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Plastic shrinkage in dry mix shotcrete Campbell, Kevin Neil


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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