1) What evidence do you have to demonstrate the performance of the system in these conditions:

2) How does one measure the chemical resistance properties of the material?

Early in our evaluation of MatCon performance, we consulted Dr. Henry Haxo, then President of Matrecon, Inc. about testing for chemical resistance. Using his previous experience in developing performance standards for geomembranes, we devised a testing program to evaluate the resistance of MatCon to attack by leachate from municipal solid waste. Matrecon then tested different MatCon modified binder formulations representing possible mixture designs, using procedures customarily associated with geomembranes. These included long-term exposure to model leachate solutions.

In Phase 2, specimens of the full MatCon 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 (M_R - a dynamic loading test that simulates heavy truck loading) 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. M_R 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."

3) Which chemicals destroy the hydraulic conductivity of the material or cause it to radically alter physical properties?

The most destructive chemicals would be petroleum hydrocarbons. Since it is unlikely that these would be present in MSW, the aqueous solutions of these were used in the laboratory tests described in question no. 2.

4) How are liners consisting of this material constructed on steep slopes? On normal landfill slopes; 3H:1V?

To place MatCon on slopes 3 to 1 or steeper it is necessary to winch the paver and rollers up and down the slopes. We recommend that slopes be 4 to 1 or flatter to eliminate the need to winch equipment.

5) What construction quality assurance measures are required to verify these properties:

a) liner thickness
b) hydraulic conductivity of impermeable and permeable layers
c) material continuity

Material uniformity is typically quite good throughout the mixture both laterally and vertically. Joints between passes of the equipment are maintained hot by limiting the distance paved before backing up and placing the adjacent pass, or lane. Further assurance can be provided by joint heaters, specially designed equipment to maintain heat in the area of joints until final compaction can be achieved. A special overlapping geometry (cross section) can be used to help assure a tight, impermeable joint, as well. Experience has shown that careful preparation and attention can result in joints readily meeting the required density and impermeability expected throughout the liner.

6) What advantages become evident when comparing this material to geosynthetic composite barriers?

7) What are the conditions of the patent on this material?

A U. S. patent was issued in 1992 for the system. Currently (1998), additional patent protection for other features of the MatCon system is in progress.

8) What is the life expectancy of the material under;

Asphalt materials, whether the residue from refined crude oil or from natural deposits such as Trinidad Lake, are very durable. Surviving examples of use in construction or preservation in antiquity are still found today. Natural deposits of asphalt have existed for thousands of years with virtually no change in properties.

Well-designed layers used in the MatCon system would be expected to survive for a very long time. Buried MatCon membranes, not exposed to air would remain essentially unchanged. Exposed layers, such as caps used for parking or storage, can also survive for long periods with routine maintenance. Fog sealing to preserve the surface could be done routinely, say every 10 years as needed. If load-associated cracks or other damage occurred, the exposed surface could be easily repaired using conventional paving techniques.

9) To what degree will you warrant the hydraulic and physical performance of this material?

A typical HDPE liner material guarantee warrants that the material will be free from defects and be able to withstand normal weathering from 15 to 20 years of normal use in approved applications. They exclude from their warranty any damage due to natural events such as earthquakes, floods, or piercing hail. They further define normal use as excluding any exposure to harmful chemicals, abuse of the liner by equipment or people, and excessive pressures or stress from any source.

Their typical workmanship warranties range from 1 to 3 years. They exclude any damage due to subsurface or overburdened soil conditions or from total or differential soil settlements.

We anticipate being able to give similar warranty periods for material and workmanship. We would warrant that MatCon would not be damaged by hail, or by appropriate use heavy equipment, people or from subsurface or overburdened soil.

10) Is it possible to use this material in conjunction with a geomembrane, if necessary?

It is possible to lay a geomembrane directly on a MatCon surface, however if a MatCon layer is to be placed over most geomembranes, an intervening layer of fine aggregate would probably be needed for protection of the geomembrane.

11) Describe the construction sequence;

12) What testing has been done to measure internal shear and interface friction properties (between the material and the subgrade soil);

This question was also addressed in No. 1. In recent years, new testing procedures have been developed as part of the Strategic Highway Research Program (SHRP). These include dynamic shear, short-term fatigue cracking, tensile strength (particularly cold weather), water sensitivity, and aging. Although only some of these methods have been applied during the evaluation of MatCon, they can be used to evaluate important or crucial projects. To date, these test methods are providing better insight into the engineering behavior as compared to older empirical tests. The results can be applied to special applications such as side slope stability (creep, for example) as well as pavement loading (storage, traffic, etc.).

The design of MatCon, with very low voids and high binder content provide good resistance to short term cracking (fatigue) and long term bending without cracking. Similarly, it would be able to resist modest earthquake loading, but we have no direct experience with larger earthquakes except in pavement such as airfields. Sliding resistance between subgrade and pavement layers is normally quite high because of the total contact to the inherent rough surface at the interface.

13) Do you perceive any regulatory barriers to the implementation of this product?

No. The basic regulations for hazardous waste landfill design are contained in RCRA Parts 264 and 265, Subpart N - Landfills. These state the requirement that landfills "must install two or more liners and a leachate collection and removal system above and between such liners…"

A MatCon-modified asphalt concrete liner engineered and installed to prevent contaminant migration does meet the RCRA definition of a liner. Use of geomembrane liners and recompacted clay have become the "standard" over time as a result of material availability and engineering practice. Specifications, testing and analysis have centered upon the measurable properties of the membrane systems. However, to our knowledge, there are no codified regulatory barriers to alternative liner systems including a MatCon modified asphalt.

14) It is perceived that roadway pavement is highly permeable. How is this product fundamentally different from roadway pavement?

The fundamental advantage of MatCon over conventional asphalt pavements is low permeability. The aggregate gradation, coupled with modified asphalt makes it easier to construct a low void, highly durable layer.

Typical permeability values may be about as follows:

For asphalt pavement (6 - 8% air voids): k @ 1x10^-5 cm/sec

For MatCon (<3% air voids) k < 1x10^-8 cm/sec

Hydraulic asphalt containing large amounts of fine material has often been promoted in the past for water or waste containment, but usually results in a design that is difficult to build and is inconsistent in its ability to reduce permeability. In order to obtain reduced permeability, the design requires large amounts of fine aggregate (dust). This, in turn, requires very high quantities of hard based (high viscosity) asphalt binder to coat the fines. This attempt to reduce permeability results in a mixture that is difficult to compact (tender), thus inconsistent in uniformity of voids and permeability. It is very difficult to compact on slopes because of its instability. In fact, one project in California failed when the side slope collapsed in "accordion fashion" when warmed by the sun. A further shortcoming is the inability to use hydraulic asphalt caps for parking or storage because it is inherently unstable (soft) under standing loads; equipment will often punch through in summer weather.

15) Can layer thicknesses be altered?

The layer thickness of MatCon can be varied even as it is being placed from 2 to 12 inches.

16) What possibilities threaten the performance of this material when used in waste containment?

The hazards to performance for any waste containment system would be similar, especially for catastrophic situations such as earthquakes or large landslides. As indicated earlier, hydrocarbon such as oil or gasoline could be detrimental, but it would be unlikely that these would be placed in a landfill. However, the design of MatCon with low voids and a modified asphalt binder provide superior resistance. This was pointed out in the evaluation by Dr. Henry Haxo, when he concluded that MatCon and geomembranes would behave similarly when in contact with aqueous organic solutions.

17) What properties and/or test methods are employed that are not common to the evaluation of paving materials?

As discussed in No. 13, new tests are available for evaluating fundamental engineering properties. Permeability is a property that is very important to MatCon, but not normally used for pavements. Dynamic or resilient modulus is used in the design and also as a means to measure and monitor structural integrity with time. Water sensitivity (stripping and/or softening) is important to MatCon but is not always used for pavement evaluation. Chemical resistance may become a standard test for liners/caps, but would not be used for pavements.