Tests has been carried out to improve the construction property of magnesia phosphate cement mortar which has high durability against the deterioration due to seawater. It is possible to obtain a flow value of 200cm or more in a handling time of about 60 minutes by adding 15% sodium borate to the cement, and replacing 40% of cement with fly ash, and a cement to sand ratio of 1:2 and water to cement ratio is 0.15. It became clear that the compressive strength of the mortar at early period is higher than that of mortar using portland cement and drying shrinkage of the mortar was very small. We proposed it as an repair mortar of the grout type.

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