Calcium Carbonate Research Articles

Enhanced MICP for Soil Improvement and Heavy Metal Remediation: Insights from Landfill Leachate-Derived Ureolytic Bacterial Consortium

This study investigates the potential of microbial-induced calcium carbonate precipitation (MICP) for soil stabilization and heavy metal immobilization, utilizing landfill leachate-derived ureolytic consortium. Experimental conditions identified yeast extract-based media as most effective for bacterial growth, urease activity, and calcite formation compared to nutrient broth and brown sugar media. Optimal MICP conditions, at pH 8–9 and 30 °C, supported the most efficient biomineralization. The process facilitated the removal of Cd2+ (99.10%) and Ni2+ (78.33%) while producing stable calcite crystals that enhanced soil strength. Thermal analyses (thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)) confirmed the successful production of CaCO3 and its role in improving soil stability. DSC analysis revealed endothermic and exothermic peaks, including a significant exothermic peak at 444 °C, corresponding to the thermal decomposition of CaCO3 into CO2 and CaO, confirming calcite formation. TGA results showed steady weight loss, consistent with the breakdown of CaCO3, supporting the formation of stable carbonates. The MICP treatment significantly increased soil strength, with the highest surface strength observed at 440 psi, correlating with the highest CaCO3 content (18.83%). These findings underscore the effectiveness of MICP in soil stabilization, pollutant removal, and improving geotechnical properties.

Optimization of Mechanical Properties and Durability of Steel Fiber-Reinforced Concrete by Nano CaCO3 and Nano TiC to Improve Material Sustainability

To meet the growing demand for sustainable building materials in modern construction projects, nanomaterials are widely used in concrete to improve its mechanical properties, durability, and environmental adaptability. The effects of different calcium carbonate nanoparticles (NC) and titanium carbide nanoparticles (NT) substitution rates (0%, 0.5%, 1% and 1.5%) on the mechanical and durability properties of steel fiber-reinforced concrete (SFRC) were analyzed by experimental studies. We also analyzed the evolution of the microstructure, chemical composition, and the evolution of functional groups of concrete by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The results demonstrated that NC replacement of 0.5% and NT replacement of 1% was the optimal combination for the preparation of composite concrete. Compared to SFRC with 0% substitution for both NC and NT (CG), the 28-day compressive strength of NC0.5NT1 increased by 35.5%, the flexural strength increased by 26.5%, and the splitting tensile strength increased by 16.3%. The durability performance of SFRC has been significantly improved. After 150 freeze–thaw cycles, the quality loss rate of SFRC cured for 28 days decreased by 40.6%, and the relative dynamic elastic modulus increased by 7.7%. Microscopic analysis indicates that an appropriate amount of NC and NT replacing cement improves the hydration reaction process of SFRC, increases the content of chemically more stable C-S-H gel, but does not change the types of hydration products of the cement. NC and NT have a filling effect, improving the pore structure of concrete, which helps enhance the mechanical and durability performance of concrete. The results of the study provide a theoretical basis for the application of NC and NT as reinforcing particles for cementitious materials in sustainable building materials.

Effectiveness Study of Chitosan from Pearl Oyster Shells (Pinctada maxima sp.) as Antibacterial in Bone Scaffold Application

Chitosan functional material is a promising material in manufacturing bone scaffolds, as it has antibacterial properties, low toxicity, biodegradability, biocompatibility with human tissues, and facilitates regenerative processes in wound healing. Graft placement is prone to bacterial invasion, and alternatives are made scaffolds with antibacterial activity. This study aims to identify changes in functional groups in each isolation process and identify the effect of chitosan concentration (5%, 10%, 20%, 40%, and 80%) on the activity of Straphylococcus aureus and Escherichia coli bacteria. Chitosan isolation methods are demineralization, deproteination, decolorization, and deacetylation by microwave irradiation. Analysis of chitosan functional groups using FTIR, while antibacterial activity test using diffusion method. Isolation of chitosan from pearl oyster shells (Pinctada maxima sp.) obtained a degree of deacetylation of chitosan of 95.37%. Pearl oyster shell powder identified typical peaks of calcium carbonate (CaCO₃). The demineralized powder sample had calcium carbonate (CO₃²⁻) peaks that disappeared. Furthermore, the deproteinated powder sample produced peaks with amide groups (C=O dan N-H) of reduced protein. Decolorized powder samples did not show drastic changes in the bands of the deproteinated powder spectra, but the spectra could show cleaner and clearer peaks without any interference from pigments. The last, deacetylated powder sample showed a decrease in peak intensity in the 1650 cm⁻¹ (C=O amide). The analysis of the ability of chitosan to inhibit the growth of E. Coli and S. Aureus bacteria was effective at a minimum chitosan concentration of 20%. In comparison, antibacterial activity in S. aureus is better than in E. coli. Therefore, chitosan from this shell can be used as an antibacterial, but it is necessary to optimize chitosan manufacturing techniques to obtain better antibacterial efficacy.

Adaptive Drainage Pipe for Crystallization Prevention: Mechanism and Experimental Study

Crystallization-induced blockages in tunnel drainage systems pose significant challenges to their functionality and longevity. To address this issue, this study proposes a novel adaptive drainage pipe designed to prevent crystallization. By constructing an indoor experimental model for anti-crystallization tests, combined with scanning electron microscopy (SEM) and molecular dynamics simulations, this study investigates the mechanism and effectiveness of the proposed system. The findings reveal that flexible PVC pipes in dynamic flow and expansion states significantly reduce crystallization compared to conventional PVC pipes. Among tested materials, EVA and TPU demonstrate superior crystallization resistance, with EVA exhibiting the lowest crystallization accumulation (7.13 g/m). Molecular dynamics simulations further elucidated the influence of material properties on the diffusion coefficient and binding energy of calcium carbonate crystals, with EVA showing the lowest binding energy with calcium carbonate at 135.11 kcal/mol, ultimately confirming EVA as the optimal material for crystallization prevention. These results offer new strategies and valuable references for managing crystallization in tunnel drainage systems.

A c-type lectin HcLec1 with dual function of immunology and mineralization from the freshwater oyster (Hyriopsis cumingii Lea)

BackgroundShell and pearl formation in bivalves is a sophisticated biomineralization process that encompasses immunological and mineralization aspects, particularly during shell repair and the initial stages of pearl cultivation when a nucleus is inserted. Here, we describe a novel C-type lectin, HcLec1, isolated and characterized from the freshwater pearl mussel Hyriopsis cumingii Lea. MethodsImmune challenge, RNA interference (RNAi) experiments, ELISA, and antibacterial assays were employed to investigate the role of HcLec1 in innate immunity. We also established shell damage repair and pearl nucleus insertion models to examine the impact of HcLec1 on the biomineralization process in Hyriopsis cumingii Lea. In vitro calcium carbonate crystallization assays were conducted to explore the direct role of HcLec1 in calcium carbonate crystal formation.ResultsThe HcLec1 gene sequence is a full-length cDNA of 1552 bp, encoding 240 amino acids. HcLec1 comprises an N-terminal signal peptide and a carbohydrate-recognition domain (CRD), with QPD (Gln-Pro-Asp) and MND (Met-Asn-Asp) motifs for polysaccharide binding. Tissue expression analysis showed that HcLec1 is predominantly expressed in the gill tissue of Hyriopsis cumingii Lea under normal conditions, and its expression is significantly elevated in both gill and pearl sac tissues following nucleus insertion for pearl cultivation (P < 0.05). After immune stimulation with Aeromonas hydrophila and lipopolysaccharides (LPS), HcLec1 expression levels significantly increased in both cases (P < 0.01), indicating a role in bivalve innate immunity. RNA interference (RNAi)-mediated knockdown of HcLec1 led to a significant decrease in the expression levels of immune-related genes (WAP, α2m, and Lyso) and mineralization-related genes (CA, CHS, Nacrein, and Pif) (P < 0.05). In animal models for shell damage and nucleus insertion in pearl cultivation, HcLec1 showed a consistent expression pattern, with an initial significant decrease followed by a marked increase, peaking at day 14 (P < 0.05). This suggests a role for HcLec1 in pearl formation and shell repair. The recombinant HcLec1 protein demonstrated binding affinity to LPS and PGN, a robust ability to agglutinate Escherichia coli, Staphylococcus aureus, Aeromonas veronii, and Aeromonas hydrophila, and significantly inhibited bacterial growth (P < 0.05). Moreover, rHcLec1 promoted calcite crystal formation in saturated calcium carbonate solutions and altered crystal morphology.DiscussionThe HcLec1 gene plays a pivotal role in both innate immunity and biomineralization in the triangle sail mussel. This study enhances our understanding of the functional diversity of C-type lectins and provides a foundation for future studies on shell repair and pearl growth.

Genetically controlled biomineralization in Cyanobacteria: diel fluctuations of ccyA transcript abundances and identification of neighboring genes putatively involved in the precipitation of intracellular amorphous calcium carbonates in Microcystis aeruginosa PCC7806

Genetically controlled biomineralization in Cyanobacteria: diel fluctuations of ccyA transcript abundances and identification of neighboring genes putatively involved in the precipitation of intracellular amorphous calcium carbonates in Microcystis aeruginosa PCC7806

Investigation of fracture properties and microbially induced calcite precipitation (MICP) restoration in coal mining areas within the diverse Terrain of Northern Shaanxi, China

The complex and diverse nature of coal mining sites, including different landforms and working conditions, presents challenges for rehabilitation efforts. To address this, we conducted a comprehensive experimental study focusing on microbially induced calcium carbonate precipitation (MICP) remediation, considering the fracture characteristics of coal mining sites. The MICP-restored samples were subjected to confined/unconfined compressive strength, uniaxial/triaxial permeability, and souring tests to assess their restoration efficacy. The results showed that under similar mining conditions, the average depth of parallel fractures was 0.185 m for loess ridges, 0.16 m for the valley, and 0.146 m for the blown-sand region, while the average depth for boundary fractures was 0.411 m for loess ridges, 0.178 m for the valley, and 0.268 m for the blown-sand region. Notably, parallel fractures showed negligible filling in all landforms, whereas boundary fractures in the blown-sand region were completely filled with wind-deposited sand. The valley landform was filled with alluvium and wind-deposited sand, whereas the loess landform was filled with wind-deposited sand and loess. MICP-restored soil samples in all landforms achieved a strength comparable to remolded fracture-free soil samples. Across all landforms, the maximum permeability coefficient of MICP-restored soil samples closely matched that of remolded fracture-free soil samples. Under similar topographic and rainfall conditions MICP restorations scoured 31.3 g on blown-sand region, 19.3 g on loess ridges, and 17.6 g on valleys. These research findings provide an experimental foundation for MICP repair of coal mining ground fractures.

Enhancing Polylactic Acid (PLA) Performance: A Review of Additives in Fused Deposition Modelling (FDM) Filaments

This review explores the impact of various additives on the mechanical properties of polylactic acid (PLA) filaments used in Fused Deposition Modeling (FDM) 3D printing. While PLA is favored for its biodegradability and ease of use, its inherent limitations in strength and heat resistance necessitate enhancements through additives. The impact of natural and synthetic fibers, inorganic particles, and nanomaterials on the mechanical properties, printability, and overall functionality of PLA composites was examined, indicating that fiber reinforcements, such as carbon and glass fibers, significantly enhance tensile strength and stiffness, while natural fibers contribute to sustainability but may compromise mechanical stability. Additionally, the inclusion of inorganic particulate fillers like calcium carbonate improves dimensional stability and printability, although larger particles can lead to agglomeration issues. The study highlights the potential for improved performance in specific applications while acknowledging the need for further investigation into optimal formulations and processing conditions.

Use of Modified Activated Carbon in Groundwater Remediation for Human Consumption

This study aimed to produce activated carbon from desilicated rice husks using various carbonization and activation methods, including a tube furnace, muffle furnace, and artisanal pyrolysis. The resulting activated carbons were characterized for their adsorptive capacity through the determination of iodine number and methylene blue adsorption; these are key indicators of specific surface area and adsorbent quality. Advanced characterization techniques were employed, such as scanning electron microscopy (SEM), which revealed a highly porous and irregular surface structure, and energy dispersive X-ray spectroscopy (EDS), confirming the effective removal of impurities and optimization of the elemental composition. Atomic force microscopy (AFM) demonstrated favorable surface roughness for adsorption processes. Among the samples, CaDH162-CADH53 exhibited the highest performance, with an iodine number of 1094.8 mg/g and a yield of 93.5%, signifying a high adsorption capacity. The activation treatments with phosphoric acid and calcium carbonate significantly improved the porous structure, further enhancing the material’s adsorptive properties. In conclusion, the activated carbons produced in this study demonstrated optimal physicochemical properties for water purification and contaminant treatment applications. These findings highlight the potential of using agricultural waste, such as rice husk, as a sustainable and scalable alternative for industrial-scale activated carbon production.

Effect of Foliar Application of Water Soluble Fertilizer and Humic Acid on Physico-chemical Properties and Fertility Status of Soil after Harvest of Rose

A field experiment on “Effect of foliar application of water soluble fertilizer and humic acid on yield and quality of rosa sp was carried out during Rabi season at PG Research unit, Horticulture Section, College of Agriculture, Nagpur during 2022-2023. The experiment was laid out in Factorial Randomized Block Design. The treatments comprised of four levels of water soluble fertilizer (19:19:19) viz., Control, 200 g, 300 g and 400 g and three levels of humic acid viz., Control, 500 ppm and 750 ppm giving twelve treatment combinations replicated thrice. The collected soil samples were processed and analysed for different soil parameter like soil pH, electrical conductivity, organic carbon, calcium carbonate, available nitrogen, available phosphorus available potassium and available sulphur using standard analytical methods. Results revealed that pH of all the samples of study area was in the neutral to alkaline. Electrical conductivity of all the samples were found normal (<1.0 dsm-1). The organic carbon content of the study area varies from low to medium. The availability of NPK after harvesting was found superior in treatment combination (F4H3), which involved application of 400 g 19:19:19 with 750 ppm humic acid.

Molecular spectroscopic and elemental analyses for the identification of multi-layered automotive coatings with Fourier Transform Infrared Spectroscopy (FTIR), Raman Microscopy and Scanning Electron Microscopy-Energy Dispersive Spectroscopy

Common automotive coatings include acrylic, amino, alkyd, polyester, nitro, and polyurethane coatings. In addition to these coatings, pigments, such as Prussian Blue, phthalocyanine blue, toluidine red, and scarlet powder are commonly added. Additives including sulphate, chrome yellow, CaCO3(calcium carbonate), TiO2(titanium dioxide), talc, dolomite and kaolin, are also commonly included in the coatings. The combination of these components makes it complex to identify them as a whole. However, the analysis of automotive coatings is not only important for coating producers in the industrial field, but also for forensic scientists investigating hit-and-run accidents. In this study, the authors aimed to establish a method that combines FTIR, Raman spectroscopy and SEM-EDS to investigate complex and multi-layered paint samples. As a result, comprehensive and detailed molecular spectroscopic and elemental information was successfully obtained for identification using this method. FTIR proved advantageous in analyzing resins, while Raman was more effective in characterizing additives and pigments. The selection criteria for infrared spectroscopy are based on the change in dipole moment in molecular vibration, while those for Raman spectroscopy are based on the change in molecular polarization. Raman spectroscopy and infrared spectroscopy have complementary application fields and can be used together to provide more comprehensive molecular vibration information. SEM-EDS can also accurately present elemental components. With this method, tiny differences in spectra can be clearly distinguished through mutual verification; corresponding components in paints can be confidently identified.

Advancing Slope Stability and Hydrological Solutions Through Biocementation: A Bibliometric Review

Biocementation is an innovative and sustainable technique with wide-ranging applications in slope stabilization, watershed management, and erosion control. Despite its potential, comprehensive evaluations of its use in hydrology and geotechnical engineering are limited. This study addresses this gap through a bibliometric analysis of 685 articles (2013–2023) from the Scopus database, employing VOSviewer and RStudio to explore global research trends, key contributors, and emerging themes. The analysis reveals that China, the United States, and Japan are leading contributors to this field, with significant advancements in microbial-induced (MICP) and enzyme-induced calcium carbonate precipitation (EICP) techniques. These methods have demonstrated effectiveness in improving soil strength, reducing erosion, and enhancing hydrological properties such as infiltration, runoff control, and water retention. Co-occurrence analysis identifies interdisciplinary connections between geotechnics and hydrology, highlighting research clusters focused on biomineralization, erosion resistance, and durability. The findings underscore biocementation’s pivotal role in addressing sustainability challenges by providing environmentally friendly alternatives to traditional soil stabilization techniques. This study not only maps the current research landscape but also offers valuable insights into the practical implications of biocementation for slope stability and hydrological management, laying the foundation for future advancements in sustainable engineering practices.

The influence of adding B. subtilis bacteria on the mechanical and chemical properties of cement mortar

BackgroundThis study investigated the effect of B. Subtilis bacteria on the properties of cement mortar. This was done by using soil samples from Sharkia, Egypt, to isolate 48 bacterial strains, after which they were cultured using the Johnson method and various media. Bacteria were then added to the cement mortar in amounts of 5% and 10% by weight to evaluate their effect on the mechanical and chemical properties of the modified mortar.ResultsThe study examined the compressive and flexural strength of the modified mortar over time, as well as its microscopic properties and chemical composition after 28 days. The results indicated that bacterial additions of 5% and 10% increased the compressive strength of the mortar after 28 and 56 days compared to the control. A 5% bacteria concentration resulted in significant improvements in strength, showing the best concentration for increasing mortar strength. The addition of 5% bacteria significantly enhanced the early flexure strength, while the 10% showed superior long-term strength after 56 days. Scanning electron microscopy (SEM) revealed high CaCO3 deposits in the bacterial samples, indicating microbial-induced calcite precipitation that filled the small cracks and increased strength. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of hydroxyl, carbonate, and silicate groups, with bacterial samples having a higher carbonate content, indicating an increase in calcium carbonate formation and microstructure.ConclusionsThe ideal bacterial concentration was 5% as it improved the compressive and flexural strength while also promoting a more flexible microstructure. This study supports the employment of microorganisms in the production of more durable and environmentally friendly building materials, enhancing the sustainability of building practices.

Decrease in Facial Bone Density with Aging and Maintenance Effect of Calcium Maltobionate Ingestion in Japanese Adult Women: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Trial

Background/Objectives: Facial bone density, including the jawbone, declines earlier than that of the lumbar spine and calcaneus. Calcium maltobionate is reported to mitigate bone resorption and maintain bone density of the lumbar spine in post-menopausal women, but its effects on facial bone density remain understudied. Therefore, this study compared variations in facial bone mineral density with variations in calcaneal bone mineral density and bone resorption markers among healthy women, examining differences between pre- and post-menopause and the effects of continuous calcium maltobionate intake. Methods: This randomized, double-blind, placebo-controlled, parallel-group trial involved 48 healthy Japanese women aged 30–69 years, divided into two groups. The test food group received tablets containing calcium maltobionate, while the placebo group received tablets containing a maltose and calcium carbonate mixture for 24 weeks. Calcaneal and facial bone densities were measured pre- and post-intervention in both groups. Results: Post-intervention calcaneal bone mineral density and bone resorption marker deoxypyridinoline (DPD) showed no statistical difference between groups in pre-menopausal women. However, in post-menopausal women, the test food group exhibited significantly higher calcaneal bone density and lower DPD levels compared with the placebo group. Facial bone mineral density increased significantly in the test food group compared with the placebo group in post-menopausal participants, with similar trends observed in pre-menopausal participants. Conclusions: Facial bone mineral density could serve as a useful indicator for monitoring bone health from middle age onward. Moreover, continuous calcium maltobionate intake appears to mitigate bone density decline in pre- and post-menopausal women, contributing to osteoporosis prevention (UMIN-CTR ID: 000046391).

Bio-Concrete and Its Self-Healing Capacity to Next-generation Sustainable Architecture: A Comprehensive Review

Concrete is commonly used as a foundation material in the construction sector. It's been around for over two centuries, and it looks like it'll keep being the material of choice for construction for the foreseeable future. Structural materials, long-term degradation creates microcracks which increases permeability and eventually lead to failure. Moreover, the identification and remediation of these fissures provide a formidable challenge, as they jeopardize the integrity and longevity of concrete buildings, particularly those subject to rigorous sealing criteria. Cement manufacturing and widespread usage both contribute to climate imbalance, with the former responsible for 5–7% of global carbon dioxide emissions. Biotechnology provides a viable alternative by allowing the culture of bacteria to produce calcium carbonate, a key ingredient in cement. Biomineralization and crystallization processes play a crucial role in the synthesis and transportation of concrete-compatible chemicals, enabling their delivery to fissure within concrete structures. This review paper discusses a methodology for advancing sustainable architecture in the future, utilizing the adaptable metabolic processes of microorganisms as a foundation. This involves integrating microbial technologies and materials created by microorganisms into the field of built environment design and construction. Currently, there is a growing presence in the market of innovative materials such as Bio-cement, which exhibit lower levels of embodied carbon compared to traditional materials. Furthermore, it discusses advancements in the synthesis and optimization of bio-concrete to address challenges in energy efficiency, structural integrity, and lifecycle performance. By bridging sustainability goals with cutting-edge technology, bio-concrete emerges as a cornerstone for resilient and eco-friendly infrastructure, laying the foundation for innovative architectural paradigms.

Calcium carbonate cycling in the Southern Ocean: insights from dissolved calcium and potential alkalinity tracers

Calcium carbonate cycling in the Southern Ocean: insights from dissolved calcium and potential alkalinity tracers

Dissolution and recrystallization behavior of microbially induced calcium carbonate: influencing factors, kinetics and cementation effect

Dissolution and recrystallization behavior of microbially induced calcium carbonate: influencing factors, kinetics and cementation effect

Magnetotactic bacteria from diverse Pseudomonadota families biomineralize intracellular Ca-carbonate.

Intracellular calcium carbonate formation has long been associated with a single genus of giant Gammaproteobacteria, Achromatium. However, this biomineralization has recently received increasing attention after being observed in photosynthetic Cyanobacteriota and in two families of magnetotactic bacteria affiliated with the Alphaproteobacteria. In the latter group, bacteria form not only intracellular amorphous calcium carbonates into large inclusions that are refringent under the light microscope, but also intracellular ferrimagnetic crystals into organelles called magnetosomes. Here new observations suggest that magnetotactic bacteria previously identified in the sediments and water column of Lake Pavin (France) were only a small fraction of the diversity of bacteria producing intracellular amorphous calcium carbonates. To explore this diversity further, we conducted a comprehensive investigation of magnetotactic populations with refractive granules using a combination of environmental microbiology, genomic and mineralogy approaches on cells sorted by micromanipulation. Several species belonging to divergent genera of two Pseudomonadota classes were identified and characterized. Scanning transmission electron microscopy coupled with energy-dispersive X-ray spectrometry support that all these species indeed form intracellular amorphous calcium carbonates. Cryo soft X-ray tomography experiments conducted on ice-vitrified cells, enabled 3D investigation of inclusions volume, which was found to occupy 44 - 68% of the cell volume. Metabolic network modeling highlighted different metabolic abilities of Alpha- and Gammaproteobacteria, including methylotrophy and CO2 fixation via the reverse Krebs cycle or the Calvin-Benson-Bassham cycle. Overall, this study strengthens a convergent evolution scenario for intracellular carbonatogenesis in Bacteria, and further supports that it is promoted by the fixation of CO2 in anoxic environments.

Freeze-Cast Composites of Alginate/Pyrophosphate-Stabilized Amorphous Calcium Carbonate: From the Nanoscale Structuration to the Macroscopic Properties.

Pyrophosphate-stabilized amorphous calcium carbonates (PyACC) are promising compounds for bone repair due to their ability to release calcium, carbonate, and phosphate ions following pyrophosphate hydrolysis. However, shaping these metastable and brittle materials using conventional methods remains a challenge, especially in the form of macroporous scaffolds, yet essential to promote cell colonization. To overcome these limitations, this article describes for the first time the design and multiscale characterization of freeze-cast alginate (Alg)-PyACC nanocomposite scaffolds. The study initially focused on the synthesis of Alg-PyACC powder through in situ coprecipitation. The presence of alginate chains in the vicinity of the PyACC was shown to affect both the powder reactivity and the release of calcium ions when placed in water (XRD, chemical titrations). In vitro cellular assays confirmed the biocompatibility of Alg-PyACC powder, supporting its use as a filler in scaffolds for bone substitutes. In a second step, the freeze-casting process was carried out using these precursor powders with varying rates of inorganic fillers. The resulting scaffolds were compared in terms of pore size and gradient (via SEM, X-ray microtomography, and mercury intrusion porosimetry). All scaffolds exhibited a pore size gradient oriented along the solidification axis, featuring unidirectional, lamellar, and interconnected pores. Interestingly, we found that the pore size and wall thickness could be controlled by the filler rate. This effect was attributed to the in situ cross-linking of alginate chains by released Ca2+ ions from the fillers, which increased viscosity, affecting temperature-driven segregation during the freezing step. Different multiscale organizations of the porosity and spatial distribution of fillers (FEG-SEM) were correlated with changes in the scaffold mechanical properties (tested via uniaxial compression). With such tunable porous and mechanical properties, Alg-PyACC composite scaffolds present attractive opportunities for specific bone substitute applications.

Influence of Different Mixing Methods for Cementitious Capillary Crystalline Waterproofing Materials on the Self-Healing Capacity of Concrete Under Various Damage Types.

Cementitious Capillary Crystallization Waterproofing Material (CCCW), as an efficient self-healing agent, can effectively repair damage in concrete structures, thereby extending their service life. To address the various types of damage encountered in practical engineering applications, this study investigates the impact of different mixing methods for CCCW (including internal mixing, curing, and post-crack repair) on the multi-dimensional self-healing performance of concrete. The self-healing capacity of concrete was evaluated through water pressure damage self-healing tests, freeze-thaw damage self-healing tests, mechanical load damage self-healing tests, and crack damage self-healing tests. The results show that the curing-type CCCW mixing method exhibited the best self-healing effect in repairing water pressure, freeze-thaw, and load damages, with corresponding healing rates of 88.9%, 92.7%, and 90.5%, respectively. The internally mixed CCCW method was also effective for repairing load damage in concrete, while the repair-type CCCW mixing method demonstrated the weakest repair effect on these types of damage. For concrete with induced pre-existing cracks, the internally mixed CCCW method, after 28 days of water-immersion curing, exhibited a significantly higher crack self-healing ability, with a self-healing ratio of 333.8%. Optical microscopy observations revealed that the crack surfaces were almost fully sealed, with a substantial deposition of white crystalline material at the crack sites. Further analysis using scanning electron microscopy (SEM) and X-ray Diffraction (XRD) provided insights into the surface morphology and phase characteristics of the self-healed cracks, indicating that calcium carbonate (CaCO3) and calcium silicate hydrate (C-S-H) were the main products responsible for crack healing.