Author: Integrated Paving Solutions
When evaluating the carbon footprint of concrete pavements, it is important to recognize the difference between cement and concrete. While cement is an energy-intensive product, concrete is actually one of the world’s most CO2- efficient and sustainable construction materials.
CO2 emissions from a cement plant are divided into two source categories:
- Combustion (40 percent of emissions)
- Calcination (60 percent of emissions)
The combustion-generated CO2 emissions are related to fuel use. The CO2 emissions due to calcination are formed when the raw materials (mostly limestone and clay) are heated to more than 2500°F and CO2 is liberated from the decomposed minerals.
During the life of a concrete pavement, the concrete that is exposed to air slowly absorbs nearly 60 percent of the CO2 released by calcination during the cement manufacturing process (Nordic Innovation Centre Project 03018). The carbonation process continues even after the pavement is demolished and the concrete is crushed and reused.
The focus of reductions in CO2 emissions during cement manufacturing is on energy use, and the cement industry is striving to continuously reduce its CO2 contribution.
* From industrial sources only, cement accounts for less than 3% of U.S. CO2 emissions, well below other materials such as petroleum (21.8%), chemicals (22.2%), and iron/steel (9%).
Putting CO2 Emissions into Perspective
The manufacture of cement produces about 0.9 pounds of CO2 for every pound of cement. Since cement is only a fraction of the constituents in concrete, manufacturing a cubic yard of concrete (about 3900 lbs) is responsible for emitting about 400 lbs of CO2.
The release of 400 lbs of CO2 is approximately equivalent to:
- The CO2 associated with using an average tank of gas in a car
- The CO2 associated with using a home computer for a year
- The CO2 associated with using a microwave oven in a home for a year
- The CO2 saved each year by replacing 9 light bulbs in an average house with compact fluorescent light bulb
This is just an extra source I throw in to help gain perspective on relationship between concrete and the environment.