Fibre-reinforced Concrete for Industrial Construction - a fracture mechanics approach to material testing and structural analysis

Sammanfattning: ABSTRACTMore efficient and industrialised construction methods are both necessary for thecompetitiveness of in-situ concrete and essential if the construction industry is to moveforward. At present, the expenditure on labour (preparation and dismantling offormwork, reinforcing, and casting and finishing of concrete) almost equals the cost ofmaterial. Fibre-reinforced concrete (FRC) extends the versatility of concrete as aconstruction material, offers a potential to simplify the construction process and, whencombined with self-compacting concrete, signifies an important step towards industrialconstruction. However, a barrier to more widespread use of FRC has been the lack ofgeneral design guidelines which take into account the material properties characteristicof FRC, i.e. the stress-crack opening ( σ-w) relationship.The presented work has been focused on FRC, showing a strain-softening response, andthe interrelationship between material properties and structural behaviour. This has beenexamined by investigating and developing test methods and structural analysis models.A systematic approach for material testing and structural analysis, based on fracturemechanics, has been presented which covers: (1) material testing; (2) inverse analysis;(3) adjustment of the σ-w relationship for fibre efficiency; and (4) cross-sectional andstructural analysis. Furthermore, recommendations for using the wedge-splitting test(WST) method for FRC have been provided. The relative small scale of the WSTspecimens makes it ideal for use in laboratory studies, e.g. for development andoptimisation of new mixes.By conducting experiments, the approach was demonstrated and it was shown that it ispossible to adjust the σ-w relationship for any difference in fibre efficiency between thematerial test specimen and the structural application considered. Full-scale experimentswere conducted on beams, made of self-compacting fibre-reinforced concrete, with asmall amount of conventional reinforcement. The results indicate that FRC can be usedin combination with low reinforcement ratios; the amount of reinforcement could bereduced to half that of conventional reinforced concrete (for the same load-carryingresistance) but still lead to improved structural performance (reduced crack width andincreased flexural stiffness). The results also suggest that the approach used for thematerial testing provides the necessary properties to perform analyses based on nonlinearfracture mechanics. Finally, when comparing the peak loads obtained in theexperiments with the results from the analyses, the agreement was good, with a highcorrelation (>0.9). Hence, this demonstrates the strength of the fracture-mechanicalapproach for material testing and structural analysis.