Distribution Of CaCO3 Research Articles

Long‐Term Performance on Drought Mitigation of Soil Slope Through Bio‐Approach of MICP: Evidence and Insight from Both Field and Laboratory Tests

AbstractDrought is a serious global environmental issue that causes water resource scarcity and threatens agriculture and food supplements. This study aims to investigate the long‐term performance of an eco‐friendly technique‐microbial induced carbonate precipitation (MICP) on drought mitigation at field and laboratory scales. Seven in‐situ slopes treated with different MICP rounds and cementation solution concentrations were subjected to 16‐month weathering. Tests were conducted to evaluate the evaporation characteristics, water retention capacity, and CaCO3 distribution. Laboratory soil samples were further prepared to provide evidence related to underlying weathering mechanisms. The results show that MICP has a time‐dependent performance on drought mitigation. After MICP treatment, soil performs a remarkable evaporation suppression ability and the evaporation rate can decrease by 50%. This is attributed to the soluble salts which increase soil water retention capability and dense hard crust which inhibits water vapor migration into the atmosphere. However, the soluble salts and crust are sensitive to weathering thus leading to degradation of MICP. Suffering 16‐month weathering, the MICP‐induced CaCO3 decreases by more than 60%. The evaporation rate of soil increases with MICP rounds and cementation solution concentrations and can reach nearly two times of untreated soil. MICP‐treated field soil exhibits weaker water retention capacity than untreated soil because MICP alters soil microstructure which expands macropores and decreases volume of micropores. Connected macropores act as favorable evaporation channels and accelerate evaporation. To ensure MICP long‐term effects, periodical treatments are necessary. The most effective MICP treatment scheme is four to six treatment rounds and 1.0 M cementation solution.

The regulation of organic molecules to the morphology and corrosion protection ability of CaCO3 coating on biomedical MgZnCa alloy

A controllable corrosion rate is an ideal condition for magnesium (Mg) alloy as biodegradable metallic materials. Calcium carbonate (CaCO3) coating has been proven to possess a robust anti-corrosion property for Mg alloy. To further regulate the morphology and corrosion protection ability of the CaCO3 coating, in current study, different organic molecules, including amino acids (Tyr and Glu), amine (DOPA), proteins (COL and BSA) and peptide (CPP), were added into the coating formation electrolyte, affecting the morphology, polymorph composition, and the crystal size distribution of precipitated CaCO3. The results revealed that Tyr exhibited little effect on the polymorph composition of the CaCO3-based coating, while Glu, DOPA, COL and BSA generally promoted the formation of vaterite but inhibited the formation of rod-like aragonite precipitates and calcite in the coatings. In contrast, CPP suppressed the precipitation of CaCO3 crystals because of its high affinity to Ca2+ ions. The addition of those organics reduced the size of calcite crystals. Consequently, the organic molecules mediated CaCO3-based coatings showed better compactness and homogeneity, which maintained the strong adhesion strength of the coatings to the substrate and further enhanced the corrosion protection abilities of the coating for the substrate. The results of the study pave the way for the development of CaCO3-based coatings with advanced properties for Mg alloys as biomedical materials.

Dual-value utilization of calcium-silica slag: Sequestration of CO2 to recover high-purity vaterite with silica fertilizer as a by-product

Calcium-silica slag (CSS) is a highly alkaline residue, rich in calcium, generated during the chemical pre-desilication process of medium- and low-grade bauxite. Mismanagement of CSS can result in detrimental environmental impacts. This study developed a novel method that combines CO2 sequestration with CSS utilization, thereby achieving simultaneous dual-value enhancement of CSS and eliminating waste discharge. Under optimized Ca2+ leaching and carbonation conditions, a remarkable Ca2+ extraction efficiency of 96.93 % was attained, while the carbonation efficiency reached 99.37 %. Consequently, this process sequestered 301.7 kg of CO2 per ton of CSS. The leaching process of Ca2+ in NH4Ac solution was realized based on the unreacted shrinking core model, which accounts for internal diffusion and chemical reaction as factors influencing leaching. The resulting carbonated product exhibited outstanding characteristics: high-purity vaterite composed of 97.43 wt% CaCO3 with a whiteness level of 95.2 %. By regulating the carbonation temperature, the crystal particulate size distribution of CaCO3 was tailored to meet specific requirements for various applications. Furthermore, silicon content was enriched in the leaching residue, increasing the effective SiO2 content from 25.2 wt% to 53.12 wt% and reducing the pH from 12.23 to 7.34, rendering it a suitable silica fertilizer for agricultural production.

Deep Ocean Circulation Governs Sedimentary CaCO3 Accumulation in the Northeast Pacific Ocean

AbstractThe meridional overturning circulation influences the deep‐sea carbon reservoir, global carbon cycle, and climate change on century to millennium time scales. However, the influence of deep‐sea circulation on sedimentary carbonate accumulation and thus deep‐sea carbonate system in the North Pacific Ocean is difficult to quantify owing to the complicated geometry of deep ocean ventilation attributed to its topographic complexity. In this study, we reanalyzed the distribution patterns of sedimentary calcium carbonate contents (wtCaCO3%) in the deep Northeast Pacific in a quantitative manner. Our results in conjunction with data from the Northwest Pacific Ocean, suggest that the deep ocean circulation plays a critical role in elucidating the basin‐scale features of sedimentary CaCO3 distribution in the North Pacific Ocean, despite elevated non‐carbonate dilution exerted by detritus from active geological processes on the topographic structure. Moreover, enhanced carbonate dissolution in the Guatemala and Panama Basins, controlled by higher flow rates of deep currents, influences the depth‐profiles of sedimentary wtCaCO3% in that region. These findings suggest a novel avenue to reconstruct past changes in ocean circulation and carbon cycling in the Northeast Pacific Ocean based on the wtCaCO3% records in sediments.

Effect of conditions on wet carbonation products of recycled cement paste powder

Wet carbonation is deemed a successful approach to recycling waste concrete powder. Controlling the growth and properties of products in the recycled cement paste powder (CPP) is highly dependent on the wet carbonation conditions. Therefore, this study aims to examine the effect of wet carbonation parameters on wet carbonation products in CPP. The wet carbonation of CPP resulted in mixed distribution of silica gel and CaCO3 without significant layering on the CaCO3. In contrast, silica gel covered the outside of the CaCO3 in the case of dry carbonation. Increasing the temperature from 25 °C to 80 °C promoted and accelerated the crystallization and growth of amorphous CaCO3, increased the crystallite size of CaCO3 by 1.1–5.1 nm, and favored the formation of aragonite and vaterite; however, it also led to a significant crystal defect and/or distortion within CaCO3. Higher temperatures also promoted silica gel formation and increased its polymerization degree by 68.2%. On the other hand, increasing the CO2 flow rate from 3 L/min to 5 L/min facilitated the crystallization and growth of CaCO3 and contributed to the increase in the crystallite size of CaCO3 by 3.0–6.6 nm. Higher CO2 flow led to the incorporation of aluminum into silica gel and resulted in the transformation of its gel pores into capillary pores. The findings of this study contribute to a better understanding of the best experimental parameters to achieve a more efficient and effective concrete waste recycling process.

Various Bacterial Attachment Functions and Modeling of Biomass Distribution in MICP Implementations

Microbial induced calcium carbonate precipitation (MICP) offers a robust technique to improve strength and stiffness properties of subsurface soils supporting infrastructures. Several unknown factors, including the MICP reactive transport parameters, however, limit the ability to predict spatial distribution of calcium carbonate (CaCO3) precipitation within a subsurface area and with depth. As it was shown that calcium carbonate distribution is highly affected by biomass profiles in subdomains, five bacteria attachment models (constant-rate, power-law, exponential, gamma distribution, and “cstr based on colloid attachment theory”) were calibrated here using data from both small- and large-scale testing programs. Out of the five models, colloid attachment theory with modified velocity and straining terms was shown to be the most promising approach in yielding the most fitted CaCO3 distribution compared with the experimental data. A new parameter, cstr, was incorporated to modify straining and the constraint peak value of biomass attachment due to straining at distances larger than a 0.14×sample size. Using the results from the numerical simulations, relationships were developed for velocity and straining coefficients of “the cstr based on colloid attachment theory” (hereafter “colloid attachment cstr”) as a function of bacteria size, soil particle size, sample size, volume of injected bacteria, and soil pore volume.

The influence of repair technique on the distribution of biogenic CaCO3 in a mimic vertical crack

Microbially induced carbonate precipitation (MICP) is a promising solution for the remediation of concrete cracks. It has great advantages of environmental compatibility and exceptional penetration of cracks owing to its low-viscosity solution. Despite of these, practical application of MICP has been hindered by challenges including limited efficiency of in situ microbial deposition of CaCO3, extended repair cycles, and suboptimal strength recovery. Addressing these issues, this study undertook a comprehensive exploration of key repair process parameters for repairing cracks within the simulated crack space through inducing CaCO3 precipitation by a urease producing bacteria, specifically, the flow rate of the repair agents (7.958, 15.91, and 39.79 μL/min), the pre-sealing length of the crack (one-third of the crack length, half of the crack length, and full sealing), and the injection port position (upper, middle, and bottom of the crack). Their impacts on the distribution of bio-CaCO3 and overall repair effectiveness were examined in detail. Optimal repair performance was achieved at a flow rate of 15.91 μL/min, with full crack sealing, and the injection port situated at the bottom. This configuration resulted in a remarkable coverage rate of crack side wall, crack surface repair rate, and crack volume filling rates of 94.38%, 79.48%, and 100% respectively, and the first two were calculated using Image J software. The crack repair depth was significantly improved. Relative contribution rates to repair effectiveness was found to be ranked as follows: injection port position > flow rate > pre-sealing length. This study provides critical insights into the optimization of MICP repair process parameters, presenting a significant advancement in the understanding and development of effective techniques for concrete crack repair.

Enhancing fiber–matrix interface permeability resistance of natural fiber-reinforced, bio-cemented sand by CaCO[formula omitted] seed pretreatment

This study explores the application of roughness pretreatment on plant-based natural fiber surfaces to enhance the sealing effectiveness of the sand-fiber interfacial. The technique roughens the reinforced material by presetting CaCO3 seeds on the fiber surface, thereby immobilizing more bacteria as nucleation sites, further increasing the interfacial bonding area by promoting bio-mineralization and achieving efficient sealing of preferential flow channels. Experimental investigation was conducted to compare the promoting effects on bio-mineralization of reinforced sand with three pretreated fibers. Results showed that the fibers pretreated with CaCO3 could fill the pores to bridge sand particles more effectively by aggregating bio-mineralized precipitates around them. The bacterial immobilization rate and calcium carbonate content of bio-cemented sands with fiber pretreatment remarkably increased with increasing fiber surface roughness characterized by fractal dimension (Fd) when compared to the samples without pretreatment, and the maximum increase was 35.66% (coir, Fd=1.390) and 152.3% (jute, Fd=1.330). The profile water-conducting rate and average hydraulic conductivity have been reduced by 46% and 86%, Among the three fibers, ramie has the lowest hydraulic conductivity of 5.396 × 10−8m/s, which is lower than that of jute and coir (1.041 × 10−7m/s and 3.885 × 10−7m/s). Furthermore, the promotion of bacteria on bio-mineralization and more even distribution (upper, middle, and lower parts are 36%, 34%, and 30%, respectively) of CaCO3 were confirmed through bacteria staining testing and dye tracer testing. Finally, the effects of average flow velocity and shear rate on bacterial immobilization and sealing of preferential flow channels are discussed.

Elucidating factors governing MICP biogeochemical processes at macro-scale: A reactive transport model development

Microbial Induced Calcium Carbonate Precipitation (MICP) influenced by biofilm metabolism in the subsurface can be exploited for a variety of engineered applications encompassing geotechnical ground improvement, environmental bioremediation, and hydraulic barriers. A reactive transport model was developed to determine the effects of controlling factors in terms of treatment protocols and experimental methods. Six column tests were calibrated and a range for the key parameters was determined. Fifteen key parameters of MICP reactive transport model were assessed in four categories (microbial activity and attachment, sample preparation, treatment protocol, and experiment dimensions). The results emphasized the effects of three main factors of microbial activity, microbial attachment process, and number of treatment (among all 15 assessed parameters) on the calcium carbonate (CaCO3) precipitation content and distribution. An increase in specific ureolysis rate (Ku) and attachment rate coefficient (Kat) by two orders of magnitude improves average CaCO3 by up to 13% and 6%, respectively with non-uniformity (COV) increase of 16%. Higher flow rates and solution concentrations contribute to more uniform CaCO3 distribution. The constant attachment rate model is useful to yield the CaCO3 precipitation profiles but more accurate models are needed to capture exact distribution. Post-treatment hydraulic conductivity, porosity and attached biomass were assessed.

Dust temporal and spatial deposition affected by climate and soil mineralogical and chemical properties in a semi-arid area

The important process of aerosol dusting is of economic, environmental and heath significance. The objective was to investigate the climatic parameters including rainfall (R), wind speed (WS), temperature (T), and relative humidity (RH), as well as soil mineralogical and chemical properties affecting dust deposition rate (DDR), in a unique and rarely studied area, the Kuhdasht watershed (456 km2) of Lorestan province, Iran. Data were collected seasonally using glass-traps inserted in ten research stations to indicate DDR seasonal and spatial variations using ARC-GIS. The spatial distribution of organic matter (OM), clay and CaCO3, and the mineralogical properties (using diffractograms obtained by XRD) of the dust and soil samples were determined. The city had the highest DDR decreasing toward the mountains. Spring (3.28–4.18 ton/km2) and autumn (1.82–2.52 ton/km2) resulted in the highest and the least DDR, respectively. The diffractograms indicated the sources of dust were local or from out of the borders. The clay minerals (kaolinite and illite) and the evaporating minerlas (gypsum, calcite, dolomite, and halite), detected in the soil and dust samples indicated their contribution to the process of DDR. According to the regression models and the correlation coefficients, DDR was highly and significantly correlated with R (R2= 0.691), WS (0.685) and RH (0.463) indicating such parameters can importantly affect DDR in the semi-arid areas.

Radial microbial grouting method by intubation for sandy soil reinforcement: Experimental and numerical investigation

The present article proposed an innovative radial microbial grouting method by intubation for sandy soil reinforcement, to improve the uniformity of CaCO3 distribution by achieving horizontal flow pathway. Considering six treatment factors, twenty-five cases of microbial grouting solidified sand column tests were designed by orthogonal method. The Ca2+ utilization and unconfined compressive strength (UCS) of solidified sand columns were examined, and the experimental results show that the three key factors affecting Ca2+ utilization are bacterial concentration, concentration of cementation solution, and reaction time, and the UCS of sand column shows a logarithmic increase with its CaCO3 content. In order to obtain reasonable grouting parameters, a mature mathematical model was used for numerical simulation to research the influences of bacterial concentration, grouting flow rate, and sand properties on radial microbial grouting. By calculating the CaCO3 distribution and sand porosity in the grouting process, the optimal arrangement for radial microbial grouting by intubation was obtained: the bacterial concentration of 0.5 (OD600), the concentration of cementation solution of 0.15 mol/L, the grouting flow rate of 5 × 10−5 m/s. Under this arrangement, the maximum solidification radius varies within 53 ∼ 57 mm, and the distance between grouting pipes can be set as 1.1 m regardless of the sand properties. These experimental and numerical investigation results can provide theoretical guidance for the engineering application of microbial grouting.

Variation of Physico-Chemical Properties among Different Soil Orders under Different Land Use Systems of the Majha Region in North-Western India

The impact of different soil orders and land use systems on the distribution of physico-chemical properties is the most critical matter to address in order to maintain sustainable agricultural production. Hence, the present investigation was carried out to study the variation in the physico-chemical characteristics of soil in diverse land use systems (LUSs), i.e., agriculture, horticulture, and forestry, under major soil orders (entisol, inceptisol, and alfisol) in the Majha region of Punjab. A total of 225 depth-wise (at 0–20 cm, 20–40 cm, 40–60 cm, 60–80 cm and 80–100 cm) soil samples were collected from three land-use systems under different soil orders. The mean values of the physico-chemical properties ranged from 6.80–7.50, 7.64–8.34 and 6.94–7.87 for pH; 0.13–0.42, 0.19–0.54 and 0.19–0.46 dS m−1 for EC; 0.14–0.99, 0.21–0.69 and 0.15–0.72% for OC; 0.75–2.07, 1.07–3.32 and 0.93–2.29% for CaCO3; 7.77–41.84, 10.56–40.23 and 7.24–39.51 kg ha−1 for P; and 98.37–334.68, 94.51–230.18 and 93.01–367.39 kg ha−1 for K under different land uses in soil orders entisols, inceptisols and alfisols, respectively. Soil parameters including pH, CaCO3, and phosphorus (P) distribution differed significantly among soil orders; however, soil EC, organic carbon (OC) and available potassium (K) did not. The inceptisols under the agricultural land use system (ALUS) had the highest soil pH, EC, and CaCO3 values. The highest soil OC content was found in entisols under forest land use systems (FLUS), followed by horticultural land use systems (HLUS). The highest values of soil-available phosphorous (P) were found in FLUS under inceptisols, while the highest amounts of soil-available potassium (K) were found in entisols and alfisols under ALUS and FLUS, respectively. Thus, the distribution of physico-chemical properties under different LUSs in each soil order is highly variable and does not follow any particular trend. In general, soil properties such as OC, P, and K content decreased with an increase in soil depth, while pH and CaCO3 values increased with depth in all land uses and soil orders. There was a positive correlation between soil OC and EC, as well as available P and K in the soils investigated. The available P and K are negatively correlated with soil pH and CaCO3 content in the soil. The principal component analysis (PCA) revealed that soil pH and OC were the most variable soil parameters, which influence the availability of other physico-chemical properties under different soil orders and land use systems. Therefore, it is suggested that the land use systems play an important role in the distribution of physico-chemical properties of soil in different soil orders. The results of the study will help students, researchers, and agricultural management staff in managing different land uses for maintaining soil fertility and productivity in alluvial soils of North-western India.

Using sodium alginate aided bio-treatment for improving the uniformity of precipitates on recycled aggregates.

The recycled concrete aggregates have high porosity and water absorption, which hinders their utilization in concrete production. Microbial-induced calcium carbonate precipitation was regarded as a very promising method for strengthening recycled aggregates. However, the uneven distribution of CaCO3 on surface of aggregates encountered in the current bio-deposition treatment weakened the efficiency, especially in the aspect of the decrease of water absorption. Therefore, this study innovatively applied a sodium alginate aided bio-deposition treatment to improve the uniform distribution of biogenic CaCO3. The principle was that sodium alginate was used to uniformly "fix" the bio-agents (urea or bacterial cells) on the surface of recycled aggregates, which was supposed to promote the uniform in-situ precipitation of CaCO3 on the surface of aggregates, and hence effectively blocking surface pores, and reducing the water absorption of the aggregates. Two concentrations of sodium alginate (0.2w% and 0.5w%) and four sodium alginate aided bio-deposition treatments were studied. It was found that CaCO3 (a mass increase of 4.05%) was formed on the aggregates after the suitable sodium alginate aided bio-deposition treatment. The participation of sodium alginate made CaCO3 uniformly deposited on full surface of the aggregates, resulting in a significant decrease (42.10%) of water absorption. The biogenic CaCO3 showed limited mass loss under ultrasonic attack, indicated a strong cohesion and bonding strength with aggregates. The results demonstrated that sodium alginate-aided bio-deposition treatment can enhance the efficiency, which was beneficial to improve the quality of recycled aggregates and their utilization of recycled aggregates in concrete production. KEY POINTS: • The SA-aided bio-treatment promoted the distribution uniformity of CaCO3 on aggregates. • The water absorption of aggregates decreased by 42.10%. • The formed CaCO3 showed excellent cohesion and adhesion.

Influence of injection methods on calcareous sand cementation by EICP technique

Calcareous sands are widely distributed on continental shelves, coastal zones, islands and reefs in the tropical oceans. For being used as construction materials, calcareous sands should be artificially treated to improve their engineering properties. Enzymatically induced carbonate precipitation (EICP) is an innovative soil treatment technique. In this paper, urease was extracted from soybean powder using artificial seawater for calcareous sands cementing by the EICP technique. Cementation tests were conducted with three injection methods (the pre-mixed, staged and proposed parallel injections) and two injection rates (2 and 5 mL/min). The hydraulic conductivity, shear wave velocity (SWV) and unconfined compressive strength tests were conducted and the cementation effects were evaluated. The hydrodynamic diameter of the particles generated in the mixed solutions was measured with reaction time by a laser particle size analyzer and the influence of injection rate on the CaCO3 distribution in the specimen was discussed. The coefficient of variation of the SWV values along the cemented specimen height was calculated for evaluation of the cementation uniformity. Results show that a high injection rate was conducive to reducing clogging and improving the cementation uniformity by completing injection within the urea hydrolysis phase. The promising parallel injection method proposed in this study provided a lag time for reaction by simultaneous injection of crude urease and cementation solutions using two separate tubes. Specimens treated at a high parallel injection rate were uniformly cemented with high mechanical strengths and high overall hydraulic conductivities because of a high proportion of CaCO3 in contact-cementing distribution.

Comparative study of EICP treatment methods on the mechanical properties of sandy soil

This study analyzed the effect of different treatment methods in enzyme-induced carbonate precipitation (EICP) on the mechanical properties of soil. Soybean crude urease was used to catalyze the precipitation of calcium carbonate (CaCO3). A multiple-phase method was proposed and further compared with commonly practiced EICP treatment methods (including the one-phase method, two-phase method, and premix-and-compact method) from the aspects of chemical conversion efficiency, CaCO3 precipitation distribution, permeability, and unconfined compressive strength. Based on the findings, the characteristics of each method were further discussed and summarized. Although the enzymatic CaCO3 precipitation generated from all the treatment methods could potentiate the soil strength to a great or less degree, using the proposed multiple-phase method could bring about a high chemical conversion efficiency, uniform distribution of CaCO3 as well as preferable permeability retention. In addition, the multiple-phase method could significantly improve the efficiency of urease usage.

Digital mapping of soil pH and carbonates at the European scale using environmental variables and machine learning

Soil pH and carbonates (CaCO3) are important indicators of soil chemistry and fertility, and the prediction of their spatial distribution is critical for the agronomic and environmental management. Digital soil mapping (DSM) techniques are widely accepted for the geospatial analysis of the soil properties. They are rapid and cost-efficient approaches that can provide quantitative prediction. However, the digital mapping of soil pH and CaCO3 are not well studied, especially at a continental scale. In this research, we mapped the soil pH and CaCO3 at the European scale using multisource environmental variables and machine learning approaches. Moderate Resolution Imaging Spectroradiometer (MODIS) products, terrain attributes, and climatic variables were considered. Meanwhile, nine machine learning algorithms, namely, three linear and six nonlinear models, were used for the spatial prediction of soil pH and CaCO3. The land use and cover area frame statistical survey (LUCAS) 2015 topsoil dataset provided by the European Soil Data Centre was utilised. The performances of different models were compared and analysed in terms of coefficient of determination (R2), root mean square error (RMSE), and ratio of performance to deviation (RPD). Specifically, nonlinear machine learning models outperformed the linear ones, and extremely randomized trees (ERT) gave the most satisfactory result for soil pH (R2 = 0.70, RMSE = 0.75, and RPD = 1.84) and CaCO3 (R2 = 0.53, RMSE = 93.49 g/kg, and RPD = 1.46). The results revealed that MODIS products and climatic variables were important in predicting soil pH and CaCO3. Moreover, spatial distribution of soil pH and CaCO3 in Europe were mapped at 250 m resolution, and the areas with high CaCO3 content always showed high soil pH value.

Incorporation of Mixing Microbial Induced Calcite Precipitation (MICP) with Pretreatment Procedure for Road Soil Subgrade Stabilization.

Microbial induced carbonate precipitation (MICP) provides an alternative method to stabilize the soil. To further improve the reinforcement effect, this study aims to propose a strategy by incorporating the mixing MICP method with pretreatment procedure. A series of laboratory tests were performed to investigate the preparation parameters (including the moisture content and dry density of the soil, the concentration of urea and CaCl2 in cementation solution), the engineering properties, the CaCO3 distribution as well as the mineralogical and micro structural characteristics of pretreatment-mixing MICP reinforced soil (PMMRS). Based on the orthogonal experiment results, the optimum preparation parameters for PMMRS were determined. The UCS of PMMRS was more strongly dependent on the moisture content and concentration of CaCl2 than the concentration ratio of CaCl2 to urea. Moreover, it was testified that incorporation of pretreatment procedure improved the stabilization effect of traditional mixing MICP method on the clayed sand (CLS). The UCS of PMMRS specimen was increased by 198% and 78% for the pure CLS and the simple mixing MICP reinforced soil, respectively. Furthermore, the CaCO3 products generated consisted of the aragonite, calcite and vaterite, which distributed unevenly inside the specimen no matter the lateral or vertical direction. The reason for the uneven distribution might be that oxygen content varied with the regions in different directions, and hence affected the mineralization reaction. In addition, the mineralization reaction would affect the pore structure of the soil, which was highly related to the stabilization effect of MICP reinforced soil.

Spatial Analysis Of Organic Material, CaCO3 and TOC in Coastal Area, Aceh Besar Regency

Most of the coastal zones of Aceh Besar are areas of accumulation of organic compounds such as C-Organic and CaCO3. Therefore, studying the distribution of organic carbon and carbonates in sediments in coastal areas is necessary. This study aims to analyze the distribution of C-Organic and Calcium Carbonate (CaCO3) coupled with pH and Salinity tests spatially on the surface at a depth of 40 - 60 cm in the coastal area of Aceh Besar District. The C-Organic content was analyzed using the Walkley and Black method, while Calcium Carbonate (CaCO3) was analyzed using the Titrimetric method. Soil pH and salinity tests were carried out in situ using a pH meter, and soil salinity tests were tested using a salinometer. The study results show that the distribution of C-Organic and Carbonate content differs in each location in Aceh Besar Coastal area. The distribution of organic carbon and carbonates in the northern part of Aceh Besar, in the Ujong Batee Puteh area, has an average value of 0.86% and 10.28%. While the distribution of C-Organic in the Lamreh area is, on average, 0.44%, and carbonate (CaCO3) is 8.03%. On the other hand, in the western part of Aceh Besar, the distribution C-Organic in the Ujong Pancu area is, on average, 2.83%, and carbonate (CaCO3) is 8.05%. The distribution of C-Organic in the Lhok Seudu area has an average value of 1.07% and carbonate (CaCO3) of 9.65%. The results also reveal the fact that there are 3 (three) factors that influence the distribution of C-Organic and CaCO3. These factors are the topographic location that allows the material to be eroded due to runoff, vegetation that enriches organic matter composition, and the depositional environment. The results of the pH distribution test in soil showed that the pH in the coastal area of Aceh Besar is relatively alkaline, and the salinity distribution is relatively low, indicating the absence of seawater intrusion and salt deposits. Further studies need to be carried out for other depth variations to obtain more comprehensive results of other distributions.

Permeable rock matrix sealed with microbially-induced calcium carbonate precipitation: Evolutions of mechanical behaviors and associated microstructure

Microbially-induced calcium carbonate precipitation (MICP) is a promising grouting material for subsurface remediation due to its water-like viscosity and excellent penetration. Current studies of MICP-grouting for subsurface remediation of both rock fractures and highly-permeable rock matrix focus on the spatio-temporal distribution of precipitated bio-CaCO3 and the resulting reduction in permeability. Conversely, we focus on the improvement of mechanical response following MICP-grouting. We contrast the improved mechanical response of MICP-treated Berea sandstones with distinctly contrasting initial mechanical properties - contrasting associated pre- and post-treatment microstructures with various durations of MICP-grouting. Results indicate that although the precipitated CaCO3 mass with time within these two rock types is similar, significant differences exist in the evolution of mechanical properties (UCS, Young's modulus and brittleness). The evolution of mechanical properties for the low-strength sandstone (initial UCS 25.7 MPa) exhibits three contrasting phases: an initial slow increase, followed by a rapid-increase and then saturation and asympotic response. After ten cycles of MICP-grouting, UCS, elastic modulus and brittleness index for low-strength sandstone increase by 229%, 179% and 177% compared with before grouting. In contrast, the mechanical properties for the high-strength sandstone (initial UCS 65.1 MPa) are not significantly enhanced, increasing UCS by only 22%, 14% and 12%. Imaging by scanning electron microscopy (SEM) indicates that the cementing minerals fill the quartz framework for the high-strength sandstone but are sparse for the low-strength sandstone. Sandstone is a clastic sedimentary rock consisting of a framework of quartz grains bonded by cementing minerals. For the high-strength sandstone infused with a large mass of cementing minerals, the calcium carbonate crystals only precipitate in the gaps between the cementing minerals or adhere to the cementing minerals. This is only capable of relatively limited enhancement in the bio-bonding strength and volume of the quartz framework. For the low-strength sandstone with fewer cementing minerals, the precipitated calcium carbonate is evenly distributed on the surfaces of the quartz gains. The bulk strength is progressively increased with the ongoing bio-cementation between quartz gains. Cementing mineral contents not only exert a considerable control on the integral mechanical properties and penetration for the sandstone, but also have a direct influence on the microscopic distribution of bio-accumulated CaCO3, controlling the effectiveness of bio-cementation by incrementing the mechanical properties.

IDENTIFICATION OF ROCK CHARACTERISTICS USING XRF, XRD, AND SEM TESTS ON API ALAM IN PAMEKASAN

Research has been conducted into the nature of geothermal rocks in Pamekasan. This place is located in Tlanakan Pamekasan. This study aims to determine the composition of mineral compounds in the soil so that fire can burst out from the soil and the soil does not melt. Three steps can be done with simple refinement and filtering methods, namely X-Ray Fluorescence (XRF), X-ray diffraction (XRD), and Scanning Electron Microscope (SEM). The results of XRF analysis show the element of Api Alam 1 is Ca 66.2%, Api Alam 2 is Si 37.4%, and in hot springs, is Si 39.6%. The XRD results show that mineral qualitatively in Api Alam 1 was in the form of CaCO3 compound at 60.1% and SiO2 at 39.9%, while in Api Alam 2, hot water sources were in the form of SiO2 compound (>90%). SEM Results on Api Alam 1 show that the sample is almost homogeneous (the distribution of CaCO3 and SiO2 is uneven), the presence of slab-shaped clumps that identify the presence of varying grain size, and with high porosity, which indicates that the sample is partially amorphous in structure, in Api Alam 2. The Hot springs show irregular aggregations and poor homogeneity of the sample. The size of the three samples is ten μm or 10.000 nm, while PSA results showed an average size of Api Alam 1 was 509.7 nm, Api Alam 2 was 891.3 nm, and Hot Springs was 468.3 nm.