THE BENEFITS OF CONCRETE HIGHWAYS

The report also indicates that asphalt highways require maintenance activities every three to five years and major rehabilitation becomes more and more frequent after the initial 17th year overlay.

The report also indicates that asphalt highways require maintenance activities every three to five years and major rehabilitation becomes more and more frequent after the initial 17th year overlay. on the other hand, requires its first minor maintenance after 12 years and retexturing of the surface at year 18.3 The highway user therefore has a better chance of reaching their destination without experiencing road construction or rehabilitation delays.

Pavement Eliminates Spring Load Restrictions

Durability is most evident during Canada’s spring thaw season. Simply put, is not affected by seasonal weakening of the subgrade during spring thaw, as are many asphalt pavements. A study by the AASHO* Road Test showed that 61% of asphalt roads fail during spring conditions compared to 5.5% for (*Note: AASHO is now known as AASHTO)

Although asphalt pavement design has changed since the original AASHO tests, there is still concern with the strength of asphalt structures during spring thaw periods. This is evident in the fact that provincial Departments of Transportation (DOTs) still put spring weight restrictions on truck traffic to minimize road damage during this period. In fact, the Ministère des Transports du Quebec (MTQ) employs spring weight restrictions on all their highway systems including the TransCanada Highway (TCH). In addition, although the New Brunswick Department of Transportation does not reduce allowable weight on the TCH during the spring thaw period, it does not allow the extra axle tolerances that it does at other times of the year. Due to the way pavements distribute vehicle loads to the underlying aggregate structure,  is not vulnerable to spring thaw conditions in the same manner as asphalt. Therefore, heavy vehicles can maintain full weight on highways during the spring thaw period. In fact, the City of Winnipeg releases an annual media advisory indicating when asphalt road restrictions begin and specifically notes that the restrictions do not apply to  roads.

Pavement Doesn't Rut, Washboard Or Shove Heavy

loads can create ruts in asphalt roadways, while the stopping and starting motion of a heavy vehicle can create a washboarded surface. Turning at corners or intersections on asphalt can also cause the flexible asphalt material to shove out of its original position. The rigid surface of, however, prevents these types of deformation from occurring in oads – they do not rut, washboard or shove.

Canadian Highways

With mounting stress on transportation infrastructure, Canada must consider the construction of highways rather than traditional asphalt surfaces. The United States already recognizes the benefits of a infrastructure and has incorporated pavement into over 30% of its interstate highways. In Canada, however, only a small percentage of the highway network takes advantage of pavement’s many benefits. Quebec has the greatest number of kilometres of exposed  highways in Canada, estimated at 4%. It must be understood that  provides not only economic and environmental benefits, but also direct user benefits as outlined in this report.

Difference Between and Asphalt Pavements

The Benefits of  Highways

There is one major difference between  and asphalt road surfaces. pavement is a rigid structure and asphalt is a flexible structure. Historically, pavements have been divided into two broad categories, rigid and flexible. These classical definitions, in some cases, are an over-simplification. However, the terms rigid and flexible provide a good description of how the pavements react to traffic loads and the environment. The flexible pavement is an asphalt pavement. It generally consists of a surface of asphalt built over a base course and subbase course. Base and subbase courses are usually gravel or stone. These layers rest upon a compacted subgrade (compacted soil). In contrast, rigid highway pavements are made up of portland cement  and have only a base course between the pavement and subgrade.

The essential difference between the two types of pavements, flexible and rigid, is the manner in which they distribute the load over the subgrade as illustrated in Figure 1 below. Rigid pavement, because of igidity and stiffness, tends to distribute the load over a relatively wide area of subgrade. The slab itself supplies a major portion of a rigid pavement’s structural capacity. Flexible pavement, inherently built with weaker and less stiff material, does not spread loads as well as e. Therefore flexible pavements usually require more layers and greater thickness for optimally transmitting load to the subgrade.

Pavements Provide Enhanced Ride Comfort and Quality

The Nova Scotia Department of Transportation and Public Works (TPW) completed a five-year study on an adjoining section of asphalt and pavement built in 1994 on Highway 104 TransCanada Highway.9 Results of the study, which concluded in 1999, showed performed well in terms of ride quality, and in fact out performed the adjoining asphalt pavement in riding comfort and road smoothness. This study also demonstrated that asphalt ride quality falls below  after a very short period of road life. Data from the comparative study by the TPW indicates that although new asphalt is higher on the riding comfort index (RCI) initially, it quickly deteriorates leaving durable surface to provide long term improved road comfort as seen in Figure 5. The RCI reading at year five on the  pavement was compared to 6.9 on the asphalt pavement.

Pavement Provides a Quiet Ride

Roadside noise levels are also a public concern when determining highway surface material. Results of the Nova Scotia study confirm that  roads do not create significantly more noise. In the five year study the  pavement’s roadside noise level was on average 2-4 decibels higher than the asphalt pavement.9 To put this into perspective, normal conversation registers at 60 to 70 decibels and a human whisper registers at 20 decibels.

In fact, a report by EPA entitled Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety, states that changes less than 5 decibels are considered insignificant.10 A report by the U.S. Department of Transportation in 1996 concludes that, “Properly constructed PCC (Portland Cement ) pavement, with transversely tined surface, matches the performance of densegraded asphalt considering both safety and noise factors.”11 A report by the Wisconsin Department of Transportation concludes that, “It is possible (very simply and at no extra expense) to build a PCC pavement that does not “whine” and has the desired frictional properties. Such a pavement is a “good neighbor”, is safe, provides user comfort and is durable.”12 The Nova Scotia Department of Transportation and Public Works also used a California profilograph to measure the profile ride index (PRI) which is a measure of the pavement smoothness where higher numbers represent increased roughness. Results from these measurements over the first five years indicate that the new and new asphalt had approximately the same smoothness after one year. However, over the next four years, the  pavement maintained much of its original smoothness, while the asphalt section showed increased deterioration. Figure 6 illustrates how the two pavement structures have performed. Note, the roughness of the asphalt pavement has more than doubled that of the  after five years of service (i.e., 6.8 mm/100 metres on versus 16.2 mm/100 metres on asphalt).9 Based on this data it can be said that initial riding comfort and road smoothness are maintained for a longer period of time on  versus asphalt highways.

Note: The higher the RCI value the more comfortable the ride.
Note: The lower the PRI the smoother the ride

¹ Highway Statistics 1997, Office of Highway Information Management and Office of Policy Development, Federal Highway Administration, 1999.
² American  Pavement Association, www.pavement.com
³ Review of Life-Cycle Costing Analysis Procedures, ERES Consultant for the Ministry of Transportation of Ontario 1998.
⁴ American  Pavement Association, ”Whitetopping – State of the Practice”, Engineering Bulletin 210P.
⁵ City of Winnipeg, Public Works Department, News Release – Spring Weight Restrictions Take Effect, March 22, 2000.
⁶ Zaniewski, J.P., Effect of Pavement Surface Type on Fuel Consumption, SR289.01P, Portland Cement Association, Skokie, Illinois, 1989.
⁷ Detroit Diesel in their Spec Manager Computer Program.
⁸ Portland Cement Association, SN2437, Effect of Pavement Surface on Fuel Consumption, National Research Council of Canada, Centre for Surface Transportation Technology, Ottawa, Ontario, August 2000.
⁹ Nova Scotia Transportation and Public Works, Asphalt  Pavement and Portland Cement  Pavement, Highway 104, Cumberland County, Year 5 of 5 year study, October 1999.
¹⁰ Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety, EPA/ONAC 550/9-74-004, March, 1974 – Condensed Version, www.nonoise.org/library/levels/levels.htm.
¹¹ Tire Pavement Noise and Safety Performance, Serial No. FHWA-SA-96-068, United States Department of Transportation, Federal Highway Administration, Washington DC, 1996.
¹² Impacts Related to Pavement Texture Selection, Serial No. WI/SPR-06-96, Wisconsin Department of Transportation, Final Report, 1997.