Field Study of Concrete Maturity Method in Very Cold Weather
This case study was compiled by FIATECH, Fluor, and the University of Alberta
Executive Summary
The study described in this report was to assess the reliability and potential benefit of using the concrete maturity method in very cold weather. Cold weather presents particular challenges for concrete construction, including: 1) assuring that fresh concrete is not damaged by the cold, 2) that the concrete reaches appropriate strength even where the curing process is slowed by colder temperatures, and 3) managing the additional and costly processes of heating and protecting concrete during curing. This report reviews the concrete maturity method, describes the technology, and describes field observations, and discusses potential benefits of using concrete maturity method and technology in very cold climates.
The concrete placement activities described in this study were conducted from January through April 2005 at Fluor Corporation’s Ultra-Low Sulphur Diesel (ULSD) Project at Imperial Oil’s Strathcona Refinery, located near Edmonton, Alberta, Canada. During this period, the maturity technique was implemented for eight concrete components (locations). The normal temperatures for this period is a daily average low of –11.7ºC, - 8.4ºC & -2.6ºC for the months of January, February and March, respectively. The concrete maturity method is based on the idea that concrete strength development is strongly correlated with the curing temperature history. Modern sensor and processing devices (loggers) are able to measure and record the temperature over time of the curing concrete and make calculations based on the maturity concept to predict concrete strength. A previous Smart Chips Project study indicated that the concrete maturity method could reliably predict the strength of in-situ concrete on a continuous (real-time) basis and that strength prediction could be used to accelerate project schedules. The study results indicated that the concrete maturity methodology enables better quality control through the accurate estimation of in-place concrete strength. In addition, the real time information available through the concrete maturity method allowed the project manager to be proactive in managing heating and protection to ensure that the proper level of concrete strength was developed. Findings from this study enabled the project general contractor to convince the concrete subcontractor to reduce the 28 days cold weather curing requirement for form and shoring removal of load-bearing structures to 14 days.
The study results also indicated a significant potential for cost savings using concrete maturity method in cold weather. For each day of early form removal, one day’s worth of heating costs can be saved. The study calculated that an estimated savings of 367.76 M-BTU heating energy could have been realized had concrete maturity been used as a primary QC method for the those structures monitored during the study. Further the study estimated that a 28% reduction in total concrete activity duration would have been possible using the concrete maturity method on the overall project, while a 16% of actual time saving was recorded. This estimated reduction in concrete schedule duration would have been reflected in reduced costs for overheads, as well rented forms, shoring, and protection materials.
