Specimens of silica sand treated via enzyme induced carbonate precipitation (EICP) showed surprisingly high strength at a relatively low carbonate content when non-fat powdered milk was included in the treatment solution. EICP is a biologically-based soil improvement technique that uses free urease enzyme to catalyze the hydrolysis of urea in an aqueous solution, producing carbonate ions and alkalinity that in the presence of calcium cations leads to precipitation of calcium carbonate. The strength achieved at less than 1.4% carbonate content via a single cycle of treatment was unprecedented compared to results reported in the literature from both EICP and microbially induced carbonate precipitation (MICP). Scanning electron microscope images show that in the specimens treated with the solution containing powdered milk the carbonate precipitate was concentrated at interparticle contacts. The impact of these results include reductions in the concentration of substrate and enzyme required to achieve a target compressive strength, reduction in the undesirable ammonium chloride by-product, and, depending on the desired strength, reduction in the number of cycles of EICP treatment. These advantages enhance the potential for development of a sustainable method of soil improvement via hydrolysis of urea.
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.
- Award ID(s):
- Publication Date:
- NSF-PAR ID:
- Journal Name:
- Scientific Reports
- Nature Publishing Group
- Sponsoring Org:
- National Science Foundation
More Like this
Tang, Qiang (Ed.)As an environmentally friendly technology, microbially induced calcite precipitation (MICP) is widely used to improve the engineering properties of soil. The goal of this study was to investigate the effect of rainfall-induced erosion on the stability of sandy slopes which were treated by MICP technology. The observation of the erosion pattern of low concentration (0.25 M Ca) and high concentration (0.5 M Ca) of MICP-treated slopes, the mechanical behaviors of MICP-treated and cement-treated samples, and the effects of rainfall-induced erosion on the roughness of 0.5 M Ca MICP-treated and 10% cement-treated slope were studied through visual observation, unconfined compressive tests, and roughness tests. For the 0.25 M Ca MICP-treated sample, surface erosion was found to occur soon after the start of the rainfall erosion test, while for the 0.5 M Ca MICP-treated sample, the slope surface remained intact after exposing to the rainfall for 24 hours. Through unconfined compressive tests, it can be concluded that the 0.5 M Ca MICP treatment achieved a high strength, which was similar to 10% cement-treated sand. The roughness test results showed that the surface of 0.5 M Ca MICP-treated slope looked smoother than the uneroded surface after 24-h rainfall-induced erosion. On the contrary, the surface of the 10% cement-treated slope becamemore »
This study characterized and evaluated the use of reclaimed fly ash (RFA) and reclaimed ground bottom ash (GBA) as alternative sources of supplementary cementitious materials (SCMs) for the production of concrete mixtures. Conventional Class F fly ash (FA) was also evaluated for comparison. The effects of SCM content on fresh and hardened properties of concrete were investigated by replacing 10%, 20%, and 30% of cement by mass. Characterization results showed that all three ashes met ASTM C618 chemical requirements (i.e., sum of SiO 2 + Al 2 O 3 + Fe 2 O 3 , CaO, SO 3 , moisture content, and loss of ignition) and 7- and 28-days strength activity index (SAI) requirements for Class F FA. In addition, RFA exhibited slightly higher SAI at 28 days of curing, followed by GBA and FA. In relation to fresh concrete properties, FA increased the concrete slump compared with the control mixture, whereas RFA and GBA decreased the concrete slump. However, GBA produced more significant slump decrements than RFA, which was attributed to the irregular angular particles of GBA. Generally, all the coal ashes produced decrements in air content compared with the control mixture. Comparatively, among the three ashes, GBA exhibited the highest 28-more »
Investigating Ammonium By-product Removal for Ureolytic Bio-cementation Using Meter-scale Experiments
Microbially Induced Calcite Precipitation (MICP), or bio-cementation, is a promising bio-mediated technology that can improve the engineering properties of soils through the precipitation of calcium carbonate. Despite significant advances in the technology, concerns regarding the fate of produced NH4+by-products have remained largely unaddressed. In this study, five 3.7-meter long soil columns each containing one of three different soils were improved using ureolytic bio-cementation, and post-treatment NH4+by-product removal was investigated during the application of 525 L of a high pH and high ionic strength rinse solution. During rinsing, reductions in aqueous NH4+were observed in all columns from initial concentrations between ≈100 mM to 500 mM to final values between ≈0.3 mM and 20 mM with higher NH4+concentrations observed at distances furthest from the injection well. In addition, soil Vsmeasurements completed during rinse injections suggested that no significant changes in cementation integrity occurred during NH4+removal. After rinsing and a 12 hour stop flow period, all column solutions achieved cumulative NH4+removals exceeding 97.9%. Soil samples collected following rinsing, however, contained significant sorbed NH4+masses that appeared to have a near linear relationship with surrounding aqueous NH4+concentrations. While these results suggest that NH4+can be successfully removed from bio-cemented soils, acceptable limits for NH4+aqueous concentrations and sorbed NH4+masses will likely bemore »
Sequestration of solid carbon in concrete: A large-scale enabler of lower-carbon intensity hydrogen from natural gasAbstract Methane pyrolysis is an emerging technology to produce lower-carbon intensity hydrogen at scale, as long as the co-produced solid carbon is permanently captured. Partially replacing Portland cement with pyrolytic carbon would allow the sequestration at a scale that matches the needs of the H 2 industry. Our results suggest that compressive strength, the most critical mechanical property, of blended cement could even be improved while the cement manufacture, which contributes to ~ 9% global anthropogenic CO 2 emissions, can be decarbonized. A CO 2 abatement up to 10% of cement production could be achieved with the inclusion of selected carbon morphologies, without the need of significant capital investment and radical modification of current production processes. The use of solid carbon could have a higher CO 2 abatement potential than the incorporation of conventional industrial wastes used in concrete at the same replacement level. With this approach, the concrete industry could become an enabler for manufacturing a lower-carbon intensity hydrogen in a win–win solution. Impact Methane pyrolysis is an up-scalable technology that produces hydrogen as a lower carbon-intensity energy carrier and industrial feedstock. This technology can attract more investment for lower-carbon intensity hydrogen if co-produced solid carbon (potentially hundreds of millionmore »