Estimation of Initiation and Propagation Periods Related to Steel Corrosion in Concrete Mixed with Seawater

Zoulkanel Moussa Garba-Say, Student, Otsuki Nobuaki, Professor, Nishida Takahiro, Assistant Professor, Tokyo Institute of Technology, Japan, & Ohara Hiroki, Engineer, JGC Co., Japan.

Introduction

The rapid growth of world population inducing intensive economic activities and the drastic climate changes affect significantly our living environment. As a result, access to clean water has become one of major crises in the 21st century. According to the World Meteorological Organization (WMO), by 2025 around half of world population will be living without enough fresh water. At that time, it will be necessary to save fresh water, by investigating the usage of seawater in concrete industry. However, because of strict restriction on the chloride ion content in concrete by many design specification codes, fresh water has been commonly used in concrete, for cleaning, mixing and curing.

N. Otsuki et al. 2011[1], throughout 20 years exposure under marine environment, reported that "Concrete mixed with seawater and blast furnace slag as admixture, could have good resistance to corrosion, especially in the long term." Therefore, in this study in order to clarify the effect of seawater usage in RC, some investigations on the corrosion phenomena have been conducted. Also some consideration to the Chloride ion immobilization effect by Blast furnace Slag (BFS) cement was focused on, in comparison to Ordinary Portland Cement (OPC).

The chloride ion diffusivity and the corrosion threshold chloride content were evaluated, in order to determine the initiation period of corrosion under chloride attack. Meanwhile, the corrosion rate was evaluated to estimate the propagation period of corrosion. Finally the lifetime of concrete mixed with seawater was quantitatively estimated, with comparison to normal concrete.

The authors are in the position that seawater must be used and we, concrete researchers, should examine the way to enable a safe use of seawater as mixing water (and curing water). So in this research, if the "end of the service life" could be "formation of cracks (by corrosion)", the combination of seawater and BFS cement might be better than the combination of tap water and OPC.

NBMCW February 2014