Cementing high-strength, cost-effective concrete using local materials

How can transportation agencies build higher-strength infrastructure while maintaining cost-effectiveness?

That’s a question Illinois Center for Transportation and Illinois Department of Transportation sought to answer in a joint project, R27-232: Utilizing a Particle-packing Approach for an Illinois-specific, Nonproprietary, Low-shrinkage UHPC.

Nishant Garg, University of Illinois Urbana-Champaign professor, and Matthew Gombeda, Illinois Institute of Technology professor, led the project with James Krstulovich and Mark Shaffer, IDOT’s engineer of concrete and soils and engineer of bridge design, respectively.

The project aimed to optimize the use of local materials in ultra-high-performance concrete, which is three to four times stronger than regular concrete but may be 15 to 20 times more expensive.

“Concrete is the most widely used building material in the world,” Krstulovich said. “However, there are special cases when structural design or structural repair and preservation would benefit greatly if concrete was optimized to a higher level, for example, strength increased at least 4 to 5 times.”

“The goal of our project was to see if it is feasible to optimize concrete to such a degree using the cement, sand, rock, and so on typically found at a ready-mix concrete producer,” he added.

Optimizing local ingredients in UHPC will reduce project costs and shrinkage while maintaining its high strength, creating longer-lasting and more sustainable structures.

Ultra-high-performance concrete has a high capacity to withstand loads that compress it (compressive strength) and resist bending (flexural strength), which, when combined with steel fibers, mitigate concrete’s poor tensile properties.

Additionally, because of how densely packed its ingredients are when combined, UHPC is nearly impermeable, allowing it to better withstand climate or chemical effects from freeze-thaw cycling and deicing substances, for example.

To develop an optimized UHPC mix, Garg and Gombeda’s team developed and tested 19 UHPC mixes with local materials to see if they met IDOT’s performance criteria using compressive strength tests, flow measurements and shrinkage assessments.

Key to the research is a particle-packing approach the researchers developed. The approach identifies how densely materials in a UHPC mix may be combined and correlates it to performance.

“We coined the ‘packing factor’ as an innovative parameter for designing 19 unique UHPC mixes with different packing profiles based on the inherent physical properties of the binders and aggregate,” Garg said.

They added steel fibers to the best-performing mixes and created small-scale beams to test tensile properties.

The developed mixes had a comparable strength to commercial UHPC mixes while reducing cement content to as low as 50%.

Reducing the cement content will lower the carbon footprint of concrete as well as lower the cost of materials and equipment for transportation agencies.

They determined the mixes could be produced at approximately $308 and $454 per cubic yard without and with fibers, respectively — a reduction from the commercial price of over $2,000 per cubic yard.

“Reduced costs and the potential to engineer a mix using readily available local materials could accelerate deployment of UHPC across the State, resulting in more resilient new construction or longer lasting repairs to existing structures, potentially reducing maintenance needs and associated disruptions to travel,” Shaffer said.

“Ultimately, higher performing, more durable concrete can be more sustainable for Illinois,” he added.