Improving quality of coarse recycled aggregates through cement coating

Abstract

This paper presents an alternative to reduce porosity of coarse recycled aggregate through coating the 4–8 mm fraction with a thin layer of cement. Coating was carried out in a lab granulator. A 0.16–0.23 mm thick cement film was placed surrounding the aggregate grain. Porosity and freeze-thaw tests carried out in the coarse coated recycled aggregate show improvement due to the encapsulation. For the same water to cement ratio, the amount of superplasticizer used in concrete made with encapsulated aggregates was reduced to a half compared to the non-coated reference, while a slight increase in strength is reported. Microstructural observation of the Interfacial Transition Zone (ITZ) between paste and coarse aggregate prove that encapsulation enhances densification of the cement matrix at the ITZ, which implies a reduction on porosity and contributes to increase strength.

Keywords:

• recycled waste concrete
• aggregates
• pore structure
• rheology
• strength

Acknowledgements

The authors want to thank the German Alexander von Humboldt Foundation for the support provided for carrying out this research. Further, the authors appreciate the support of the Laboratory for Building Materials at the Ecole Polytechnique Federal de Lausanne for carrying out microstructural observations.