The square root method for chloride ingress prediction - Applicability and limitations

Abstract

A recent observation showed a square root time dependency of the ingress depth of a fixed (reference) chloride concentration of 0.05% chloride by mass of concrete for submerged exposure in Kattegat and the Baltic Sea. The purpose of this paper is to assess the applicability and limitations of the observation, widen the scope of validity and propose it as a method. Field data from submerged, tidal, splash, atmospheric and inland deicing salt exposure at various geographical locations was analyzed at a range of reference concentrations. In total 237 combinations of concrete, exposure, and reference concentration were analyzed. Our results showed that chloride ingress of a reference concentration followed a linear relationship with an average R2 of 0.96, when the penetration depth of the reference concentration was plotted against the square root of the exposure time. The square root observation appeared valid for the studied Portland cement based concretes with fly ash, silica fume and ground granulated blast furnace slag exposed in submerged and tidal exposure zones, when applying reference concentrations of 0.1–1.8% chloride by mass of binder, and reference concentrations of 0.1–0.5% chloride by mass of binder in atmospheric exposure zone. It was found that the parameters describing the straight line depended on the chosen reference concentration and concrete composition, and that the slope of the straight line (ingress parameter) in addition depended on the exposure. It was concluded that the square root method appears to be a promising method for predicting further chloride ingress into concrete.