A CONSIDERATION ON MIX-PROPORTION TO UTILIZE LOWQUALITY FINE AGGREGATES IN AIR-DRY CON

Abstract

This study aims to investigate the utilization of air-dry recycled fine aggregate and its effects
on the fresh and hardened properties of mortar. Low quality Recycled Concrete Fine Aggregates (RCFA) are
mainly composed of aggregate and hardened cement paste. Therefore, they induce an enormous water
demand, poorer compressive strength, and high variability in mechanical behavior, which makes their
application challenging in the production of mortar and concrete. In this study, two types of fine aggregates,
gabbro-rock crush sand, and recycled sand are used to produce mortar. Recycled fine aggregate was obtained
from waste concrete by pulse power technology. The water absorption of both fine aggregates is comparably
calculated by the electrical conductivity method. Cylinder specimens of 50mm in diameter and 100mm in
height were prepared and tested for compressive and split tensile strength. The water absorption of fine
aggregates progressed rapidly during the first 30 minutes interval of absorption time. Air-dry state of sands
was proved promising in affecting the compressive and split tensile strength of mortar. During mixing mortar
mixture, the extra-added water was not immediately absorbed by the oven and air-dry RCFA particles.
Therefore, the slump flow of mortar increased and it reduced the compressive strength. According to X-ray
CT scanned images, the volume of voids were different from each other in RCFA particles. Therefore, the
boundary between fine aggregate and water-penetrated areas could not be distinctively observed.