AU2016203551A1

AU2016203551A1 - Flexible pavement structure for streets and highways consisting of a stabilized lower base and a low thickness upper surface course

Info

Publication number: AU2016203551A1
Application number: AU2016203551A
Authority: AU
Inventors: Guzmán Jara Carlos Rodolfo
Original assignee: Proes S A
Current assignee: PROES SA
Priority date: 2009-08-05
Filing date: 2016-05-30
Publication date: 2016-06-16
Also published as: WO2011014975A1; AU2009350901A1; ECSP12011705A; BR112012002659A2; MX2012001594A

Abstract

A pavement structure to be preferably used in roads exposed to high traffic loads, wherein such structure comprises at least two layers: a first lower or base layer that provides all or almost all the pavement structure through CBR > 100% and Compressive Strength > 20 Kg/cm2, which corresponds to a layer consisting of the originally existing soil that is treated through a physical chemical stabilization process; and a second upper layer, corresponding to a low thickness asphalt surface course or other having a flexible behavior, which may have low or no contribution of structure. C'.4 wL

Description

FLEXIBLE PAVEMENT STRUCTURE FOR STREETS AND HIGHWAYS CONSISTING OF A STABILIZED LOWER BASE AND A LOW THICKNESS UPPER SURFACE COURSE

DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION

This invention refers to a pavement structure having improved stability, strength, and impermeability characteristics, wherein such structure consists of two layers, a lower or base layer, which bears the most significant traffic loads due to its physical-chemical structure; and a low thickness upper layer or surface course, intended to bear abrasive action of traffic.

The pavement structure of the invention is mostly used in both public and private high load roads, as well as in industrial yards and warehouses. Its advantages in terms of cost and environmental sustainability make it useful in mining, forest, and electric project roads, which could not be paved at a reasonable price until now.

BACKGROUND OF THE INVENTION

Traditional asphalt roads are designed to withstand traffic loads in each of the layers that make it up, and particularly in upper layers, a situation implying the need of having higher thickness asphalt surface courses, with the resulting consequences in paving costs.

This invention is based on the increased capacity of road gradient support using the material already existing in the soil to which solid and liquid elements are added, so that a relatively weak soil improves its stability, strength and impermeability characteristics as a result of chemical type reactions.

Road base or gradient thus stabilized can absorb a significant part of traffic loads, due to which asphalt surface course requirements are exclusively reduced to low thickness layers mainly intended to withstand abrasive action of traffic.

Shear strength is the main relevant load withstood by the soil (Π). The equation ruling this type of loads is: τ = C+σ Tg φ where C is the shear strength component given by cohesion capacity of soil particles; and where aTgij) is the shear strength component given by physical characteristics of the soil, that is, friction coefficient between particles, granulometry, and density.

In consequence, to obtain proper stabilization of a specific soil, this must be treated through physical-chemical reactions adding both solid and liquid additives that modify physical characteristics of the soil, such as, granulometry, electric charges, and others, in order to increase thus its capacity to withstand shear strengths.

Available soils do not usually meet quality requirements on their own to be used as bases or gradients. The process used to improve the soil in order to meet established requirements is called “Stabilization”. In general terms, stabilization has been restricted to a single aspect of soil improvement: replacement of improper quality material with a different specially prepared material.

Mechanic stabilization consists of improving soil properties through changes in its graduation that can be obtained using mixtures of two or more soils, adding some specific fraction, or totally or partially removing any size through screening. This stabilization method is traditionally used in a flexible pavement design. Disadvantages of this kind of stabilization are connected to aggregate quality and availability. Good quality aggregate is often very distant from the worksite, dramatically increasing the cost of this material.

Many prior art patent publications have suggested the possibility of stabilizing soils using chemical additives, such as, the Japanese patent JP2001187885 that raises the problem of providing a cement base for soil stabilization using small solid and liquid separations, strongly dispersed and cured in short time, even when injected into the water, obtaining thus a high strength cured product and generating a consolidated and high volume earth body; stabilizing thus the solid by means of the chemical. The solution provides a chemical liquid cement base for soil stabilization with a viscosity exceeding 900 cP that is obtained adding a water-soluble polymer and stabilizing foam to each content of mostly liquid hydraulic cement, with a hardened content of hardening liquid, adjusting its viscosity greater than or equal to 900 cP and mixing them.

In addition, US patent application 2002152933 describes a composition for soil treatment and stabilization, the preparation method thereof, and use of such preparation, wherein the composition comprises a calcium-based powder solid with a particle size lower than 2 mm. The composition also includes a fluid agent that increases particle binding.

On the other hand, patent application CL 2590-2005 describes a chemical stabilization process for soils existing in the gradient or surface of a determined road or terrain, wherein one of its stages consists of adding a solid additive to a soil volume, and preparing a pre-mixture either simultaneously or afterwards with a liquid additive, which is made up by hydrocarbons and sulphates that are previously diluted in water with an acid pH in order to be subsequently applied. When additives and soils are mixed, the soil increases its support and impermeability capacity, improving thus its structural capacity.

The basic difference of above mentioned prior art documents, as well as any others that may be found in the literature, consists of the fact that the invention discloses a pavement structure made up by two layers, wherein the lower layer has been designed to provide optimum stability, strength, and impermeability conditions, in order to withstand highest loads of the road, with which the upper layer becomes a low thickness surface course that may be easily repaired at low cost, mostly intended to withstand loads connected to abrasion.

DESCRIPTION OF THE FIGURES

Figure 1 shows a prior art pavement structure cut.

Figure 2 shows a pavement structure cut of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In reference to figure 1, which shows a prior art traditional type pavement structure, it is possible to observe that it consists of a granular base (2) usually prepared through a change of graduation of the existing soil that may be obtained using soil mixtures and/or a change in granulation size through sieving. This kind of granular base usually has a support capacity (CBR) higher than or equal to 80%. In order to improve support capacity of the structure as a whole in this kind of pavements, it is necessary to use a surface asphalt layer of a significant thickness (1), substantially increasing manufacture costs.

On the other hand, figure 2 shows the pavement structure of the invention, preferably used in roads and streets for any use that are exposed to high traffic loads and industrial use It can be seen that such structure comprises at least two layers. The first layer is the lower or base layer (4), having a support capacity higher than or equal to 100% (CBR>100%) and/or a Compressive Strength > 20 Kg/cm2, corresponding to a layer that is made up from the originally existing soil, which is treated through a physical-chemical stabilization process. This first or base layer practically withstands all the loads to which the road is subject, and for being chemically stabilized, it has a thickness lower than the equivalent layer in a traditional type road. The second layer is an upper layer (3), corresponding to an asphalt surface course, notoriously lower than the upper asphalt layer of a prior art traditional road, which provides practically no support capacity to the pavement structure.

Figure 1 clearly shows that road loads are absorbed on a comparable basis both by the upper layer and the lower layer, a situation totally opposed to such observed in Figure 2, where the upper layer does not absorb any load, and loads are then completely assumed by the lower layer.

In this invention, the first lower or base layer consists of the soil originally existing in the ground where the road is to be built, a portion of solid additives, and a portion of liquid additives. Such portion of solid additives corresponds to hydroxides, silicates, carbonates, clays and/or chlorides, which are either jointly or separately added to the originally existing soil. In addition, the portion of liquid additives consists of hydrocarbons and sulphates diluted in water, which are added to the originally existing soil and to such portion of solid additives.

In order to determine proper volumes and portions of solid and liquid additives to be added to the existing soil in the ground where the road is to be built, it is necessary to conduct a physical analysis of the solid allowing establishing characteristics, such as, size, shape, consistency limits, density, specific weight, and volume of the fine portion of the soil. In addition, mineralogical structure of the fine part of the soil is analyzed (under mesh 40) through X ray diffraction tests that determine electric constitution of the existing soil, and particularly, the polarity of the fine portion thereof through the analysis of the minerals that make it up. Then, taking into consideration the goal consisting of reaching high levels of CBR support and compressive strength in the base layer, amounts and compositions of such additives to be added to the soil are determined. Particularly, the solid additive is present in such a volume and composition that it allows neutralizing electric charges of the existing soil, and liquid additive is added in an amount determined by maximum dry granulometry and density of the mixture that favors the ionization process of fine components.

Considering the lower or base layer structure and the support capacity obtained through the addition of both solid and liquid additives, it is possible to design the road so that the upper or asphalt layer has a minimum thickness to withstand loads caused by abrasion.

In addition, the construction process includes a third intermediate layer consisting of a priming or tack coat, preferably a water-diluted slow breaking anionic type emulsion, which only allows bonding such first lower or base layer to such second upper layer or surface course, and is usually an asphalt composition highly diluted in a determined solvent.

Design of the pavement structure of this invention considers that the first lower or base layer has a thickness ranging from 150 to 450 mm. On the other hand, the second upper layer or asphalt surface course has a thickness ranging from 3 to 50 mm.

In some cases, for example, where there are relevant static loads or when asphalt is scarce or too expensive for specific industrial uses, the asphalt layer may be replaced with solutions, such as, adocrete, special polyurethane paints, or other elements having a flexible behavior.

Several field developed experiences have given rise to the preferred modalities of this invention, which illustrate embodiments, which shall in no case be deemed to limit the scope of protection. This invention has thus been tested where the soil receiving the physical-chemical stabilization treatment for implementation of the first layer of the pavement structure of the invention corresponded to the soil existing in the ground (or mixtures of the existing soil with any other material), having a maximum size of 2", mean plasticity (IP higher than 1% and lower than 12%; LL < 40%), Tyler mesh No. 200 must be higher than 10% and lower than 22%, and CBR > 20%. In soils having these characteristics, a pavement structure has been obtained wherein the base layer has a thickness ranging from 150 to 300 mm, and the upper asphalt layer has a maximum thickness of 40 mm.

On the other hand, table 1 below shows the results of the application of the invention in different soils with different support capacities.

Claims

1. A flexible pavement structure preferably used in roads and streets for any use exposed to high traffic loads and, more preferably, in industrial type roads and streets, WHEREIN such structure comprises at least two layers; a first lower or base layer that essentially provides all the support capacity, being such support capacity given by a parameter CBR 5 100% and/or Compressive Strength > 20 Kg/cm2, wherein such base corresponds to a layer made up by the originally existing soil, treated by a physical-chemical stabilization process; and a second upper layer, corresponding to a low thickness asphalt surface course that provides essentially no support capacity.

2. A pavement structure according to Claim 1, WHEREIN such pavement structure comprises a third intermediate priming layer or tack coat, only allowing bonding of such first lower or base layer to such second upper layer or surface course.

3. A pavement structure according to the above mentioned Claims, WHEREIN such first lower or base layer is made up by the originally existing soil, plus a portion of solid additives and a portion of liquid additives.

4. A pavement structure according to the above mentioned Claims, WHEREIN the originally existing soil optionally includes other soils to obtain a mixture meeting a maximum size of 2”, mean plasticity (IP higher than 1% and lower than 12%; LL < 40%), and Tyler mesh No. 200, higher than 10% and lower than 22%, and CBR > 20%.

5. A pavement structure according to Claims 3 and 4, WHEREIN such portion of solid additives corresponds to hydroxides, silicates, carbonates, clays and/or chlorides, which are added either jointly or separately to the originally existing soil and are present in a certain volume and composition to neutralize the electric charge of the fine portion of such existing soil.

6. A pavement structure according to Claims 3, 4 and 5, WHEREIN such portion of liquid additives consists of water-diluted hydrocarbons and sulphates, which are added to the originally existing soil and to such portion of solid additives, and are present in a usually constant amount.

7. A pavement structure according to the above mentioned Claims, WHEREIN such first lower or base layer has a thickness ranging from 150 to 450 mm.

8. A pavement structure according to the above mentioned Claims, WHEREIN such second upper layer or asphalt surface course has a thickness ranging from 3 to 50 mm.