For the past 15 years, synthetic macrofibers have been used to control concrete shrinkage and curling in both interior and exterior slab-on-ground applications. Synthetic macrofibers were used in the 2009 Warehouse Trial Study project in Chicago, funded and monitored by CONCRETE CONSTRUCTION magazine. The project saw confirmed curling reductions on high-fiber slabs. Since that time, macrofibers at concentrations of 0.5% by volume (7.5 lbs/cu yd) have been used successfully to extend joint spacing and reduce joint-related deterioration and repairs in slab and pavement projects all over the world. In these cases, the high volume of fibers has provided the mechanical means to control the short- and long-term effects of shrinkage cracking, with plasticizing chemicals used only to maintain mix flowability and user-friendliness.
The history of steel fibers in the U.S. dates back to the 1970s but has been mostly limited to industrial floors, precast, and pavements. Internationally, though, steel fibers have proven their worth in a wide variety of projects, including jointless, seamless, liquid-tight floors as well as mat foundations and floors on piles. Successful floors are being designed every day with price competitive dosages of steel fiber per cubic yard that have had joint spacing as high as 100 feet square or even no joints. In several European countries more than 50 % of all floors in large distribution centers are jointless floors reinforced with steel fibers. Over this period of 25 years a lot of knowledge has been gathered in the proper design and construction of jointless floors.
Recent admixture developments have suggested that high fiber volumes are perhaps not necessary to obtain large-panel objectives when used in combination with newer SRA (Shrinkage Reducing Admixtures) or CRA (Crack Reducing Admixtures). However, the contributions to long-term ductility and durability of these admixtures have not been proven. Continued real-world research and discussion are needed to compare slab shrinkage, curling, ductility, and fatigue ramifications for fibers versus admixtures for shrinkage reduction.
Speakers at the 2015 Quality in Concrete Slabs Luncheon and Forum will include Dan Biddle, Forta; Hendrik Thooft, Bekaert; and Tarek Khan, BASF.