Selected Technical Claims and Major Benefits of the CRAM Pavement

TECHNICAL CLAIMS:

The technical advantages of CRAM Pavement result from specific component improvements and from combined effects of the specific component improvements. The beneficial claims are described below. The quantification of the beneficial effects relative to the claims are in accordance with mechanistic concepts. Such concepts, as presently accepted, are described in the third volume of the recently completed AASHTO Guidelines for Design of Pavements. The technical advantages are:

POSITIVE DRAINAGE

Positive control of surface waters is achieved in the CRAM Pavement via the open graded aggregate atop the base asphalt layer. The latter is modified with increased asphalt content to reduce air voids, increase density and provide for corresponding reductions in permeability. On projects exposed to typical Mediterranean climates, e.g., such as in Southern California where an anticipated intermittent as opposed to a continuous seasonal rainfall effect on subgrade conditions exists, it is estimated that this improved condition will cause a probable increase in fatigue resistance of two-fold. The effect on rutting is similar.

IMPROVED FATIGUE RESISTANCE

Improved fatigue resistance for the base course is accomplished in the CRAM Pavement by selecting a more viscous bitumen, for example, by using an AR 8000 as opposed to the more commonly used AR 4000, and by using a greater bitumen content, the latter causes a corresponding increased density and reduced air voids content. The estimated maximum effect of this improvement is a minimum five-fold increase in fatigue life.

IMPROVED RESISTANCE TO CHEMICAL DETERIORATION

Improved resistance to chemical deterioration is achieved in the CRAM Pavement for all components below the surface layer with the critical component being the base asphalt concrete layer. The increased bitumen content causes an estimated two to three-fold decrease in diffusion coefficient in this layer with a proportionate reduction in oxidation. A slightly moist condition as would be expected for this buried layer would reduce this value even more. This location below layers of aggregate and the surface layer provides for additional improved protection against oxidation by providing a more favorable thermal environment as it is now insulated against extreme high temperatures. It is also protected against ultraviolet deterioration.

POSITIVE SEPARATION FROM SUBGRADE

Positive separation between the pavement structural section and subgrade soils is achieved in the CRAM Pavement via the Modified Dense Graded Asphalt Concrete placed directly atop the subgrade. The value of this separation in preventing contamination of aggregate materials in the structural section can not be easily quantified. However, contamination of base or subbase materials in conventional pavement systems causes reduced stiffness, increased permanent deformation and substantially reduced salvage value.

FAVORABLE SURFACE STRESS ENVIRONMENT

A favorable compressive stress operates on the surface layer of the CRAM Pavement and enhances resistance of this layer to mechanical and chemical deteriorations by preventing cracks from penetrating the upper surface.

FAVORABLE THERMAL ENVIRONMENT

Thermal insulation of the Modified Dense Graded Asphalt Concrete provides protection against adverse temperatures and temperature changes. The good insulation characteristics of the drained aggregate materials and the surface asphalt concrete layers provide the CRAM Pavement with sufficient insulation to cause complete dampening of the diurnal temperature changes. Temperature changes of 30 to 40 degrees can cause stiffness changes in conventional pavements of nearly an order of magnitude; whereas, the Modified Dense Graded Asphalt Concrete in the CRAM Pavement will be consistently nearer the lower temperature and, consequently, the higher stiffness. On typical projects, this improved condition will conservatively cause an increase in fatigue resistance of two-fold and an even more favorable effect against rutting.

FAVORABLE RESISTANCE TO STATIC LOADS

Use of (Portland) Cement Treated Aggregate for the uppermost aggregate interlayer provides a built-in resistance to stationary loads, often required for heavy parking and storage yards such as airport aprons and sea port container transfer yards, without exposing the pavement to adverse effects of pavement pumping (Conventional asphalt pavements which normally are not susceptible to pavement pumping; however, do not provide the static load resistance typically of a Portland cemented concrete pavement).

FAVORABLE RESISTANCE TO STATIC LOADS

Use of (Portland) Cement Treated Aggregate for the uppermost aggregate interlayer provides a built-in resistance to stationary loads, often required for heavy parking and storage yards such as airport aprons and sea port container transfer yards, without exposing the pavement to adverse effects of pavement pumping (Conventional asphalt pavements which normally are not susceptible to pavement pumping; however, do not provide the static load resistance typically of a Portland cemented concrete pavement).

TECHNICAL CLAIMS:

SUBSTANTIAL CONSTRUCTION SAVINGS

Construction contract prices with engineering are generally 20 to 40 percent less than conventional pavement systems. These CRAM Pavement will actually carry over 10 times the loading of the conventional systems before they mechanically fail.

SUBSTANTIAL INCREASE IN PAVEMENT LIFE

The increase in pavement life derives from "designing in" a more robust pavement structure and then from the inherent improvements brought about by such features as the positive internal drainage, and the improved fatigue strength and the more favorable thermal insulation of the Modified Dense Graded Asphalt Concrete layer, factors not considered in the comparative life analysis with the replaced conventional pavement. The former is a direct consequence of the economic efficiencies in the use of the construction materials. The latter provides, in addition to improved mechanical strength, the greater resistance to chemical deterioration or the non-traffic ravages of time. Mechanistic analyses concepts have clearly demonstrated that the life potential of the CRAM Pavement can easily exceed 50 years where the replaced conventional pavement has a useful life of 15 to 20 years at best. Savings from extended life, of course, provide by far the greatest value, typically as much as two to three times the initial construction cost.

SUBSTANTIAL REDUCTION IN MAINTENANCE

The savings here follow naturally from the much greater resistance to mechanical loading and chemical deterioration built into the CRAM Pavement. Using California maintenance practices suggest savings approximately equal to the initial construction cost.