By: Fares Abdo, PCA Market Manager, Pavements
Sustainable development—a construction concept that began by focusing on buildings—has expanded to other sectors, including road construction.
At its core, sustainable development seeks to find a balance between the economic, environmental and social effects of growing population attempts to lessen the impacts of our built environment.
Highways, roads and other pavements should account for long service life, conservation of energy and natural resources, and maintaining the quality of natural water supply. The value of concrete pavements can be applied to social aspects of traffic congestion, fuel conservation and use of recycled materials.
The durability of concrete is key to addressing all aspects of sustainable design. Fifty-year-old pavements are common in the U.S. According to the American Concrete Pavement Association, when looking at existing concrete roads more than 50 years in age, over half of them have a Pavement Serviceability Rating, based on AASHTO’s 1962 Road Test Scores, of 3.1 or greater on a scale of 5. A rating between 3 and 4 is good; between 4 and 5 is very good.
For instance, I-10 west of Los Angeles was constructed in 1946 as part of U.S. Rte. 66. It was ground 19 years later to correct joint faulting and spalling. This was the first continuous grinding project in North America. It was ground two more times; once in 1984 and again in 1997. The concrete highway is 63 years old and still going—a true testament to concrete pavement sustainability.
Longevity’s most important sustainable contributions are (1) conservation of natural materials by reducing frequency of reconstruction or rehabilitation; (2) reducing energy consumption to mine, manufacture and transport new materials; (3) less damage to roads from transporting these new materials; and (4) lowering community impact by reducing waste and by reducing traffic congestion at construction zones. Add to that lower emissions from all phases of the construction which impacts air quality and health.
During construction, the difference in fuel consumption to produce asphalt vs. concrete is huge. This is mainly due to the energy required to heat asphalt materials. Additional factors include equipment needed for placement, and multiple lifts vs. single-lift construction.
Approximately 500 million tons of hot-mix asphalt (HMA) is placed in the U.S. annually. If one-fourth of these asphalt pavements were converted to concrete, annual fuel savings during construction would be greater than 375 million gal, a CO2 savings equivalent to taking 1 million cars off the road. It also is important to consider that asphalt binder is made from petroleum, which is an energy source as well. This is known as feedstock energy, because of petroleum as part of the raw materials also has energy value.
Athena Sustainable Materials Institute analyzed total embodied primary energy and feedstock energy for various equivalent concrete and asphalt pavement structures for several different road types in various geographic regions during a period of 50 years. Athena’s analysis showed huge energy savings when using concrete and considering both primary energy and feedstock energy.
