Improvement of Fine Recycled Aggregates by Microbially Induced CaCO3 Precipitation

The non-stop construction activities generate significant amount of construction and demolition waste (CDW) which should be recycled effectively in order to sustain a circular economy. The use of CDWs as recycled aggregates in construction materials is an environmentally friendly approach fitting in the circular economy and waste valorization concepts. This research presents improvement of fine recycled aggregates by microbially induced CaCO3 precipitation (MICP) to enable their reuse in concrete. Fine recycled aggregates with 6 different size fractions were microbially treated by using a non-axenic microbial culture. MICP was carried out by coupling two metabolic pathways, namely; urea hydrolysis and nitrate reduction. The improvement procedure consisted of two consecutive stages: (i) microbial attachment, (ii) biomineralization. Upon treatment, CaCO3 was precipitated in and around the pores of the aggregates. The former led to a decrease in the water absorption of fine recycled aggregates up to 24%. Moreover, weight increase was obtained in all aggregate sizes varying between 0.6% and 7.0%. Precipitated CaCO3 crystals were also confirmed by SEM analysis. These results indicated that MICP is a promising bio-based strategy to upgrade fine recycled aggregates and to improve sustainability of construction industry.