CaCO3 Deposition Research Articles

Innovative and environmentally friendly MICP surface curing: Enhancing mechanical and durability properties of concrete

Concrete curing is a critical factor influencing its mechanical properties and durability. Traditional curing methods, such as water curing and plastic film curing, have significant limitations, including high water consumption and environmental pollution. This study introduces Microbial Induced Carbonate Precipitation (MICP) as an innovative, environmentally friendly curing method for ready-mixed concrete, addressing the urgent need for sustainable construction practices. The feasibility of MICP surface curing is investigated through comprehensive mechanical and durability tests, coupled with microscopic analyses to understand the underlying mechanisms. The results demonstrate that MICP curing substantially enhances concrete performance. Compared to traditional water curing, the samples cured using MICP have increased compressive strength and splitting tensile strength by up to 31.69% and 24.66%, respectively. Additionally, MICP surface curing significantly reduced capillary water absorption, electric flux, and chloride ion migration coefficient by 12.83%, 15.50%, and 17.36%, respectively. It is found that the optimal concentration of Ca2+ in the MICP solution initially improves concrete performance, which then diminishes at higher concentrations due to bacterial activity inhibition. Spraying the MICP solution at appropriate intervals and increasing the number of treatments further improved concrete properties by ensuring a more extensive and dense deposition of CaCO3. Microscopic analyses, including XRD, TG, and SEM-EDS, revealed that MICP surface curing leads to the formation of vaterite and calcite, which densely cover and fill microscopic cracks and pores, ensuring adequate hydration and simultaneously enhancing the concrete's mechanical and durability properties. This study concludes that MICP surface curing provides superior performance than traditional methods and offers a more sustainable and environmentally friendly curing method.

Application of Laser-Induced Breakdown Spectroscopy to quantify the changes in plasma characteristics in calcite-precipitated soils

The changes in calcium carbonate precipitation of modified soil by Enzyme Induced Calcite Precipitation (EICP) were investigated using Laser-Induced Breakdown Spectroscopy (LIBS). This experiment enabled elemental composition analysis of the soil samples. The plasma electron density and temperature were also extracted from the collected spectra of distinct soil samples i.e., W1 and W2 treated with EICP. The type of the crystal of CaCO3 deposited during the treatment process was investigated using scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. This research was conducted by utilizing an Nd: YAG laser with a wavelength of 532 nm, a pulse duration of 6 ns, and an energy of 25 mJ, from where the plasma temperature and electron density of modified soil throughout several treatment cycles were analyzed. The spectra were collected from different locations within the sample and the spectral range considered for the study was 370 nm-800 nm. The plasma electron density and plasma temperature determined using LIBS spectral data increase with the increase in the treatment cycle. With the increase in the treatment cycle, the deposition of CaCO3 was found to increase and correspondingly plasma temperature increased by 220 % for soil W1 and 117.3 % for soil W2. A similar rise in plasma electron density was noticed at the highest cycle of the treatment process; plasma electron density is augmented by 106.4 % for W1 and 21.50 % for W2. This investigation of the LIBS spectral data information indicates a positive correlation between the number of treatment cycles and the plasma temperature, meaning that as the treatment cycles rise, the plasma temperature also increases indicating a larger deposition of CaCO3. The findings are valuable in the domain of geotechnical engineering, where lasers are extensively employed for the examination of the soil profile and can prove to be a useful method for the characterization of the modified soils.

Response of nitrifiers to gradually increasing pH conditions in a membrane nitrification bioreactor: Microbial dynamics and alkali-resistant mechanism

Nitrification and nitrifiers are pH-sensitive especially under the alkaline environment in the activated sludge system. However, it is unclear how nitrifiers and nitrification respond to long-term alkaline environment. This study employed a continuous flow membrane nitrification bioreactor to investigate the dynamics of nitrification efficiency and microbial community adaptation under a 320-day alkaline operation. Results showed that activated sludge adapted remarkably to a progressive increase in pH from 7.5 to 10.0, achieving robust nitrification with average ammonia removal efficiencies of 96.6 ± 2.2%. Subsequently, an integrated alkali-resistant mechanism of nitrifiers was proposed. Specifically, under the long-term operation of pH 10.0, certain bacteria secreted enhanced extracellular acidic polysaccharides (i.e., up to 10.95 ± 0.27 mg·g−1 MLVSS in soluble extracellular polymeric substances (EPS)) and acidic organic compounds (e.g., humic acids increased by 1.47-fold in tightly bounded EPS) to neutralize external alkalinity. Moreover, significant enrichments in both the ammonia oxidizing bacteria Nitrosomonas (by 1.3%) and the nitrite oxidizing bacteria Nitrospira (by 5.4%) were observed in a 170-day operation of pH 10.0 condition. Meanwhile, norank_f__JG30-KF-CM45 (2.0%) and Rhodobacter (0.9%) also contributed to ammonia removal at pH 10.0. On the cellular-level, bacteria enabled to maintain intracellular pH stabilization primarily through cation/proton antiporters, evidenced by significant increases in NhaA, TrkA and KefB activities by 98.0%, 151.7% and 115.2%, respectively. A 43.1% increase in carbonic anhydrase activity also facilitated consumption of aqueous OH− ions through biomineralization, leading to CaCO3 deposition on microbial surface. These findings further enhanced understandings of physiological adaptation of nitrifiers in the long-term alkaline activated sludge system.

Salt scaling dynamics in microfluidic channels: Impact of channel geometry and process parameters

Salt scaling, a prevalent challenge in industrial processes, often leads to reduced efficiency, equipment failure, and environmental impact. Understanding and mitigating scaling in miniaturized systems for process intensification applications is crucial. In this study, we indigenously developed and utilized microfluidic reactors to investigate calcium carbonate (CaCO3) scaling dynamics in microfluidic channels, offering real-time visualization under continuous flow; a significant advancement over static methods. We explore the impact of channel geometry (curvature of 0°, 45°, 90°, and 135°) and process parameters (temperature, supersaturation index (SI), and flow velocity) on CaCO3 deposition behavior. Our findings reveal significant influences: higher temperature and SI promote deposition, while microchannel curvature and increased flow velocity enhance removal. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses confirmed the morphology and phase changes of the deposited CaCO3. Calcite and aragonite were the dominant polymorphs, with their occurrence influenced by temperature and SI. These insights can be translated to the design and operation of miniaturized equipment for process intensification, such as micro heat exchangers. By understanding and controlling scaling phenomena, this research might pave the way for improved performance, sustainability, and resource efficiency in various industrial settings.

Mechanical and microstructural properties of biogenic CaCO3 deposition (MICP) on a specific volcanic sediment (unwelded Tuffs) by Bacillus pasteurii and Bacillus subtilis

Microbially induced calcite precipitation has garnered significant attention in recent years as a promising and environmentally friendly process for addressing sand stabilization and soil consolidation. While its potential to stabilize sand dunes and mitigate soil liquefaction is well-documented, the applicability of MICP in the consolidation of stone materials has not been thoroughly investigated. Tuffs, which are silicate-laden pyroclasts, have historical significance as hybrid materials for cement, emphasizing their importance in cultural heritage. In previous MICP applications, there has been a lack of exploration regarding the incorporation of urease-producing bacteria (UPB) into Tuffs. Consequently, the potential of MICP in substrates such as Tuffs has been largely overlooked. The primary objective of this study is to assess the feasibility of incorporating UPB into Tuffs as a consolidating agent to facilitate calcium carbonate precipitation. We aim to investigate the microstructure of the resulting polymorphs and the previously unknown mechanism of increased resistance to W-D cycles in the treated samples at the nanoscale. In this study, we compared the cementation response of Tuff when subjected to two different UPBs by evaluating changes in key parameters, including capillary water absorption (CWA), cyclic tests such as wet-dry and salt attack, and uniaxial compressive strength. Furthermore, the characteristics of crust formation were examined using FESEM, and an in-depth analysis of the microstructure of the deposited bacterial CaCO3 was conducted. The mechanism of increased W-D resistance in Tuffs reinforced by MICP has not been previously addressed by researchers. Our study demonstrated that the increase in resistance to W-D cycles was more pronounced in samples treated with Bacillus pasteurii. Further FESEM analysis showed the presence of Bacillus pasteurii spores in the nanopores of the (W-D) exposed samples. N2 adsorption analysis revealed that nanopore alteration occurred only in samples treated with Bacillus pasteurii. Additionally, Tuffs are prone to disjoining pressure, which occurs in nanopores. Based on these observations, we postulate that the increased resistance to W-D cycles in the samples treated with Bacillus pasteurii was caused by a decrease in disjoining pressure due to the recrystallization of amorphous calcium carbonate (ACC) in the nanopores of the studied Tuff.

Synergistic effect of CO2-mixing and steel slag addition on performance and microstructure of concrete

This study systematically investigated the influence of varying carbon dioxide (CO2) dosages and steel slag (SS) replacement rates on the fresh and hardened properties of concrete through the injection of CO2 gas during the mixing process. The composition of hydration products, degree of hydration, and the evolution of microstructural characteristics within the CO2-SS-cement system were analyzed. The results showed that CO2 addition during the mixing process enhanced early strength in SS concrete. For concrete with a 10 wt% SS replacement rate, the incorporation of CO2 ranging from 0.4 wt% to 1.2 wt% of the total mass of cementitious materials resulted in notable compressive strength increases of 1.26%–12.47%, 0.64%–6.14%, and 11.79%–18.24% at ages of 1 d, 3 d, and 7 d, respectively. CO2 rapidly reacted with SS to form calcite-type CaCO3 and promoted the generation of C-S-H through synergistic hydration with cement. However, a high CO2 dosage (1.2 wt%) led to issues such as microcrack propagation and interface loosening due to CaCO3 deposition, which could be mitigated to some extent by appropriately increasing the SS content.

Strategy to prevent calcification by restricting surface adhesion of Ca2+: Reduced affinity of extracellular polymeric substances for Ca2+ by mild acidic conditions

Controlling CaCO3 precipitation within anaerobic granular sludge (AnGS) is crucial for the anaerobic treatment of paper recycling wastewater. A viable strategy was proposed to control calcification by adjusting a mild acidic condition in an anaerobic reactor without hindering organic degradation. The results indicated that lowering the bulk pH (6.5 to 6.8) reduced calcium precipitation by 60.1 % in calcium-rich influent (Ca2+ 1200 mg/L) and eradicated CaCO3 deposition on AnGS. Extracellular polymeric substances (EPS) have proven to be crucial participants in Ca2+ migration. The acidic solution weakens the interactions between EPS and Ca2+ and then diminishes the EPS adsorption capacity and affinity for Ca2+. The mild acidic environment goes beyond reducing CaCO3 formation in wastewater. EPS protonation reduced the probability of Ca2+ adhering to the AnGS surface, which halted calcium transportation from bulk liquid to granule. This work offers a feasible strategy to prevent AnGS calcification in high-calcium wastewater.

Enhancing alkali resistance of recycled GFRP fibers and mechanical performances of cement mortars with microbial induced carbonate precipitation

Applying the recycled glass fiber reinforced plastic (rGFRP) fiber to reinforce cement-based materials is a promising way to reuse this massively waste material. However, rGFRP fiber is prone to be corroded in the alkali environment of cement. To solve this problem, the rGFRP fiber was treated with microbial induced CaCO3 precipitation (MICP) technique. The effects of MICP treatment on the rGFRP fiber and the reinforced mortar were investigated. It was revealed that the alkali resistance of the rGFRP fiber was significantly modified by CaCO3 deposition, which was increased with the concentration of mineralizing solution and treating time. The tensile strength and aging resistance of the rGFRP fiber reinforced mortar were all improved by MICP treatment, since fiber-cement friction, fiber-cement compatibility, microstructural compactness and cement hydration degree were enhanced by the properly precipitated CaCO3 crystals on fiber surface. However, excessive MICP treating process was detrimental for effective CaCO3 precipitation. The rGFRP fiber treated in the mineralizing solution of 1.0 mol/L for 3 times with 24 h/time (1−24−3) had the most promising modification effect on the rGFRP fiber and the reinforced mortar in this study. The 1–24–3 rGFRP fiber had similar alkali resistance to the alkali resistance glass fiber, which increased the tensile strength of mortar by 34.1 % and improved the bending strength of mortar by 10.8 % after accelerated aging. The MICP technique was used on modifying rGFRP fiber and the reinforced mortar for the first time, which would benefit the durability of rGFRP fiber and its wider application in cement-based materials, while the long-term performance of rGFRP fiber reinforced mortar should be studied in the future.

Late Holocene changes in the water table at an alkaline fen in Central Latvia: Their impacts on CaCO3 deposition at the fen and relation to the hydroclimate patterns of the Eastern Baltic Region

Sediments of CaCO3-precipitating alkaline fens, comprising biotic and abiotic indicators of water table changes, are among the most reliable archives for obtaining palaeohydrological data. The study uses a semiquantitative method based on a combination of selected indicators (plant macrofossils, mollusc shells, degree of peat decomposition) to estimate the relative changes in the water table position at Lustūžkalns alkaline fen, Latvia, Eastern Baltic Region. The study also aims to determine the time frames of CaCO3 deposition at the fen using loss on ignition and carbon and oxygen stable isotope records. The chronology of the three sediment sequences studied is based on the AMS radiocarbon dating of terrestrial plant macrofossils. Although the reconstructed water table positions revealed differences between the cores, the major shift from the low water tables persisting since ca. 5000 cal yr BP to the prevailing high water stands at ca. 3000 cal yr BP was common to all the sequences. The major shift observed is consistent with a change from low to high water tables in peatlands in Latvia and at numerous fens and bogs across the Eastern Baltic Region, Fennoscandia and NW Europe. Concurrent with the increase in the water tables was the onset of CaCO3 precipitation on the Lustūžkalns fen surface, which began at ca. 3000 cal yr BP and accelerated from ca. 2500 cal yr BP. The Late Holocene CaCO3 precipitation at Lustūžkalns can be attributed to the change from warm and dry conditions during the Holocene Thermal Maximum (HTM) to cooler but humid during the Late Holocene. In contrast, in Central and Western Europe, the main period of freshwater carbonate precipitation occurred during the warm and humid HTM.

Exploring Endogenous Processes in Water Supply Systems: Insights from Statistical Methods and δ18O Analysis

Water used for water supply undergoes numerous changes that affect its composition prior to entering the water supply system (WSS). Once it enters the WSS, it is subject to numerous influences altering its physical and chemical composition, redox potential, and microbial quality. Observations of water quality parameters at different locations within the WSS indicate that it is justified to assume that these processes take place from the source to the end user. In this study, we used the results of routine everyday analyses (EC, T, pH, ORP, chloride, nitrate, nitrite, ammonium, and bacteria) supplemented by experimental data from a one-year sampling campaign assessing the main cations and anions and stable isotopes δ2H and δ18O. Through these data, the statistical significance of the differences between the concentrations of the basic water quality parameters among different WSS locations was determined, together with the water retention time in the system. The results indicate minor changes in water chemical composition within the observed WSS, remaining below the prescribed Maximum Contaminant Level (MCL) for human consumption. However, factors such as water retention time, CaCO3 deposition, pH fluctuations, and bacterial growth may influence its suitability, which necessitates further investigation into potential risks affecting water quality.

Study on the inhibition mechanism of corrosion under inert deposit-covered X65 steel by three corrosion inhibitors

In order to solve the problem of under-deposit corrosion caused by typical inert minerals in oil and gas fields, three corrosion inhibitors with small molecular weight thiourea (TU), oil-soluble alkyl imidazoline (IM) and water-soluble thiourea imidazoline (TAI) were selected. The corrosion inhibition effect and mechanism of the them under SiO2 and CaCO3 deposit were studied by surface analysis, electrochemical analysis and theoretical calculations. The results show that TU, IM and TAI can adsorb on the metal surface through the deposits, and the corrosion inhibition efficiency is η(TAI) > η(TU) > η(IM). TU and TAI are mixed corrosion inhibitors that inhibit both the cathode and the anode reactions, and the thiourea group in TU and TAI can form coordination chemical bonds with the empty d orbital of iron atoms as electron-rich regions. Due to hydrophobic groups, the adsorption film formed by TAI on the metal surface is denser. However, it is difficult for IM to form a continuous protective corrosion inhibitor film under the two deposits, so it shows poor corrosion inhibition performance.

Enhancing permeability and mechanical properties of rubber cement-based materials through surface modification of waste tire rubber powder

In this study, the authors present a detailed investigation into the surface mineralization of recycled rubber powder (RP) to enhance its performance in cement mortars. A modified rubber, referred to as RTC, is produced by employing a straightforward and efficient method involving the deposition of tannic acid (TA) and calcium carbonate (CaCO3, <5 μm) on the surface of RP. The main objective of this research is to elucidate the impact of RTC on the impermeability, mechanical properties, and pore structure of rubberized mortar. Through a comprehensive set of characterizations and tests, we demonstrate the successful deposition of TA and CaCO3 on the RP surface, resulting in RTC with excellent chemical activity and hydrophilicity, while also providing nucleation sites for hydration products. This modification process facilitated improved interfacial affinity with cement paste, enhancing bonding between rubber and cement paste. Remarkably, the incorporation of rubber into mortars with markedly enhanced resistance to permeation, with RTC mortars demonstrating particularly noticeable improvement. The marginal decrease in density in comparison to conventional mortars arises from the rubber's lightweight properties. Moreover, rubber exerts a minor adverse influence on hydration kinetics, yet this detrimental impact is alleviated in mortars incorporating RTC. Notably, the study elucidates the nuanced changes in porosity induced by rubber incorporation, underscoring its influence on the mechanical performance of rubberized cement mortars. The RTC5 mortar with a 5% content demonstrates the most remarkable enhancement compared to RP5 mortar. Overall, this study highlights the potential of surface mineralization of RP as a promising approach for improving the performance of rubberized cement mortars.

Magnetic treatment as a suppressive method for CaCO3 scale deposition in hard waters in the presence of air bubbles

Calcium carbonate (CaCO3) scale deposition in hard water is a common problem affecting the performance and efficiency of various industrial applications such as water heating systems and pipelines. The aim of this study was to investigate the effectiveness of magnetic treatment as a suppressive method for CaCO3 scale deposition in hard water in the presence of air bubbles. A series of experiments were carried out using a laboratory-scale setup. The different CaCO3 concentrations (100 mg/L, 500 mg/L and 1000 mg/L) were considered. The hard water samples according to the various water circulation times (10, 20 and 30 min) were pumped with the flow rate of 50 L/h and passed through the region of the magnetic lines and air bubbles. A neodymium magnet (NdFeB-NB12) with a non-uniform magnetic flux density of 0.2 T on the inner walls and 0.05 T at the center was used. The CaCO3 particles deposition rate was measured using turbidity amount. The results demonstrated that the magnetic treatment significantly reduced CaCO3 deposition in hard waters in the presence in air bubbles. Turbidity changed from 0.3 NTU to 0.65 NTU at the CaCO3 concentration of 100 mg/L. It changed from 0.5 NTU to 2.25 NTU at the CaCO3 concentration 500 mg/L. Moreover, in CaCO3 concentration 1000 mg/L turbidity altered from 0.8 NTU to 3 NTU over circulation time 30 min. The simultaneous presence of magnetic fields and air bubbles reduced the amount of CaCO3 scale deposition and increased the nucleation in the bulk of the water. Aeration-based magnetic treatment is a promising alternative to chemical-based methods and an eco-friendly approach for hard waters treatment.

Study on the prompting effect of basalt fibers on the change from two-dimensional to three-dimensional deposition of CaCO3 to improve the healing properties of microbial mortars

Microbial-induced calcium carbonate precipitation (MICP) is utilized to effectively seal microcracks in concrete. In this study, coconut shell charcoal was used as a carrier for adsorbed bacteria to act as a biomass self-healing agent, and the healing effect of microbial mortar was enhanced by the addition of basalt fibers. The effect of the combined action of biomass self-healing agents and fibers on the mechanical properties and healing ability of mortars has been investigated. The complete process of microbial metabolism in the cement matrix was firstly revealed by microscopic experiments. Optical microscopy was used observed the deposition paths of the fillers under multifiber conditions at different depths. The results showed that a large number of fibers changed the healing products that transformed from two-dimensional to three-dimensional due to the bridging effect between the calcium carbonate grown on the neighboring fibers, which enhanced the healing ability of the cracks.

The impacts of CaCO3 deposition in natural wood on its viscoelastic properties

In this study, we discuss the methods used for depositing calcium carbonate (CaCO3) and the resulting 2D and 3D particle distributions of CaCO3 in two types of wood, which were quantified using scanning electron microscopy (SEM) and X-ray computed tomography (CT). We also present the results of dynamic mechanical analysis (DMA), which was used to measure the impact of CaCO3 deposition on the viscoelastic properties of the wood. X-ray CT scanning showed that CaCO3 deposits inside the wood scaffold with increased amounts as the deposition cycles were iterated. However, DMA results did not indicate significant improvement in storage moduli (E′) of CaCO3 deposited wood. SEM images revealed that the particles did not fill all the voids to provide stress transfer between the wood scaffold and the particles, indicating a lack of composite action between the wood and CaCO3 components. To address this issue, we hypothesized that heat-pressing would lead to a mechanical bond between the particles and the matrix. After heat-pressing, DMA results showed a dramatic increase in E′ not only in CaCO3 deposited wood samples but also in control wood samples. In other words, the densification of the structure led to significant increases in E′, primarily due to densification, while the impact of the presence of CaCO3 particles was minimal. This is mainly because the volume fraction of the deposited CaCO3 particles is small as compared to the total volume of the composite.

A numerical study of CaCO3 deposition on the membrane surface of direct contact membrane distillation

This numerical study investigates the effect of CaCO3 deposition on the performance of direct contact membrane distillation (DCMD). It is the first numerical study to directly evaluate the deposition and film thickness of CaCO3 on the membrane surface. Therefore, a 3D computational fluid dynamics (CFD) model, which combines momentum, heat, species transport reaction, and the Eulerian wall film model, is used to analyze the CaCO3 mass deposition rate and scaling deposition thickness on the membrane surface. HSC Chemical Software is used to evaluate the ion compositions and reaction kinetics, including the activation energy (Ea) and pre-exponential factor (Ar). The CFD model is validated with experimental results. The results reveal that the CaCO3 deposition rate increases significantly at a high temperature, velocity, and salinity of the solution. The CaCO3 mass deposition increased by 15 times and scaling deposition thickness increased from 0.05 nm to 1 nm when the temperature was raised from 318.15 K to 348.15 K, whereas an increase of approximately 25 % in deposition was observed with an increase in velocity from 0.17 to 1.38 m/s at a concentration of calcium (Ca+2) ions, 0.03 % and bicarbonate (HCO3−) ions 0.004 %. The results also indicate that CaCO3 deposition decreases the flux and efficiency of the DCMD by 2 % with a low concentration of Ca+2 ions, 0.03 %, and HCO3− ions, 0.004 %. The findings indicate that the high feed salinity (75.23 g/l) increases CaCO3 mass deposition and scaling deposition thickness on the membrane surface due to the high concentration of Ca+2 ions, 0.07 %, and HCO3− ions, 0.01 %, significantly reducing the permeate flux by 14 %. The study's model development and implementation can be adjusted to offer guidance for studying the MD process in treating high saline water with fouling issues.

Short- to Medium-Term Corrosion of Mild Steel in Highly Calcareous Seawaters: Effects of Calcium Carbonate Concentration, Coupon Orientation, and Nutrient Addition

Mild steels exposed to marine immersion conditions in which carbonate solubilities are exceeded, leading to deposition of calcareous material, have been shown to exhibit much-reduced corrosion rates compared with corrosion under conditions in which there is no exceedance of solubility limits and therefore no calcareous deposition. However, the differences in corrosion including the potential effect of microbiologically influenced corrosion (MIC) in these conditions have not been examined systematically in the literature. The study reported herein involves short- to medium-term marine immersion exposures (up to 18 month) of mild steel coupons in natural seawater (control) and in environments using the same seawater source dosed with (1) CaCO3, acting as an inorganic particulate suspension representative of that encountered in seawater with elevated calcareous content; and (2) a nitrate salt, acting as an industrial pollutant and bacterial nutrient source. The results show the extent to which the deposition of particulate CaCO3 from suspension in seawater onto and into the rusts reduces the rate of corrosion of mild steel; a rate that was found to be dependent on the coupon orientation within the seawater. Coupons that were permanently buried beneath a cap of settled CaCO3 particles exhibited a 70% reduction in corrosion rate compared with the representative control coupons. The results also show that for these exposure durations and conditions, while iron-related bacteria and sulfate-reducing bacteria populations were identified in high concentrations (respectively ∼1 × 106 cfu/g and ∼1 × 102 to 4 × 106 cfu/g, depending on coupon orientation) within the rust products themselves after 18 month of exposure, there was no clear evidence of MIC. These findings indicate that short and medium-term (nonaccelerated) studies of MIC for mild steel are insufficient or even misleading for the prediction of long-term corrosion rates in these environments.

Combination of cellulose nanofiber and artificial fusion protein for biocementation

Biomineralization occurring in living organisms is mostly controlled by organic macromolecules such as polysaccharides and proteins. Recently, biomineralization has been attracting much attention as a green and sustainable cementation technique including enzyme-induced carbonate precipitation (EICP), where CaCO3 is formed by hydrolysis of urea by urease in the presence of calcium ions. In this study, we have developed a novel hybrid biocementation method combining CaCO3 and cellulose nanofiber (CNF). In nature, matrix proteins work as a binder at the interface of organic and inorganic materials to form hybrid biomaterials. By mimicking the natural system, we designed an artificial fusion protein to facilitate the deposition of CaCO3 on CNF. Calcite-binding peptide (CaBP) and carbohydrate-binding module (CBM) were introduced in the artificial fusion protein CaBP-CBM to connect CaCO3 and cellulose. The addition of CNF in the EICP system resulted in the formation of a number of small particles of CaCO3 compared to a non-additive system. The addition of the fusion protein CaBP-CBM to CNF led to an increase in the size of CaCO3 particles. Furthermore, the combination of CaBP-CBM and CNF provides higher strength of samples in sand solidification. Therefore, introduction of CNF and the fusion protein would be promising for novel biocementation techniques.

Application of ultrafine bubbles for enhanced carbonation of municipal solid waste incineration ash during direct aqueous carbonation

Municipal solid waste incineration fly ash was selected as the alkaline Ca-bearing solid waste, and a series of direct aqueous carbonation experiments using 10% CO2 gas were conducted to showcase the capability of ultrafine bubbles (UFBs) in enhancing carbonation efficiency. Results from the experiments, conducted using a one-pass water flow system, revealed that carbonation without UFBs increased the CO2 content of the ash from 59 to 200 mgCO2/g (an increase of 141 mgCO2/g), while the presence of UFBs elevated it to 237 mgCO2/g (an increase of 178 mgCO2/g). Consequently, the introduction of UFBs led to a 26% increase in CO2 content in ash [(178−141) / 141]. This improvement was primarily attributed to the enhanced carbonation efficiency for particles ≥ 46 µm. The positive impact of UFBs was more evident (62% increase in CO2 content in ash) in experiments using a water circulation system, where carbonation proceeded at a faster rate compared to the one-pass water flow system. In terms of the mechanism, X-ray diffraction and scanning electron microscopy analyses indicated that UFBs facilitated the removal of CaCO3 deposition, which inhibited Ca(OH)2 dissolution. To the best of our knowledge, this study is the first to demonstrate the favorable influence of UFBs on fly ash carbonation efficiency.

Effect E. coli Bacteria Concentration as Self Healing on Compressive Strength and Hydrophobic Properties on Micro Cracks of Concrete

Buildings are facilities created by humans to support various human activities. Potential damage to old buildings, such as the appearance of cracks in building concrete. Self-healing is carried out by bacteria to repair micro cracks that occur in concrete by deposition of CaCO3. Bacteria-based preservatives consist of bacterial spores and organic compounds that are incorporated into the concrete structure. This research aims to determine the effect of variations in the concentration of E. coli bacteria on compressive strength and contact angle. Based on the results of the research data, two research results can be stated. First, the concentration of bacteria affects the compressive strength of the concrete and the maximum compressive strength occurs on day 14. Second, the concentration of bacteria affects the contact angle of the concrete so that it can be said that the concrete is hydrophobic. As for the XRD characterization, intensity data (I), diffraction angle ( ) were analyzed using High Score Plus. FTIR characterization was carried out in the range 4000 cm-1-500 cm-1. SEM characterization to see the morphology of the concrete with a magnification of 2500 times. SEM can also show E. coli bacteria in concrete