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  1. Abstract

    Researchers have made headway against challenges of increasing cement infrastructure and low plastic recycling rates by using waste plastic in cementitious materials. Past studies indicate that microbially induced calcium carbonate precipitation (MICP) to coat plastic in calcium carbonate may improve the strength. The objective of this study was to increase the amount of clean and contaminated waste plastic that can be added to mortar and to assess whether MICP treatment enhances the strength. The performance of plastic-filled mortar was investigated at 5%, 10%, and 20% volume replacement for cement. Untreated, clean plastics at a 20% cement replacement produced compressive strengths acceptable for several applications. However, a coating of MICP on clean waste plastic did not improve the strengths. At 10% replacement, both MICP treatment and washing of contaminated plastics recovered compressive strengths by approximately 28%, relative to mortar containing oil-coated plastics. By incorporating greater volumes of waste plastics into mortar, the sustainability of cementitious composites has the potential of being improved by the dual mechanisms of reduced cement production and repurposing plastic waste.

  2. Free, publicly-accessible full text available November 1, 2023
  3. Abstract. The kinetics of urea hydrolysis (ureolysis) and induced calcium carbonate(CaCO3) precipitation for engineering use in the subsurface wasinvestigated under aerobic conditions using Sporosarcina pasteurii(ATCC strain 11859) as well as Bacillus sphaericus strains 21776and 21787. All bacterial strains showed ureolytic activity inducingCaCO3 precipitation aerobically. Rate constants not normalized tobiomass demonstrated slightly higher-rate coefficients for both ureolysis(kurea) and CaCO3 precipitation (kprecip)for B. sphaericus 21776 (kurea=0.10±0.03 h−1, kprecip=0.60±0.34 h−1) compared toS. pasteurii (kurea=0.07±0.02 h−1,kprecip=0.25±0.02 h−1), though these differences werenot statistically significantly different. B. sphaericus 21787showed little ureolytic activity but was still capable of inducing someCaCO3 precipitation. Cell growth appeared to be inhibited duringthe period of CaCO3 precipitation. Transmission electron microscopy (TEM) images suggest this is dueto the encasement of cells and was reflected in lower kureavalues observed in the presence of dissolved Ca. However, biomass regrowthcould be observed after CaCO3 precipitation ceased, which suggeststhat ureolysis-induced CaCO3 precipitation is not necessarilylethal for the entire population. The kinetics of ureolysis andCaCO3 precipitation with S. pasteurii was furtheranalyzed under anaerobic conditions. Rate coefficients obtained in anaerobicenvironments were comparable to those under aerobic conditions; however, nocell growth was observed under anaerobic conditions with NO3-,SO42- or Fe3+ as potential terminal electronacceptors. These data suggest that the initial rates of ureolysis andureolysis-inducedmore »CaCO3 precipitation are not significantlyaffected by the absence of oxygen but that long-term ureolytic activity mightrequire the addition of suitable electron acceptors. Variations in theureolytic capabilities and associated rates of CaCO3 precipitationbetween strains must be fully considered in subsurface engineering strategiesthat utilize microbial amendments.« less