:  Fiber reinforced concrete has a long history of usage in highway infrastructure.  Some promising applications include reducing crack sizes and reducing the amount of steel rebar.  Either macro synthetic (rigid plastic), glass, basalt, or steel fibers are used to improve the performance of hardened concrete.  These fibers are designed with proprietary combinations of aspect ratios (diameter versus length), material type, and unique fiber design to improve the anchorage to the concrete.  Also, the fibers can be used between 0.25% and 0.75% by volume in the concrete.   While the fibers are responsible for improving the performance of the hardened concrete it is also essential that the concrete designed with the fibers is constructible.  For example, high dosages of fibers can create issues with pumping, finishing, and an overall loss of workability.  This means high dosages of fiber can cause constructability issues with the concrete.  This shows that fiber design is a balance between structural performance and constructability.   The current tests to evaluate fiber reinforced concrete include the slump test (ASTM C 143) and the residual strength in cracked concrete (ASTM C 1609).  While these tests are useful, more insights are needed to determine how fibers perform.  The research team at Oklahoma State University has developed two tests to provide new insights into fiber reinforced concrete performance.  These include the Split Beam Test and the Float Test.   The Split Beam Test is an indirect tension test that measures the ability of the fibers to reduce service cracking.  The Split Beam Test uses a 6” x 6” flexural beam mold with a rebar cast in the center of the beam.  Wedges are cast in the top and bottom of the beam.  Each wedge is shaped like a “V” but the sides of the wedge are not connected at the base.  As the wedge is loaded, this will cause the wedge to spread.  This spreading will cause a crack within the concrete beam at a known location.  For a given load or stress the size of the crack is measured.  The test is run with a #3 rebar cast in the center.  The crack size for a fixed number of loadings is compared for mixtures with and without fibers.  This provides a quantitative way to compare different fiber types and dosages to performance with only rebar.  This can be used as a performance-based test method.  The Split Beam Test is valuable as it measures the fibers' ability to reduce the size of cracks that form in concrete.  The Split Beam Test provides different information than the post crack strength measured by the ASTM C 1609 test and the Split Beam can be measured by any laboratory with a basic hydraulic press such as a concrete compression machine.   The Float Test evaluates the ability to finish the surface of a concrete mixture.  The tests use wood forms that are filled with concrete.  The surface of the concrete is struck off and three 1” diameter and 1” deep holes are placed in the concrete.  A metal float is used to smooth the surface of the concrete and fill in the holes.  The lower the number of passes required to create a smooth surface and fill the holes the better the performance of the mixture.  The Float Test has been a useful tool to investigate different concrete mixtures and determine the effect of the fiber dosage and type on the surface finishing of the concrete.  This is helpful as some fibers may be limited in dosage because they make it too challenging to finish the surface of the concrete.  The Float Test can help this be quantified.  The Float Test and Split Beam Test are useful performance-based tests that could help DOTs classify the performance of different commercial fibers and dosages.  This would allow DOTs to specify the desired performance for a certain application.  The performance of the mixtures in these tests will help guide which fibers are used in practice.  This means that different commercial fibers may need to be used at different dosages to provide the required performance.  This will ensure that the correct fiber design and dosage are chosen to meet the performance required by the DOT.  Also, a creep test will be developed to investigate the performance of fibers.  This test will be based on the split beam test, but it will not contain any rebar in the beam.  The beam is first loaded to create a crack of known size with a hydraulic load frame.  The beam will be removed, and either dead weight or a hydraulic accumulator will load the wedge.  This will hold a constant load on the beam.  These results will be compared to the creep performance of individual fibers to help understand the creep stresses within a concrete member.  The fibers will be rated into different categories of creep performance.  This will help design these fibers for use with concrete bridge decks or other locations where stresses may be significant.

:  This work aims to develop a prescriptive and performance-based specification that states could adopt to ensure the required performance in both crack resistance and contractibility of the fiber reinforced concrete.  This specification would use the Split Beam Test, ASTM C 1609, creep, and the Float Test to set performance limits for the different fibers.  This performance could then be specified based on the required performance or safe dosages of fibers could be prescribed based on the member.  For example, a sidewalk, overlay, and bridge deck may have different performance criteria.

:    Based on the objectives the following deliverables will be produced:

·         Standards for the Split Beam Test and Float Test,

·         Round robin testing with the Split Beam Test and Float Test,

·         Performance criteria for different applications such as bridge decks, overlays, and sidewalks,

·         Creep performance of macrosynthetic fiber,

·         Model specifications for different elements,

·         Guide document for producers on how to design and troubleshoot fiber reinforced concrete.

·    The expected contribution from interested agencies would be $30,000 per year (for three years).

·      All new funding commitments will need to be made on the Pooled Fund Website to this new project and all new funds will be transferred to the Lead State/Agency by the partners. The Lead State/Agency will have the responsibility for Receiving, Obligating, Expending, and Balancing the funding for this project.  Dr. Tyler Ley from Oklahoma State University will serve as the PI for this study.  The areas of coverage for this study would be Bridge, Structures and Highway design.