CEE researchers are examining ways to develop unreinforced jointless rigid pavement with improved structural resiliency and durability while reducing cost and improving environmental sustainability using an Engineered Cementitious Composite (ECC). The team, led by Victor Li–the E. Benjamin Wylie Collegiate Professor and James R. RIce Distinguished University Professor–along with He Zhu – a research scientist at UM, and Visiting Professor Esayas Ftwi, a faculty member at the Addis Ababa Institute of Technology of the Addis Ababa University, Ethiopia, is testing ECC enabled with high Modulus of Rupture (MOR), Low Elastic Modulus (E), for shrinkage-free and improved fatigue endurance to form a jointless rigid pavement used on a portion of the U-M Mcity track.
Sensors were recently placed at edge, center and corner points of the rigid pavement at Mcity to monitor the stresses that this pavement will encounter over time due to material hydration, weather conditions and traffic loads. “We tailored the design of this specific ECC material for the last 6 months, and we have obtained convincing laboratory results both from material and structural performance points of view and we want to apply this not only in the lab, but in the field as well.” said Prof. Ftwi.
The pavement currently used in most roadway projects is concrete or reinforced concrete, and most of it has joints every 12 to 15 feet. These joints create discomfort for passengers when driving, and they require load transfer elements at the joints and hence higher labor and material cost. Joints are also where concrete cracks tend to form. “We are trying to develop a pavement without joints, and at the same time, with a thickness half that of the conventional Jointed Unreinforced-doweled Concrete Pavements (JUCP). The 50 percent reduction in thickness will reduce cost, and lower the CO2 footprint and embodied energy of the pavement,” Prof. Ftwi said.
One of the key features of ECC is its bendable quality. “It has high ductility with strain-hardening behavior (2 to 3 orders higher than the conventional concrete), so it has high resilience against crack development and delays failure,” Prof. Ftwi said. “At the same time, we have incorporated a behavior which makes it non-shrinking, providing high MOR and Lower Elastic modulus. The combination of the ductility with strain hardening, high MOR, Lower E, non-shrinking behavior and enhanced fatigue resistance – all contribute to jointless function of the pavement with great reduction of cost, CO2 footprint and energy use.”
The previous pavement that was removed from Mcity had three segments with 8-inch thickness. “We cast a continuous ECC pavement without a joint, 32 feet by 6 feet, with 4-inch thickness, and we placed sensors to monitor the behavior of this,” Prof Ftwi said. The sensors will register temperature distribution at the top and bottom parts of the edge, center and corner locations of the pavement. The sensors are also monitoring the amount of strain on the pavement due to material chemistry, traffic loads and weather and environmental conditions.
“We want to see how this material performs in practice,” Prof Ftwi said. “When traffic passes through this pavement, we will know how the ECC pavement is responding at different points in time. The prior pavement that was removed had several random cracks between the joints and around the edges of the manhole cover present. We have convincing laboratory results that support our ECC pavement demo will be free from shrinkage related cracks. This will be a good test for our material, from a visual point of view, as well as from the information the sensors will provide.”
Prof. Ftwi said that he was grateful for the opportunity to participate in this research at CEE, led by Prof. Victor Li, the developer of ECC. “This is a very exciting project,” Prof. Ftwi said. “We are trying to pull important infrastructural features into one and provide sustainable solutions to the construction industry. As civil engineers, as much as we contribute to society by building infrastructures, we are also responsible for the CO2 emissions due to the enormous volume of materials used in construction. We need to be very cautious, aware and careful to ensure the sustainability of the infrastructures we build. I am optimistic about this ECC project. We have improved economic aspects, and the CO2 footprint will be much lower–about a 40 percent reduction, in addition to improved structural and durability performance with reduced maintenance cycles. Many pavements around the world are currently suffering and are in poor condition due to corrosion, fatigue and other environmental and material factors. We are bringing this technology to address these issues. I hope to see this flourish in practice as a result of this research.
Prof. Ftwi has been at U-M CEE as a part of his sabbatical. His title is Associate Professor of Concrete Materials and Structures at Addis Ababa University, and he will return to Ethiopia on December 31, 2022. Prof. Ftwi will continue work on the project remotely through next year. He is excited about the additional development of ECC programs.
“There are a lot of opportunities we can harness from this project,” he said. “Given the important findings demonstrated in this material, I hope this will lead to implementation of the results in a very short time. I am hopeful we will see this implementation soon in industry and by transportation departments globally.
“I want to express my gratitude and appreciation for the opportunity to work on this very exciting project. This was a dream come true to be able to contribute to this study.”