عنوان مقاله [English]
In this study the effect of polymeric and steel fibers in controlling drying shrinkage cracking of concretehas been investigated by the restrained ring test according to ASTM C1581 and the cracking potential of various mixes has been determined. In addition the effect of various fibers on physical and mechanical properties of concrete such as a compressive and tensile strength and free shrinkage was investigated. Fibers used included, macro polymeric fiber of single-strand type, spun multi-strand type and a hooked end steel fiber, which were used at dosages of 0.25, 0.5 and 1 %. Furthermore a micro polymeric fiber at dosage of 0.25% was investigated.
The results show that use of steel fibers up to 1% and macro polymeric fibers up to 0.5%have no appreciable effect on compressive strength.With regards to tensile strength, the effect of fibers up to 0.5%was similar to that described for compressive strength. However, at the dosage of 1%, the use of steel fibersincreased the tensile strength while macro polymeric fiber slightly decreased this parameter.
Free shrinkage test resultsindicate that the effect of fibers on free shrinkage is negligible.
The effect of micro and macro polymeric fibers at the dosage of 0.25%in decrease cracking potential of concrete is lowand cracking potentials are classified as “High”. At this dosage steel fiber has shown slightly better performance and the cracking potential was“Moderate to High”. With increasing the dosage of fibers to 1%the cracking potential for macro polymeric fibers and steel fibers were determinedas “Moderate to Low” and “Low” respectively.
Crack width measurements show that macro polymeric fiber and steel fiber at a dosage of 0.25% decrease crack widths by about 35% relative to the control mix.At fiber contents of1%, the maximum crack opening for the macro polymeric fibers show a decrease of about 60%compared to the control mix.The steel fiber show the best performance at this dosage and is able to completely prevent shrinkage cracking.