Shrinkage of polypropylene fibre reinforced high strength concrete

摘要

In this diploma paper we deal with the analysis of high strength concrete, micro-reinforced with polypropylene fibers. We used four different lengths of polypropylene fibers: 6mm, 12 mm, 18 mm and 30 mm. The share of fibers in each concrete mixture is 0.5 % of the total volume. With high strength concretes autogenous shrinkage is very intensive, so the first day we measured it electronically with dial gauges. Later we measured the shrinking with a mobile displacement transducer. We measured autogenous shrinkage on sealed samples, and on the unsealed samples we measured the total shrinkage of high strength concrete. We also analysed shrinkage of the concrete due to drying, which represents the difference between total and autogenous concrete shrinkage. In the analysis we compared concrete shrinkage of 1-, 3-, 7- and 28-day-old concretes. In addition we tested the liquid shrinkage reducing admixture Eclipse Plus which works by reducing surface tension in capillary pores. Through experimental researches we discovered that polypropylene fibers do not contribute much to reducing high strength concrete shrinkage. The most efficient were, especially in the early stages of autogenous shrinkage, short polypropylene fibers (6mm).