Mechanical performance of 100% recycled aggregate concrete (RAC) bricks

Abstract

Urbanization and modern development of expanding infrastructure have resulted in large construction activities. With the expeditious growth in the construction industry, the rate of demolition has also increased. This is causing considerable increase in Construction and Demolition (C&D) waste all around the globe. To minimize its impact on society and environment, preventive measures are required to be taken on urgent basis, and for this reason construction industry has proposed the use of recycle concrete aggregates in different applications and there is dire need to investigate experimentally the properties of concrete products made using Recycled Aggregate Concrete (RAC). In this regard, this study focused to investigate the mechanical properties of 100% RAC bricks prepared with two different compositions with respect to coarse to fine aggregates ratio (i.e., 70:30 and 60:40), cement dosage (i.e., 10% and 15% by weight of total aggregates) and casting pressure (i.e., 25 MPa and 35 MPa). Recycled concrete aggregates required for this study were produced by crushing tested concrete samples having compressive strength of 21 MPa to 28 MPa. Mechanical tests were performed on bricks to determine their compressive strength, flexural strength, shear strength, impact energy in compression and flexure. In addition to these destructive tests, non-destructive (rebound hammer and ultra-sonic pulse velocity) tests were also performed. To draft a comparison, Natural Aggregate Concrete (NAC) bricks and first class burnt clay bricks were also tested. The results indicated that the compressive strength of NAC bricks was about 30% higher than the compressive strength of RAC bricks. However, RAC bricks exhibited higher compressive strength as compared to burnt-clay bricks. The flexural strength of RAC bricks containing 60% coarse aggregates and 40% fine aggregates and RAC bricks containing 70% coarse aggregates and 30% fine aggregates was found to be almost similar but their flexure strength was 37.3% and 20.7% lesser than their corresponding NAC bricks. Flexure strength of RAC bricks and burnt clay bricks was found to be almost same. Qualitative assessment by ultrasonic pulse velocity (UPV) tests showed that the NAC and RAC bricks were of good quality as per the standard criteria. The findings of this study indicated that RAC bricks satisfied the strength requirements as stated by local and international standards. Further, RAC bricks performed better than commonly used first class burnt clay bricks. Production and use of RAC bricks in masonry structures will not only help to conserve the depleting resources of natural aggregates and clay but also help to protect our environment from pollution by reducing CO2 emission caused by the coal-burning as fuel in kilns for the manufacturing of burnt-clay bricks.