Change Leader: Quantifying the Usability of Recycled Concrete
Yahya Kurama is a professor and associate chair of the University of Notre Dame’s Department of Civil & Environmental Engineering & Earth Sciences. A recent research project focuses on the reusability of recycled concrete for building structures rather than just as road base. But to make recycled concrete a legitimate choice as a recycled building material for new construction, more needs to be known about its properties.
Research has focused on classifying old crushed concrete with an eye on quantifying its strength, durability and long-term deformation. Experimental and analytical research is being applied to understand the economic and environmental benefits of recycled concrete as well as many performance factors. Ultimately, the project will develop performance-based requirements, mix-design guidelines, acceptance tests and structural design/analysis/construction guidelines to achieve acceptable performance of concrete members using recycled concrete aggregates.
There is increasing focus on sustainability for how people plan, design and engineer infrastructure. And it’s difficult to talk about sustainability without discussing concrete, a resource-demanding product that’s involved in most infrastructure projects.
“What we’re doing isn’t new in terms of the idea of recycling concrete—that has been going on for a long time,” says Kurama. “When you look at the material properties of recycled concrete, there is a lot of variability, and that is one of the engineering constraints with the material. Our research tries to address that variability and also elevate the use of recycled concrete for structural applications.”
By quantifying the properties and setting guidelines, the team aims to set a hierarchy of quality and prove the material’s worth for use in building superstructures.
The research team has been asked questions on the need to find new uses for recycled concrete other than its traditional use as road-base material. Through their research, the team visited many concrete recycling yards and witnessed piles and piles of material; some facilities aren’t even accepting new material because they can’t get rid of their existing supply.
“The amount of demolished concrete will further increase as we replace our deteriorating infrastructure and using recycled concrete for building applications would be a way to increase demand to match the supply,” notes Kurama. “This could also give recycling yards guidance on the quality of their material. If you give more value to higher-quality aggregate, then the market will develop for higher-quality recycled materials. Then the different materials would be sorted according to their properties, and they would be used for different applications.”
Recycling concrete from demolished buildings, roads or bridges and using that concrete for road base takes a high-quality product and puts it on the ground where the demands on the material aren’t very high. If builders can use recycled concrete in beams, columns and slabs, where loads and service demands are higher, the materials retain their utility and value.
“There are sustainability goals, of course, but you can’t sell the idea if you can’t make it economically viable,” adds Kurama. “What we’re trying to do is minimal processing of the material so that it’s more economically appealing than getting natural aggregate for applications where its performance fits.”
With a group of researchers from the University of Texas at Tyler and New Mexico State University, the team is working on lifecycle cost analysis to quantitatively show the economic benefits.
Transitioning recycled concrete from road-base to structural applications requires a lot of investigation. The research team is busy investigating many aspects of the material, ranging from its mechanical properties to variability and durability. The goal is to understand what the effects are and then design around those effects.
“We aren’t promoting the use of this material in exterior applications,” notes Kurama. “For example, using recycled concrete in a bridge application would not be a good idea. The material is generally more absorbent than natural aggregates, so with a lot of water around, it will pull in more of the chemicals, and eventually they could reach the reinforcement and cause it to deteriorate.”
Best Fit First
The research team is pursuing reuse in the precast/prestressed concrete market, as it has a great potential for entering practice. Many of these facilities already own or work closely with concrete recycling facilities to deal with rejected or discarded products, but they haven’t pursued recycling the material back into new precast concrete products. They also have tight controls on their concrete quality, so the resulting recycled concrete is also of high quality.
“We are currently working with two precast producers, one in Michigan and the other in Indiana,” adds Kurama. “We’ve collected materials and are looking at their effects on concrete strength, prestressed strand bond characteristics, and service and ultimate behavior of prestressed concrete members.”
Recently, the research expanded with a National Science Foundation grant that has enabled the study to begin quantifying materials from around the country to add to the knowledge base of materials from the Midwest that have already been assessed.
Read the full interview here.