Method for treating recycled aggregates via microbial-induced calcite precipitation

A method for enhancing the properties of recycled concrete aggregates (RCA) by microbial-induced calcite precipitation, comprising:

• applying to the RCA in two consecutive steps, in any order:
• (i) an immobilization gel comprising sodium alginate at 4% to 6% by weight per volume, urea, nutrients comprising peptone, HM peptone B, yeast extract and sodium chloride, and a bacterial strain selected from Lysinibacillus sphaericus or Priestia megaterium, wherein the bacterial strain is provided in lyophilized form and rehydrated in the immobilization gel immediately prior to application, and
• (ii) a calcium chloride solution,
• wherein urea and calcium chloride are provided at a 1:1 molar ratio during treatment, and wherein urea and calcium chloride are each initially provided at a base concentration of 41.6 g/L±2% with stepwise increases up to 582.8 to 832.5 g/L while maintaining the 1:1 molar ratio, and wherein water absorption of the resulting RCA ranges from 0.5% to 3.0%, and Los Angeles abrasion mass loss measured after 500 revolutions ranges from 15% to 21%.