Abstract

A large amount of waste concrete generates an environmental problem due to demolition of old concrete structures. To solve this problem, it is necessary to collect recycled aggregate from waste concrete. The conventional recycling technique of recycled aggregate from waste concrete does not indicate a significant quality to be re-used for making a new concrete. We proposed new techniques to produce high grade recycled aggregate by heating-grinding (H-G) method and heating-grinding-acid (H-G-A) method. To ensure the quality of the concrete made from recycled coarse aggregate concrete, the non-destructive evaluation was conducted in this research. High grade recycled aggregate concrete were prepared in advanced using two methods mentioned earlier. Then, new concrete specimens were produced using those types of recycled aggregate concrete. After 28 days curing time, rebound hammer test and ultrasonic pulse velocity test were performed on recycled coarse aggregate concrete to examine the surface hardness and ultrasonic wave velocity of the concrete. Almost similar quality to natural coarse aggregate in terms of density, water absorption, sieve analysis achieved by both H-G recycled coarse aggregate and H-G-A recycled coarse aggregate. However, the surface hardness and ultrasonic wave velocity of H-G-A recycled coarse aggregate concrete is better than those of H-G recycled coarse aggregate concrete. That acid solvent enables to dismantle the cement paste from aggregate surface more effectively, so this types of recycled aggregate shows a better performance than the other one. Continued delamination reduces pores in the interfacial transition zone resulting better bonding mechanism between new cement paste and recycled aggregate surface.

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