Abstract
This paper presents the findings of an investigation of the fiber content variations in concrete being discharged from a ready-mix truck at the construction site. Concrete samples were extracted from the truck drums at the beginning, middle and end of discharge. Subsequently, fibers in each sample were separated from the concrete, and weighed. Presumably, synthetic macro fibers will float towards the top, i.e. towards the drum opening, of the inclined, revolving truck-drum, while, on the other hand, steel fibers will tend to gravitate towards the lower parts of the mixer drum. Accordingly, the discharge batch, containing synthetic macro fibers, will contain a higher amount of synthetic fibers per unit volume at the start of discharge than the average unit volume fiber content of the mix, and the content will gradually decrease further down the batch. The discharge batch of steel fiber concrete will contain fewer fibers per unit volume at the start of discharge than the average unit volume fiber content of the mix, and the content should gradually increase further down the batch. The correctness of the foregoing is partly confirmed. A certain percentage of the truck loads did not comply with the proposed requirements, mainly steel fiber reinforced batches, indicating the necessity of a code or guideline amendment. A change in the Norwegian shotcrete directive was made in 2011, based upon experimental research work (2010), which, in combination with the subsequent University of Life Sciences report (2012), constitutes the foundation of this article.
Highlights
1.1 Purpose and Applicability of These InvestigationsConcrete structures are crack-prone
The box-plot diagram Fig. 4, of the steel fiber weighing, visualizes the results presented in Table 3 and by the scatterplot, Fig. 3
All synthetic macro fiber concrete tests did meet the Proposal I requirement, and only one synthetic fiber truckload did not comply with the Proposal II requirements, by yielding one single test-sample containing more fibers than would be permitted
Summary
The durability of concrete is impaired by cracks, as they provide a path for the transportation of potentially harmful liquids and gases. Cracks of small width reduce the deterioration risk due to diminished influx of potentially damaging substances (Concrete Construction Staff 1997; The Concrete Society 2013). The mechanisms of concrete self-healing will only mend cracks of small breadth (Van Tittelboom et al 2013). This article is published with open access at Springerlink.com the widths of cracks caused by plastic and drying shrinkage. The higher the amount of fibers, the more effective is the crack limitation. To achieve uniform crack control throughout the concrete pour, the fibers should be evenly distributed. Irregular fiber distribution may give varying workability, e.g. pumping suitability, and affect separation tendencies
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