Frequently Asked Questions
What does MatCon mean?
It is an acronym that stands for Modified Asphalt Technology for Containment. The asphalt binder is highly modified in order to achieve the qualities required for impermeability and durability.
How long is MatCon expected to last? What are the longevity expectations?
Asphalt cement, or bitumen, the black sticky binder that holds aggregate together and provides the cohesion, is the end process of natural or artificial (man-made) refining of crude oil. It is a very durable material, having been found in artifacts dating several thousand years ago. When used in MatCon, the composite material can last many decades or more when properly maintained. The modified asphalt binder coupled with very low air voids prevents the natural elements such as air and water from entering and aging the mixture, as is often the case with conventional asphalt paving.
What is the oldest MatCon site, and how is it performing?
The first MatCon project was constructed in 1989 at the Recomp facility in Ferndale , Washington . It was used as a cap for incinerator ash and for temporary storage of additional ash. It is still performing well, has required minimal maintenance of some small cracks, and is used daily for storage of heavy equipment and for recycling vactor waste, and other materials.
Can MatCon be used for both a liner and a cap?
Yes. The design and materials are the same for either application.
How is MatCon different from conventional asphalt pavement?
Asphalt pavements that are used in conventional highways and airports are subject to loading and environmental exposure and potential damage as well as normal wear. There are five things that can happen to these pavements, including:
- Fatigue cracking due to repeated loading
- Permanent deformation or rutting
- Thermal cracking due to wide range of temperature change
- Water damage, mainly due to stripping of asphalt from the aggregate, and
- Aging, mainly oxidation, due to exposure to air and water.
If MatCon is so good, why isn’t it used for highway pavements?
It is too expensive for highways because they are funded mainly based on first cost rather than life cycle costs. In general, highways are funded through the tax system with annual income that pays for the pavement construction and maintenance, much like financing one’s car. If the financing system could utilize life cycle costing procedures, longer life pavements could be constructed.
How can MatCon be called “seamless” if it has both hot and cold joints?
Seamless means that there is no difference between MatCon mixture at the joints or other portions of the cap between joints. Hot joints are preferred, and are used whenever possible, resulting in uniform properties such as density and permeability. When cold joints are required, such at the end of the day, or due to some delay, Granite uses a proprietary joint design to ensure that the density and permeability are maintained at the cold joint as well. MatCon does not have a different specification for joints in terms of density and voids, such as is used by agencies such as FAA for longitudinal joints in airfields.
How does MatCon perform under freeze-thaw conditions?
Repeated freezing and thawing do not affect MatCon in any detrimental way, unlike for Portland cement concrete. In concrete, there are very small pores that become saturated with water and then expand upon freezing, causing disruptive forces and cracking. This is a mechanism that is unique to Portland cement concrete and especially when repeated many times. With conventional asphalt mixtures, the much larger pores or air voids can fill with water and freeze, causing some damage because the asphalt binder is harder and brittle at freezing temperatures. But with MatCon, no water enters the few small voids, so no damage due to freeze-thaw of the water can occur. In addition, the MatCon binder is more forgiving and elastomeric, even at lower temperatures.
How does MatCon perform in repeated wet-dry conditions?
Damage due to repeated wetting and drying in asphalt mixtures is caused by the accelerated aging through contact with water. Stripping of the asphalt binder from the aggregate surface is the most common damage that is caused by some softening of the asphalt when wet, and oxygen-hardening when dry. As noted above, no water enters the MatCon mixture, so these mechanisms cannot occur.
How does MatCon perform in very dry conditions? How about in UV exposure?
Very dry climates, especially in high deserts, expose the asphalt binder to drying, oxygen hardening, and other phenomena such as volatilization, whereby the lighter ends of the asphalt evaporate, leaving a harder, more brittle binder that is subject to cracking in the pavement. With conventional pavements, this occurs throughout the mixture because of the air voids permit access to the dry air. With MatCon, the low air voids do not allow the entry of dry air, so the hardening effect is minimized.
How does ultraviolet radiation affect MatCon?
UV exposure has very little effect except in the top one or two millimeters, where the original black color is faded to grey. UV light does not penetrate beyond this layer, so no change in the overall performance or life would be expected.
Can MatCon be placed on poor subgrade material? On waste material? Organics?
The limitations on where MatCon can be used is mostly due to the strength or stiffness of the substrate. There are two main considerations when using MatCon as a cap, for example:
- There needs to be sufficient strength to support the loads during its expected service life. For example, if trucks were expected to use the facility, then the subgrade and base courses need to be designed accordingly, in the same way as for a pavement. A recommended practice is to test the site using a device such as the Falling Weight Deflectometer (FWD) or a smaller version called the LWD to test the stiffness of the underlying material; the results of this type of survey can then be used in the pavement design process. A rule of thumb for MatCon caps has been a minimum stiffness of 80 MPa (Mega Pascals) (or about 12,000 psi) on top of the base course on which the MatCon will be paved.
- The MatCon needs to be compacted to its design density (and hence, low permeability), and sufficient resistance to the compactors or rollers is needed to provide the required reaction. The stiffness of 80 MPa noted above will usually provide more than adequate resistance for compaction. Lacking these data, a proof rolling the site with a fully loaded dump truck will often help locate soft areas that need to be improved by replacing or re-compacting the base, or increasing the thickness of MatCon in those locations.
What sort of chemical resistance does MatCon have?
The modified asphalt binder in MatCon is highly resistant to almost all chemicals except hydrocarbon solvents, and possible concentrated nitric acid. Being a hydrocarbon, it is solvent in some other hydrocarbons, therefore MatCon is not recommended for storage of these materials. More likely would be oil or hydraulic fluid spills from construction equipment or trucks and other equipment such as garbage trucks which carry a large amount of hydraulic fluid. In those instances where occasional spillage or leakage is likely, prompt clean-up will usually suffice to prevent any permanent damage. Bulk storage of dry chemicals or materials such as aggregate, construction debris, etc. would not pose a problem.
In Phase 2, specimens of the full MatCon HMA mixture (including mineral aggregates) using a range of modified binders were exposed to tap water and a dilute aqueous solution of toluene (selected from Phase 1 as having a strong effect on the binder). Every 30 days over a 240-day exposure period, the toluene in solution was measured and the specimens were removed and tested for resilient modulus to evaluate the structural integrity. Results of these studies showed the MatCon modified mixtures absorb far less leachate (<0.39%) than those made with conventional asphalt binders. Low void content (<3%) and thus low water absorption, is important to overall performance. MR appeared to correlate with leachate absorption, but the MatCon modified mixtures retained modulus much better than unmodified. It was concluded by Dr. Haxo that even though these mixtures performed well using the model leachates, it was recognized that absorption by in-service MatCon liners "should be less than the absorption by the specimens immersed in the dilute aqueous toluene solution because of the presence of dissolved salts in MSW or MSW incinerator ash landfills."
Does MatCon leach any undesirable materials into the soil and groundwater?
MatCon was developed nearly 20 years ago to be a more durable and longer-livedcontaminated material isolation barrier than conventional systems. Pursuant to gaining regulatory agency approvals for the first full-scale MatCon installation as a RCRA cap, MatCon was subjected to a series of studies at the direction of Harding Lawson Associates, Inc. to show that MatCon posed no hazard to the environment. These studies examined the leachability of semi-volatile organics and heavy metals from MatCon in the presence of various extraction fluids. The results of those tests, and the following technical discussion support the conclusion that MatCon will leach fewer constituents than traditional asphalt concrete pavement.
Third, MatCon modifiers do not contain heavy metals or other hazardous material constituents. Further, the physical binding and chemical bonding characteristics provided by the supplemental modifier enhances the ability of the host MatCon end product matrix to retain such components if present in the conventional asphalt cement and, more importantly, aggregates added in the mix.
Fourth, the decreased permeability of MatCon (<1 x10-8 cm/sec) will prevent the intrusion and pass-through of potential carrier fluids. Without the ability of a fluid to pass through the MatCon matrix, only surfaces of the matrix will be subjected to leachable conditions. Analytical testing performed on MatCon pavement samples examined leachability of various analytes to various aqueous extraction fluids including deonized water, solid waste landfill leachate, and methyl ethyl ketone.
In summary, the testing and analysis has shown that all potentially hazardous compounds such as PAHs are tightly bound within the MatCon and not subject to leaching.
How flat can a site be for paving with MatCon? Is there a minimum slope required?
The preferred minimum cross-slope for MatCon surfaces such as caps is 1.5%. This slope provides for adequate drainage from rain without ponding or other disruption of operations. Constructing MatCon on a flat level surface is not recommended because the tolerance for construction would result in occasional basins or bird-baths that would hold water. Although the water is not detrimental to the MatCon since it is designed with very low permeability, bird-baths may create a safety hazard, especially in winter when they may become frozen. Designers of MatCon should make every attempt to provide adequate cross-slope drainage.
What is the maximum slope that MatCon can be constructed, for example side slopes of a basin?
The maximum slope such as side walls for a landfill or water basin that can be constructed using conventional paving equipment is 4:1. However, each project must be evaluated for constructability and there may be other limitations or situations that would allow for a different design.
What quality assurance measures are incorporated in the construction of MatCon?
Granite Construction has a detailed protocol for quality control and quality assurance that incorporates many features that go well beyond those used for other paving construction such as highways. The protocols are made available when a specific project is under consideration, and are proprietary to Granite. However, they include inspection and monitoring of the binder manufacture, MatCon HMA plant and production, and paving operations in a very detailed manner. QA is one of the principal features of the success of MatCon to provide a facility that will retain its impermeability over a very long period.
Can MatCon be used in conjunction with conventional geomembranes?
Yes. If required, a geomembrane can be installed underneath the MatCon as added insurance, but it would be like wearing both a belt and suspenders and add cost. Some designs have used a geomembrane underneath a conventional asphalt pavement (in order to provide for parking or other re-use), but this is usually not cost effective. Conventional asphalt pavement is porous, shorter lived, and requires more maintenance than MatCon.
Another application is where a MatCon cap adjoins a cap or liner made from a geomembrane such as HDPE, such as on a very steep slope. Granite has a proprietary design whereby the edge of an HDPE membrane could be tied to the MatCon by sandwiching it between two layers of MatCon, thus providing a continuous cap without special anchors, etc.
What are the properties that are covered in the warranty?
The normal 5-year warranty covers protection against loss of permeability as specified, including sealing any miscellaneous cracking that may occur. It also covers cracking or rutting due to MatCon material deficiencies that are caused by traffic that goes beyond 500,000 ESALs. These features are explained in the Warranty provisions for each project, because the actual planned use may vary.
Is an extended warranty or maintenance plan available?
An extended warranty (beyond the initial 5 years) may be negotiated at the time of construction or at any time beyond for a given project. For example, an owner may find that maintaining a cap made of MatCon may fall outside of his area of competence or interest, and would prefer that someone else look after it on his behalf to satisfy the requirements as set forth by regulators.
What are the regulatory barriers to the use of MatCon?
Most often, the regulators such as USEPA or a State EPAs may be more familiar with traditional caps or liners that utilize layers of geomembranes, geotextiles, clay, and other materials. These designs emerged following the early requirements for environmental barriers as a “fail safe” solution, but in later years, they have been found to perform at a level less than desirable, and include actual failures.
Since 1989, when MatCon was developed, regulators have been more open to new ideas, including asphalt. Beginning in 1999, the USEPA tested MatCon in their SITE program (stands for Superfund Innovative Technology Evaluation), and found that it was quite acceptable as an alternative solution. The results of this study are summarized elswhere (SITE results) and show the superior properties of MatCon HMA over conventional HMA.
Where has MatCon been approved for use?
All 10 Regions of the USEPA accept MatCon as “approved”, and have allowed MatCon to be constructed whenever it was requested by an owner/designer. Most State agencies have also been approached with similar approval fortcoming. In not instance has MatCon not been approved.
What is permeability, and how is it measured?
Permeability, as it pertains to an environmental barrier, is usually designated as the coefficient of permeability and is the rate or velocity that a liquid such as water will pass through it under standard conditions. For example, EPA requires a permeability value for RCRA sites to be less than 1x10-7 cm/sec. MatCon typically far exceeds this value and is usually < 1x10-8 cm/sec, which is an order of magnitude less. By way of translation, this means that water would take about 6 months for a drop to penetrate the 4-in MatCon layer. This is why it is essentially “impermeable”.
Why is MatCon always constructed 4 inches thick and in one lift?
A thicker lift has been proven to be beneficial for several reasons:
Paving in a single lift provides for longer heat retention and more time for compaction, thus allowing for better hot joints.
The middle 3 inches or so is typically better compacted than the top and bottom ½ inch of thickness because these extremes cool faster, and is less dense, resulting in uncertain impermeability. When the 4-inch lift is tested, then the entire depth is considered as the impermeable barrier, and not just the top or bottom portion.
Compacting in more than one lift creates, in effect, a horizontal cold joint between lifts over the entire site and provides more opportunity for water to enter and migrate laterally.
Paving in two lifts is the normal practice for highways, but is done to improve smoothness for high speed traffic, and this is not a factor in MatCon caps.
Paving in one lift is faster because the paving is covered in a single pass rather than paving twice.
For special situations, MatCon may be constructed in multiple lifts, say up to 12 inches thick. The added thickness may be for either added structural strength or to meet special geometric constraints.
Does MatCon come in colors other than black? Can striping or other marking be used?
Basic black is normal, but for special cases coloring can be added by using coatings made for this purpose. Each case would need to be assessed in order to determine feasibility. Striping, for parking space designation, can be done using thinned striping paint. Note that one can often observe cracks in an asphalt pavement that parallel the edge of a parking stripe. This is caused by the different temperature of the pavement under the stripe compared to the naked surface; these cracks may develop sufficiently to compromise the integrity of the MatCon. Therefore, it is recommended that the owner consult Granite/MatCon regarding solutions such as thinning the paint and not using stick-on striping that would have highly different levels of albedo.
Can MatCon be used for parking?
Yes. Parking of cars and legal load trucks is a normal use for MatCon, and is part of its multi-use concept.
How long does it take to pave a MatCon project?
Rapid construction is an important attribute of MatCon compared to alternatives such as clay and geomembrane construction. Once a site is prepared for paving, i.e., the base is graded and compacted to specified conditions, up to 2.5 acres per day are reasonable when the obstructions such as buildings or protrusions are minimal. For very large projects, it would be feasible to use two paving crews working en echelon for up to 5 acres per day (10-hours).
How near to the site does a hot mix asphalt plant need to be?
The concern is that the MatCon HMA would cool too much prior to being placed. Up to one hour haul time is reasonable, since the MatCon HMA leaves the plant very hot, and it is protected using truck tarps, etc.
For large projects, it would be feasible to set up a portable hot mix plant on site in order to reduce the haul time and other delays. This approach would also save considerable energy by reducing fuel usage due to hauling.
What is the load limitation for MatCon?
For any particular project, the specific limitations for loading are spelled out in the Operations & Maintenance Plan for that project, which may have special requirements. But in general, repeated wheel loads such as cars are unlimited, and trucks that are legal to drive on the public highways without permits are ok, within the limits of the warrantee, 500,000 ESWLs. For point loads, the general maximum is 100 psi, which may need to be calculated during the design phase. Lugged vehicles such as bulldozers are prohibited, especially in hot weather.
How can MatCon be used for heavy use and loading, such as a road or loading area?
MatCon can serve as the surface pavement or as an intermediate layer within the pavement structure. It is very strong and durable, but if there will be sustained use by heavy loads such as trucks, there may need to be a more robust base course and other underlying pavement layers to sustain the loads. A separate pavement design would need to be done for each project.
Is MatCon durable under very heavy loads and aggressive use such as for docks?
As indicated above, the MatCon can carry heavy loads, but if the surface is to be used aggressively such as by fork lifts, container carriers, etc., then some protection measures may be in order. For example, since MatCon contains asphalt, it is temperature sensitive, becoming softer in hot weather. As such, it may tear or abrade under turning or scraping loads. One solutions is to place the environmental impervious cap under a sacrificial layer of conventional asphalt pavement that can be repaired and/or replaced as needed. Another protective layer such as MatCon Armor Top could be used, as described below.
What is MatCon Armor Top, and what does it provide that MatCon does not?
Armor Top is a pavement layer constructed about 1.5 inches thick that is placed on top of MatCon impermeable asphalt pavement. It consists of a layer of open-graded MatCon that has the air voids filled with a proprietary cement/polymer grout to form a dense, very hard and durable wearing surface. As such, it can withstand the aggressive use and abrasion of heavy equipment and other operations while still protecting the MatCon layer and its impermeable properties. In addition, it has no joints and does not crack as is the case with portland cement concrete. It has a lighter color, similar to portland cement concrete, and can be used to reduce the heat island effect in hot weather.
Can local aggregates or recycled asphalt pavement be used in MatCon?
Local aggregates may be used if they meet the rigid requirements for quality, and if they are convenient to the asphalt plant. High quality aggregates are not always available near a project, and need to be imported from afar, increasing the hauling cost.
What are the uses for open-graded MatCon?
Open-graded MatCon was originally used for the middle drainage layer in three-layer MatCon caps as part of the lysimeter to test the permeability of the top layer. It was also conceived as the drainage layer to collect leachate that might leak through a damaged landfill liner. During early testing of lysimeters, it was found that field testing was not practical nor necessary, so they were discontinued.
Another use for the open-graded version is as a stormwater dissipation system at the perimeter of a MatCon cap. In some instances, there is a berm at the edge of the facility, and intense rainstorms tend to cause erosion on the side slopes. Some improvement is made using large stone rip-rap, but it is not always practical. Other designs have included geotextile materials, but these have poor performance and durability. By placing a lift of open-graded mixture, say one paver width (10 ft), around the edge, the result is a zone that can capture the runoff water and ease it into the soil without eroding the slopes.
What is the cost of MatCon compared to other alternatives?
The cost per square yard will vary, depending on the site conditions, current cost of the base asphalt, and the location. Each project will need to be carefully evaluated, usually in conjunction with the design engineers, in order to come up with the most economical solution. A specific price is then offered to the owners for that project.
Who is responsible for inspection, repairing, and maintenance of the MatCon?
The MatCon Team will make periodic inspections of the MatCon project during the warrantee period, sometimes as often as annually. During these inspections, any defects that fall under the warranty will be identified and arrangements made to have them repaired, including any routine maintenance such as filling a crack. As indicated earlier, the warranty is for thermal cracks and permeability. Any damage due to other causes not covered, such as misuse of the site will be noted and repair options recommended to the owners, who will be responsible for making the repairs. All materials and methods for repair will need to be approved by the MatCon Team in order for the warranty to remain in place.
Are there limitations as to use, such as an Operations and Maintenance Plan?
At the completion of each MatCon project, a detailed O&M Plan will be provided that includes any limitations of use, and guidelines that will be used for inspection and repair if any is needed. The limitations are not extensive, but they are important to the survival and performance over long time. It is expected that the owner become familiar with the Plan and respect the need to provide continuous environmental protection as intended.
What type of maintenance is required for MatCon?
If any maintenance is required, it is most commonly crack sealing and possible seal coating. If a crack does appear, it can be sealed using the same methodology as for highways; the crack can be routed out using special equipment, and then filled with hot MatCon Mastic. Minor cracks, if the occur, may not require routing, especially if they penetrate only a short distance into the MatCon mat. Longer term, perhaps in 7 to 10 years following construction, a seal coat may be applied as a preventive measure to preserve the integrity of the mat.
How do you make repairs such as patching or for utility cuts?
If the MatCon must be penetrated for some reason, it can be repaired in one of several ways. A hole for a fence post, a light pole, or some similar feature, for example can be drilled slightly oversized to provide some space around it, which is then filled with MatCon Mastic. If a larger intrusion is required, for example a utility trench, then the MatCon would be sawed out, using a step-wise approach that would leave a stepped cross-section. After the feature is installed, an aggregate backfill used as a base course would be installed and compacted to the level of the bottom of the MatCon mat. The cut surfaces would then be sealed using a heavy tack coat, then repaved using MatCon HMA or a similar material approved by the MatCon Team.
How do you seal around features such as concrete slabs, foundations, posts, light standards, pipes, and other protrusions?
If the feature is present during the initial construction, a special mastic-coated geotextile is used in a manner similar to roof flashing. When the hot MatCon HMA is installed, it melts the mastic, which bonds to the structure (say a concrete foundation) and the new MatCon, providing a permanent seal. Optionally, a bead of hot mastic can also be applied adjacent to the concrete that stands proud to the surrounding surface and provides for water runoff.
What type of structures or other facilities can be placed on MatCon?
Lightweight (fabric) buildings, spread foundations for equipment and other features have been placed on top of MatCon. The guiding criteria for building on top, is to minimize any penetrations such as anchors, and to recognize the maximum allowed 100 psi contact pressure as well as other limitations noted in the O&M Plan. For athletic playing fields such as soccer, artificial turf may be placed directly on the MatCon. Living vegetation such as shrubs or small trees would need to be placed in pots sitting on top of the MatCon.
Can MatCon be used as a pond or reservoir liner?
Yes. One of the key attributes of MatCon is its impermeability over a long life. Storing water or other non-hydrocarbon liquids is most feasible and is a recommended use.
What are some of the other anticipated uses for MatCon?
Recent activities by the US EPA, and other agencies, have been focused on the construction of alternative energy (solar, wind, biofuel) projects on top of cleaned-up hazardous waste sites. Many of these alternative energy projects require large tracts of land, and otherwise under-utilized real estate such as mine dumps could be put to good use. One option is to first construct a MatCon cap over the site, the energy project would have a safe base on which to build.
What happens to the MatCon in the case of differential settlement of underlying materials?
MatCon HMA has the ability to resist deformation and cracking under differential settlement much better than conventional HMA. The details of the testing and analysis of this claim is shown in some detail under Technical Issues elsewhere in this website. The idea is that when a localized settlement of underlying materials occurs, the cap should be able to resist tensile and shear stress that develops.
The MatCon Team seems to be very competent and is proud of their excellent product. Is it true that you use a dollop of MatCon Binder in your oatmeal every morning? And does this improve your longevity?
So it is said. It also helps the oatmeal stick to our ribs.