capacity at an upper surface of a roadbed of the same structure. The result shows a smaller displacement, i.e. a better bearing capacity provided by the coarse graded reinforcing layer, as in (1) above.
(3) As for changes in bearing capacity due to the decrease in the thickness of the sub-base, when a thickness of sub-base was decreased by 100 mm, the bearing capacity of the sub-base showed about 20% decrease, evaluated with equivalent thickness theory according to the TA method.
The graph on top of
(1) The higher value of tensile strain at a lower surface of an asphalt mixture layer shows that the asphalt mixture layer is more prone to cracking failure. Comparing the specimen No. 1 and No. 2, the tensile strain of No. 2 was about a half of that of No. 1 indicating that No. 2 was less prone to cracking failure.
(2) Comparing the specimen No. 2 and No. 4, although the thickness of sub-base of No. 4 was a half of 200 mm of No. 2, the value of the tensile strain was similar to that of No. 2. This indicates that even when a bearing capacity of a sub-base was reduced (estimated to be a 20% decrease in this case), a coarse graded reinforcing layer provided a load distribution to improve a resistance against cracking failure of an asphalt mixture.
The graph on bottom of
(1) The higher value of compressive strain at an upper surface of a roadbed shows that the pavement is more prone to deformation (rutting) caused by wheel loads. Comparing the specimen No. 1 and No. 2, No. 2 shows less compression of the whole pavement owing to a pavement thickness increase provided by the coarse graded reinforcing layer.
(2) Comparing the specimen No. 1 and No. 4, the total thickness pavement of No. 1 was slightly more than that of No. 4. No. 4 was provided with the coarse graded reinforcing layer though the thickness of the sub-base was reduced to 100 mm. The compressive strain measured at the upper surface of the roadbed of No. 4 was slightly smaller than that of No. 1 showing constraining of a compressive deformation provided by the coarse graded reinforcing layer.
The table in
(1) The number of wheel loads to fatigue failure for the specimen No. 2 provided with the coarse graded reinforcing layer is about 950,000 that is more than 6 times greater than that of the specimen No. 1. This indicates that the coarse graded reinforcing layer provided improvement durability of an asphalt pavement. As a result, the design traffic volume class of the specimen No. 2 is 1 class higher than that of No. 1.
(2) While the number of wheel loads to fatigue failure for the specimen No. 3 is about 50,000, the number of wheel loads to fatigue failure for the specimen No. 4 provided with the coarse graded reinforcing layer is about 250,000 that is about 5 times greater than that of the specimen No. 3.
This indicates that even when a bearing capacity of a sub-base was reduced due to the reduced thickness of the sub-base, a coarse graded reinforcing layer provided an improvement of durability of a road pavement.
Number | Date | Country | Kind |
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2007-292914 | Nov 2007 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2008/003292 | 11/12/2008 | WO | 00 | 8/24/2010 |