Microstructure analysis of hardened recycled aggregate concrete

Fifty percent of the total weight of construction and demolition waste is concrete. Consequently, the utilisation of crushed waste concrete must be considered as imperative in concrete production. Recycled aggregates are formed basically by adhered mortar and original aggregates. Adhered mortar is a very porous material, with a high absorption capacity and high permeability. Four different percentages ( 0, 25, 50 and 100%) of wet recycled coarse aggregates were used in the production of the concrete tested, the same compressive strength being obtained in all four mixes. The microstructure of recycled aggregate concrete was analysed using a fluorescent light optical microscope, which made it possible to observe the high porosity of recycled aggregates with and without adhered mortar, the increment of air void percentage in new cement paste when high amounts of recycled aggregates are used and the effectiveness of new interfacial transition zone in recycled aggregate concrete.