Mining our Aging Infrastructure for Natural Resources

When an Illinois Department of Transportation (IDOT) project required the replacement of the Abraham Lincoln Memorial Bridge concrete bridge deck on I-39 crossing the Illinois River, there was only one location to dispose of the massive amounts of concrete. The City of Peru, Illinois operates a landfill and has a use for all of the concrete being removed from the project. IDOT did not want the material to be buried in a pit, therefore when the City of Peru offered to take the concrete from the project to process into Recycled Concrete Aggregate (RCA), IDOT had found a new home for the old Abraham Lincoln Memorial Bridge Deck.

The project was divided into two phases for replacement, the first being replacement of the south bound bridge lanes with phase two of the project being the replacement of the north bound lanes. The Abraham Lincoln Memorial Bridge has the longest arch bridge span in the state of Illinois. Once demolition of the 20 year old bridge deck began the contractor systematically removed the concrete guard rail and bridge deck by first saw cutting off the guard rail and loading it onto flat bed semi trailers for transport to the Peru Municipal Landfill.

Next the bridge deck was saw cut into 10’ x 10’ sections and shipped via truck to the landfill. Now that the material had arrived on-site, the City of Peru was ready to proceed recycling the concrete into a reusable form. The City has a need for primarily two aggregate products; 6” to 12” Rip Rap and CA-6 aggregate. Rip Rap is used to armor shore lines and stream beds against water and sometimes ice erosion. CA-6 is an aggregate base typically made from crushed rock comprised of material capable of passing through a 1¼” rock screen. The crushed material particles will vary in size from 1¼” down to dust. The material can be made of virgin (newly mined) rock, or of recycled concrete or asphalt. CA-6 aggregate is used as a base course in roadways; concrete pads such as side walks, in foundations and as back fill material for underground pipelines and other underground utilities

The City of Peru utilizes several machines in the process of reducing the material from the 10’ x 10’ to CA-6. First a Cat 928 loader moves the oversized concrete to the primary processing area using lifting forks. Secondly a 330 Cat excavator fitted with a mechanical processor attachment is used to reduce the material size to 12” minus. This process also breaks the concrete off of the steel rebar used to reinforce the concrete bridge decking. When this steel rebar is removed it is sold to the steel scrap yard and recycled. Once the concrete is separated from the rebar, it is loaded with a clamshell crane onto a grizzly screen which allows any material smaller than 6” to pass through, retaining the 6” x 12” Rip Rap to be used by the City. The remainder of the material is stock piled to be processed at a later time into CA-6 base RCA.

When the Peru Municipal Landfill needs to process the remaining 6” minus material into CA-6 RCA, the same 330 Cat excavator used to process the oversized concrete is fitted with an excavator bucket to feed the concrete into a Rubble Master RM80 Compact Recycling Crusher. In one pass through the RM80 the material is crushed to 100% passing the 1¼” screen size making the second aggregate product primarily used by the City of Peru for its many municipal construction projects. Previously it was estimated that the City would buy more than $100,000 worth of CA-6 each year.

The city is constantly asked if they would sell the RCA CA-6 to the general public. Many studies have been conducted to evaluate the application of Recycled Concrete Aggregate as used in applications where natural stone is used by such organization as the Portland Cement Association (PCA) and the Federal Highway Administration (FHWA). These studies have revealed that RCA requires nearly 20% less labor to compact into place when compared to natural crushed stone due to the geometry of the finished product. The angularity of RCA provides increased structural integrity resulting in improved load bearing capacity and compaction. The environmental benefits of using RCA include the reduction of landfill space required to dispose of these construction and demolition (C&D) materials as well as the conservation of virgin aggregate resources.

Experts estimate that on average, C&D materials like this concrete make up more than 25% of our nation’s waste stream, prematurely filling our nation’s landfills. In order to defray the cost of recycling C&D materials, most landfills charge tipping/dumping fees to offset the cost of recycling these materials. The City of Peru had the foresight on this IDOT project to reduce the dumping fees in order to utilize this valuable resource called Recycled Concrete Aggregate (RCA). As a result, the City of Peru has taken in nearly 160,000 tons of concrete from the Abraham Lincoln Memorial Bridge resurfacing project. The economic payback of utilizing this single project’s materials in lieu of our natural resources is amazing.

Once crushed into a usable product, the value of the Recycled Concrete Aggregate is estimated at nearly $10 per ton. The value of recycling the steel rebar imbedded in the concrete bridge deck varies with the scrap market but has been as high as $.15 per lineal foot. These numbers alone do not sound so impressive, but when you consider the massive size of the project with over 160,000 tons of concrete and over 1.5 million lineal feet of steel rebar being brought into the Municipal Landfill, the recycle value of this project immediately sky rockets to well over $1.8 million in revenue potential from this one recycle project alone. As more and more regions adopt Green Community policies, the requirements on recycling will increase. Many cities already require a high percentage of waste from demolition projects to be recycled. Several cities have mandated the use of recycled concrete aggregate (RCA) be used for base material, while others have gone so far as requiring that all demolition projects require a minimum of 50% of all C&D materials be recycled. With all of these compelling reasons, On-Site Recycling must always be considered.

We applaud the City of Peru for their forward thinking and progressive approach to recycling. Mining our aging infrastructure for natural resources is not only environmentally responsible, but economically beneficial to communities large and small.