Mechanically Stabilised Semi-Rigid Pavements

Abstract

The present invention relates to a semi-rigid pavement comprising: an upper course comprising upper course aggregate and a hydrocarbon binder; a support layer comprising chemically-stabilised aggregate, the support layer located below the upper course; and a subgrade, the subgrade located below the support layer; wherein a geosynthetic is at least partially embedded in the chemically-stabilised aggregate that comprises the support layer.

Claims

1. A semi-rigid pavement comprising: an upper course comprising upper course aggregate and a hydrocarbon binder; a support layer comprising chemically-stabilised aggregate, the support layer located below the upper course; and a subgrade, the subgrade located below the support layer; wherein a geosynthetic is at least partially embedded in the chemically-stabilised aggregate that comprises the support layer.

2. The semi-rigid pavement of claim 1, wherein the semi-rigid pavement has two configurations: a first configuration wherein the support layer is monolithic, the support layer being chemically and mechanically stabilised; and a second configuration wherein the support layer is cracked, the support layer being mechanically stabilised.

3. The semi-rigid pavement of claim 1, further comprising a base course.

4. The semi-rigid pavement of claim 1, further comprising a layer of a granular fill.

5. The semi-rigid pavement of claim 1, wherein the geosynthetic is selected from geogrids, geotextiles, geonets, geocells, geocomposites, and combinations thereof.

6. The semi-rigid pavement of claim 5, wherein the geosynthetic comprises a geogrid or is a geogrid.

7. The semi-rigid pavement of claim 6, wherein the geogrid is a multiaxial geogrid, optionally the multiaxial geogrid is a triaxial geogrid or a geogrid with multiple geometries.

8. The semi-rigid pavement of claim 7, wherein the triaxial geogrid has one or more of the following properties: i. product weight of from 0.120 to 0.400 kg/m.sup.2, more preferably of from 0.150 to 0.350 kg/m.sup.2, most preferably of from 0.170 to 0.310 kg/m.sup.2, for example from 0.180 to 0.300 kg/m.sup.2; and/or ii. pitch of at least 30 mm, preferably of from 40 to 150 mm, more preferably of from 50 to 140, most preferably of from 65 to 125 mm; and/or iii. junction efficiency of at least 90% preferably at least 95%, more preferably of at least 97%, most preferably of at least 99%, for example of 100%.

9. The semi-rigid pavement of claim 7, wherein the geogrid with multiple geometries has one or more of the following properties: i. Apertures with triangular, trapezoidal, and hexagonal geometries; and/or ii. Pitch of at least 30 mm, preferably of from 40 to 150 mm, more preferably of from 50 to 140, most preferably of from 65 to 125 mm; and/or iii. Rib aspect ratio of at least 1, preferably, between 1 and 4; and/or iv. Minimum rib thickness of at least 3 mm, preferably at least 5 mm; and/or V. Where the geogrid has a solid inner layer and a two compressible outer layers, the two compressible outer layers are at least forty percent (40%) of the overall height of the geogrid, preferably at least seventy percent (70%).

10. The semi-rigid pavement of claim 6, wherein the geogrid has a multilayer structure, optionally wherein the geogrid has a solid inner layer and compressible outer layers.

11. The semi-rigid pavement of claim 1, wherein the geosynthetic is located at the base of the support layer.

12. The semi-rigid pavement of claim 1, wherein the chemically-stabilised aggregate comprises a biochemical binder, a polymeric binder, a hydrocarbon binder, lime, cement, or a combination thereof, optionally wherein the chemically stabilised aggregate comprises cement, optionally up to 10% by weight cement, further optionally from 0.1 to 8% by weight cement, optionally from 0.5 to 5% by weight cement, yet further optionally from 1 to 4% by weight cement, and still further optionally from 1.5 to 3% by weight cement.

13. The semi-rigid pavement of claim 1, wherein the chemically stabilised aggregate and/or the upper course aggregate comprise a continuously graded aggregate.

14. The semi-rigid pavement of claim 1, wherein the support layer has a thickness of from 50 to 400 mm, optionally of from 75 to 300 mm, further optionally from 100 to 200 mm, yet further optionally of about 150 mm.

15. The semi-rigid pavement of claim 1, wherein the upper course has a thickness of from 10 to 100 mm, optionally of from 25 to 75 mm, further optionally of about 50 mm.

16. A method of constructing a semi-rigid pavement, the method comprising: a) providing a geosynthetic above a subgrade; b) providing aggregate and binder over the geosynthetic such that the geosynthetic is at least partially embedded in the aggregate; c) setting the binder to form a support layer comprising chemically-stabilised aggregate; and d) providing an upper course comprising an upper course aggregate and a hydrocarbon binder above the support layer.

17. A method of constructing a semi-rigid pavement with an improved lifespan, the method comprising: a) at least partially embedding a geosynthetic within an aggregate and a binder; and b) setting the binder to form a support layer comprising chemically-stabilised aggregate, wherein the support layer is incorporated into the semi-rigid pavement during construction.

18. A method of constructing a semi-rigid pavement with a reduced thickness, the method comprising: a) at least partially embedding a geosynthetic within an aggregate and a binder; and b) setting the binder to form a support layer comprising chemically-stabilised aggregate, wherein the support layer is incorporated into the semi-rigid pavement during construction.

19. Use of a geosynthetic to increase the lifespan of a semi-rigid pavement, the use comprising at least partially embedding a geosynthetic within an aggregate that is chemically-stabilised with a binder and incorporating into the semi-rigid pavement.

20. Use of a geosynthetic to decrease the thickness of a semi-rigid pavement with a pre-determined lifespan, the use comprising at least partially embedding a geosynthetic within an aggregate that is chemically-stabilised with a binder and incorporating into the semi-rigid pavement.

21. A method of operating a semi-rigid pavement, the semi-rigid pavement comprising a subgrade, a support layer of chemically-stabilised aggregate above the subgrade, wherein a geosynthetic is at least partially embedded in the layer of chemically-stabilised aggregate, and an upper course above the chemically-stabilised aggregate, wherein the semi-rigid pavement is capable of exhibiting: a first operating mode wherein the support layer is substantially monolithic, the support layer being chemically and mechanically stabilised such that load applied to the upper course is transferred to the subgrade; and a second operating mode wherein the support layer is at least partially cracked, the support layer being mechanically stabilised such that load applied to the upper course is transferred to the subgrade; the method comprising permitting traffic to pass over the semi-rigid pavement in at least one of the first and second operating modes.

22. A method of designing a semi-rigid pavement for a location, the semi-rigid pavement comprising: an upper course comprising upper course aggregate and a hydrocarbon binder; a support layer comprising chemically-stabilised aggregate, the support layer located below the upper course; and a subgrade, the subgrade located below the support layer; wherein a geosynthetic is at least partially embedded in the chemically-stabilised aggregate that comprises the support layer: the method comprising: a) determining a target lifespan for the semi-rigid pavement; b) determining the properties of the subgrade present at the location; c) selecting the support layer of chemically-stabilised aggregate above the subgrade, wherein a geosynthetic is at least partially embedded in the layer of chemically-stabilised aggregate; d) selecting the upper course; e) predicting a predicted lifespan of the semi-rigid pavement comprising the subgrade, the selected support layer, and the selected upper course; f) comparing the predicted lifespan with the target lifespan; and g) repeating steps c) to f) if the predicted lifespan is less than the target lifespan.

23. The method of claim 22, wherein the semi-rigid pavement further comprises a base course and/or a granular fill and the method further comprises additional steps of selecting a base course and/or a granular fill.

24. A method of designing a semi-rigid pavement for a location, the method comprising: a) determining a target lifespan for the semi-rigid pavement; b) determining the properties of a subgrade present at the location; c) selecting a pre-designed semi-rigid pavement for the location, the pre-designed semi-rigid pavement comprising the subgrade, the selected support layer, and the selected upper course; d) predicting a predicted lifespan of the pre-designed semi-rigid pavement; e) comparing the predicted lifespan with the target lifespan; f) if the predicted lifespan is less than the target lifespan, at least partially embedding a geosynthetic in the support layer and repeating steps d) and e).

25. A method of maintaining a semi-rigid pavement, the semi-rigid pavement comprising: an upper course comprising upper course aggregate and a hydrocarbon binder; a support layer comprising chemically-stabilised aggregate, the support layer located below the upper course; and a subgrade, the subgrade located below the support layer; wherein a geosynthetic is at least partially embedded in the chemically-stabilised aggregate that comprises the support layer; the method comprising: a) determining acceptable values for one or more properties of the semi-rigid pavement; b) waiting a survey period; c) surveying the semi-rigid pavement and determining if the one or more properties of the semi-rigid pavement satisfy the acceptable values; d) undertaking maintenance if the one or more properties of the semi-rigid pavement do not satisfy the acceptable values; and e) repeating steps a) to d).

Description

DESCRIPTION OF THE DRAWINGS

[0192] FIG. 1 depicts a schematic cross-section of constructions tested in Example 1 described below. The left hand figure relates to the control construction, which comprises, from top to bottom, a 50 mm upper course (10), a 150 mm granular base (20), a 150 mm cement-stabilised subbase (30), and a 300 mm granular fill (40). The right hand figure relates to a construction according to the present invention, which comprises, from top to bottom, a 50 mm upper course (10), a 150 mm granular base (20), a 150 mm cement-stabilised subbase (30) including a geosynthetic (50) near its base, and a 300 mm granular fill (40). Below each construction would be an in situ subgrade, which has been compacted, but this is omitted from both figures for clarity.

[0193] FIG. 2 depicts a plan view of a Heavy Vehicle Simulator (HVS) test section used in Example 1. The left hand area (210) is of the construction according to the present invention, the right hand area (220) is of the control construction, and between these areas is a transition area (230), which is ignored for evaluation.

[0194] FIG. 3 is a graph showing an average rut depth per repetition for the testing undertaken in Example 1. The upper trace (310) relates to the control, while the lower trace (320) relates to a construction according to the present invention.

[0195] FIG. 4 is a graph showing a maximum rut depth per equivalent standard 80 kN axle loads (E80) for the testing undertaken in Example 1. The upper trace (410) relates to the control, while the lower trace (420) relates to a construction according to the present invention.

[0196] FIG. 5 is a graph showing the surface deformation per pass for the testing undertaken in Example 2. The left-hand trace (510) shows the deformation for a control construction, while the right-hand trace (520) shows the deformation for a construction additionally comprising a geogrid.

EXAMPLES

[0197] Materials specified herein (e.g. G5, G9) are specified as per COTO (2020) technical specifications.

Example 1Full Scale Trafficking Testing

Test Pavement Design

[0198] A schematic of the test bed is shown in FIG. 1. The control pavement comprised a 50 mm upper course of continuously graded asphalt (Class A), a 150 mm granular base of graded crushed stone (Class G1), a 150 mm cement-stabilised subbase (Class C3), and a 300 mm granular fill comprised of a 150 mm layer of gravel soil (Class G5) over a 150 mm layer of gravel soil (G9). In the geogrid containing pavement, a 20 m length of InterAx geogrid was incorporated into the cement-stabilised subbase. An 8 m HVS test section was designated (see FIG. 2), the test section centred on the transition point between the control pavement and test pavement.

Test Pavement Construction

[0199] A test bed with a length of 30 m and a width of 4.5 m was excavated to the required depth and the existing subgrade compacted.

[0200] A layer of G9 material was deposited and compacted to a depth of 150 mm, followed by a layer of G5 material being deposited and compacted to a depth of 150 mm. Taken together, these layers form the 300 mm granular fill depicted in FIG. 1.

[0201] A 20 m length of InterAx NX750 geogrid was placed at one end of the test bed. The InterAx NX750 geogrid comprises multiple aperture geometries including hexagons, trapezoids, and triangles, as is described in WO 2021/262958 A1, with the ribs being three layers of coextruded polypropylene the outer two layers being foamed, as is described in WO 2022/182411 A1. The ribs are rectangular and have a pitch of 80 mm and an aspect ratio of >1.0. G5B material was then deposited along the entire length of the test bed, and treated with cement at a loading of 2 wt %, and compacted to a depth of 150 mm to form the C3 subbase.

[0202] A layer of G1 material was deposited and compacted to a depth of 150 mm, followed by deposition of 50 mm of continuously graded asphalt.

Heavy Vehicle Simulator Test

[0203] The following HVS dual wheel load applications were applied to the control pavement and geogrid containing pavement simultaneously, using a constant tyre pressure of 740 kPa: [0204] 135,282 repetitions of a 40 kN dual wheel load (simulating a standard 80 kN axle load); [0205] 245,056 repetitions of a 60 kN dual wheel load (simulating a 120 kN axle load); [0206] 171,507 repetitions of a 80 kN dual wheel load in the dry condition (simulating a 160 kN axle load); and [0207] 512,979 repetitions of a 80 kN dual wheel load in the wet condition (simulating a 160 KN axle load).

[0208] The total number of repetitions applied to the test bed is 1,030,523. This equates to approximately 14 million equivalent standard 80 kN axle loads (E80) (using a damage coefficient of 4.2).

[0209] A Wireless Laser Profilometer was used to measure the surface permanent deformation/total rut depth. During HVS testing, profilometer readings are typically measured at 0.5 m intervals along a portion of the 8 m HVS test section, and at intervals of 1 cm across the HVS test section. The maximum permanent deformation/total rut depth values as well as the average maximum values of the surface permanent deformation at each point are calculated from this data.

[0210] The variation in average rut depth per repetition (i.e. the average rut depth recorded for each pavement on a given repetition) is shown in FIG. 3. It can be seen that there is a small improvement for the geogrid-containing pavement including the geogrid compared to the control pavement in the early testing under dry conditions. Under wet conditions, from around 750,000 repetitions onwards, this improvement increases dramatically and by the end of the testing the control pavement had an average rut depth of 20 mm while the geogrid-containing pavement had an average rut depth of only 10.9 mm.

[0211] The variation in maximum rut depth per E80 is shown in FIG. 4. Again, it can be seen that there is a small improvement for the geogrid-containing pavement under dry conditions, which becomes more evident under the more challenging wet conditions. By the end of the testing, the control pavement had a maximum rut depth of 23.9 mm, compared to 13 mm for the geogrid-containing pavement. The control pavement reached the maximum acceptable rut depth of 20 mm at around 1,240,000 million E80s. The geogrid containing pavement did not reach the maximum acceptable rut depth, even after 14,000,000 E80s.

[0212] Overall, inclusion of the geogrid in the cement-treated subbase lead to an almost 100% improvement in performance.

[0213] The main mode of failure was rutting in the granular base layer due to the aggressive trafficking combined with in-depth water addition and the cracking of the cement-stabilised layer that reduced the support to the base. No cracking was observed in the upper course. Without wishing to be bound by any particular theorem, it is reasonable to conclude that the geogrid is improving the properties of the cement-stabilised layer both before and after cracking of this layer. The maximum rutting on the geogrid section was about half of that of the control section, indicating that the expected life of the pavement structure when the geogrid is included in the cement-stabilised layer is potentially at least double that of the equivalent structure without a geogrid. Alternatively, incorporation of a geogrid in the cement stabilised layer could permit a reduction in the thickness of the layer, or other layers in the construction, while achieving the same lifetime.

Example 2Small Scale Trafficking Testing

[0214] The performance of a chemically-stabilised support layer containing a geosynthetic for resisting rutting due to vehicle traffic was evaluated using a small scale trafficking test. Such tests, such as the one described in Webster, S. L.; Geogrid Reinforced Base Course for Flexible Pavements for Light Aircraft: Test Section Construction, Behavior Under Traffic, Laboratory Tests, and Design Criterial, Report DOT/FAA/RD-92, December 1992, are well established in the field of pavement design for determining the performance of pavements. The small scale test was designed to reproduce the results of the full scale trafficking test in terms of the differences between the support layers containing geosynthetics and those without geosynthetics, without requiring the extensive time and material commitments of the full scale testing. In other words, it is the relative difference in performance that is important, not the absolute difference.

[0215] In general, a test section consisting of an underlying clay subgrade and a support layer of chemically-stabilised aggregate geogrid, the latter optionally containing a geosynthetic. The test section is subjected to the load of a single weighted wheel. The wheel traverses the test section along a single horizontal path, constantly reversing direction from one end of the test section to the other until failure of the test section. The surface deformation (i.e. rutting) of the test section is monitored throughout. A control test with no geogrid present will fail rapidly under such testing.

[0216] A control test was performed using a cement-stabilised layer with a thickness of 65 mm over a normal clay subgrade with a thickness of 75 mm. The clay subgrade was a brown slightly sandy clay developed for trafficking testing. The clay has a typical California Bearing Ratio (CBR) measurement of 0.5% when measured with a MEXE CBR probe, an undrained shear strength of 19 kPa when measured with a hand shear vane and a typical moisture content of 32% when measured to BS EN ISO 17892-1:2014. The cement-stabilised layer used 0-10 mm graded aggregate with 3 wt % cement, which was compacted and allowed to cure for 5 days. The single weighted wheel with a contact area of 100 cm.sup.2 was loaded to provide a force of 4 kN and an applied pressure of approximately 400 kPa. After 29 passes, the surface deformation of the control exceeded 50 mm and was judged to have failed.

[0217] The test was repeated, with the addition of an NX750 geogrid (a geogrid comprising multiple geometries as described herein) embedded in the base of the cement-stabilised layer. After 56 passes, the surface deformation of the geogrid-containing test bed exceed 50 mm and was judged to have failed.

[0218] The results are illustrated graphically in FIG. 5, which shows that the inclusion of the geogrid in the chemically-stabilised layer nearly doubles the lifetime under the test conditions used.