Concrete water tanks in Ontario

Abstract

Since 1981, an Ontario provincial government study has been undertaken on the 53 concrete water tanks built in the province since 1956. Results of mainly external, but some internal, inspections, condition surveys, and ratings on an ascending 0–9 scale revealed a wide range in performance. This varied from failed tanks, rated 0 (two tanks), to very good performance, rated 9. The ratings were generally related to the tank types and construction method used. The best performance was exhibited by posttensioned bonded (PTB) types. The survey results and defects analysed revealed various problems and causes. These varied from specific construction methodology faults, such as slipform jack rods (pipes) left in the walls of certain types of tank, which filled with water and froze, to common defects, such as cold joints, experienced in all types, leading to leakage and freezing, and ice expansion in voids in tank walls during the winter. Actual concrete tensile stresses induced by internal ice formations, thermal gradients, and shrinkage stresses were found to be higher than those used in most designs or allowed in international codes or standards. As a result of the study, a provincial government rehabilitation programme for ministry-built tanks in need of repairs and leakproofing was started in mid-1982 in the order of priority ratings established during the study.