Part II: Durability Assessment of Recycled Concrete Aggregates for use in New Concrete

Currently the use of recycled concrete as aggregate in the United States is predominately limited to use in pavement base or subbase material and non-structural fill with a vast majority landfilled. As natural aggregate sources diminish and government initiatives as well as public demand push the use of sustainable construction practices the need for alternative aggregate sources continues to rise. One of the most logical and environmentally friendly practices is to recycle concrete taken out of service into a source of aggregate for new concrete construction. This is a common practice in asphalt materials, aluminum, steel and glass industries -…

Currently the use of recycled concrete as aggregate in the United States is predominately limited to use in pavement base or subbase material and non-structural fill with a vast majority landfilled.  As natural aggregate sources diminish and government initiatives as well as public demand push the use of sustainable construction practices the need for alternative aggregate sources continues to rise.  One of the most logical and environmentally friendly practices is to recycle concrete taken out of service into a source of aggregate for new concrete construction.  This is a common practice in asphalt materials, aluminum, steel and glass industries - to name a few.  However, the use of RCA in transportation infrastructure has been limited.  This lack of widespread use is centered on a lack of scientific evidence showing how RCA can be used effectively, efficiently and with no greater risk to achieving construction goals than virgin construction materials.  Of particular concern is a stigma that RCA is a substandard material and that long-term performance (e.g. durability and serviceability) cannot be guaranteed.  No uniform guidance from the Federal level has been made available to ensure that engineers, state DOTs, ready-mix suppliers and/or contractors use RCA in a consistent and reliable manner. 

This research project, started in the 2009-2010 funding cycle, has the primary goal of investigating the long-term durability of concrete incorporating RCA through accelerated laboratory testing.  Of particular interest is the possibility of pronounced alkali-silica reaction, an expansive reaction that results in cracking and a reduction in the service-life of concrete structures, in new concrete incorporating RCA which may have active ASR.  This area of concern was identified by several states as a major research need in a recent FHWA study.1

While significant progress has already been made in the initial 6 months of the first phase of this project, the research team has indentified research objectives for the second phase of funding that can address critical national needs identified through the current OTREC RFP for 2010-2011.  The objectives of Phase II of this research project include: 

- Verification of accelerated laboratory testing methods (identified in Phase I) that will provide prediction of ASR in concrete including RCA. 
- Investigate mitigation strategies to reduce and/or eliminate the risk of deleterious ASR in new concrete incorporating RCA [which may promote ASR if left unmitigated
- Recommend “Best Practices”  for successful use of RCA in new concrete which may suffer from ASR
- Establish a “clearing house"in the form of a website (off of OTREC) and/or a software program that state DOTs, designers, ready-mix suppliers, contractors and other interested parties can access for rapid dissemination of research results and guidance for using RCA in new concrete. 
- Continue to expand existing literature and the state-of-knowledge for RCA through OTREC published reports and presentations at select conferences for testing methodologies to assess the risk of ASR in concrete incorporating RCA

Perhaps the most exciting Phase II research topic will be the development of a guideline for using RCA in new concrete to ensure long-term performance while meeting the structural requirements of a variety of transportation infrastructure projects.  The focus will be on new concrete incorporating RCA susceptible to ASR.  However, this type of document will identify further areas for research regarding long-term performance of concrete incorporating RCA.  Through ongoing discussions with FHWA a much larger research initiative stemming from the work is envisioned.  Discussions are already underway with FHWA representatives who are interested in teaming for a larger project investigating durability of concrete incorporating RCA - which is a direct result of the initial OTREC 2009-339 Phase I project.  Presentations at national conferences (TRB, ACI, ACPA, etc.) will provide awareness of project outcomes as well.