Concrete inFocus - Spring 2015 - (Page 18)

sustainability How the Concrete Paving Industry is Incorporating Sustainability into Our Practices Jim Mack O ver the last five years, I have had the honor to work with the Concrete Sustainability Hub (CSHub) at the Massachusetts Institute of Technology as it has researched processes and developed tools to be used by decision-makers in order to make more informed decisions on pavement designs that are both cost-effective and environmentally responsible. Because of this unique view, I was recently asked to comment on how the cement, concrete and concrete paving industries are implementing sustainability practices into our daily activities to lower the environmental footprint of concrete pavements. In reflecting on this, I concluded that our activities are being driven by these two questions. 1. What are we doing - looking inward - to improve our products 2. What are we doing - looking outward - to ensure that Pavement Life Cycle Assessment Processes are done as best as possible to capture the true environmental impact of pavement decisions With respect to "Inward looking", our industry has made and is continuing to make a number of advancements that improve our products: These include: Increasing the use of "Low Carbon Concrete Mixes." As is well known, cement is the 800 pound gorilla with respect to CO2 emissions for concrete pavements. To have meaningful sustainability reductions, the industry 18 ı SpriNg 2015 needs to address this issue and we have initiated several activities to do exactly this. First, we are improving our mix designs by using optimized mix gradations, recycled concrete and asphalt aggregates, and supplementary cementitious materials (fly-ash, slag and other products) to not only lower our environmental impact, but to also improve the concrete so that our pavements perform better. Nowadays, it is not uncommon to see concrete mixes with supplementary cementitious material replacements rates between 20 and 50 percent. Along similar lines, we are trying to increase the use of limestone cements. The use of limestone as a component of portland cement has been common practice in Canada and Europe for about 30 years. In Europe, limestone contents can be as high as 35 percent. In the U.S., the industry and the state Department of Transportations have recently unified the ASTM and AASHTO standards so that limestone cements can be more readily used. If the use of limestone cements can get to the same level of use as other parts of the world, the U.S. will see a 10 to 15 percent reduction of CO2 from the production of cement. The cement and concrete industries are also investing in research to lower the environmental impact with the production of cement. In fact, a very recent finding from the CSHub shows that if the ratio of calcium to silicate in the cement nano-structure is altered, it can decrease greenhouse gas emissions in two ways - first by lowering the energy required to produce cement and second by reducing the amount of carbon dioxide released from limestone during the manufacturing process (see stronger-greener-cement-0925). In the same manner, the cement industry has had a huge focus on energy efficiency. Over the past four decades, we have seen energy reductions of over 40 percent (Figure 1) and currently have several alternative fuel projects under development that will lead to additional decreases as the use of alternative fuels increases. While the industry has been working on lowering the impacts of cement and concrete mixes, it has also been working to make sure that concrete pavements are not being "overdesigned." Many concrete pavements in the past were designed too thick. While this can be a benefit for long term performance, the extra thickness is not the most cost-effective or environmentally friendly approach to improve sustainability on a particular project. This is why the industry is adamant about using the most up-to-date design tools, such as the AASHTO Pavement-ME Design Procedure for highways and StreetPave for lower volume roads, to optimize pavement designs, and using new products such as Concrete Overlays and Roller Compacted

Table of Contents for the Digital Edition of Concrete inFocus - Spring 2015

Ready Mixed Plant Innovations
Data Security of Credit Card Processing in the Concrete Industry
Oldcastle Material Group
How the Concrete Paving Industry is Incorporating Sustainability into Our Practices
Index of Advertisers
The Trail to Your Future Business Should be Paved with Concrete
Your Biggest Environmental Threat in 2015 is NOT Who You Think!
Why is the Air There? Thinking about Freeze-Thaw in Terms of Saturation

Concrete inFocus - Spring 2015