The Sustainable Benefits of Concrete Pavements

1) Embodied Primary Energy – Life cycle assessment research by the Athena Institute shows the energy use footprint for concrete pavement structures is substantially lower than asphalt pavement structures.

  1. Athena Institute study, A Life Cycle Perspective on Concrete and Asphalt Roadways: Embodied Primary Energy and Global Warming Potential identified the embodied primary energy used ranged from 2.3 to 5.2 times more for asphalt pavement structures.
  2. The embodied primary energy of a product is equal to the primary energy plus the feedstock energy.
  3. Primary energy refers to the quantity of fossil fuel required to manufacture, supply, and maintain a product over a specified period of time, usually 50 years. 
  4. Feedstock energy is the gross combustion heat value of the fossil hydrocarbon material input into the product which is a source of energy, such as liquid bitumen, but is not being used as an energy source.  
  5. ISO 14040 section 4.2.3.3.2 states, “Energy inputs and outputs shall be treated as any other input or output to an LCA. The various types of energy inputs and outputs shall include inputs and outputs relevant for the production and delivery of fuels, feedstock energy and process energy used within the system being modeled.” Therefore, gross combustion heat value of liquid bitumen must be included in any LCA analysis.

2) Heavy Truck Fuel Saving When Operating on Concrete Pavement  – National Research Council of Canada (NRC) studies comparing the fuel consumption of heavy vehicles operating on different types of pavement surfaces concluded that there is a savings ranging from of 0.8 to 6.9 percent when operating on concrete pavement compared to asphalt pavement.

  1. The hypothesis for the savings is based on heavy vehicles causing greater deflection on flexible pavements than on rigid pavements.  This increased deflection of the pavement absorbs part of the vehicles rolling energy that would otherwise be available to propel the vehicle.
  2. Several variables were included in the analysis such as pavement type, pavement roughness, vehicle type, different loading conditions, different speeds, different seasons (spring, summer day, summer night, fall and winter), pavement grade and wind speed.
  3. Fuel savings are based on comparing smooth asphalt pavements versus smooth concrete pavements.
  4. Phase II study demonstrated statistically significant fuel savings for tractor tanker semi-trailers (5-axle) vehicles traveling on smooth roads from 4.1% to 6.9% depending on operating speed.
  5. Phase III study demonstrated statistically significant fuel savings for tractor van semi-trailers (6-axle) vehicles traveling on smooth roads from 0.8% to 3.9% depending on operating speed.  The summer night data was excluded from the analysis, even though it was in concrete’s favor, due to it not being statistically significant.

4) Pavement Roughness Progression – A Case study, by the Transtec group, on FHWA Long-Term Pavement Performance data demonstrated that the rate of change of pavement roughness is significantly greater for the asphalt pavement sites than similar concrete pavement sites.

  1. Although the asphalt sites had superior initial smoothness, roughness of the asphalt sites increased 69.9 % over the 8 to 9 year evaluation period compared with 3.7 % for the concrete pavements.
  2. Concrete pavement sections carried 3.5 times more traffic than the asphalt sections.
  3. The rate of change of pavement roughness is significantly greater for the asphalt sites than the concrete sites – 53 times more for the Kansas sites – normalized to accumulated traffic.

5) ECO CERTIFIED Concrete Facility - This program is designed to provide owners and customers with the highest degree of assurance that the concrete facility, company and products they have selected to supply their project, address sound and responsible Environmental and Sustainable Development Facilities management and operations, and that manufacturing practices and protocols support their choice of Responsible Material Procurement. It identifies Environmental and Sustainable Development stewardship and responsibility of the facility’s processes following LEED rating system and categories to minimize the environmental footprint.

6) Recycled Concrete: Concrete that is crushed and reused – source can be old in-situ concrete or returned fresh concrete that is allowed to harden. This concrete can be 100% recycled into a number of practical uses, decreasing the requirement to use virgin non-renewable resources. This recycled material can be used for road base, backfill, stabilization or concrete aggregate; therefore, keeping it out of landfills.
Please note that it is becoming standard practice for fresh returned concrete to be immediately reclaimed or reused in its plastic state, diverting this from any land fill or other process.

7) Supplementary Cement Materials (SCMs) – SCMs are widely used and accepted as good practice in today’s cement and concrete production. Two of the more common SCMs are slag and fly ash which are by-products of steel manufacturing and thermal power generation respectively. Cement and concrete incorporating SCMs will have a reduced CO2 footprint, yet saving the environment by preventing these hazardous materials ending up in the landfill sites.

8) Reducing Urban Heat Island Effect - Paved surfaces (such as highways, roads, runways, parking areas, sidewalks, and driveways) typically constitute about 30 to 40% of developed urban areas. In the past few decades, the bane of urban cities has been the increased heating of the city by sunlight due to dark, heat-absorbing materials used in the construction of pavements and buildings. Urban areas are oftentimes up to 2 to 4°C warmer than the surrounding rural area, creating “urban heat islands.” Concrete pavement provides reflective surfaces that minimize the urban heat island effect because it is lighter in color with higher solar reflectance (albedo), also saving energy by reducing the demand for air conditioning and reducing power plant emissions. Cooler air can also reduce air pollution by slowing the chemical reactions that produce smog.

9) Superior Solar Reflectance - Albedo, or solar reflectance, is the ratio of reflected solar radiation to the total amount that falls on that surface, known as incident solar radiation. Albedo values range from 0, for perfect absorbers, to 1, for perfect reflectors. In pavement structures, the topmost surface is the only layer which affects albedo. Therefore, pavement type selection should also include a consideration of albedo where heat generation is a concern. Field measurements indicate that new, cured gray-cement concrete pavement has an albedo in the range of 0.35 - 0.40. As concrete ages, it tends to darken because of dirt and tire wear, so older concretes have albedos in the range of 0.20 – 0.30. The use of white cements and slag cements can also influence a concrete’s albedo immensely. New asphalt is very dark, so it has an albedo of 0.05 - 0.10, and aged asphalt has an albedo of 0.10 – 0.15. Research for Transport Canada (1977) found an approximately 40% drop in luminance levels under the same illumination conditions for concrete roads overlaid with bituminous asphalt. Thus concrete surface provide safer roadways for public driving, in particular, in pedestrian areas such as central business district streets and plazas, parking lots, parking garages, and around shopping malls, lighting enhances safety, and can help improve commerce and maintain property values.

10) Two-Lift Construction – This a paving technique for a pavement consisted of two layers, wet on wet, with the top layer consisting of a special mix to provide a quiet, durable and friction resistance surface. The bottom layer is normally a mixture of virgin aggregate with recycled concrete/asphalt aggregates and higher volumes of SCMs incorporated in it, which would normally not meet the top surface high quality requirements. This helps to minimize the use of virgin aggregate resources, yet prevent old concrete/asphalt being dumped in the landfill sites.

11) Full Depth Reclamation (FDR) - This process rebuilds worn out asphalt pavements by recycling the existing roadway. The old asphalt and base materials are pulverized, mixed with cement and water, and compacted to produce a strong, durable, stabilized base for either an asphalt or concrete surface. FDR uses the old deteriorated asphalt and base material for the new roadway base. There’s no need to haul in aggregate or haul out old asphalt material for disposal, greatly reducing the construction truck traffic. FDR with cement conserves virgin construction materials and makes smart economic and strategic sense. Continuing to exhaust these valuable resources to rebuild existing roads only propagates and accelerates the problem. Additionally, if old asphalt and base materials are not recycled, they must be disposed of or stockpiled, increasing transportation costs and occupying valuable landfill space.  

12) Cement Industry GHG and Energy Use Reduction Initiatives – As identified in the 2008 Canadian Cement Industry Sustainability Report the Canadian cement industry is committed to the continued reduction of its environmental footprint.  For example, between 1990 and 2006, Canada’s cement manufactures improved energy efficiency of their production operations by 11 % per tonne of cement, and reduced the greenhouse gas emissions (GHG) intensity of their production by 6.4 % per tonne of cement. Several additional methods to reduce the industries energy and CO2 footprints are currently being pursued including the following:

  • Reducing the clinker to cement ratio by intergrinding the cement with up to 15 % limestone. A new CSA Portland Limestone Cement standard will soon be released and a revision to the CSA concrete standard is to accompany it.
  • Increasing the use of supplementary cementing materials (SCMs) which again decreases the amount of cement being used, thereby, also decreasing the CO2 and energy footprint.  
  • Using alternative and renewable energies in the cement kilns as a replacement for coke or coal can also help reduce GHG emissions and energy use.  The more these fuels are accepted and utilized, as in Europe, the greater the GHG emissions reductions will be.