Recycled Concrete—A Source for New Aggregate

Recycling concrete rubble as aggregate material for the construction programs in the Middle East, where high-quality mineral aggregate is scarce, offers an excellent ecological and economic opportunity. Based on tests carried out on 21 mixes, this investigation attempts to develop data especially on the strength, failure mechanism, and durability characteristics of the recycled aggregate in comparison with the conventional concrete. Results show that for a W/C ratio of 0.35 the recycled aggregate concrete has 30% lower strength than conventional concrete. The strength differential narrowed for increasing values of W/C ratio until the strengths were about equal for a W/C ratio of 0.55. No significant increase in the strength of recycled aggregate concrete was obtained by reducing the W/C ratio below 0.40. It is indicated that the quality of recycled aggregate concrete will improve with the quality of recycled mortar or if the recycled material has a high aggregate-cement ratio. The recycled aggregate concrete showed somewhat better workability characteristics than conventional mixes although its modulus of elasticity and durability characteristics were lower. It is proposed that satisfactory concrete can be made by recycling concrete as aggregate where disposal problems exist or where natural aggregate is either inaccessible or of inferior quality.