Fordeling av fibre i fersk fiberarmert betong

Abstract

This study examines the distribution of steel - and plastic fiber in fresh fiber reinforced concrete. This is in relevance to, whether the use of fiber reinforced concrete in structural concrete is advantageous or not. The thesis is divided into the following two parts: 1. Literature study, focusing on the fiber reinforced concrete properties, fiber distribution in concrete and previous field trials. 2. Field work at the site of construction, consisting of two series of experiments; quantitative measurements of plastic fibers and steel fibers in fiber reinforced concrete. In order to investigate whether variation occurs in the fiber distribution of the concrete batch as delivered at the construction site, samples were taken from each concrete truck at three different time intervals: at the start-, middle- and end of discharge. Based on the experimental results in this study, the following conclusions may be drown: • In steel fiber reinforced concrete with 25 kg fiber/m3, the deviation in fiber content from the quantity specified increases towards the end of discharge. • In plastic fiber reinforced concrete with 7 kg fiber/m3, the deviation in fiber content from the quantity specified decreases towards the end of discharge. • 33 % of the steel fiber samples from fiber reinforced concrete do not comply with the suggested upcoming requirement of a minimum fiber content of 0,85 x fiber content specified in individual samples, and a minimum 0,9 x fiber content specified in an experimental 3 tests series per truck. Therefore, in cases where the fiber-reinforced concrete is specified in structural concrete, it will, in accordance with the new guidelines for the use of fiber reinforced concrete, be a requirement to introduce fibers to the batch during mixing at the ready – mix plant, which also will ensure documentation of added fibers. • Each one of the plastic fiber samples complied with the upcoming requirements. • Fiber reinforced concrete used in conjunction with modern structurally integrated formwork systems, like Cofraplus 77, seems to be a rational way to do concrete work, even though the fibers only take care of the shrinking. • Test methods used in this study to separate fiber from concrete, proved to serve their purpose. The size of samples are larger than before, but not too big to handle.