Original paper(Vol.45 No.9 pp.1008)
Properties of concrete using lapilli as coarse aggregate
Kagaya Makoto; Tokuda Hiroshi; Iimura Wataru
Abstract:This research was carried out to study the basic properties of concrete making good use of the properties of lapilli as coarse aggregate. The following resilts were obtained.
(1)The level of specific gravity under an oven dried condition and the percentage of solid volume of this lapilli were L and A in the classification of lightweight aggregate. The 24hr absorption was 70.45% and the percentage of floating particles in the lightweight coarse aggregate was 11.5%. The 10 min absorption was about 80% of 24hr absorption.
(2)The concrete weight was almost the same as that of grade 2 lightweight concrete, and the maximum compressive and flexural strengths were 105 and 23.8 kgf/cm2 at the age of 28-days, respectively.
(3)The 24 hr absorption and drying weight loss percentage of the lapilli concrete were much greater than those of the gravel aggregate concrete. The drying shinkage was almost half that of the gravel aggregate concrete before the age 14 days and then approached that of gravel aggregate concrete. The thermal conductivity was 60% that of gravel aggregate concrete.
(4)The washed finish by use of 20% super retarder solution was effective to expose color of lapilli on the concrete surface. The reduction of flextural strength by the finish was only about 5%. The impact absorption and elastic repulsion on the concrete surface could be improved to the level of an elastic asphalt mixture, which can reduce a burden to a body due to exercise.
(5)The concrete blocks with exposed lapilli on the surface were used experimentally for pedestrain pavements. The depth of the surface absorption was about 0.8 mm and the color tone was good enough after 10 months of use.
Key Words:lapilli, concrete, unit weight, mechanical properties, shrinkage, thermal conductivity, washed finish, impact absorption, elastic repulsion, concrete block