Recycled concrete aggregates (RCA) can substitute natural aggregates in concrete with the disadvantage of needing a major quantity of cement and water as consequence of their moderate quality. The objective of this study is to precipitate calcium carbonate crystals over RCA by consuming atmospheric CO2 with a green and sustainable process achieved by microorganisms (MO), improving the mechanical and durability properties of RCA. Bio-carbonation is the result of the metabolism of MO, which must possess three main characteristics; the ability to precipitate calcium carbonate, grow under alkaline conditions (between 11 and 13 pH) and to form complex colonies known as biofilm. In this study, a selection of bacteria isolated from RCA was done with the aim to obtain the species with the capacity to grow in alkaline conditions and to form biofilm. Even if these bacteria are not able to precipitate calcium carbonate crystals, we could fusion their characteristics of growth with other bacteria that perform calcium carbonate synthesis such as Bacillus Halodurans. Microbiological techniques were employed to perform isolation and selection of wild species. An incubation process over a mortar disks was performed to observe the possible behaviour of bacteria to colonize a surface. As result, three wild bacteria species growing in liquid nutrient broth pH 11 were obtained. The isolated bacteria grew under a matrix made of nutritive agar culture over a mortar at pH 13 through biofilm formation. Spherical structures (possibly calcium carbonate crystals) of around 20-30 micrometres appeared near to the zones were bacteria developed. The experimental design of this study opens a new gate of research that seeks an evolution in the use of concrete before and after its life span having as aim a tangible contribution in the reduction of atmospheric CO2 generating RCA of high quality.