Reinforcing concrete pavement with structural fibers improves its durability and helps protect against potential faulting and cracking. MnDOT has used fiber-reinforced concrete (FRC) on some concrete bridge decks and pavements. Winter weather, freeze-thaw cycles and road salt, however, still hasten concrete deterioration. In a recent study, researchers evaluated FRC in the context of performance engineered mix design methods, giving MnDOT confidence in the parameters that FRC needs to meet to help withstand Minnesota’s harsh weather.
MnDOT is a leader in using the performance engineered mixture (PEM) design method for pavements, which provides for a variety of testing to simulate actual conditions during pouring and throughout the concrete service life. Traditional concrete testing methods have been used for decades but are generally empirical, do not represent field conditions and are not specific to FRC. PEM design, on the other hand, uses new measurement technologies to identify the parameters a mixture should have to maximize strength and durability.
“This was our first study assessing fiber-containing concrete as a performance engineered mix, and we now understand the parameter ranges our fiber mixes need to have,” said Robert Golish, concrete engineer, MnDOT Office of Materials and Road Research.
To ensure fiber-containing concrete mixtures have the qualities that can help withstand Minnesota’s often harsh weather, MnDOT was interested in applying PEM design methods to verify the values for the FRC properties that would be specified to produce long-lasting pavements that reduce maintenance costs and improve road quality.
The goal of the study was to identify PEM target specifications for FRC mixtures to provide for durable and long-lasting pavement.
To begin, researchers performed a literature review on the PEM design procedure and key engineering parameters, fiber types and FRC properties. In the lab, they designed and tested 57 concrete mixes with PEM design methods. The mixes varied by fiber and aggregate type, workability and air voids.
With MnDOT’s input, researchers chose two synthetic fibers commonly used in pavement and three classes of coarse aggregates based on MnDOT’s standard construction specifications. Three target plastic air contents (4%, 6% and 8%) were tested, and the mixes were kept within acceptable workability ranges.
Researchers conducted concrete tests on each mix to understand the effect of the structural fibers. Significant tests in the PEM design method for fresh concrete included:
Other tests measured hardened concrete properties, including compressive strength, flexural toughness and stiffness, and the resistivity to water penetration and freeze-thaw cycles.
“MnDOT engineers can have confidence in using fiber-reinforced concrete in the PEM platform as they now have target ranges for a more durable concrete,” said Manik Barman, associate professor, University of Minnesota Duluth Department of Civil Engineering.
Using the test results, researchers developed draft specifications for the recommended parameter ranges for FRC mixtures.
Applying the PEM design procedure to FRC, researchers demonstrated the appropriate ranges of fresh concrete properties:
The tests for hardened concrete showed fiber had little effect on the compressive strength of concrete, while flexural toughness, or crack resistance, and residual strength improved significantly.
This work supports MnDOT in incorporating specifications for fresh concrete properties of fiber-containing concrete into MnDOT’s Standard Specification for Construction and provides confidence that FRC mixes developed in accordance with the PEM design procedure will be durable and long-lasting for use in pavements and bridge decks.
Additional investigation into field mixes and testing, particularly to find an appropriate range for the V-Kelly index for FRC, may be warranted.
ULTRA HIGH PERFORMANCE CONCRETE w/fibers is currently being used in New York State and has been approved by the FhWA. DD
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Crossroads is a collaborative effort among MnDOT’s Office of Research & Innovation, the University of Minnesota’s Center for Transportation Studies and the Minnesota Local Road Research Board. This jointly produced blog is devoted to highlighting the latest news and events in transportation research and innovation in Minnesota.