The Effect of Qualities of Artificial Lightweight-Aggregate upon Compressive Strength of the Concrete

Abstract

Qualities of lightweight aggregate such as its specific gravity, shape of particles and grading can be controled in its producing process, and these factors will have important effect on the quality of structural lightweight concrete. To find sufficient quality of the aggregate to be used in structural lightweight concrete, the relation between these factors and compressive strength of concrete were investigated.Four types of coarse aggregates were used; the coated-type expanded shale, the peletized-type expanded shale, and the river gravel and crushed stone. River sand was used in all concrete mixes. The particles of expanded shales were previously divided into 7 groups of specific gravity ranging from 0.9 to 1.6, and a certain class from them in which all particles had almost uniform specific gravity was used in a concrete mix. The concrete mix was determined by trial mixes so as to obtain the highest possible volume fraction of coarse aggregate using 1:1 mortar (W/C=30%).The compressive tests were carried out on φ10×20cm cylinders, and the main results obtained are as follows.(1) The relation between the specific gravity of expanded shale aggregate and the compressive strength of concrete appeared differently in accordance with the strength level of concrete. In the case of high strength concrete, the strength was limited by inherent strength of aggregate, and its inherent strength of aggregate was proportional to the specific gravity of the aggregate.(2) If we evaluate the desirable quality of lightweight concrete in the form of specific strength, the ratio of strength to the specific gravity, there is the most suitable specific gravity of the aggregate which brings the maximum specific strength of concrete. From the results of this experiment, the most suitable value of specific gravity was estimated as follows for each strength-levels of concrete:The required concrete strength (kg/cm2) Suitable s.g. (Saturated Surface-dry)200∼300 1.3about 400 1.4about 550 1.5about 700 1.5∼1.6(3) The shape of the particles does not make any difference to the specific strength of the concrete, whereas the grading is one of the factors that affect the strength of concrete.