MatCon® offers these additional advantages:

• MatCon® does not crack like compacted clay or lose plasticity like HDPE in arid climates or become brittle in arctic climates. Nor is it subject to UV damage below the top millimeter or so, which is exposed.

• MatCon® resists erosion, remains stable on slopes and conforms well to differential settlement of underlying materials.

• A thinner cross-section (4 to 12 inches vs. 2 to 9 feet) means less material import and more waste storage capacity.

• MatCon® can be rapidly installed on a prepared subgrade (~1½ acres/day) and used the next day.

• More than 300 highway-paving contractors nationwide have the skill, equipment and trained personnel required to execute the MatCon® Guide Specifications.

• Wilder’s experience and proprietary MatCon® Quality Control protocols make it uniquely qualified to oversee the manufacture of modified asphalt for environmental applications and its installation by local paving contractors.

Wilder Construction Company (founded in Blaine, WA in 1911) is a leading heavy civil and environmental contractor, building highways, dams, ports, runways and remediating sites primarily in the Northwest and Alaska with revenues in excess of $160 million per year.  Wilder’s first hot-mix asphalt facility was producing asphalt in 1946.  In the last ten years alone Wilder has produced over 8 million tons of asphalt—enough for a 4-inch thick, 25-foot widehighway stretching from Seattle to Detroit (over 2300 miles).  Wilder installed the first engineered landfill liner and cover in Washington State in 1984. A 14-acre geosynthetics landfill cover it installed in 1989 was the largest in the state up to that time [Figure 3, Snohomish County Regional Landfill].  Wilder’s experience with conventional RCRA covers and liners, and the frustrations that almost always come with such projects, led to its interest in the MatCon® technology.

Wilder acquired the patent for MatCon® in 1989 and began gathering laboratory and empirical data, using a third-party lab under the supervision of Dr. Henry Haxo, as to MatCon®’s impermeability, resilience, durability and resistance to leachates. Dr. Haxo is known for his work on the EPA’s test methods for geo-synthetic covers.

MatCon®’s inventor, Dr. Ronald L. Terrel, has devoted 40 years to developing new technology based on modification of construction materials such as asphalt, concrete, and aggregates with alternative binders and additives.  In addition to his work in industry, Dr. Terrel was a Professor of Civil Engineering at the University of Washington (1967-85) and is currently Professor Emeritus.  He was also a research professor at Oregon State University (1989-1994) as a leader of the USDOT Strategic Highway Research Program (SHRP) that sought to discover why highways were failing prematurely.  Dr. Terrel’s work with the SHRP program contributed to the development of the Performance Graded (PG) asphalt specifications and Superpave™ now adopted throughout the country.  During these years, Dr. Terrel was an active leader in numerous professional organizations including ASCE, AAPT, ASTM, and TRB.  Dr. Terrel has published more than 150 technical papers and reports in key journals.

As in the SHRP program, Dr. Terrel relied upon resilient modulus as an engineering parameter to evaluate performance of MatCon® across a range of temperatures and stresses.  Empirical techniques such as traditional Marshall stability testing proved inadequate to predict the failure of highways.  Predicting the longevity of an environmental cover is no less critical than projecting how long a road might last.

In order to develop MatCon® as a new alternative environmental cover, Dr. Terrel and Wilder elevated the evaluation of asphalt to a new level.  There is no PG asphalt rating for environmental containment.  Technical development and evaluation of MatCon® has exceeded the scope of the SHRP program since MatCon® must offer qualities

•        Low permeability
•        Strength and Resilience
•        Longevity

that surpass those associated with highway construction.  Low permeability is not even a factor in the design of conventional pavements.  Strength and elasticity, especially resistance to cracking, may be less crucial and a maintenance consideration for highways, but they are the basis of integrity for an environmental cover. When hazardous materials are to be contained, low maintenance covers are needed that last much longer than typical highways.

The dilemma faced when developing a successful asphalt technology for environmental applications like MatCon® is that achieving any of the above three qualities tends to compromise realization of the other two.  Impermeable asphalt can be made simply by increasing the binder content to reduce air voids, but this results in a mix that is too soft to bear

traffic.  This impermeable mixture can be stiffened, but many of the techniques to accomplish this lead to premature cracking and aging.  MatCon® simultaneously succeeds in all three areas, making MatCon® the only asphalt product that satisfies existing environmental regulations and requirements.

Low Permeability. MatCon® is designed to comply with RCRA permeability requirements with a coefficient of hydraulic conductivity of <1 x 10-7 cm/sec. Wilder's field and laboratory data show MatCon® typically surpasses this standard by at least a full order of magnitude (<1x10-8 cm/sec) when properly installed. Figure 4 shows how this compares to the permeability of conventional highway pavements. MatCon® achieves this low permeability by reducing air voids to a level where they do not interconnect. Two photographs of cross-sections of MatCon® and conventional pavement, with air voids indicated by fluorescent epoxy, tell the story. [Figure 5, 2 Void Photos]. Achieving low permeability is actually the easiest task since virtually any asphaltic material, if applied in sufficient quantity to fill the air voids, can be used to make an impermeable asphalt. Unfortunately, "hydraulic" asphalts are generally too soft to permit site reuse, and subject to ultra-violet light and oxidative degradation.

Strength and Resilience When conventional asphalt was first considered as an environmental containment material it was rejected, in part, because it was to sensitive to temperature changes.  As depicted in the attached Temperature/Viscosity curves, [Figure 6, Temperature/Viscosity Graph] conventional asphalt (dashed line) is a liquid at 300º when it is mixed, but at very low temperatures can be as brittle as glass.  Ideally asphalt would look like the solid line, with the same viscosity or stiffness at all temperatures below that required for mixing. While that is not possible, the dotted line shows how the suite of modifiers in MatCon® both increases stiffness in hot weather and elasticity in arctic climates.  MatCon®’s superior resistance to low temperaturethermal cracking was established by fixing specimens between rigid metal chucks within a temperature chamber; temperatures were lowered until the specimens cracked and failed.  Data for conventional asphalt and MatCon® show that MatCon® develops stress more slowly and fails at a considerably lower temperature. [Figure 7, Low Temperature Cracking Results].

A practical consequence of these superior structural properties is MatCon®’s extraordinary ability to perform within a wide range of temperatures and loadings by resisting deformation under extremes of these parameters.  This was confirmed using the resilient modulus test to evaluate the stiffness of the MatCon® HMA under a range of loading and temperatures.  In another related evaluation, a special bending beam test was developed to demonstrate and evaluate MatCon®’s ability to conform to underlying conditions such as differential settlement.  Figures 9a and 9b show that a nominal 4-inch MatCon® layer will deflect more than three times as much as conventional pavement without cracking. 

Longevity. The best explanations for the longevity of the MatCon® at Ferndale, 12 years of heavy use with no cracking and no maintenance costs, are the considerations of permeability and resilience we have just discussed.  If air and water cannot enter the material through air voids or cracks, the thermal expansion, stripping and oxidation that make parking lots and driveways look the way they do does not occur.  To evaluate these combined effects, Dr. Terrel invented an apparatus called the Environmental Conditioning System (ECS) as part of his contribution to the SHRP Program. [Figure 10, Photo of ECS]   The device simultaneously exerts repetitive loads, cycles temperatures between 0° and 140° degrees every six hours, while drawing air or water through specimens.  These combined factors rapidly destroy conventional asphalt. MatCon® emerges from the ECS virtually unchanged.  Laboratory evaluation also included accelerated testing such as exposure of MatCon® to high oven temperatures, UV radiation, repeated air and water spray, and solvents such as kerosene and other petroleum hydrocarbons that confirmed MatCon®’s longevity. 

Even with a good “recipe,” success requires expertise and experience in combining essential modifiers with the bewildering range of materials loosely called “asphalt”.  Wilder performs a two-part design for each job.  First, the quality of local asphalt and its compatibility with MatCon® modifiers are confirmed.  Second, Wilder confirms the quality of local aggregate and confirms its compatibility with MatCon® Binder.  Often, superior materials must be imported from outside the project area.    From these and other evaluations, the Job Mix Formula for MatCon® HMA is produced.  Once a successful mix design is achieved, the challenges of manufacturing and installation begin.

Wilder must provide its own quality control at the hot mix facility to be sure that a homogenous product meeting our specifications is produced. Even the best paving crews will be unfamiliar with the challenges of paving a surface that is not only smooth, but also impermeable, even within its joints.  Wilder provides quality control for lay-down and field density monitoring of the material and thus its permeability.  The success of the installation can then be monitored visually any time during or after its construction.

If a site requires an impermeable cover and its owners wish to reuse the site after closure or if MatCon® simply represents a lower-cost closure alternative, Wilder will always welcome an opportunity to meet with regulators, design engineering firms, and other concerned parties to answer their questions. MatCon® has been well received by the environmental industry and regulators.  MatCon® has been approved by State regulatory agencies for all projects where it has been proposed as an environmental cap including: Washington, Delaware, Illinois, California, Florida, Texas, New Mexico, Pennsylvania, and Kentucky.

Wilder Construction Company offers MatCon® nationwide in the form of a binder liquid. Aggregate is procured locally, when it meets our rigorous material selection criteria. Wilder preforms a site-specific mix design for every job to insure the compatibility and performance of the materials. Wilder provides this mix design, and comprehensive Quality Control supervision during installation free of charge. At approximately $120,000/acre for an installed 4”-thick cap (figure does not include site and grade preparation), MatCon® is less expensive than many RCRA caps that, unlike MatCon®, do not permit site reuse.

Wilder’s commercial role may be limited to that of the vendor of the binder material; MatCon® can then be procured through whatever contractual arrangements a potential user has in place or wishes to create. Alternatively, Wilder can provide a turnkey installation by subcontracting local site preparation and paving contractors. However MatCon® is procured, Wilder provides the same high level of Quality Assurance and technical support.