Roughness analysis of recycled aggregates and the influence on paste-aggregate adhesion in cementitious composites: The new approach with surface microscopy

The mechanical strength of concrete and mortars is influenced by the characteristics of the aggregate, including shape, composition and roughness. Recycled aggregates have a more porous surface and variable composition compared to natural aggregates, contributing to the interlocking of the system and increasing the transition area between the paste and the aggregate. The objective of this work is to investigate the influence of the roughness of recycled coarse aggregates on the adhesion with cementitious mortar. The roughness of the aggregates was varied through mechanical treatment and manual sanding to obtain different levels, and it was quantified using laser confocal micoscopy. Using the mortar immersion method developed in this study, the interfacial transition zone was analyzed through scanning electron microscopy. The results indicate that mechanical treatment should be performed in a controlled manner to ensure a balance between removing adhered mortar and not creating an excessively rough surface that compromises the interaction with the cement paste. It was concluded that surface topography is a determining factor for paste-aggregate adhesion and improvement in the mechanical behavior of concrete made with construction and demolition waste. Moderate roughness, with well-defined and alternating valleys and depressions, favors the penetration of the cement paste and creates a denser interfacial bond.