Shrinkage of Polypropylene Fiber-Reinforced High-Performance Concrete

In this paper, the results of laboratory investigations into the time development of the shrinkage of polypropylene fiber-reinforced high-performance concrete have been analyzed. The volumetric content of polypropylene fibers contained in the investigated concretes varied from 0 to 0.75%. Within this context, the influence of both dry and previously moistened polypropylene fibers added to the concrete on the shrinkage of the composites was examined. Electronic measurements conducted from the beginning of the hardening of the concrete also covered the early stage of autogenous shrinkage that, in high-performance composites, accounts for a significant part of total shrinkage. To compare the shrinkage of fiber-reinforced concrete with that of a comparable concrete without polypropylene fibers, the shrinkage of such a comparable concrete without fibers was also included in the measurements. The measurement results of the shrinkage of polypropylene fiber-reinforced concrete and of a comparable concrete without polypropylene fibers, as presented graphically in this paper, clearly show that the autogenous as well as the total shrinkage of fiber-reinforced concrete is less than the shrinkage of a comparable concrete without fibers. By increasing the content of the fibers up to 0.5% of the volume of the composite, the shrinkage of the fiber-reinforced concrete was considerably reduced, whereas with further increasing of the fiber content, the shrinkage reduction rate became relatively insignificant. The concrete that had been reinforced by previously moistened polypropylene fibers, which served as an internal water reserve, exhibited a lesser degree of early autogenous shrinkage than the concrete that had been reinforced by dry polypropylene fibers. The drying shrinkage of high-performance concrete, reinforced by previously moistened polypropylene fibers, was, however, approximately twice as large as that of dry polypropylene fiber-reinforced high-performance concrete. Whereas the workability of the composite deteriorated considerably already in the case of a volumetric content of moistened polypropylene fibers greater than 0.25%, in the case of the use of dry polypropylene fibers, this deterioration was even more conspicuous.