The effect of silica fume inclusion on the properties of recycled concrete aggregate- containing concrete

Abstract

Protecting the environment against the hazards of construction and demolishing (C&D) wastes is crucial. Elimination of C&D wastes by using them as recycled concrete aggregates (RCA) within the manufacture of new concretes is a promising solution for this problem. Since RCA coming from demolished structures have poor qualities, overall performance of new concrete should be monitored carefully. Without achieving a satisfactory strength performance, manufacturing concretes with RCA could not be widely accepted in construction sector. This study investigates the effects of silica fume, which is an effective pozzolanic material, on the properties of concrete mixtures made with 50%RCA as a replacement to quarried aggregates. RCA used was obtained from a 25-years old public building in Nicosia that was structurally failed and demolished. Results obtained indicated a 12.3% water demand increase for obtaining the targeted slump when SF was added in fresh concrete. The increase in compressive strength of concrete with SF in 28 days was 1.5%, where this increase was recorded as 8.1% at 90 days, yielding more than 65MPa strength. Also, addition of SF was observed to improve flexural strength of concrete samples up to a 4.3% at the age of 28 days, enabling the manufacture concrete mixtures apt for structural use.