During our GreenExpo365 webinar earlier in this year, "Paving The Way To The Triple Bottom Line", there were a number of questions that we didn't have time to respond to. In working with our friends at Roanoke Cement, here are answers to a few (more to follow).

Q: Any Data on the number of barrels of oil that can be saved per unit of conc vs asphalt unit?

A: The costs associated with asphalt do not stop with the purchase of the materials. Asphalt pavements require a tremendous amount of energy, or fossil fuels, to heat materials to the requisite 325°F temperatures at the production plant. Next, the asphalt is delivered to the construction site, where asphalt pavers and compaction rollers use even more fossil fuel to place the road in 12-ft. wide multiple layers (often with three or more layers for highways).

According to the Federal Highway Administration (FHWA), asphalt requires approximately 8,981 gallons of diesel fuel per mile (gpm) or 214 barrels of oil for production and 1,737 gpm or 41 barrels of oil for hauling and placement. Compare this to 548 gpm or 13 barrels of oil for production of concrete and 1,369 gpm or 33 barrels of oil for placement. So, from production to placement, asphalt requires at least 5.5 times more energy than concrete.


Q: Why haven't the regulations been changed to require a higher quality patch to include a sealer coat emerged ? This would to increase the longevity, reduce future repair costs and increase sustainability/durability of asphalt roadways. Better yet, why not start requiring patching with concrete?

A: As patching is viewed with various agencies, a more durable patch would be a full depth, a minimum of 6” or more and brought to grade with the existing roadway. In the case of potholes, during a time in which it is too cold to place asphalt, cold mix can be placed by a Departmental maintenance team (City, County, State, etc). Spray injection pothole patching is another alternative that has caught the attention of many agencies in which some agencies have invested in the equipment of perform this process. It claims a 3-4 year durability.

The mix for this process uses CRS-2 emulsion that is fast setting and durable. It is an easy observation when driving down the road to see the failure in many asphalt patch jobs. The question is what are the expectations of the agencies for the life span of the patching. Are there plans to resurface the roadway in the future and if so the patching and the resurfacing can be done at the same time and the contractor can bill that customer accordingly.

For roadway construction sealer are normally used for more expansive work than patching. Seal coats commonly used in roadway maintenance are fog seals, scrub seals, slurry seals, and chip seals.

Utilizing concrete as a patch with an asphalt roadway is very rare. Possibly in the event there may be issues of underground utilities a concrete patch may be used, but it is viewed less costly to utilize asphalt.


Q:. Doesn't grooving concrete pavement increase resistance even though it reduces noise

To answer this question correctly we must first clarify the difference between diamond grinding and grooving. In knowing the difference we can review the benefits of each.

Diamond grinding is one of the most cost effective concrete pavement restoration (CPR) techniques. The same technique and equipment is used for diamond grooving. However, while the purpose of grinding is mainly to restore ride quality and texture, grooving is generally used to reduce hydroplaning and accidents by providing escape channels for surface water. In terms of design, the main difference between grinding and grooving is in the distance between the grooves – about 6 times higher in the case of grooving.

Grooving improves drainage characteristics of a pavement, as well as provides a surface with excellent breaking traction. Grooving should only be applied to pavement sections where wet weather crashes occur, not to an entire project except when the number of accidents throughout the project is significant. Diamond grooving has been shown to be an effective method for providing macrotexture to new concrete pavements. Spacing, depth, width, and orientation of the grooves have a significant influence on the friction and tire/surface noise characteristics of the completed surface.

Diamond grinding is known to improve the functional properties of jointed plain concrete pavements in many ways:

• Improves skid resistance and reduces the risk of hydroplaning (safety).
• Corrects wheelpath rutting caused by chain wear in cold climatic regions.
• Corrects faulting at joints and cracks if there are no voids at the joints.
• Corrects permanent slab warping at the joints.
• Corrects built-in construction or rehabilitation roughness.
• Improves drainage by correcting transverse slope.
• Reduces noise from tire-pavement interaction > a likely bigger use going forward as “quiet pavement” concepts emerge and the likely genesis of this question


Q: Can you please name some of the best Products + manufacturers that you have used for permeable paving (precast concrete pavers or other materials) ?

A: One of the best products that I have been exposed to and seen in use would be Pervious Concrete. It is a product that promotes drain water solutions and can be produced by a local concrete producers. With the assistance of a Licensed Engineer (Geotechnical,etc) the specifications in addressing stormwater management will provide the owner with an effective system. I do recommend that the company performing the placement display enough of a resume’ of placement which will allow the owner the opportunity to review the drainage of the production over complete seasons. If one can not be located easily I would refer to the NRMCA’s database on certified Pervious Concrete Craftsman, Installers, and Technicians. That database link: http://www.nrmca.org/certifications/pervious/Search/PERVIOUS/ShowPERVIOUSTablePage.aspx