Search

US-12624370-B2 - Method for treating recycled aggregates via microbial-induced calcite precipitation

US12624370B2US 12624370 B2US12624370 B2US 12624370B2US-12624370-B2

Abstract

Novel method to enhance the properties of recycled concrete aggregates by microbial-induced calcite precipitation. The present invention utilizes a microbial-induced calcium carbonate precipitation (MICP) as a novel treatment process to enhance the properties of RCA. The MICP application of the present invention is a natural process where bacteria produce calcium carbonate during their metabolic activities.

Inventors

  • Hilal El Hassan
  • Tamer EL MAADDAWY
  • Ashraf Aly Hassan
  • Mohammed ALZARD

Assignees

  • UNITED ARAB EMIRATES UNIVERSITY

Dates

Publication Date
20260512
Application Date
20230707

Claims (14)

  1. 1 . 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%.
  2. 2 . The method of claim 1 , wherein the bacterial strain is Lysinibacillus sphaericus.
  3. 3 . The method of claim 1 , wherein the bacterial strain is Priestia megaterium.
  4. 4 . The method of claim 1 , wherein calcite precipitation occurs in an alkaline medium at a pH of least 9 and at a temperature of 20 to 25° C.
  5. 5 . The method of claim 1 , wherein the two consecutive steps comprise spraying RCA with the immobilization gel and spraying the calcium chloride solution in sequence.
  6. 6 . The method of claim 1 , wherein the two consecutive steps comprise spraying RCA with the immobilization gel and soaking in the calcium chloride solution in sequence.
  7. 7 . The method of claim 1 , wherein the two consecutive steps comprise soaking RCA in the immobilization gel and soaking in the calcium chloride solution in sequence.
  8. 8 . The method of claim 1 , wherein the two consecutive steps comprise soaking RCA in the immobilization gel and spraying the calcium chloride solution in sequence.
  9. 9 . The method of claim 1 , wherein the two consecutive steps comprise spraying RCA with the calcium chloride solution and soaking in the immobilization gel in sequence.
  10. 10 . The method of claim 1 , wherein the two consecutive steps comprise soaking RCA in the calcium chloride solution and spraying the immobilization gel in sequence.
  11. 11 . The method of claim 1 , further comprising a step of soaking RCA in the calcium chloride solution, wherein soaking in the calcium chloride solution lasts 12 to 24 hours under static conditions.
  12. 12 . The method of claim 1 , wherein each of peptone, HM peptone B, and yeast extract is present at 2% to 5% by weight per volume and sodium chloride is present at 0.5% to 3% by weight per volume in the immobilization gel.
  13. 13 . The method of claim 1 , wherein size of the RCA is at least 5 millimeters and less than 25 millimeters.
  14. 14 . The method of claim 1 , wherein, before the first of the two steps, the RCA is rinsed with water to remove loosely attached fines or dirt.

Description

TECHNICAL FIELD The present invention relates to a novel method to enhance the properties of recycled concrete aggregates via microbial-induced calcium carbonate precipitation. BACKGROUND Rapid growth in the global population and economy has led to increasing demand for infrastructure development. As the most widely used construction material, concrete is responsible for the depletion of natural resources. Its main component by mass and volume is aggregates. They are sourced from non-renewable natural resources. Meanwhile, construction and demolition activities have led to the generation of a significant amount of concrete waste. This type of waste is called construction and demolition waste (CDW). Typically, CDW is sent to landfills for disposal, which is not a sustainable solution owing to the scarcity of stockpiling sites and environmental consequences. Thus, there is a need to beneficially reutilize CDW. One such means is to reuse it as aggregates, denoted as recycled concrete aggregates (RCA). RCA has been presented as an attractive alternative to replace natural aggregates (NA) in concrete production and has been praised by several scholars. However, the challenge is that the physical properties of RCA are inferior to those of NA, due to the attached mortar on its surface and its high porosity. This is caused by the high percentage of capillary pores and microcracks on the surface and often in the internal transition zone (ITZ). As a result, concrete made with RCA experienced reductions in workability, compressive strength, splitting tensile strength, and flexural strength, among other properties. This fact has hindered the adoption of RCA by the concrete industry. Therefore, RCA requires pretreatment or preprocessing to enhance its properties prior to utilizing it in concrete products. Different treatment methods have been established. These can be categorized as enhancing the . . . properties of RCA, strengthening the attached mortar, or a combination of both. Treatments related to enhancing the properties of RCA include removal of the attached mortar, autogenous cleaning, mechanical grinding, heat grinding, acid treatment, and thermochemical treatment. Conversely, strengthening the attached mortar treatments comprises pozzolanic slurry, emulsion polymer, carbonation curing, cement slurry coating, sodium silicate solution, and bio-deposition of calcium carbonate. Microbial-induced calcium carbonate precipitation (MICP) has been recently explored as a promising technology for improving the engineering properties of different construction materials. This technology is based on a natural process whereby bacterial cells produce inorganic minerals as part of their basic metabolic activities. MICP has been used extensively in the production of self-healing concrete and mortars to seal cracks. Yet, there is significant room to refine this technique to yield the maximum benefit of MICP. Therefore, there is a need for a new environmentally friendly simple method that can used at room temperature with no energy consumption, utilizing a variety of microorganism for medical and industrial applications. SUMMARY The present invention utilizes a microbial-induced calcium carbonate precipitation (MICP) as a novel treatment process to enhance the properties of RCA. The MICP application of the present invention is a natural process where bacteria produce calcium carbonate during their metabolic activities. The utility of this invention toward a circular economy is threefold. First, the product of this treatment method, i.e., treated RCA, will replace NA, thereby preserving non-renewable natural resources. Second, the use of RCA, which is inherently from construction and demolition waste (CDW), will serve to recycle such waste materials rather than disposing of them in stockpiles. And third, the utilization of CDW will alleviate the demand for land needed for stockpiling. In one embodiment, disclosed herein is a method for enhancing the properties of RCA, comprising the application of microbial-induced calcite precipitate to the RCA by the application of a treatment agent comprising a bacterial strain, an immobilization gel comprising alginate, nutrients and ureas, and a calcium source. In another embodiment, the method comprises the treatment application of two solutions selected from the group consisting of an immobilization gel and a calcium source. In one aspect, the calcium source is calcium chloride. In some aspects, the bacterial strain can be a bacterium or a lyophilized bacterium. In another aspects, the bacterial strain is gram-positive. In a further aspect, the bacterial strain is aerobic. In a preferred aspect, the bacterial strain includes bacteria that can form a carbonate precipitate in an alkaline medium. In a more preferred aspect, the bacterial strain includes genus Lysinibacillus and genus Priestia. In a most preferred aspect, the bacterial strain may include one or more strains including Lysinibaci