Free Shrinkage of High Performance Steel Fiber Reinforced Concrete

The paper deals with the results of an experimental investigation into the free shrinkage of high performance steel fiber reinforced concrete (HP-SFRC). The development over time of the autogenous, total, and drying shrinkage of HP-SFRC, with a steel fiber content of between 0.25 % and 2 % by volume and that of a comparable high performance concrete (HPC) without fibers, was studied. The laboratory investigations were also concerned with the effect of the length of steel fibers on the shrinkage of the composites. The results of measurements of the autogenous shrinkage of the investigated concretes, at an early age, are also shown. From the results of the experimental investigation, it can be seen that both the autogenous shrinkage and the total shrinkage of HP-SFRC are less than the values corresponding to the comparable HPC. By gradually adding longer steel fibers (l=30 mm) up to 1 % of the composite volume, the shrinkage of the HP-SFRC can be significantly reduced, whereas if the fiber content is further increased, only a relatively small reduction in the composite shrinkage can be achieved. When using shorter steel fibers (l=16 mm), the shrinkage of the composite can, with an increase in the fiber content, be noticeably reduced only up to a fiber content of 0.75 % by volume of the composite. When the volume content of the steel fibers is higher than 1 %, the workability of the composite becomes significantly poorer, especially when longer fibers are used.