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Materials and Structures

, Volume 42, Issue 5, pp 567–579 | Cite as

Plastic shrinkage cracking in cementitious repairs and overlays

  • N. Banthia
  • R. Gupta
Original Article

Abstract

A study was undertaken to investigate the influence of mixture proportions on plastic shrinkage cracking in cementitious repairs and overlays. The following variables were studied: water-cement ratio (w/c), sand-cement ratio (s/c) aggregate-cement ratio (a/c), fly-ash content, and the presence of a shrinkage reducing admixture (SRA). A recently developed bonded overlay method was used. In this method, the cementitious material to be investigated is cast on a substrate base with protuberances and the entire assembly is subjected to drying in an environmental chamber. With a high degree of restraint, cracking develops in the overlay over time which is then characterized with the help of magnification device and image analysis software. Results indicate that a lower water-cement ratio significantly reduces crack widths and crack areas and also reduces the ‘time to first crack’. The exact influence of s/c on cracking could not be established. The study further demonstrated that increasing the a/c provided internal restraint and significantly reduced early-age cracking. The addition of Class C fly-ash increased the amount of cracking but also increased the ‘time to first crack.’ This was however true only to a certain threshold value of fly-ash content beyond which fly-ash can be effective in reducing early age shrinkage cracking. Finally, the addition of a shrinkage reducing admixture was effective in reducing cracking but the cracks occurred sooner.

Keywords

Concrete Early-age Restraint shrinkage Cracking Fly-ash Shrinkage reducing admixture 

Notes

Acknowledgements

Thanks are due to Pozzolanic International Limited for supplying the fly-ash, and to Natural Sciences and Engineering Research Council of Canada for their financial support. The laboratory assistance of technician at UBC, and of Willy Breda and Maxime Trocme of Ecole des Mines de Douai, France, is also greatly appreciated.

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Copyright information

© RILEM 2008

Authors and Affiliations

  1. 1.Department of Civil EngineeringUniversity of British ColumbiaVancouverCanada

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