Use of polypropylene fibres in concrete slabs-on-grade
University of New Brunswick
Plain concrete has been used traditionally in the design of slabs-on-grade, with relatively closely spaced joints to account for shrinkage and temperature effects. The use of welded wire fabric (WWF) in ground slabs is also common as a form of secondary reinforcement to help control temperature and shrinkage cracks. Polypropylene fibres have been used as an alternative to using either WWF or steel fibre reinforced concrete (SFRC) for crack control in floor slabs. The main reason for using polypropylene fibre reinforced concrete has been to control plastic shrinkage cracks, but other benefits such as increased strength and toughness have been suggested. The load capacity and deformation response were investigated for two concrete slabs containing polypropylene fibres. Two slabs (2.5m x 2.5m x 0.15m) containing 0.1% by volume (900 gm/m3) were tested, one on a loose subgrade and the other on a dense compacted subgrade to get some indication of the soilstructure interaction effects. A centrally applied load was used to measure the load carrying capacity and deformation behaviour of the slabs. The project compared the behaviour of the two concrete slabs containing the recommended amount of polypropylene fibres to results from earlier slabs tested containing either WWF or SFRC reinforcement. It was shown that using 0.1% by volume of polypropylene fibres in concrete slabs does not improve the first cracking load when compared to SFRC slabs or WWF reinforced slabs. The PFRC slabs did not exhibit post-cracking strength as demonstrated by the other types of slabs (WWF and SFRC). The PFRC slabs demonstrated an inability to transfer the load due to a lack of post-cracking flexural capacity, resulting in major surface cracking.