Bio-cementation of Demolition Wastes and Recycled Aggregates for Sustainable Production of Paving Blocks

Concrete block pavements have recently become an attractive engineering system, increasingly used in parking areas, pedestrian walks, traffic intersections, container yards, and low-volume roads. However, the production of paving blocks is in high demand for Portland Cement and natural aggregates. The exhaustive use of such resources has become a serious threat, resulting in a scarcity of resources and negative environmental impacts. To alleviate these traits, the authorities heightened laws to restrict the construction practices that heavily contribute to carbon footprint. This study proposes the bio-cementation of demolition wastes and recycled aggregates as a new sustainable alternative for producing paving blocks. The method harnesses the bacteria containing active urease to biochemically induce the cementation. The feasibility and efficiency of using five different types of demolition wastes were investigated. Recycled concrete coarse aggregates (R-CCA), recycled concrete fine aggregates (R-CFA), recycled concrete aggregate dust (R-CAD), recycled concrete mortar dust (R-CMD), and recycled brick aggregates (R-BA) were derived by crushing the building demolition wastes and prepared in standard molds. The bacteria used herein were Sporosarcina pasteurii. During the batches of treatment, the bacteria culture was percolated into the specimens along with aqueous urea and calcium chloride. The evaluation program consisted of unconfined compressive strength (UCS) tests, scanning electron microscopy (SEM) analysis, and the measurements of precipitation content. The SEM results revealed that the bio-cement treatment could induce the formation of calcium carbonate within the pores and facilitate the binding of aggregates in all the categories. However, the achieved UCS on R-CFA was the highest (~2 MPa), that on R-CCA was the next (~1.48 MPa), while that on R-CAD and R-BA were the worst. R-CMD achieved a moderate UCS (~0.6 MPa). The gradation and the nature of the waste material were found to determine the efficiency of strengthening and uniformity in the cementation profile.