For most of the twentieth century, the economic expansion of nearly every major global industry was built upon linear production and life cycle processes.  In linear processes, resources were harvested, processed and converted, used, and at the end of their life, disposed of as waste.  The energy required for linear processes was likewise dissipated without intent of recovery or conversion.  Beginning in the 1960’s, economists began to examine the beneficial potential of cyclical economic systems, wherein finite material and energy resources are not dissipated in the manufacture of one-use products.  Sixty years later, in the 2020’s, we are beginning to see expansion of global initiatives aimed at creating circular economies where products are manufactured with the intent for the dual purposes of high performance and minimum or zero waste.  No longer can consumers with good conscience employ the practices of the mid-to-late 20th century era, in which room was made for a new refrigerator or TV, a new clothing item or lounge chair, a new lawn mower or pick-up truck by sending the old item to the trash heap.

For asphalt technologists, with long careers in the asphalt construction, preservation, and rehabilitation sectors, the notions of energy reduction, resource conservation, circular economic processes may seem to be part and parcel of our daily routine rather than a revolutionary new economic model.  Minimizing waste, recycling asphalt materials, conserving energy, and lowering greenhouse gas emissions has been a part of industry’s common practices for decades.  In the 1970’s, petroleum scarcity induced by the 1973 Nixon oil embargo and the 1979 Carter Iran crisis prompted asphalt paving technologists to begin using RAP and asphalt emulsions to conserve natural resources and fossil fuels. The use of polymer-modified asphalts, which was first introduced in France to prevent stone loss from chip seal pavements, became a common practice in the USA through the 1980’s in the construction of improved-durability load-bearing pavements. In the 1990’s, the SHRP Superpave initiative provided our industry the lab-based tools for testing binders and mixtures to ensure that the mix design process yielded the highest-performing asphalt pavement structure possible.

Along with initiatives aimed at improving the performance and durability of asphalt pavements, industry leaders were also examining in more formal ways, the environmental impact of our asphalt construction practices.  In 2003, Colas’ Michel Chappat and Julien Bilal published their seminal “Environmental Roads of the Future.”  (Their life cycle assessment is open-sourced in websites such as the following: www.colas.com/sites/default/files/publications/route-future-english_1.pdf.)  Chappat and Bilal considered the materials and energy inputs and waste and pollution outputs in three key stages of the production of 20 different load-bearing pavement layers.  Table I and Figure 1 are excerpted from the website source mentioned above. Their work confirmed what our pioneers of asphalt emulsion recycling knew back in the late 1970’s and early 1980’s:  cold in-place emulsion-based recycling is highly energy efficient and low polluting.  According to this document, it consumes roughly 20% the energy of conventional hot mix (20.4 = 100*139/680). 

Table I.  Energy Consumption for Harvesting, Processing, Transportation, Manufacturing, and Laying

Figure 1.  Energy Consumption for Harvesting, Processing, Transportation, Manufacturing, and Laying

Table II.  GHG Emissions Associated with Harvesting, Processing, Transportation, Manufacturing, and Construction

Figure 2.  GHG Emissions Associated with Harvesting, Processing, Transportation, Manufacturing, and Construction

Into this third decade of the twenty-first century, government and industry have aligned on the value of implementing circular economic policies and practices, and they are working diligently in numerous ways to convert all sectors of all industries into net zero operations.  The era of “take, make, waste,” is gone. 

But we in the asphalt emulsion industry can take pride in the fact that we have been ahead of this trend for decades.  We have the experience and knowledge to build sustainable, low-energy, low-emissions pavements using cold technologies.  We have the lab tools and field equipment as well as industry-accepted best practices and specifications to ensure the performance of cold mix pavement layers.  Combined, the pavement construction, preservation, and rehabilitation technologies developed by the asphalt emulsion industry provide the world with a path to net zero.   

1970’s – Scarcities induced by the 1973 Nixon oil embargo and the 1979 Carter Iran crisis prompt asphalt paving technologists to begin using RAP and asphalt emulsions to conserve natural resources and fossil fuels.

1987 – The EU’s Bruntland’s commission gave a definition to the economic concept of sustainability.

1988 – Allen V. Keese published “The Economics of Natural Resources,” which is often cited as the original source of the phrase “circular economy,” although this author could not find the phrase in the text.  This often-cited paper also speaks of man-induced climate change, intergenerational justice, and “sustained yield” economics, a forerunner of “sustainability” initiatives.  

1983 – The first polymer-modified asphalt emulsion-based, open-graded, load-bearing pavement was constructed in New Mexico.

1990’s – The SHRP research program aimed to development of lab-based binder and materials testing protocol to ensure the design and construction of high-durability asphalt pavements

1992 – Kyoto Protocols on greenhouse gas reductions

2010’s – Governments begin to craft legislation around sustainability and zero waste concepts.  India, in 2012, legislates electronics manufacturers must “take back” products at their end of life.  The World Economic Forum, in 2014, published “Towards a Circular Economy:  Accelerating the Scale-up across Global Supply Chains.”  In 2015, the EU began discussions of strategies to move from a linear to a circular economy, and the same year, the US Chamber of Commerce in conjunction with the EllenMacAuthor Foundation, the Dow Chemical Company, and Accenture produced “Achieving a Circular Economy:  How the private sector is reimaging the future of Business.”  The Netherlands government adopted a “roadmap to a circular economy” in 2018, and projects that by 2050 will be the first nation with a 100% circular economy.