Application of Bacillus mucilaginosus microorganisms to remove cement stone from the surface of crushed stone extracted from concrete scrap

The ability to remove cement stone from the large aggregate out of concrete scrap using a nature-like technology was investigated. A washing solution with Bacillus mucilaginosus microorganisms, capable selectively destroying chemical bonds in cement stone making it brittle, was used. According to the results of the granulometric analysis, it was found that the washing solution works only on cement stone, without destroying the coarse aggregate from the concrete scrap. The aggregate extracted from the concrete scrap was tested for strength, crushing capacity, water absorption, porosity, and frost resistance. It is shown that the indicators for coarse aggregate extracted from concrete scrap and freed from cement stone are not significantly inferior in their values to natural crushed stone. An assessment of the mechanical properties of concrete made with secondary coarse aggregate, previously cleaned from cement stone, was also carried out. The compressive strength is 42–44 MPa, and the bending strength reaches 12.5 MPa.