Microstructural investigation of concretes with recycled aggregates using X-ray microtomography

Abstract

Recycled aggregates (RA) derive from reprocessed materials from construction and demolition activities. Although the use of RA has been growing worldwide, material standardization and new mix design protocols still need to be developed to enable its use on larger scales. For this, an investigation of the properties of this material is necessary. The present study used microcomputed tomography (microCT) to observe the material's porous structure in cylindrical concrete samples of reference concrete (RC) with natural aggregates and sustainable concrete (SC) with the addition of RA. Through a computational routine, the images obtained were evaluated qualitatively and quantitatively. The pore volume and shape in concretes with and without recycled aggregates were analyzed and correlated with their respective compressive strengths. Even though the SC samples' resistance was lower than the RC samples, the values found followed the required standards. Porosity, pore volume, and shape were similar for the two kinds of concrete. The Pore Network Modeling (PNM) approach was applied to characterize further the pores' spatial distribution and connectivity. The analysis showed that 98.20 % and 97.26 % of the pores were disconnected for the RC and SC samples, respectively. The results indicate that the addition of RA is not detrimental to the properties of concrete. Further PNM-based analysis can help evaluate both samples' absolute and relative permeability to various fluids.