J.J. Grabe
February 1992

Through the years, engineers have been developed a great number of standards for the selection of materials for the road construction, at the moment the construction materials and soil standards are classified using these guides of consultation. Each country has its own standards based on conditions environmental, mainly geologic and climatic, perceivably different from which prevails in other countries. The standard one generally specifies the granular quality, the qualification of the gravel and the specific rank of the plasticity index and the minimum capacity of load.

Most of the specifications for the paved ways so much for rural ways have been developed as urban roadways, taking into account high volumes of traffic. These standards have been extrapolated to reduce the conditions of the volume of traffic, with little scientific base. The quality of the materials for each layer in the way is specified carefully depending on the layer, of the design of the traffic and the environmental conditions that prevail. A different situation is from the roadways without paving in the categories of light traffic, as the agricultural or residential roadways. The use materials must necessarily be locally available.

The construction materials for roadways that fulfill all the necessary requirements have become scarce and very expensive to obtain. They often need a long processing in a gravel pit or extraction site, also are have to being carried from long distances, in such a way that they become inaccessible in cost for slight structures of pavement, besides to be little satisfactory under heavy loads and wet conditions. If the local materials do not fulfill the requirements minimum can be improved through the soil stabilization, which can be obtained using the following methods:

MECANICAL STABILIZATION:

CHEMICAL STABILIZATION:

The main preoccupation of the civil engineer talks about the characteristics of the ground that affect their capacity to support load. These characteristics are determined in the first place by the presence or the absence of argillaceous minerals, and secondly by the interaction of these minerals with the water.

All these methods increase the cost of the material significantly, since the added materials are expensive and all require of positioning, of mixing themselves, of irrigation and work. In addition, an increase in the supervision and the control of quality are necessary.

The diminution of the availability to find usable materials and the increase of the cost of the construction equipment along with the uncertain economic climate, will locally mean that the engineer will need to consider methods economically feasible to construct new roadways, or rehabilitate the existing ones, using the materials available on site (in-situ) even though these do not fulfill the required standards.

The situation still more gets to be critical when it is the always-increasing demand for the road construction in the underdeveloped rural areas and the informal establishments near the metropolitan centers. In addition, the pressures increase when the agricultural, mining, forestry and other industries make the road construction necessary for optimal operation with the smaller costs and the minimum maintenance. All it takes to the necessity to develop appropriate techniques of design for the road construction.

The use of materials on site (in situ) is an available alternative that offers the advantage for the processing of such soil materials and an important reduction of the costs and from transportation, reducing to the minimum the environmental erosion that produces the import of materials although it provides a regular performance.

Nevertheless, most of the materials on site (in situ) they will not provide a laying of foundations adapted without a certain treatment soil stabilization treatment.

Engineers specialized in road construction, with some years of experience, know or that most of the premature faults of a roadway they are possible to be attributed, directly or indirectly, to the excessive humidity presence on them. The main reason of this is the effect of the water in the reinforcement of the natural materials.

Although many materials have suitable force to support loads whereas they are in relative a dry state, the excessive water presence produces the degradation of the materials and the increase of the porosity, which debilitates the road base materials.

It will have to be taken into account that the water is an essential element in the process of the construction and when it is added in the correct proportion reduces the energy to use to compact the material to a certain density. If the humidity content is increased, the layer of the pavement detrimentally would be affected.

In order to obtain the maximum benefit to use the local materials it is necessary to reach a High Density and later to avoid an increase in the humidity content. A form to obtain this is to modify the properties of absorption of the water in the clay that composes the gravel of the construction.

If the engineer is forced to consider economic factors to modify the properties of materials little adapted to make them more advisable for the anticipated intentions, is necessary the understanding:

The following section concentrates in a discussion on the composition and properties of argillaceous minerals, of the way of which they can interact with the water and how CBR PLUS can be used to modify its properties of a predictable form.