Treatment of recycled concrete aggregates using silica fume impregnation and its influence on the properties of concrete

• Main Authors: Cunanan, Alvin B., Tang, Anthony John T.
• Format: text
• Language: English
• Published: Animo Repository 2017
• Subjects: Aggregates (Building materials); Strength of materials; Civil Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_bachelors/14882
• Institution: De La Salle University

Recycled concrete aggregates (RCA) are aggregates sourced form construction demolition and debris. As such, the use of RCA as coarse aggregate often results in weaker concrete in comparison to concrete utilizing natural aggregates. The factor that significantly affects this is the adhered mortar, that is present in RCA. It is necessary to target this old mortar in order to treat and enhance the properties of RCA. Two treatments were conducted in this study: sulfuric acid bath (SA) treatment, and silica fume impregnation (SF) treatment. SA treatment utilizes a sulfuric acid solution with a 0.5 molarity and reacts with the old cement mortar which dissolve and remove adhered mortar on the RCA. SF treatment utilizes silica fume to penetrate the void spaces and irregular spaces along the surface of RCA. Silica fume also reacts with cement during the hydration process which produces additional C-S-H, creating a stronger layer of cement around RCA. A combination of these two treatments were also conducted. The treatments resulted in insignificant changes in the physical properties of RCA. SA treatment was found to have a detrimental effect on the surface of RCA, which developed a weaker layer of adhered mortar on the RCA surface thus by causing a reduction in the mechanical strength of the concrete. SF treatment resulted in improved compressive strength in comparison to untreated, SA, and combined treatment RCA concrete. It was also found that a value of 50% replacement of RCA in all treatment samples was the optimal in maximizing the strength of RCA concrete.