DEAR FRIENDS !
We were very surprised when we saw our website stats. So many visitors, and the number is still increasing. That means there is a big problem with cracks on roads and airports runways. Of course, we knew that. We have been working with that problem for many years. Many visitors have asked what starts these problems, and we will explain below why this happens.
If you have a specific problem or want some help, don't hesitate to contact us with your questions which we will answer directly or on our web site. Our email address is info@macpave.com.
The phenomenon of reflective cracking in new asphalt overlays has been around for many years. Most joints or cracks in an existing pavement, over time will reflect through the new overlay, causing continuing maintenance activity. These reflection cracks may be random, transverse or longitudinal in nature, and for the most part are located directly over or just adjacent to the substrate fissures. This condition occurs over both flexible and rigid pavements.
Early attempts at addressing the reflective cracking problems included the use of solid metal stripes, mesh or plates, expanded metal, boards, roofing materials. etc. .These attempts, which now seen rudimentary, did provide valuable background data for the more successful attempts to follow.
In the early '70s, several woven and non-woven fabrics came into use as reinforcements for flexible overlay mixes. This approach was predicated on the fabric absorbing and retaining a quantity of liquid asphalt cement for waterproofing and reinforcement. The pure fabrics achieved some degree of success in delaying reflective cracking over alligatored flexible substrates.
Many engineers, however, in their enthusiasm for the products, began specifying these fabrics for more difficult applications such as thermal cracking in flexible pavements and over longitudinal and transverse joints in rigid pavements. It soon became evident that the pure fabrics were not a cure-all, and engineers must be more judicious in their specifying of same.
The next step in fabric evolution was the addition of a thin, polymer-modified asphalt backing to the fabric. Many of these products vere be used in bridge deck, pipe wrap, and below-grade waterproofing markets and were pressed into service as a reflective crack reductions systems. Some of the major manufacturers of fabrics for highway/runway applications began employing a similar adhesive backing on their existing fabrics. Unlike the pure fabrics, these products are rarely used in total coverage applications, but are applied as strips over filled and prepared cracks.
Another method has been to construct a built-up type system on the pavement, utilizing a mopped coat of polymer-modified asphalt, an open-weave, high tensile, fiberglass and additional mopping of modified asphalt.
Given this prior art, in the late seventies an extensive study was made of the products available on the market which proposed to prevent or retard reflective cracking. Evaluations included both lab and field data. The conclusion drawn was that no product available significantly prevented/retarded reflective cracking when applied over the more difficult conditions of thermal cracking in flexible pavement and rigid pavement joints. (The theory is that materials which best perform the function of vibration damping are in the form of a heavy, high density mass. Further, movement of structural material is communicated to the damping material with the dissipative effects of flexure and internal friction inherent to the deadener.)
These properties were to be incorporated into product development for the highway/runway reflective market.
Thirty different mastic formulations were evaluated, as well as different laminate material. Materials with a fabric web on one side and a polymer-modified asphalt on the other were manufactured, evaluated, and rejected.
Internally reinforced product was manufactured, evaluated and rejected.
Extensive field testing was conducted on all combinations of materials, and it was found that field data did not always correlate with lab data.
In our opinion, emphasis should always be placed on field data under varying conditions. MacPave, which resulted from this development effort, is composed of a high-tenacity, polyester top web, a high-density mastic core, and a high-tenacity polyester bottom web. This combination is why you can find MacPave around the globe in various applications - on highways, runways, and both steel and concrete bridge decks. In the latter case, it also acts as a waterseal barrier and protector from the salt corrosion from de-icing operations.
In order to stop/retard crack propagation through an overlay, the parameters of density, weight, caliper, tensile and retention of the caliper under loading are considered paramount to product performance.
MacPave is best utilized as a heavy-duty crack reducer in the following applications:
- Rigid Concrete
- Joints & Cracks
- Thermal Cracking In Flexible Pavement
- Waterproofing
SUMMARY
Reflective cracking in new asphalt overlays is a most difficult problem to resolve. Vertical movement in the substrate, contractile and expansion forces and loading are all conditions which must be addressed. For the control of these conditions, fabrics offer a viable option to the engineers. However, care must be exercised that the proper materials are specified for any given problem and properly applied on the deteriorated or cracked area. Our engineers are highly qualified to help you with yours particular problems around the globe. If you have any questions regarding any kind of cracking problems, don't hesitate to contact us.
We also get many questions regarding the environmental aspect of MacPave. All material used in MacPave is classified under the ISO 9002 standard, and the manufacturing is the also. It is possible to mill the road/runway material and reuse the asphalt again. MacPave is the only water-sealing membrane what can withstand the water/moisture that penetrates the subbase over the long term and can still be reused again.
Another frequent question is how MacPave stops the reflective cracking from returning in the overlay. Many engineers say they have tried 99 different materials and wonder why only the 100th - MacPave - works out. The philosophy of MacPave is that the material is working together with nature. (Nobody has defeated nature so far!)
The membrane registers the temperature range throughout the year and has a built-in expanding and re-expanding flexibility that follows the cracks' movement but is strong enough to stop the crack from entering the top layer. Because of the water-sealing factor, no moisture and water can enter the sub-base and cause more damage to the road banks. (This is why you always get a bump on the crack. There are always micro-cracks in an overlay where water can enter, and if you have a crack underneath, it passes through to the sub-base.)
A highway/runway is always moving during a very hot summer day, and in the evening and throughout the night when the temperature is drops, there is a tremendous movement in the structure. From our experience in Scandinavian countries, even steel mesh is deformed and, in some cases, breaks apart. We use the membrane only over cracks with a width of 50 to 100 cm and don't need to cover the full area. This means that MacPave membranes are very economical in the long run.
When you are applying the membrane on the road/runway, there is no traffic interruption. As soon as the asphalt tacks have lost their stickiness, the road/runway is ready for traffic. Even in the overlay procedure, it is easier because there is no mesh that can rip up and stick to the paver and cause problems for the crew. MacPave is glued to the asphalt/concrete.
The membrane can withstand traffic of 15,000-20,000 cars per day per month before the overlay procedure has to be done. On runways, we recommend approximately 14 days, depending on the traffic intensity and weight of the aircrafts (Boieng747 and others). We are now working with some airports to prepare the runways for the new generation of Airbus Super Jumbos which weigh approximately 645 tons. Some airports have concrete runways and should apply an asphalt overlay so have cracks won't come back.
GENISIS HEAVY-DUTY STRESS RELIEF INTERLAYER
When I developed the first-stress relief interlayer in 1978, I already had 21 years experience in all phases of asphalt: manufacturing, pavement design, production, quality, research and development. I was, in fact, Director of Research and Product Development for asphalt products for 10 years and have developed many asphalt-based products.
From that experience and the process of having patents issued, I can assure you that extensive laboratory and field testing was involved prior to bringing a new product to market. In short, I believed I had a product that offered a resolution to the age-old and most difficult problem of reflective cracking in asphalt overlays.
When I formed my own company and "hit the road" to sell this concept, I was thinking "this will be a piece of cake." Sitting at this desk 23 years later, I can most assuredly tell you that it was not." Taking a product from laboratory to the field is not an easy task. Despite the laboratory testing, models and specifications, I faced the following questions in the "real
world" of asphalt pavements:
- Where has it been used? For how many years?
- How thick of a lift is necessary? One or two?
- Must the crack or joint be filled first? Over what distance will the product span?
- Can this product be left exposed and open to traffic for weeks prior to overlaying?
- Can active runways be utilized with the product prior to paving?
- Will the product deform under loading?
- Will the product show under the paver?
- Will it perform over transverse joints? Longitudinal joints? Random cracking?
- What vertical movement will it tolerate? Will it be effective over pumping joints?
- Temperature extremes - ambient -40 F ( 45 C ) to 110 F (+ 45 C)?
- Total coverage on bridge decks? Will it waterproof the bridge deck?
- State approvals? How many states? Airport authorities?
- Municipalities - counties: how many?
- NATO Approval?
- Foreign countries?
I should add that when I left the marketplace, these and many other questions were addressed with satisfaction, and the product, developed in 1978, was rated No.1 for its effectiveness in the field.
The list goes on. These questions are pertinent and should be asked of any new product entering the marketplace. MACPAVE Management carries on this tradition of experience around the globe with an aggregate of over 100 years of asphalt paving experience.
R.R. McAdams
President, McAdams and Associates
International Paving consultants
WARRANTY
After more than 20 successful years of minimizing the detrimental effects of reflective cracking on hot mix asphalt overlays, both on concrete and flexible asphalt, we underwrite the specifications to the world of pavement management.
Our confidence and many years of experience with the MacPave reinforced mastic stress reliever on highways, airports and bridge decks around the globe, and its unique performance, allows us to guarantee our product will provide you and your customers with complete satisfaction.
MacPave users have enabled us to establish an unequalled performance record in protecting hot mix asphalt overlays on highways, airports, aprons, taxi-ways, bridge decks and parking lots, And we are proud to provide additional protection with this unprecedented warranty.
Check it out - want to know more about our warranty? We invite you to contact us by E-mail - info@macpave.com - to get more information regarding our limited warranty for asphalt overlays.
