Methods, systems, and apparatus, including computer programs encoded on computer storage media, for processing recycled concrete aggregate (RCA). One of the methods includes obtaining first optical measurements of RCA particles as the RCA particles are conveyed past the first optical sensors; determining, based on the first measurements, an initial characterization of the RCA particles; iteratively performing a carbonation process on the RCA particles, obtaining second optical measurements of the RCA particles, and determining, from the second measurements, a second characterization of the RCA particles, wherein conditions of the carbonation process are initially set based on the initial characterization, and the conditions of the carbonation process are adjusted based on the second characterization; ceasing the iterative performance of the carbonation process in response to the second characterization meeting target carbonation characteristics; iteratively performing a densification process on the RCA particles, obtaining third optical measurements of the RCA particles, and determining, from the third measurements, a third characterization of the RCA particles, wherein conditions of the densification process are initially set based on the initial characterization or the second characterization, and the conditions of the densification process are adjusted based on the third characterization; and ceasing the iterative performance of the densification process in response to the third characterization meeting target densification characteristics.