Calcium Formate Research Articles

A crystallin mutant cataract with mineral deposits

Connexin mutant mice develop cataracts containing calcium precipitates. To test whether pathologic mineralization is a general mechanism contributing to the disease, we characterized the lenses from a nonconnexin mutant mouse cataract model. By cosegregation of the phenotype with a satellite marker and genomic sequencing, we identified the mutant as a 5-bp duplication in the γC-crystallin gene (Crygcdup). Homozygous mice developed severe cataracts early, and heterozygous animals developed small cataracts later in life. Immunoblotting studies showed that the mutant lenses contained decreased levels of crystallins, connexin46, and connexin50 but increasedlevels of resident proteins of the nucleus, endoplasmic reticulum, and mitochondria. The reductions in fiber cell connexins were associated with a scarcity of gap junction punctae as detected by immunofluorescence and significant reductions in gap junction-mediated coupling between fiber cells in Crygcdup lenses. Particles that stained with the calcium deposit dye, Alizarin red, were abundant in the insoluble fraction from homozygous lenses but nearly absent in wild-type and heterozygous lens preparations. Whole-mount homozygous lenses were stained with Alizarin red in the cataract region. Mineralized material with a regional distribution similar to the cataract was detected in homozygous lenses (but not wild-type lenses) by micro-computed tomography. Attenuated total internal reflection Fourier-transform infrared microspectroscopy identified the mineral as apatite. These results are consistent with previous findings that loss of lens fiber cell gap junctional coupling leads to the formation of calcium precipitates. They also support the hypothesis that pathologic mineralization contributes to the formation of cataracts of different etiologies.

Synthesis of calcium carbonate-loaded mesoporous SBA-15 nanocomposites for removal of phosphate from solution.

Removal of phosphate from water is very crucial for protecting the ecological environment since massive phosphorus fertilizers have been widely used and caused serious water deterioration. Thus, we fabricated a series of calcium carbonate-loaded mesoporous SBA-15 nanocomposites with different Ca:Si molar ratio (CaAS-x) as phosphorus adsorbents via a simple wet-impregnation method. The multiply approaches including X-ray diffraction (XRD), N2 physisorption, thermogravimetric mass spectrometry (TG-MS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) were used to characterize the structure, morphology, and composition of mesoporous CaAS-x nanocomposites. The phosphate adsorption efficiency of the CaAS-x nanocomposites was studied through adsorption and desorption batch tests. Results showed that the increases of Ca:Si molar ratio (rCa:Si) improved the phosphate removal capacity of CaAS nanocomposites, especially CaAS with the optimum synthesis molar ratio of Ca:Si as 0.55 showed the high adsorption capacity of 92.0 mg·g-1 to high concentration of phosphate (> 200 mg·L-1). Note that the CaAS-0.55 had a fast exponentially increased adsorption capacity with increasing the phosphate concentration and correspondingly showed a much faster phosphate removal rate than pristine CaCO3. Apparently, mesoporous structure of SBA-15 contributed to high disperse of CaCO3 nanoparticles leading to the monolayer chemical adsorption complexation formation of phosphate calcium (i.e., =SPO4Ca, =CaHPO4-, and =CaPO4Ca0). Therefore, mesoporous CaAS-0.55 nanocomposite is an environmental-friendly adsorbent for effective removal of high concentration of phosphate in neutral contaminated wastewater.

Influence of Waste Filler on the Mechanical Properties and Microstructure of Epoxy Mortar

This paper presents experimental investigations on epoxy mortar produced using industrial wastes. In some recent studies, coal bottom ash and polyethylene terephthalate (PET) waste have been chosen as a filler to replace sand, and fly ash and silica fume have been chosen as micro fillers for epoxy mortar production; enhanced results in terms of compressive and tensile strengths and durability have been achieved. However, these approaches failed to boost the strength and durability compared to the epoxy steel slag, epoxy sand, epoxy marble dust, and epoxy polyvinyl chloride (PVC) waste. This present research work has investigated the influence of waste filler on the mechanical properties and microstructure of epoxy mortar, produced by using sand and industrial wastes, i.e., steel slag, marble dust, and polyvinyl chloride waste. Based on the composition ratio, the prepared samples of epoxy resin mortar containing 25% epoxy binder (epoxy resin plus epoxy hardener) and 75% filler (1:3) were compared to the cement mortar. However, each specimen of epoxy resin mortar was prepared by mixing with different fillers. The properties such as compressive strength, tensile strength, and microstructural changes were measured using different characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared radiation spectroscopy (FTIR), and scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDX). From the obtained results, it was found that the strength of the specimens increases when blended with steel slag and marble dust, which is attributed to their peak densities and enhanced particle interactions. The XRD, SEM, FTIR, and SEM-EDX analyses showed the formation of calcium, magnesium, and other phases in the microstructure of epoxy resin-based mortars. This resulted in lower water absorption and porosity, as well as improvements in both compressive and tensile strengths. This research can help in understanding the important role of different industrial wastes as feasible fillers in epoxy resin-based composites.

Mix proportion optimization and early strength development in modified foam concrete: an experimental study

The influence of the single polycarboxylate superplasticizer (PCE) and blending it mixed hydroxypropyl methylcellulose (HPMC) on hardening moulding quality and surface pulverisation of foam concrete was investigated. An orthogonal experimental design was employed to determine the optimum combination of parameters for four property indexes (PIs) in this paper. A multi-index matrix analysis method was used to evaluate the parameter combinations and obtain the overall optimal performance for the PIs. The effect of calcium formate (CaF) on the early compressive strength of modified foam concrete with the most optimal combination in different density grades was also studied. The results indicate that the incomplete cement hydration reaction is the essential cause of pulverisation, which can be alleviated by adding a suitable PCE. Defoaming and precipitation occur when the PCE incorporated exceeds 0.1%, which can be mitigated by the addition of 0.02 to 0.06% HPMC. The orthogonal analysis indicates that the anti-cracking agent has a more substantial effect on the strength of the foam concrete than the thickening agent. The most significant factor of mechanical properties is PP fiber followed by dispersible latex powder (DLP). The optimal combination of foam concrete is 0.06% HPMC, 0.3% DLP, and 0.5% PP fiber. The early compressive strength of foam concrete can be significantly enhanced by increasing the CaF content. However, increasing the density level results in a decrease in the 28-day compressive strength of the foam concrete.

Cytotoxicity and Mineralization Activity of Calcium Silicate-Based Root Canal Sealers Compared to Conventional Resin-Based Sealer in Human Gingival Fibroblast Cells.

Root canal obturation is performed by gutta-percha cones and sealer. Therefore, these materials, specially sealers, must be biocompatible. This study investigated the cytotoxicity and mineralization activity of two calcium silicate-based sealers (Endoseal MTA and Ceraseal) and an epoxy resin-based sealer (AH26). In this experiment, the cytotoxicity of Endoseal MTA, Ceraseal, and AH26 on human gingival fibroblast cells was examined using Methyl-Thiazol-Tetrazolium assay at time intervals of 24, 48, 72, and 120 hr. The mineralization activity of sealers was evaluated by Alizarin red staining assay. Prism, ver.3, software was used to perform statistical tests. One-way analysis of variance analysis, followed by Tukey's test, was used to determine the group differences. P-values < 0.05 were considered statistically significant. Cytotoxicity of sealers decreased gradually (P < 0.0001). AH26 showed the highest level of cytotoxicity (P < 0.001). In terms of cytotoxicity, no considerable differences were observed between the two-calcium silicate-based sealers (P > 0.05). AH26 showed the lowest mineralization activity (P < 0.0001). Among the calcium silicate-based sealers, mineralization and formation of calcium nodules were more frequently observed in the Endoseal MTA group (P < 0.001). The examined calcium silicate-based sealers had less cytotoxicity and higher mineralization activity than the resin-based sealer (AH26). There was negligible difference between the cytotoxicity of the two-calcium silicate-based, but the cell mineralization caused by Endoseal MTA was higher.

The influence of calcium formate on the hydration of calcium sulfate hemihydrate

In this study, the influence of calcium formate (CF) on the hydration of a synthesized calcium sulfate hemihydrate (HH) powder was investigated. Isothermal calorimetry measurements showed that CF retards the hydration reaction of HH. This was confirmed by XRD of stored samples and pore solution analysis. Two retardation mechanisms were identified. The combination of pore solution and laser granulometric experiments revealed that firstly, the initial dissolution of hemihydrate decelerates because of high Ca2+ ion concentrations, donated by the faster dissolving CF. Secondly, the HCOO− species of CF adsorb on surfaces of the gypsum crystals, as further pore solution measurements showed. This impedes their formation kinetic. The gypsum crystals exhibited anisotropic peak narrowing in XRD measurements when CF was added. This was caused by a morphology change, which could be verified using the anisotropic domain size morphology approach during Rietveld refinement analysis and SEM images. Gypsum crystals exhibit a blockier shape with CF addition compared to the usual acicular shape in pure water.

INFLUENCE OF SULFATE ION ENVIRONMENT ON THE CEMENT MATRIX MODIFIED BY REDISPERSIBLE POLYMERS

Injection of sulfate ions into the cement matrix with water by wet spraying due to high moist in the environment is the reason of the deterioration acceleration and durability decrease with time. The effects of introduction of redispersible polymers (RP) and calcium formate on the increasing of the durability and decreasing of the deterioration effect caused by sulfate ions on the cement matrix were studied. Vinyl-acetate/versatate, vinyl-acrylic copolymer and calcium formate were mixed into nine separate cement mixtures at a concentration of additives 1 %, 3 % and 5 % respectively. Three different sulfate ion environment were sprayed through the fog environment at high moist concentration using a salt spray device “Salt Fog Chamber”. Test results showed that different additive in different sulfate environment has various affects both on the deceleration of the structure deterioration and the reduction of the strength of cement matrix. Vinyl-acetate/versatate and calcium formate in concentrations of 1% and 3% have high stability while maintaining strength at the level of exploitational properties of the matrix. While, vinyl-acrylic copolymer at 5 % has more resistance to strength loss after 168 days of withholding in an aggressive environment compared to 1 % and 3 %. Detailed observation of the structure formation of the cement matrix at 168 days shows formation that relate both to the hydrated cement minerals and complexes of organic salts. This formation allowed at the late age of the experiment to decrease the strength loss under intensive impact of SO42– migration through the matrix due to the encapsulating of cement minerals at early ages of hydration in polymer films with RP and active early formation of Ca(OH)2 for formate. This allowed the cement matrix to retain its shape for a long periods, become more stable, reduce the washing out of soluble cement components at early ages, and reduce the content of active Ca by bonding it into semisoluble compositions that cause the decreasing of the negative effect on cement matrix by SO42–.

Ablation of TRPC3 disrupts Ca2+ signaling in salivary ductal cells and promotes sialolithiasis

Clinical studies and structural analyses of salivary stones strongly suggest a linkage between higher saliva calcium (Ca2+) and salivary stone formation, sialolithiasis; however, the process and the mechanism leading to Ca2+ overload during sialolithiasis is not well understood. Here, we show that TRPC3 null (−/−) mice presented with a reduction in Ca2+ entry and current in ductal cells with higher saliva [Ca2+] suggesting diminished transepithelial Ca2+ flux across the salivary ductal cells, leaving more Ca2+ in ductal fluid. Significantly, we found that TRPC3 was expressed in mice and human salivary ductal cells, while intraductal stones were detected in both mice (TRPC3−/−) and patient (sialolithiasis) salivary glands. To identify the mechanism, we found that TRPC3 was crucial in preventing the expression of calcification genes (BMP2/6, Runx2) in ductal cells which may be due to higher extracellular Ca2+ in SMG tissues. Similarly, inflammatory (IL6, NLRP3), fibrotic (FN1, TGFβ1) and apoptotic (Bax1/Bcl2) markers were also elevated, suggesting that the loss of TRPC3 induces genetic changes that leads to salivary gland cell death and induction of inflammatory response. Overall, ablation of TRPC3−/− leads to higher saliva [Ca2+], along with elevated detrimental gene expressions, altogether contributing to salivary gland stone formation.

Structural characterization, defect evolution and luminescence properties of natural CaF2 under 10 MeV electron irradiation

Present study investigates the response of various coloured variants of natural fluorite (CaF2) to 10 MeV electron beam irradiation at accumulated dose of 5–10 MGy. The fluorite specimens did not show any post irradiation radioactivity. However, after irradiation the specimens developed purple colouration of different shades depending on the dose. In-depth characterization of the as-received and irradiated specimens using XPS and Raman spectroscopy confirm the relocation of fluorine (F) anions at interstitial sites and formation of metallic calcium (Ca). The calculated displacement cross sections for F and Ca indicate that it is easier to form fluorine anion interstitials within lattice structure. However, the estimated lower fraction of interstitial fluorine (∼14%) as compared to metallic Ca (>50%) is attributed to their surface diffusion and desorption. Electron irradiation was found to cause photoluminescence quenching in all the CaF2 specimens that is likely caused by a radiation-induced formation of competing recombination channels.

Study on mechanical and shrinkage properties of ES-UHPC

Some road and bridge projects to be repaired require materials that can quickly and easily obtain high mechanical properties. Added early strength agents are commonly used to improve the early strength of Ultra-high performance concrete (UHPC). Previous studies focused primarily on improving the early strength of UHPC, and few studies on how to reduce early age shrinkage of UHPC. This paper selected two inorganic early-strength agents, lithium carbonate (Li2CO3), nano-calcium carbonate (NC), and two organic early-strength agents, calcium formate(CF), triethanolamine(TEA),and an CaO expansion agent, which are commonly used. Experimental studies were carried out for single and compound early-strength agent systems in a cement-based UHPC system. The results showed three early-strength agents (NC, Li2CO3,CF) reduced the setting time and improved the early-strength of the UHPC. TEA had an adverse effect in the both single and compound systems. The 1-d compressive strength of the group(L0.15N3P10) reaches 84.5 MPa, with good workability and lower shrinkage. It can be used to prepare early strength ultra-high performance concrete (ES-UHPC) at room temperature. In terms of strength, shrinkage, and workability, it is suggested that the combination content of Li2CO3 is 0.15%, NC is 3%, and the expansion agent is 10% for fast repair and reinforcement projects.

Additive Based on Synthetic Aluminosilicates for Dry Lime Construction Mixtures

The possibility of increasing the durability of coatings based on lime dry construction mix by introducing an additive containing synthetic aluminosilicates is substantiated. The regularities of the structure formation of the lime composite in the presence of an additive containing synthetic aluminosilicates, which additionally consists of a formation of calcium–sodium hydrosilicates and minerals of the zeolite group, an increase in the amount of chemically bound lime by 8.74%, are revealed. X-ray diffraction analysis and thermodynamic calculations have established that the mineralogical composition of the crystalline phase of the additive based on synthetic aluminosilicates is represented by thenardite, gibbsite, and the minerals of the zeolite group. It is shown that the content of the amorphous phase is 77.5%. It was found that the additive based on synthetic aluminosilicates is characterized by high activity, which is more than 350 mg/g. It was also found that the introduction of an additive based on synthetic aluminosilicates into the formulation of a lime dry mixture accelerates the curing of coatings and increases the compressive strength after 28 days of air-dry hardening by 1.9 times.

Late accretion of Ceres-like asteroids and their implantation into the outer main belt

Low-albedo asteroids preserve a record of the primordial Solar System planetesimals and the conditions in which the solar nebula was active. However, the origin and evolution of these asteroids are not well constrained. Here we measured visible and near-infrared (about 0.5–4.0 μm) spectra of low-albedo asteroids in the mid-outer main belt. We show that numerous large (diameter >100 km) and dark (geometric albedo <0.09) asteroids exterior to the dwarf planet Ceres’ orbit share the same spectral features, and presumably compositions, as Ceres. We also developed a thermal evolution model that demonstrates that these Ceres-like asteroids have highly porous interiors, accreted relatively late at 1.5–3.5 Myr after the formation of calcium–aluminium-rich inclusions, and experienced maximum interior temperatures of <900 K. Ceres-like asteroids are localized in a confined heliocentric region between about 3.0 au and 3.4 au, but were probably implanted from more distant regions of the Solar System during the giant planet’s dynamical instability. The large, low-albedo asteroids in the main belt between 3.0 au and 3.4 au share spectral characteristics and history with Ceres. Accreted in different parts of the outer Solar System, they might have been implanted into the main belt by the dynamic upheaval created by the giant planets’ instability.

Isolation and characterization of apical papilla cells from root end of human third molar and their differentiation into cementoblast cells: an in vitro study

BackgroundPeriodontal regeneration, treatment of periodontal-related diseases and improving the function of implants are global therapeutic challenges. The differentiation of human stem cells from apical papilla into cementoblasts may provide a strategy for periodontitis treatment. This study aimed to evaluate the differentiation of primary human stem cells apical papilla (hSCAPs) to cementoblast cells.Material and methodsSCAPs cells were isolated from human third molar and then incubated for 21 days in a differentiation microenvironment. Alkaline phosphatase (ALP) and Alizarin red S staining assays were performed to evaluate the calcium deposition and formation of hydroxyapatite in the cultured hSCAPs microenvironment. Real-time polymerase chain reaction (RT-PCR) assay was performed for cementum protein 1 (CEMP1), collagen type I (COL1), F-Spondin (SPON1), osteocalcin (OCN), and osteopontin (OPN) as specific markers of cementoblasts and their progenitors.ResultsALP phosphatase activity in day 21 of treatment demonstrated a significant increase in ALP compared to the control. Alizarin red S staining assay showed that the differentiated hSCAPs offered a great amount of calcium deposition nodules compared to the control. The increased expression level of CEMP1, OCN, OPN, COL1 and Spon1 was observed in days 7, 14 and 21 compared to the control, while greatest expression level was observed in day 21.ConclusionIn conclusion, the differentiation microenviroment is convenient and useful for promoting the differentiation of hSCAPs into cementoblast.

Evaluation of bacterial attachment on mineralized collagen scaffolds and addition of manuka honey to increase mesenchymal stem cell osteogenesis

The design of biomaterials to regenerate bone is likely to increasingly require modifications that reduce bacterial attachment and biofilm formation as infection during wound regeneration can significantly impede tissue repair and typically requires surgical intervention to restart the healing process. Further, much research on infection prevention in bone biomaterials has focused on modeling of non-resorbable metal alloy materials, whereas an expanding direction of bone regeneration has focused on development of bioresorbable materials. This represents a need for the prevention and understanding of infection in resorbable biomaterials. Here, we investigate the ability of a mineralized collagen biomaterial to natively resist infection and examine how the addition of manuka honey, previously identified as an antimicrobial agent, affects gram positive and negative bacterial colonization and mesenchymal stem cell osteogenesis and vasculature formation. We incorporate manuka honey into these scaffolds via either direct fabrication into the scaffold microarchitecture or via soaking the scaffold in a solution of manuka honey after fabrication. Direct incorporation results in a change in the surface characteristics and porosity of mineralized collagen scaffolds. Soaking scaffolds in honey concentrations higher than 10% had significant negative effects on mesenchymal stem cell metabolic activity. Soaking or incorporating 5% honey had no impact on endothelial cell tube formation. Although solutions of 5% honey reduced metabolic activity of mesenchymal stem cells, MSC-seeded scaffolds displayed increased calcium and phosphorous mineral formation, osteoprotegerin release, and alkaline phosphatase activity. Bacteria cultured on mineralized collagen scaffolds demonstrated surfaces covered in bacteria and no method of preventing infection, and using 10 times the minimal inhibitory concentration of antibiotics did not completely kill bacteria within the mineralized collagen scaffolds, indicating bioresorbable scaffold materials may act to shield bacteria from antibiotics. The addition of 5% manuka honey to scaffolds was not sufficient to prevent P. aeruginosa attachment or consistently reduce the activity of methicillin resistant staphylococcus aureus, and concentrations above 7% manuka honey are likely necessary to impact MRSA. Together, our results suggest bioresorbable scaffolds may create an environment conducive to bacterial growth, and potential trade-offs exist for the incorporation of low levels of honey in scaffolds to increase osteogenic potential of osteoprogenitors while high-levels of honey may be sufficient to reduce gram positive or negative bacteria activity but at the cost of reduced osteogenesis.

FEATURES OF THE INTERACTION OF SHEELITE WITH HCl SOLUTIONS AT 400 AND 500 ° C, 100 MPa AND VARIOUS f(O2) (ACCORDING TO EXPERIMENTAL AND CALCULATED DATA)

Experimental studies were carried out on the solubility of scheelite in HCl solutions in the concentration range from 0.01 to 0.316 mol•kg-1 H2O at 400 and 500°C, a pressure of 100 MPa and the fugacity of oxygen (hydrogen) specified by the buffers Cu2O-CuO, Fe3O4-Fe2O3, Ni-NiO and Co-CoO. It was found that scheelite in HCl solutions at the specified parameters dissolves incongruently. In solutions containing from 0.01 to 0.0316 m HCl, minor amounts of tungsten oxides WO3 and (or) WO3-x are found in the run products, along with scheelite. In solutions containing from 0.1 to 0.316 m HCl, the formation of calcium tungsten bronzes (CTB) CaxWO3 is observed, the average composition of which corresponds to the formula Ca0.07WO3. Based on the analysis of the experimental data obtained, the free energies of the formation of tungsten oxides WO3, WO2.9, scheelite and calcium of tungsten bronze were calculated. Using mutually agreed thermodynamic data, the solubility of Sch in solutions of HCl, (Na,K)Cl with the participation of alumino-silicates is calculated. It is shown that the scheelite has a wide area of congruent solubility in saline systems.

ДОСЛІДЖЕННЯ ВПЛИВУ ДОБАВОК НА ОТРИМАННЯ НИЗЬКОТЕМПЕРАТУРНИХ РЕЖИМІВ У ТЕХНОЛОГІЇ ВИРОБНИЦТВА ЗАЛІЗОБЕТОННИХ ШПАЛ

Today the characteristic feature of modern building technology is the wide use of chemical additives to achieve the re-quired properties of concrete, reducing the material consumption and energy resources in the production of this material and when using it for the production of constructions and products.It was found that perspective direction for reducing energy intensity of the precast reinforced concrete is using of the low temperature regimes of thermal treatment and taking into account the heat of cement hydration. To achieve the set goal the possibility of using additives such as Sika Раvег НС-1, Nitkal S45 and calcium formate in sleeper technology was considered.The influence of additives on the strength characteristics of concretes, which hardened under different temperature con-ditions, was considered.Results of the researches on the effect of introduction additives in the production of concrete mixture on the strength characteristics of concretes are presented. Taking into account the fact that laboratory and industrial conditions of concrete mixes and concretes have certain dif-ferences, the influence of additives is considered in laboratory and industrial conditions.Competent use of cements in production technology leads to energy saving, therefore, the complex effect of additives and binders that contain mineral additives wasdetermined

PRODUCTION OF FERROALLOYS, CALCIUM CARBIDE, AND PHOSPHORUS FROM HIGH-SILICON PHOSPHORITE

The article provides information on the interaction of Chilisai phosphorite with carbon, coke, and iron with the production of ferroalloy and calcium carbide and the extraction of phosphorus into gas. Research is conducted using computer thermodynamic modeling, mathematical planning of experiments, and electric smelting of phosphorites in an arc electric furnace. It is found that under equilibrium conditions the interaction occurs with the formation of iron silicides, calcium, silicon carbides, calcium, elemental silicon, aluminum, calcium, silicon oxide (ІІ), gaseous phosphorus (P4, P2), and iron phosphides. An increase in the amount of iron at 1,500-2,000oC increases the degree of extraction of silicon in the alloy but decreases the extraction of calcium in the calcium carbide, the concentration of silicon in the alloy, and the amount of calcium carbide. In the temperature range of 1,900-2,000oC in the presence of 16.8-19.8% of iron, phosphorus completely converts to gas, and there forms an alloy with 45-47.8% of Si and 1.6- 1.9% of Al and calcium carbide in the amount of 150-215 dm3 /kg (with the extraction of 60-63.6% of Si into the alloy and 50-56.4% of Ca into calcium carbide). Electric smelting of phosphorite in an arc furnace produces ferrosilicon of grade FS45 (40-44.7% of Si) with the extraction of 73.8% of silicone into it, as well as calcium carbide up to the second grade in the amount of 200-252 dm3 /kg. Phosphorus is almost completely (99.0-99.4%) reduced during electric smelting and converted into the gas phase.

Preparation and performance investigation of a high efficiency cement permeation type waterproofing materials

The active chemicals play the primary waterproof role in Cementitious Capillary Crystalline Waterproofing Materials (CCCW). Based on the combined mechanism of precipitation reaction and complexation precipitation reaction, precipitation component, complexing agent, calcium ion compensator, surfactant, and defoaming agents were determined as the composition of the active chemicals in this study. Based on the multiple performance tests, the material components and the content of active chemicals were investigated with the single and orthogonal factors. The results showed that with the increase of sodium silicate content, the flexural and compressive strengths of the specimens at 28 d increased, and the water absorption of the specimens gradually decreased. When the sodium silicate content was 2 wt%, the flexural and compressive strengths of the specimens at 28 d increased by 55% and 16%, respectively, and the water absorption of the specimens decreased by 27%. When the content of the complexing agent was constant, the setting time of the specimen gradually prolonged with the increase of the proportion of the hydroxyl and carboxyl groups in the molecular structure. Meanwhile, the flexural and compressive strengths of the specimen decreased gradually with the increase of the content of the complexing agent. With the increase of calcium formate content, the strength of the specimens tended to increase first and then decrease. When the ratio between calcium formate and calcium hydroxide was 10:90, the compressive strength of the specimens cured for 28 d increased by 42%. Based on the analysis of the mechanical properties, water absorption, and expansion of the specimen under orthogonal factors, the mixing ratio of the active chemicals was: precipitation component 2 wt%, complexing agent 1 wt%, calcium ion compensator 3 wt%, surfactant 1.5 wt%, and defoaming agents 0.7 wt%. The impermeability pressure ratios of specimens with and without CCCW coating reached to 275% and 200% at 28 d, respectively. The water resistance of the specimens increased with the increase of curing age, and the water absorption of the specimen was reduced by 56% at 28 d.

Study of the effect of calcium nitrate, calcium formate, triethanolamine, and triisopropanolamine on compressive strength of Portland-pozzolana cement

This study aims to assess the effect of using some chemical admixtures including Calcium nitrate tetrahydrate (CN) and Calcium formate (CF), Triethanolamine (TEA), and Triisopropanolamine (TIPA) on the early-age compressive strength of Portland cement mortar containing natural pozzolan (Portland-pozzolana cement: PPC). To this end, CN and CF were added to the PPC mortar during its preparation step. Afterward, TEA and TIPA as an aqueous solution were added to the mixture of clinker and natural pozzolan during grinding; finally, the physical and chemical properties of produced cement mixtures were investigated by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR), respectively. The results showed that the effect of TEA and CF was far better than TIPA and CN, so that, adding 0.01 wt% of TEA to PPC was led to a 62 % increase in the 1-day compressive strength of this sample. Moreover, the compressive strength of samples indicated, on average, an increase of 54 % and 39 % on days 2 and 3, as well as 7-to-56 respectively, compared to cement (as the control group). While adding 1 wt% of CF to PPC was led to a 41 %, 23 %, and 22 % increase in its compressive strength on days 1, 2, and 3, as well as 7-to-56, respectively, than the control group.

New insights into the early stage nucleation of calcium carbonate gels by reactive molecular dynamics simulations.

The precipitation of calcium carbonate (CaCO3) is a key mechanism in carbon capture applications relying on mineralization. In that regard, Ca-rich cementitious binders offer a unique opportunity to act as a large-scale carbon sink by immobilizing CO2 as calcium carbonate by mineralization. However, the atomistic mechanism of calcium carbonate formation is still not fully understood. Here, we study the atomic scale nucleation mechanism of an early stage amorphous CaCO3 gel based on reactive molecular dynamics (MD) simulations. We observe that reactive MD offers a notably improved description of this reaction as compared to classical MD, which allows us to reveal new insights into the structure of amorphous calcium carbonate gels and formation kinetics thereof.