This study was carried out to examine the properties and the durability of light-weight concrete which used lapilli. As a result, it was made clear that stable compressive strength of 24N/mm2 was provided by making 50% of lapilli by volume ratio. However, Lapilli are materials of the high absorption that is many apertures quality. As for the concrete using lapilli, progress of hardening of concrete and drying shrinkage are thought about enough. Therefore I decided to mix steel fiber as an improvement method here. The steel fiber mixture stabilizes the strength and durability property, and furthermore it seemed that I can expect it for expression of flexural toughness and restraint of drying shrinkage. As for the result, drying shrinkage and water loss are relatively similar to lightweight concrete II at 50% of lapilli by volume, steel fiber mixture ratio 1.5%, it may be said that the use of 50% of lapilli by volume is possible enough from a strength property.
