STUDY ON ARTIFICIAL SUPER LIGHTWEIGHT AGGREGATE FOR PRECAST CONCRETE.

The paper reports on the development of and research work connected with such aggregates. Both pelletized and unpellitized expanded shale aggregates with oven-dry specific gravities in the range of 0. 8 to 1. 0 were produced from expanding shale in a small test rotary kiln. Mass production of unpellitized expanded shale with an oven-dry specific gravity of 1. 0 was acheived in the practical rotary kiln. Chemical properties of the super lightweight gravel was approximately equal to those of conventional lightweight gravel. As for the physical properties, oven-dry specific gravity was 1. 0 and was 20% lighter, with 28-day compressive strength in excess of 300 kg/cm**2 could be produced with cement contents of 450 kg/m**3, water cement ratio of 40% and slump of 8 cm. Super lightweight concrete for precast concrete panels with an air-dry unit weight of 1. 35 ton/m**3 was produced with cement contents of 320 kg/m**3, water cement ratio of 50%, and slump of 8 cm; whose 28-day compressive strength was in excess of 230 kg/cm**2 on moist cured specimens. Drying shrinkage of super lightweight concrete was the same or slightly higher than conventional lightweight concrete.