There is a construction method which uses precast concrete members with very high strength in the 150 N/ mm2 class and connects each member by the joint mortar. The purpose of this investigation is to develop mortar which is injected into the joint. It is needed for the mortar to have several capacities, such as fluidity and strength almost equal to the strength of precast concrete members without special curing. By the experiment that changed the water cement ratio or the sand cement ratio, compressive strength reached until 182-day up 200 N/mm2. A satisfactory filling for the joint, a narrow section with a 3 cm opening for instance, was ensured without detecting any flaw or unfilled part when the fluidity of the mortar was controlled with the flow time of J14 funnel.
