The MatCon® (Modified Asphalt Technology for Waste Containment)
The MatCon® (Modified Asphalt Technology for Waste Containment) system is an advanced modified asphalt technology that combines MatCon's proprietary binder with tightly specified aggregates. MatCon Hot Mix Asphalt (HMA) offers unique advantages for environmental capping and containment. Unlike conventional asphalt concrete, MatCon permeability (k<1 x 10-7 cm/sec) is lower than that required under RCRA, while also offering resilience and longevity.
These qualities make MatCon a superior containment alternative for environmental applications, particularly when site reuse is an objective. When MatCon is installed as a nominal 4-inch thick cap, a site that once had no value will have a variety of potential alternative uses: parking, equipment storage, truck/train intermodal facilities, multi-use sports facilities. In these and other ways, a liability on a balance sheet can be transferred to the asset ledger.
The first MatCon RCRA cap was installed in Ferndale, WA in 1989 [Figure 1]. This cap maintains its low permeability (k<1x10-8cm/sec) today, despite the constant operation of heavy equipment and material staging operations directly on its surface. Throughout its dual use as a RCRA cap and active work surface, the MatCon has required only limited maintenance. In contrast, multi-layer geosynthetic or membrane type systems are subject to damage during construction and thereafter even from plant roots and small animals. On the strength of this history and extensive laboratory evaluation, Wilder Construction Company began to offer MatCon® nationwide as a new tool for waste containment in 1999.
From the beginning of its commercialization, MatCon® attracted the interest of the USEPA. Even before work began on the cap at Dover AFB in 1999, the EPA made MatCon a part of its Superfund Innovative Technology Evaluation (SITE) Program, devising a comprehensive test protocol comprising both standard environmental measurements of permeability and ASTM and specialized pavement tests to measure MatCon’s durability and potential longevity. A year later, the EPA added the MatCon cover at Tri-County Landfill Superfund Site, Elgin, Illinois to the evaluation. These results are now available on the EPA’s website; the conclusion offered in the report was:
"The evaluations at the Dover Air Force Base and Tri-County Landfill Superfund sites indicate that the MatCon cover is better than conventional RCRA Subtitle C or D covers as it relates to infiltration of water. The MatCon cover is significantly better than conventional asphalt covers in relation to permeability, flexure, load/deformation, thermal crack resistance, tensile strength and aging/degradation properties. The MatCon cap is significantly faster to install than conventional RCRA C or D covers and is comparable in cost to installation of conventional covers."
One reason why it has been accepted by regulators is that, unlike buried membranes or geosynthetics, a MatCon cap can be visually inspected anytime.
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 inches vs. 2 to 9 feet) means less material import and more waste storage capacity.
MatCon can be rapidly installed on a prepared subgrade (~2½ 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.
Experience and proprietary MatCon Quality Control protocols developed by the MatCon team make it uniquely qualified to oversee the manufacture of modified asphalt for environmental applications and its installation by local paving contractors.
MatCon was originated by Wilder Construction Company (founded in Blaine, WA in 1911) and was a leading heavy civil and environmental contractor, building highways, dams, ports, runways and remediating sites primarily in the Northwest and Alaska. Wilder was acquired by Granite Construction Company in 2008. Wilder’s first hot-mix asphalt facility was producing asphalt in 1946. 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 2]. 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 MatCon technology 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. Similarly, predicting the longevity of an environmental cover is no less critical and required a new approach.
In order to develop MatCon as a new alternative environmental cap, Dr. Terrel and Wilder evaluated the performance 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 ...
Strength and Resilience
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 approach 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. Figure 3 shows the sensitivity of binder content in the laboratory and Figure 4 is at least one example of a poorly designed asphalt mix, including too much asphalt binder. 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 k<1x10-7 cm/sec. Field and laboratory data show MatCon typically surpasses this standard by at least a full order of magnitude (k<1x10-8 cm/sec) when properly installed. MatCon achieves this low permeability by reducing air voids to a level where they do not interconnect. Two photographs [Figure 5] of cross-sections of MatCon and conventional pavement, with air voids indicated by fluorescent epoxy, tell the story. Achieving low permeability is actually the easiest task since virtually any asphalt 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 too sensitive to temperature changes. As depicted in the attached Temperature/Viscosity curves, [Figure 6] 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 cold climates. MatCon’s superior resistance to low temperature thermal 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 [Figure 7] show that MatCon develops stress more slowly and fails at a considerably lower temperature.
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 [Figure 8] was developed to demonstrate and evaluate MatCon’s ability to conform to underlying conditions such as differential settlement. Figure 9 shows 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, in use since 1989 with very low 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]. 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 degrade 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”. The MatCon team performs a two-part design for each job. First, the quality of available asphalt and its compatibility with MatCon modifiers are confirmed. Second, the MatCon team 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.
The MatCon team provides 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. Quality control for lay-down and field density monitoring of the material and thus its permeability are provided as part of the package. The success of the installation can then be monitored visually any time during or after its construction.
If a site requires an impermeable cap and its owners wish to reuse the site after closure or if MatCon simply represents a lower-cost closure alternative, we 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, Indiana, California, Texas, New Mexico, Pennsylvania, and Maryland.
MatCon Inc offers the MatCon materials nationwide in the form of a binder liquid. Aggregate is procured locally, when it meets our rigorous material selection criteria. Our team performs a site-specific mix design for every job to insure the compatibility and performance of the materials. This includes the mix design, and comprehensive Quality Assurance supervision during installation free of charge. MatCon is less expensive than many RCRA caps that, unlike MatCon, do not permit site reuse.
MatCon can be procured through whatever contractual arrangements a potential user has in place or wishes to create.