Researchers at the University of Minnesota Duluth have explored a promising solution to a major problem faced by thin concrete pavements: adding small synthetic fibers to the mix to extend their service life writes Megan Tsai for MnTAP News. Thin pavements, constructed over an existing base layer, are an attractive and economical option for low- to moderate-volume roads. However, they are highly susceptible to distress from traffic loads and weather, particularly transverse joint faulting. This faulting occurs when a noticeable difference in elevation develops between adjacent concrete slabs at a crosswise joint, creating a “washboard-like effect” that compromises ride quality and shortens the pavement’s lifespan.
The research, led by Associate Professor of Civil Engineering Manik Barman, was a pool-funded project of the National Road Research Alliance focused on mitigating transverse joint faulting. Faulting in thin pavements is typically caused by poor joint load transfer—the mechanism that distributes pressure from vehicles across the joint from one slab to the next. In standard pavements, this is achieved either with dowel bars (not viable in thin slabs less than seven inches thick) or through aggregate interlock, where embedded rock chunks connect to stabilize the slabs. Unfortunately, the thin structure of these pavements largely prevents effective aggregate interlock from occurring naturally, making the slabs highly vulnerable to shifting.
To quantify the fibers’ contribution, researchers built a model based on data from earlier test sections constructed at the Minnesota Road Research facility. The model revealed that the performance of the fiber-reinforced thin concrete pavement was heavily dependent on the vertical stiffness of the joints. The necessary joint stiffness was achieved through a combined contribution: the base layer provided 30 to 40 percent of the support, aggregate interlock contributed 15 to 20 percent, and the structural synthetic fibers accounted for the remaining 30 to 40 percent. Based on these findings, the team developed a new procedure called the “modulus of fiber support” to characterize the fibers’ contribution to load transfer, and determined a recommended value for its application in thin concrete pavements.
In the final phase, the researchers tested various synthetic fibers to identify the optimal design for improving joint load transfer. By embedding and then pulling out single fibers, they measured the force required and found that fibers featuring indentations and surface irregularities exhibited increased peak load and toughness. This result points toward a next-generation fiber design. The research team is now planning to continue its work by developing this type of “bumpy” fiber engineered with the needed modulus of fiber support value. They also aim to create a simple test to screen and characterize fibers specifically for use in concrete pavement applications to effectively mitigate joint faulting.
Read more here: https://mnltap.umn.edu/ltapnews/2025/october/concrete