The need for the corrosion diagnosis of reinforcing bars is likely to increasing owing to the increasing use of seawater-mixed concrete and the aging of existing structures. In this paper, new methods were introduced to diagnose the corrosion of reinforcing bars. In addition, an outline of the salt damage deterioration diagnosis method was provided to the engineers at Kuwait Institute for Scientific Research （KISR）. Further, a comparison was conducted between values obtained through on-site corrosion diagnosis of concrete structures and two types of laboratory-based electrochemical measurements.

An electrochemical impedance measurement of mortar specimen was performed to investigate the relationship between the impedance spectrum and the pore structure in mortar. The mortar specimens with different pore size were prepared for the impedance measurement. The capacitive loop or part of loop, which are related to the physical properties of mortar, were observed in the impedance spectra of mortar specimens. The mortar resistance between the pores and the capacitance between pores filled with solution in mortar specimen（R_Mpore and C_Mpore）were estimated by curve-fitting of impedance spectrum using an equivalent circuit. The values of R_Mpore and C_Mpore were increased and decreased, respectively, when the size of pores became smaller in mortar specimens. These results imply the decreasing the water pathway of pores in mortar due to the increasing small pores in mortar.

In this 21^st century, sustainability is an issue of extreme importance for humankind. As regards drinking water, a serious shortage is expected by 2050, when one-third of the world's population is predicted to lack sufficient access to drinking water. In the field of concrete, billions of tons of freshwater is consumed annually for mixing, curing and washing concrete. Seawater is presently not permitted to be used for these purposes. Active use of seawater in the field would contribute to more effective use of freshwater resources.

Based on this social situation, JCI （Japan Concrete Institute） set the committee to research the possibility of seawater usage in concrete production, such as concrete mixing, concrete curing etc. Based on the results, issues surrounding the use of seawater and possible solutions are proposed. In this report, readers are expected to find the committee activities and committee attitude. In Kyushu University, recent several years, a research on concrete characteristics mixed with seawater is continued. In this paper, a discussion on seawater utilization as concrete mixing water based on the research results is also summarized.

Actually, this paper is a summary paper of three presentations by authors, Hamada, Patah, Harahap, in the JSCE conference held in Toyama, 2018 October.

To examine rebar corrosion in cracked concrete, we have exposed cracked test pieces of pre-stressed concrete containing two rebars to the outdoors and observed the electrochemical behavior. After one year from the start of the exposure test, the potential difference between rebars increased, so it seemed one of rebars has corroded. However, as the exposure test proceeded, the potential difference decreased to the initial state. In addition, destructive observations of test piece revealed that only one rebar had corroded. These results indicate that just one rebar was repassivated after the depassivation in cracked concrete.

The authors participated in a project “Technical collaboration project on seawater utilization for concrete structure of petroleum facilities as construction and maintenance management, Kuwait” that Japan Society of Corrosion Engineering （JSCE） received from Japan Cooperation Center Petroleum （JCCP）, and supported research in Kuwait.

This paper is based on the knowledge of JCI Technical Committee Report on the Use of Seawater in Concrete and others about corrosion of rebar in concrete using seawater as mixing water.

In Kuwait, where freshwater resources are scarce, the use of seawater-mixed concrete has been considered. In the Middle East countries where sulfate soils are widespread, it is necessary to confirm sulfate resistance of concrete. In a concrete member constructed in sulfate-bearing soil, different deterioration phenomena are expected to occur in the ground water level, from the ground water level to the ground surface, and above the ground surface. As a result of Na₂SO₄ immersion test using 10 mix proportions of mortar specimens, an admixture designed to precipitate larger amount of ettringite was found ineffective for sulfate resistance in seawater-mixed concrete. Based on the results of these experiments, it is necessary to prepare specimens using materials in Kuwait and to carry out exposure tests in the actual soil environment in Kuwait.