Effect of surface treatment of recycled concrete aggregate by cement -silica fume slurry on compressive strength of concrete

Abstract

Recycled concrete aggregate (RCA) used as an alternative to natural aggregate (NA) contains weak adhered mortar. The adhered mortar adversely affects the properties of RCA, and compressive strength of concrete with RCA. Therefore, a treatment method by coating surface of RCA with cement-silica fume slurry (CSS) at concentrations of 20, 40, and 60% was done to evaluate its effects on crushing value and water absorption of RCA, and compressive strength of concrete with treated RCA. The replacements of natural coarse aggregate by RCA for concrete production were 0, 25, and 50% by volume. Compressive strength of the concrete having a constant water-to-cement ratio of 0.35 was tested at ages of 3, 7, 28, and 56 days. Results showed that crushing value and water absorption of the treated RCA were more improved when compared with those of the untreated RCA due to new products formed from cement hydration and pozzolanic reactions on its surface detected by using scanning electron microscope. The surface treatment with CSS at concentration of 60% was the most effective method when compared with that with CSS at concentrations of 20 and 40%. The higher the concentration of CSS, the higher the compressive strength of concrete with the treated RCA. The treatment of RCA led to a significant improvement of compressive strength of the concrete at later ages (i.e., at 28 and 56 days) when compared with the concrete using untreated RCA.

Keywords

• recycled concrete aggregate
• cement-silica fume slurry
• surface treatment
• pozzolanic reaction
• compressive strength