Service Life Prediction Model for Concrete
by Jessica Jackson, Technical Service Engineer
Under the jurisdiction of ACI committee 365, a new service life prediction model for concrete structures has been introduced. Developed by Professor Mike Thomas, University of Toronto, LIFE-365 is to become the standard model for predicting service life for the entire concrete industry. The first production version was released in October 2000. The committee is hoping for ACI acceptance of the model within 5 years.
This model uses four analyses to estimate total cost of the structure over its predicted service life. They are:
1. Predicting the initiation period (time to onset of corrosion)—uses Fick’s Second Law (diffusion) to estimate the concentration of chlorides at the reinforcing steel. Initiation begins when the chloride threshold has been exceeded. The model also takes into consideration average monthly temperatures of where the structure is located, type of structure, and mix design.
2. Predicting the propagation period—the time from when corrosion starts until the first repair is needed.
3. Determining the repair schedule after the first repair—uses a 10 year repair schedule after the first repairs, and includes cost for repairing up to 10% of the total surface area at each repair.
4. Estimating the life cycle costs—based on the initial concrete (and other protection) costs and future repair costs. Costs are given on a discounted (today’s value) basis.