FIELD OF THE INVENTION The present invention relates to a method to structurally design a pavement based on soil stabilization and roller compacted concrete (RCC). Particularly, the present invention relates to a method to build a stable, durable pavement based on RCC in soils with high groundwater level. Furthermore, the final road has a dynamic load on single wheel between 2.5 kN and 400 kIM.

BACKGROUND OF THE INVENTION

Soil stabilization is a technique that combines mechanical, physical and/or chemical methods to improve soil properties to make it suitable for a specific engineering function. Such properties may be, for example, its strength, bearing and resistance to natural and/or man made environments, firmness, compressibility, decrease permeability or volume steadiness. After being stabilized, the soil has a bigger load-carrying capacity and resists better to physical and chemical stress and, consequently, so does the structure that is built. The stabilization may occur with the use of admixtures - that act as densifiers and/or waterproof agents -, as well as without, for example, by thermal and electrokinetic methods, vitrification, electroosmosis or by simple preparation of soil-aggregate and further compaction. Soil stabilization can be used to steady the ground before a pavement is placed, in the cases when the level of ground water is close to the surface level and/or in places with heavy precipitation levels and/or in soils with high content in clay. Therefore, the soil stabilization technique allows constructions to be built in places where, before its application, it was impossible to construct, due to the intrinsic characteristics of the soil.

Naturally, the specificities of the stabilization process will depend on the natural characteristics of the soil, as well as the requirements of the specific project in hands, in terms of mechanical strength needed or the environment involving the project. No document of the state-of-the-art has so far disclosed a method to structurally design a pavement based on soil stabilization and roller compacted concrete where said structural design is based on engineered layers that allow for the best performance of the pavement being built.

CN 102493308 discloses a bio-enzyme modified roller compacted concrete road engineering construction technology, where the bio-enzyme acts as curing agent, said technology providing good soil stabilization.

DESCRIPTION OF THE INVENTION The present invention provides a method to build a road, comprising the steps of:

(a) excavating and removing the top layer of the soil, to a max depth Y located between the natural surface and the X ₃ layer, where Y is equal to or larger than X ₂ + Xi, whereas X ₂ ranges from 5 to 40 cm and X-i ranges from 1 to 20 cm,

(b) removing the material of X ₃ layer, comprising X3' and X3", wherein part of the removed material is mechanically, physically and/or chemically treated and placed back in its original location to reach a thickness X3" with dimensions located between 2 to 30 cm and filling the remaining depth between X3" and the level defined by natural soil level minus the distance Y by a material selected from the group consisting of compacted gravel, aggregates and sand or a combination thereof, over a X3' distance located between 5 and 100 cm, obtaining a stabilized X ₃ layer with a thickness ranging from 7 to 130 cm, wherein the top surface of stabilized X ₃ layer remains at a distance Y from the natural surface and

(c) placing a concrete to reach at least a thickness X ₂ , on top of the stabilized X ₃ layer, herewith method of the invention. The methodology according to the present invention enables to produce a stable, durable Roller Compacted Concrete (RCC) based pavement in a soil with high water level or great clay content. Particularly, it allows for the use of the RCC based on typical zero slump concrete. . The final road built according to this method has a dynamic load on single wheel between 2.5 kN for a car and 400 kN for a full overloaded truck, according to EUROCODE 1 and AASHTO.

The solid stabilization step in the present invention is made by excavating and removing a top layer of the soil and modifying the mechanical and physical properties of the revealed layer by scarifying said layer. Also, a stabilizing agent may be added to the scarified soil. On top of the scarified soil, a layer of sand, gravel, aggregates or a combination of said materials may be added.

Common equipment for excavating and removing the soil may be used, such as excavators, bulldozers, trailer scrapers, semitrailer scrapers, self-propelled scrapers, graders or autograders.

Common methods to scarify the soil may be used. Such methods comprise, for example, disc trenching. This technique comprises a pair of powered mattock wheels, which go up and down as the machine moves forward.

Another embodiment is the method of the invention, wherein the concrete layer of step (c) has a thickness equal to the dimension Y. Another embodiment is the method of the invention, wherein an asphalt layer X1 with thickness from 1 to 20 cm is placed on top of the concrete layer X2, being X1 plus X2 equal to Y.

Another embodiment is the method of the invention, wherein in step (b), a further component is added to the material selected from the group consisting of compacted gravel, aggregates and sand or a combination thereof, wherein said further component is selected from the group consisting of water, cement, lime, fly ash, calcium chloride, cement kiln dust, lime kiln dust, sodium silicate, potassium silicate and a polymer or a combination thereof. Another embodiment is the method of the invention, wherein said polymer is a polymer derived from a vinyl, acryl or latex monomer.

Another embodiment is the method of the invention, wherein said polymer is added in a concentration from 0.05% w/w to 2% w/w.

Another embodiment is the method of the invention, wherein the cement added as further components is a cement containing from 0 to 100% of Ordinary Portland Clinker, in concentrations ranging from 0.5 and 10% in weight with respect to the dry soil. In step (c), the added concrete may have a zero-slump consistency in the fresh state. The VEBE time is influenced by the consistency of the concrete of the method of the invention. VEBE values should range from V0 to V2 according to European Standard EN 12350- 3:2009. A concrete suitable for step (c) of the method of the invention has a minimum initial paste volume with fillers (cement, water, fines) of at least 100 l/m ³ . Hence, another embodiment is the method of the invention, wherein the concrete used in step c) has a zero-slump consistency in the fresh state and VEBE values ranging from V0 to V2 and containing at least a volume of cementitious paste of 100 liters/m ³ .

Another embodiment is the method of the invention, wherein the concrete used in step (c) is pervious concrete, having an open porosity between 12 and 30% in volume and containing between 80 and 250 liters/m ³ of cement paste.

Another embodiment is the method of the invention, wherein the concrete used in step c) is pelletized concrete, characterized in that it has compressive strength between 30 MPa and 200 MPa, is applied on the concrete layer (layer X ₂ ) to provide with a layer X-i with a thickness in a distance between 1 cm to 20 cm, preferably between 3 cm and 10 cm.

Another embodiment is the method of the invention, wherein a supplementary layer of high performance concrete is placed on top of the asphalt layer X-i , whereas the final layer Xi has a thickness between 1 cm and 20 cm.

In the present application, "high performance concrete" means concrete that conforms to a set of standards above those of the most common applications. Some of the properties that may be required include: ease of placement, compaction without segregation, early age strength, long-term mechanical properties, permeability, density, heat of hydration, toughness, volume stability, long life in severe environments, resistance to chemical attack, toughness and impact resistance, volume stability and inhibition of bacterial and mold growth. Compressive strength is in the range of 50-200 MPa. High-performance concretes are made with carefully selected high-quality ingredients and optimized mixture designs; these are batched, mixed, placed, compacted and cured to the highest industry standards. Typically, such concretes will have a low water-cementing materials ratio of 0.20 to 0.45. Plasticizers are usually used to make these concretes fluid and workable. High-performance concrete almost always has a higher strength than normal concrete. However, strength is not always the primary required property. For example, a normal strength concrete with very high durability and very low permeability is considered to have high performance properties.

Another embodiment is the method of the invention, wherein in step (c) bituminous emulsion is applied on the X-i layer and the X-i distance is from 0.01 mm to 10 mm.

Another embodiment is the method of the invention, wherein the concrete used in step (c) is compacted after placement by means of rolling equipment. This rolling equipment is typically a roller, which compacts asphalt or concrete, but also soil or gravel during the construction of infrastructure using those said materials.

The concrete in step (c) is typically placed using a paver, that is a piece of equipment used to lay asphalt or zero-slump concrete on the sub-base when a pavement, road, bridge, parking lot or other such infrastructure is being built. Pavers lay the asphalt or concrete flat and provides minor compaction before the roller.

Pelletized concrete as described in document PCT/EP2014/057144 may be used in the method of the invention.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 . Soil diagram, showing layers X1 , X2 and X3.

Figure 2. Diagram of the road used in Example 1. Figure 3. Grain size of soil used in Example 3. Figure 4. Results of compressive strength at 7 days in Example 3. Figure 5. Results of compressive strength at 7 days in Example 3.2. Figure 6. Grain size of soil used in Example 4.

Figure 7. Results of compressive strength at 7 days in Example 4.1. Figure 8. Permeability results in Example 4.2.

Figure 9. Results of abrasion at 7 days in Example 4.3.

EXAMPLES OF THE INVENTION

Example 1 In this example the following steps were carried out:

1. Removing soil to a depth of 15 cm; putting that soil aside

2. Removing extra soil to a depth of 20 cm, therefore the total depth of soil removed in both steps 1 and 2 was 35 cm.

3. Treating the soil removed in step 2 with soil stabilization admixtures. Two types of treatment being used: soil cement alone and soil cement together with a latex-based polymer.

4. Applying again the treated soil from step 3 - this corresponding to layer X ₃ " in Figure 1. This layer having a depth of 20 cm.

5. Applying a 15 cm layer of Roller Compacted Concrete on top of the stabilized soil. This RCC layer corresponding to layer X ₂ in Figure 1.

6. Compacting said RCC surface.

The method of the invention has been applied on a segment of a 28 km rural road. The total length of the segment where the test was carried out was 100 meters. The type of soil was clayey.

Fig. 2 is a drawing representative of this example. The total area was 700 m ² .

Soil cement was applied on an area of 50x7m (350 m ² ). Cement Dosage: 14.28 Kg/m ² , 3% wt of dry soil treated. Soil cement + Latex based polymer was applied on an area of 50x7m (350 m ² ). Latex based polymer 1 dosage: 0.33 L/m ² , diluted in water with a ratio Polymenwater = 1 :1 Rest of parameters were:

Thickness of the treated soil: 20 cm

Soil Optimal humidity: 27%

Humidity before applying cement: 30.02%, 34.0%, 32.8%

Humidity after applying cement: 28.6%, 28.8%

Compaction was 95% on soil cement area and 95.5% on Soil Cement + Latex based Polymer area.

Solidification and impermeable protection was observed by visual Inspection.

After the soil has been stabilized as described above, it was reapplied on the road. On top of this layer, Roller Compacted Concrete was applied. The mix design for this RCC was:

A roller compacted the applied concrete to finish the job. The road produced had a maximum dynamic load on single wheel around 50 kN, ideal for a rural road.

Example 2 In this example the following steps were carried out: 1. Removing old layer soil

2. Preparing a new layer of soil

3. Spraying stabilization admixtures

4. Apply a RCC layer

5. Compacting

6. Final surface

The depth of the layers removed follow the next table:

Description of the soil of this example:

Type of soil: limestone

Optimal moisture content: about 7 %

Max. unit weight: 21.52 kN/m ³

Bulk density dry soil: 1454 kg/m ³

Table 1. Realistic Humidity

After final

Type Before After application

compaction admixtures application (Monday)

(Thursday)

Styrene Acrylic

8.3 8.4 8.9 Polymer 1

Humidity [%]

Latex Based

8.3 8.5 8.7 Polymer 1

Table 2. CBR test

Type Humidity before Humidity during CBR - 2.5 mm CBR - 5.0 mm admixtures compact [%] test [%] [%] [%]

None 4.7 1 .9 322 > 360

Styrene Acrylic

5.2 2.2 222 251 Polymer 1

Latex-based 5.7 2.4 195 246 Polymer 1

CBR stands for "California bearing ratio", a test developed to evaluate the mechanical strength of road subgrades and basecourses. The test was developed to measure the load- bearing capacity of soils used for building roads.

Characteristics of the admixtures:

Styrene Acrylic Polymer 1

Density: 1050 kg/m ³

Dosage: 0.17 l/m ² (thickness 100 mm)

Quantity for test: 17.21 I (18.07 kg)

Mixing with water: 1 :3 (RD 332 : water)

Overall quantity for test: 68.84 I Latex-based Polymer 1

Density: 1090 kg/m ³

Dosage: 0.17 l/m ² (thickness 100 mm)

Quantity for test: 17.21 I (18.76 kg)

Mixing with water: 1 :3 (RD 332 : water)

Overall quantity for test: 68.84 I

Mix design of the applied RCC:

A roller finished the job. Example 3. This example was carried out to understand how different admixtures used in the treatment of the soil influence the final properties. The test methods A, B and C mentioned correspond to the test methods mentioned by the ASTM D698 method.

Table 3. Characterization of the Soil

Grain size of soil is shown in Fig. 3.

Table 4. Summary of this example

The test methods A, B and C mentioned correspond to the test methods mentioned by th ASTM D698 method.

Example 3.1.

Table 5. Equipment

Big Hobart (mixer for mortar)

Manual Marshall hammer

Table 6. Type of admixtures used

1 Latex-based polymer 1

2 Styrene Acrylic based polymer 1 3 Latex-based polymer 2

4 Latex-based polymer 3

5 Vinyl-based polymer 1

6 Vinyl-based polymer 2

Compressive strength at 7 days is shown in Fig. 4.

Table 7. Equipment

Big Hobart (mixer for mortar)

HILTI vibration hammer

Different curings were used:

1. Oven at 40°C

2. Curing chamber - 35°C, 50% humidity

Table 8

Compressive strength at 7 days is shown in Fig. 5. Example 4. This example was carried out to understand how different admixtures used in the treatment of the soil influence the final properties. The test methods A, B and C mentioned correspond to the test methods mentioned by the ASTM D698 method.

Table 9. Details of the soil used

Classification of soil ASTM D2487-1 1

Liquid Limit ASTM D4318-10

Plastic Limit ASTM D4318-10 Plasticity Index ASTM D4318-10

Table 10. Summary of this example

After drying in oven (max 60°C according to standard) has 3.5% soil humidity. Optimal water to be added is 1 1.0%.

Table 12

Table 13. Curing chamber Temperature 35°C

Humidity 50%

Example 4.1

Compressive strength at 7 days is shown in Fig. 7.

Example 4.2

Permeability at 7 days is shown in Fig. 8. Example 4.3

Abrasion at 7 days is shown in Fig. 9. Example 5.

In this example, a table is shown with possible depths for each of the layers depicted in Figure 1 for three roads: two highways, one built on a soil comprising clay and sand and the other on a sandy + gravel soil, both with a maximum dynamic load on single wheel of 300 kN and one national road, with a maximum dynamic load on single wheel of 150 kN:

In the next table, one may see the mix design for the RCC used in each of these examples:

Material Unit 1 2 3

Cement kg/m3 250 400 250

Fly ash % on cem 20 - 20