| Summary: | Plastic shrinkage cracking of dry-mix shotcrete is a common problem encountered within the
construction industry. Dry-mix shotcrete is used in a wide variety of applications most
commonly, the repair and rehabilitation of deteriorated concrete structures. Dry-mix
shotcrete is also used as a tunnel liner, for slope stabilization, and for refractory applications.
Plastic shrinkage cracks pose a significant threat to the durability and aesthetic appeal of
shotcrete structures. This work was intended to develop a simple test used to study
restrained plastic shrinkage in shotcrete overlays.
Plastic shrinkage cracking of bonded dry-mix shotcrete overlays subjected to a severe drying
environment is investigated. A novel test method was developed to study the effects of
fibers and various admixtures on restrained plastic shrinkage. Shotcrete is cast directly onto
fully matured, roughened sub-base that provides dimensional restraint. The assembly is
immediately transferred to a drying chamber where plastic shrinkage cracking is monitored
under controlled conditions. It is found that this method is effective in estimating the potential
and degree of plastic shrinkage cracking in shotcrete, and also in assessing the
effectiveness of various fiber types and admixtures. Steel and synthetic fibers were found to
delay the formation of plastic shrinkage cracks as well as substantially reduce both the
amount and width of cracking.
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