Recycling Concrete v. Placing it in a Landfill: A Comparison of Greenhouse Gas Emissions
As one of the most abundantly used resources in the world -- second only to water, according to some measures -- determining what to do with concrete once it is no longer needed in its original application is a major issue. Most of the time, waste concrete is not structurally flawed or degraded, but the building or structure it was used in is simply no longer needed or is being rebuilt and so the concrete must be torn down while there is still a great deal of usefulness in it. Recycling the concrete thus seems like a very good idea, and to be sure recycling concrete can lead to a major reduction in the raw materials needed around the globe each year for a variety of concrete construction projects. A great deal of energy is also required for the various steps of the recycling process, however, and this has a negative environmental impact in the form of carbon emissions from the burning of fuels to create the needed energy.
The following pages will attempt to present a comparative analysis of the greenhouse gas emissions that result from the various stages and processes involved in recycling concrete and the emissions from the other commonplace method of dealing with waste concrete, putting it in a landfill. Certain parts of this process are nearly identical while others are of course drastically different, ultimately leading to very different emission levels for the two different options. An examination of greenhouse gas emission does not tell the full story of concrete disposal's environmental impact, of course, but it provides an excellent starting place.
Similar First Steps
The initial demolition or removal of concrete from a building or construction site is the first step in concrete's journey wither to a landfill or to the recycling facility, and the bigger the job the more likely it is to involve powerful tools that are ultimately powered by fossil fuels (often pneumatic tools hooked up to air compressors hooked up to gasoline generators). As the emissions that result from this initial demolition would occur regardless of whether the concrete is ultimately recycled or disposed of in a landfill, however, it is not necessary to consider them in this comparison of emissions. The same is true of the next stage of the concrete's journey.
The recycling of concrete can take place at demolition sites with the use of mobile units, but it is more typical for waste concrete to be transported to large static plant for processing into new concrete material. This transportation can itself result in a significant amount of greenhouse gas emissions, as each truckload of waste concrete represents only a few miles to the gallon given the heaviness of the standard load and the size of the transport trucks. While an exact figure for these emissions is impossible to determine given the large variances in travel distance, fuel efficiency, and other factors, these transportation emissions are definitely a part of the environmental impact of recycling concrete, and they also apply to putting waste concrete in landfills. The same transportation emissions that are created driving waste concrete to processing plants for recycling are created driving waste concrete to landfills (again, exact levels cannot be determined).
Landfill Equipment and Processes
It is once the waste concrete arrives at its destination -- either a recycling plant or a landfill -- that the emission potential of the processes really begins to diverge. Even here, however, some of the needs and equipment are the same for recycling concrete as they are for processing it for landfill disposal. Both processes require that the concrete be broken down to a certain degree -- in recycling, this is so the concrete and be better "purified" by passing it through screeners, while landfills are simply trying to maximize the efficiency of the physical space and the equipment being used by working in thin layers to pack everything as tight as possible: concrete dust can get squeezed much thinner than large chunks of the building material (Bliss, 2011; Everett, 2009). Sending concrete to the landfill actually avoids several pieces of heavy duty equipment used to separate materials in the recycling process; the same type of crushers can be used to simply pulverize the concrete and anything embedded in it…