Influence of Combined Expansive Agent and Supplementary Cementitious Materials Against Chloride Effects in Offshore Concrete

The performance of hardened concrete may be degraded by the chemical action of chlorine ions (Cl- ) or sulfate (SO4 2- ) in sea water. Thus, supplementary cementitious materials (SCMs) are used in replacement of OPC for the purpose of improving the durability of concrete, but show weaknesses such as drying shrinkage. Judging that the sole use of SCMs has limitations in designing concrete durability to cope with the environment of salt damage, this study suggests the use of aluminum-based inorganic salts (AIS) in the form of chemical agents. This study aims to select material of the highest efficiency in enhancing the durability of offshore concrete, by performing the durability evaluation of typical four SCMs and four AISs that are intermixed as single materials. There has been almost no domestic or overseas research on Al-based organic salts intermixed in the form of chemical agents for the purpose of improving resistance to salt damage and offsetting drying shrinkage. It was confirmed that mortar intermixed with Al-based chemical admixtures showed great performance improvement in the rates of length change. The mixture proportion intermixed with sulfate ion (SO4 2- ) as binding anion tended to show unfavorable reaction in terms of resistance to sulfate erosion and drying shrinkage. On the other hand, the mixture proportion set with nitrite ion (NO3 - ) as cation showed excellent performance improvement in all evaluation items, compared with non-intermixture. It is deemed that it will be necessary to highlight further and make use of the expansion properties and chloride binding performance of Al-based organic salts through the design of offshore concrete mixture proportions.