Spring 2007


Recycling of Demolished Concrete as Coarse Aggregate

    Suvash Chandra Paul and Md. Maksus Ahmad


    In Bangladesh, due to the booming of real estate business, many low rise buildings are demolished for replacement by relatively high rise buildings. Also, due to the deterioration of concrete structures, many old buildings are necessary to demolish and replace by new buildings. The demand of normal aggregate for construction can be reduced by recycling of demolished concrete as coarse aggregate. Therefore, this study was carried out to check the possibility of using demolished concrete as coarse aggregate for new construction. Concrete blocks from the eight demolished building sites were collected and crushed into coarse aggregates. The recycled aggregates were investigated for unit weight, absorption capacity and abrasion. Concrete cylinder specimens were made and investigated for unit weight, compressive strength, and stress-strain curves. The workability of the fresh concrete was also investigated. The results were compared with normal aggregates.


The % of wear value (abrasion value) of recycled aggregates is higher than the normal aggregates due to the adhered mortar portion with the recycled aggregates. The % of absorption of recycled aggregates is also higher compared to the normal aggregates. For the same W/C, the strength and Young’s modulus of recycled aggregate concrete are lower than the same made with normal aggregate concrete. But if the W/C is reduced compared to the normal aggregate concrete, recycled aggregate concrete gives higher strength and Young’s modulus compared to the same of normal aggregate concrete made with a higher W/C. The workability of recycled aggregate concrete is lower than the corresponding normal aggregate concrete. It can be improved by coating recycled aggregate with a cement paste before using as coarse aggregates for new concrete. Cement paste coated recycled aggregates also give higher strength and Young’s modulus compared to the same of non-coated recycled aggregates.