Improvement of Recycled Brick Aggregate

Abstract

A study was conducted to improve the quality of recycled brick aggregate (RBA) for use in concrete as coarse aggregates. For this, demolished concrete blocks were collected and crushed into pieces (5 mm to 25 mm). For the improvement of RBA, three types of coatings were used, such as cement paste coating, fly ash plus hydrated lime coating, and slag plus hydrated lime coating. Both single layer coating and double layer coating were applied on the RBA. The properties of recycled aggregates and coated aggregates, such as specific gravity, absorption capacity, and abrasion loss were investigated. Cylindrical concrete specimens (diameter 100 mm and height 200 mm) were made with W/C of 0.45 and 0.55, cement content of 340 kg/m3, and sand to aggregate volume ratio of 0.44. As a control case, virgin brick aggregate was also investigated. A separate mixing method of concrete was also investigated by considering mixing of RBA with cement paste before adding other ingredients of concrete. In addition to the cylindrical concrete specimens, mortar specimens were also made by screening concrete with a #4 sieve (opening 4.75 mm). After mixing concrete, slump test was conducted for fresh concrete. Concrete specimens were tested after 7, 14, and 28 days for compressive strength, tensile strength, and Ultrasonic Pulse Velocity (UPV). Rapid chloride migration test (RCMT) was also conducted after 28 days. Moreover, interfaces of aggregate were also investigated using a Scanning Electron Microscope (SEM) at 28 days. The abrasion of coated RBA is reduced and also coated RBA showed higher specific gravity. The compressive strength of concrete is increased for the coated RBA, especially for the cases with double layer coating with cement or slag plus hydrated lime coating. Mixing of RBA with cement paste before adding other ingredients of concrete in the mixture also showed better performance.