Title:
Influence of Type and Replacement Level of Recycled Aggregates on Concrete Properties
Author(s):
Keun-Hyeok Yang, Heon-Soo Chung, and Ashraf F. Ashour
Publication:
Materials Journal
Volume:
105
Issue:
3
Appears on pages(s):
289-296
Keywords:
recycled aggregate; strength; water absorption
DOI:
10.14359/19826
Date:
5/1/2008
Abstract:
Test results of nine recycled aggregate concretes and a control concrete using only natural aggregates are reported. The recycled aggregates used were classified into three different types according to their measured specific gravity and water absorption, namely, RG I for recycled coarse aggregate having a specific gravity of 2.53 and water absorption of 1.9%; RG III for recycled coarse aggregate having a specific gravity of 2.4 and water absorption of 6.2%; and RS II for recycled fine aggregate having a specific gravity of 2.36 and water absorption of 5.4%. The replacement levels of both recycled coarse and fine aggregates were 30, 50, and 100% in separate mixtures. Slump loss and the amount of bleeding with time were recorded for fresh concrete. Compressive and tensile strengths, moduli of rupture and elasticity, and unrestrained shrinkage strain were also measured for hardened concrete. The properties of fresh and hardened concrete tested, together with a comprehensive database reported in the literature, were evaluated with respect to the relative water absorption of aggregates combining the quality and volume of recycled aggregates used. In addition, the properties of hardened concrete with different replacement levels and quality of recycled aggregates were compared with the design equations of ACI 318-05 and empirical equations proposed by Oluokun for natural aggregate concrete, whenever possible. Test results clearly showed that the properties of fresh and hardened concrete containing recycled aggregates were dependent on the relative water absorption of aggregates. In addition, the moduli of rupture and elasticity of recycled aggregate concrete were lower than the design equations specified in ACI 318-05, when the relative water absorption of aggregates is above 2.5% and 3.0%, respectively.