Saturated Calcium Research Articles

Localized corrosion of steel in alkaline solution with low-level chloride and elevated sulfate concentrations

Localized corrosion developed on post-tensioned steel strand in deficient grout, relating to elevated concentrations of sulfate ions. The deficient grout can also have low-level chloride ion concentrations below threshold values originating from the base materials. Open-circuit potential, linear polarization resistance (LPR), and electrochemical noise (EN) measurements were made on steel specimens exposed in saturated calcium hydroxide solution with 0.012 M Cl−, 0.04 M SO42−, or combined. Results showed that the combined presence of sulfates in low-level chloride alkaline solutions elevated the corrosion rate and the extent of corrosion pitting. The EN technique was shown to provide corrosion rate estimates consistent with LPR and was able to identify pitting characteristics. The outcomes of the research provides supporting evidence that analysis of deficient grout for chlorides alone may not capture the risk for corrosion and that corrosion associated with elevated sulfate concentrations can be exacerbated in presence of low-level chlorides.

Coupling effect of cementitious capillary crystalline waterproof material and exposure environments on self-healing properties of engineered cementitious composites (ECC)

Due to the healing mechanism of self-healing technologies, there are some limitations and challenges for application in concrete structures. Based on the characteristics of cementitious capillary crystalline waterproof material (CCCW) in powder and active materials moving along cracks, this work presents CCCW as a direct internally mixed self-healing material, and quantitatively explored the coupling effect of CCCW and exposure environments on the self-healing properties of engineered cementitious composites (ECC). Four types of ECC mixtures with CCCW doping of 0%, 1.5%, 3% and 4.5% were prepared. Exposure environments contained water, air and saturated calcium hydroxide solution. The self-healing behavior of ECC was evaluated by the recovery of mechanical properties, water impermeability and closure behavior of crack. Microscopic analysis of healing products was performed by scanning electron microscope (SEM), thermogravimetric analysis (TG) and X-ray diffraction (XRD). The test results showed that the recovery of mechanical properties and water impermeability of ECC was improved by directly adding CCCW. The percentage of re-opened healed cracks number in specimen EC45 with 4.5% CCCW content was 83.33% lower than that in specimen EC0 without CCCW. The normalized closure rate of crack area was raised by 167.98% by mixing 4.5% of CCCW in saturated calcium hydroxide solution, compared with that without CCCW. While it was enhanced by 132.44% in water. There was a superimposed enhancement of CCCW and calcium hydroxide solution. Microscopic analysis of healing products showed that CCCW facilitated the production of healing products, especially in saturated calcium hydroxide solution. Finally, the additive effect coefficient Ki was introduced to quantitatively characterize the coupling effect of environments and CCCW on the self-healing properties of ECC.

High temperatures and CO2 dissolution can cause nitrogen losses from urine stabilized with base

Human urine is rich in valuable nitrogen which can easily be lost due to biological urea hydrolysis and subsequent ammonia volatilization. While this enzymatic reaction can be prevented by alkalizing the urine, recent studies suggest that chemical urea hydrolysis can result in substantial nitrogen losses when drying alkalinized urine at high temperatures. Furthermore, it was previously suggested that CO2 dissolution from the air used to evaporate water from alkalinized urine could result in a pH decrease to values which allows for biological urea hydrolysis and subsequent ammonia losses. This study aimed to determine the kinetics of chemical urea hydrolysis in alkalinized human urine and confirm the effect of CO2 dissolution with controlled laboratory experiments. We measured the change in urea concentration at different temperatures and pH values for real human urine and determined the corresponding rate constants for chemical urea hydrolysis. We showed that the rate constant increases as a function of temperature and that pH has a negligible effect on the rate of chemical urea hydrolysis in the high pH range of alkalized urine (>11). The rate constants for chemical urea hydrolysis in a saturated calcium hydroxide solution were found to be 0.00147 d−1, 0.00595 d−1, 0.0204 d−1 and 0.0848 d−1 for temperatures of 25°C, 40°C, 55°C and 70°C, respectively. The effect of CO2 dissolution on urea hydrolysis was determined by aerating human urine alkalinized with calcium hydroxide (Ca(OH)2). In order to represent biological urea hydrolysis, urease was added to the solution. The computer simulations of the experimental results showed that CO2 dissolution and the subsequent dissociation of carbonic acid to carbonate ions, bicarbonate ions and protons is the main cause of the pH decrease, but CaCO3 precipitation, and NH3 volatilization foster the pH decrease. However, biological urea hydrolysis prevents the pH from decreasing below 9. Residual undissolved Ca(OH)2 was shown to substantially delay the pH decrease. Overall, this work provides valuable insights into the mechanisms of urea hydrolysis in alkalinized urine during dehydration, which can be used to design more efficient decentralized sanitation systems and minimize nitrogen losses.

Electrochemical Assessment of Galvanized Steel Corrosion in Alkaline Sulfate Solution

Corrosion of steel prestressing strand in bonded post-tensioned bridge tendons have been associated with elevated concentrations of sulfate ions in deficient grout that can develop due to grout segregation [1]. Previous research indicated that the early presence of elevated sulfate ion concentration in the deficient grout in contact with the embedded steel can impair steel passivity. Metastable pitting was observed for steel in saturated calcium hydroxide solutions with sulfate ion concentrations greater than 1,300 ppm and pitting was observed in solutions above 20,000 ppm [2-4]. In addition to steel strand corrosion, galvanized steel ducts in direct contact with the deficient grout with elevated sulfate ion concentrations were also observed to have severe localized corrosion [1]. Galvanized steel in alkaline solutions, such as in cement pore water, have been characterized to have greater resistance to chloride-induced corrosion with chloride threshold concentrations as much as 2.5 times greater than carbon steel [5]. Information relating to sulfate concentrations is less available. Electrochemical testing including the electrochemical noise (EN) technique was conducted to identify the role of early sulfate ion presence on corrosion of galvanized steel.EN provides a test method to assess the corrosion modality without the influence of an external excitation that can affect the electrode surface and electrolyte chemistry (such as metal oxidation and oxygen reduction) [6-7]. The testing aims to identify the corrosion mitigation characteristics of the galvanized steel such as zinc activity and protective barrier surface oxide layers in presence of sulfate ions as well as combined cases with chloride ion contamination below reported threshold concentrations for galvanized steel. In the testing here, steel specimen were exposed to alkaline solutions simulating pore solutions with pH 12.6 with varying sodium sulfate levels and sodium chloride. Supplemental electrochemical experiments included the steady-state condition (open circuit potential, linear polarization test, and electrochemical impedance spectroscopy). References K. Lau, and I. Lasa. "Corrosion of prestress and post-tension reinforced-concrete bridges." Corrosion of steel in concrete structures. Woodhead Publishing, 2016. 37-57. DOI: https://doi.org/10.1016/B978-1-78242-381-2.00003-1.S. Permeh, K. K . Krishna Vigneshwaran, K.Lau., and I.Lasa. “Corrosion of Post-Tensioned Tendons with Deficient Grout. Part 3: Segregated Grout with Elevated Sulfate and Vestigial Chloride Content.” Corrosion 75 (2019) pp.848-864.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Initiation of localized steel corrosion in alkaline sulfate solution.” Materials and Structures, 54 (2021), pp.1-17.S. Permeh, K. Lau, M. Duncan, and R. Simmons. “Identification of steel corrosion in alkaline sulfate solution by electrochemical noise.” Materials and Corrosion, 72(2021), pp.1456-1467.S. Yeomans. Galvanized steel reinforcement in concrete. Elsevier, 2004.S. Permeh, and K. Lau. "Electrochemical Behavior of Steel in Alkaline Sulfate Solutions with Low Level Chloride Concentrations." ECS Meeting s. No. 10. IOP Publishing, 2021.K. Lau, S. Permeh. “Assessment of durability and zinc activity of zinc-rich primer coatings by electrochemical noise technique.” Progress in Organic Coatings, 167(2022): 106840.

Corrosion of aluminium in ordinary Portland cement paste: Influence of matrix porosity and the presence of LiNO3 corrosion inhibitor

AbstractThe Belgian reactor 1 fuel cladding is made of aluminium. If disposed of in a geological disposal repository, aluminium could come into contact with ordinary Portland cement and is going to corrode to form hydrogen gas and aluminium hydroxide. In this study, the long‐term corrosion was evaluated by electrochemical impedance spectroscopy on metal embedded in cement paste immersed in saturated calcium hydroxide solution under anaerobic conditions. Mass transfer effects were investigated by embedding aluminium in cement paste with two different porosities. LiNO3 was also added to the systems to study its corrosion inhibiting effect. After high initial values, the corrosion rate rapidly declined to reach a steady state after a few days. After ~100 days, the corrosion rate was the lowest when cement paste possessing a low porosity with the addition of LiNO3 was used and the highest when cement paste with high porosity without LiNO3 was used. Finally, scanning electron microscopy–energy X‐ray dispersive spectroscopy revealed that the corrosion product layer was thicker than expected by electrochemical impedance spectroscopy measurements, while it is only composed of aluminium and oxygen. Aluminium was found to diffuse into the cement paste close to this corrosion product layer.

Influence of a Show Case Polish Coating on Corrosion Resistance of Mild Steel in Simulated Concrete Pore Solution

Mild steel is relatively less expensive. So in reinforced concrete, mild steel can be used. Mild steel in concrete structures may experience corrosion. To avert corrosion of mild steel, a number of inhibitors are used along with concrete admixtures. In this category of research, saturated calcium hydroxide solution is considered as simulated concrete pore solution (SCPS). Numerous corrosion inhibitors have been utilized in this field along with organic coatings. In the present investigation show case polish coated mild steel has been used in concrete. The corrosion resistance has been calculated by electrochemical studies such as polarization study and AC impedance spectra. When show case polish coated mild steel is immersed in SCPS, the corrosion resistance of mild steel increases. This is long-established by the facts that in presence of show case polish coating , the linear polarization resistance value increases, corrosion current value decreases, charge transfer resistance increases, double layer capacitance decreases, impedance increases, and phase angle increases. The protecting layer functions as anodic inhibitor and controls the anodic reaction primarily. The protective coating offers 99.99% inhibition efficiency. It implies that the show case polish coated mild steel can be used in concrete technology. This will increase the lifetime of the rebars.

The immediate and short-term degradation of the wood surface in a cement environment measured by AFM

This study aims to measure the pit torus and border to monitor the immediate and short-term degradation of wood surfaces after the concrete is cast and the cement hydration releases heat. The surface morphology and adhesion force curves were measured by atomic force microscopy during the treatments in saturated calcium hydroxide solutions ranging from 1 h to 27 days. The results showed that the pit torus and pit border showed different degradation processes. The adhesion force was sensitive to the type of the surface chemical components exposed during the degradation, while the surface modulus, deformation and jump-off force ratio were sensitive to the surface structural strength. The surface modulus of the pit torus degraded to 0.61–0.66 of the untreated original (95% CI) after 7-h treatments, and degraded almost completely after 48-h treatments. The surface modulus of the pit border degraded to 0.83–0.95 of the untreated original (CI) after 10 days and to 0.20–0.23 of the untreated original (95% CI) after 27 days of treatments. The treatment temperature 50 °C caused a 10-times faster degradation in the torus modulus compared to the temperature 20 °C.

The Effects of Graphene Oxide-Silica Nano-Hybrid Materials on the Rheological Properties, Mechanical Properties, and Microstructure of Cement-Based Materials.

Despite their excellent performance, two-dimension nanomaterials have certain limitations in improving the performance of cement-based materials due to their poor dispersity in the alkaline environment. This paper has synthesized a new two-dimension stacked GO-SiO2 (GOS) hybrid through the sol-gel method. Nano-SiO2 is coated on the surface of GO with wrinkling characteristics, and the atomic ratio of C, O, and Si in GOS is 1:1.69:0.57. The paper discusses the impacts on the spreading, Marsh cone flow time, rheological properties, mechanical properties, and microstructure of cement-based materials for the GOS at different mixing quantities. Furthermore, with the same mixing quantity of 0.01%, the influences on the dispersity, flow properties, rheological parameters, and mechanical properties of GOS and graphene oxide (GO) are compared. Lastly, fuzzy matrix analysis has been adopted to analyze the comprehensive performance of cement-based materials containing GOS. The research results indicate that, compared with the reference sample, the spreading for the GOS cement mortar with 0.01% mixing quantity was reduced by 4.76%, the yield shear stress increased by 37.43%, and the equivalent plastic viscosity was elevated by 2.62%. In terms of the 28 d cement pastes, the compressive and flexural strength were boosted by 27.17% and 42.86%, respectively. According to the optical observation, GOS shows better dispersion stability in the saturated calcium hydroxide solution and simulated pore solution than GO. Compared with the cement-based materials with the same mixing quantity (0.01%), GOS has higher spreading, lower shear yield stress, and higher compressive and flexural strength than GO. Finally, according to the results of fuzzy matrix analysis, when the concentration of GOS is 0.01%, it presents a more excellent comprehensive performance with the highest score. Among the performance indicators, the most significant improvement was in the flexural properties of cement-based materials, which increased from 8.6 MPa to 12.3 MPa on the 28 d.

The association between dietary fat and mineral intake with semen parameters: A cross-sectional study in infertile men.

Background Infertility has been a significant problem for couples in recent decades, and the issue can often lie with the male rather than the female.ObjectiveThis study aimed to investigate the effects of fats and minerals intake on semen parameters in infertile men.Materials and MethodsThis cross-sectional study was performed on 260 infertile men referred to Isfahan Infertility Clinic, Isfahan, Iran in the summer of 2018. Semen parameters regarding sperm concentration, total motility, normal morphology, and sperm volume were considered. To assess dietary intakes, a validated food frequency questionnaire was used.ResultsIn the adjusted model, the prevalence of abnormal concentration was 5.23 times higher in the top quartile of calcium intake, compared with the bottom quartile (p = 0.03). Also, the prevalence of abnormal morphology was 68% lower in the third quartile of calcium intake (p = 0.03). Additionally, the prevalence of abnormal concentration was 84% lower in the top quartile of folate intake in comparison to the bottom quartile (p = 0.01) and the prevalence of abnormal morphology was 70% lower in the top quartile of folate intake (p = 0.03). Additionally, the prevalence of abnormal concentration was 72% lower in the top quartile of selenium intake in comparison to the bottom quartile (p = 0.04). Furthermore, in the crude model, the prevalence of abnormal volume was 64% lower in the second quartile of linoleic acid intake rather than the first quartile (p = 0.01).Conclusion In conclusion, diets containing higher amounts of folate and selenium, and lower amounts of cholesterol, saturated fatty acid and calcium were associated with more favorable semen quality parameters.

Children's School-Day Nutrient Intake in Ontario: A Cross-Sectional Observational Study Comparing Students' Packed Lunches from Two School Schedules.

This study compared the caloric and nutrient values of packed lunch contents and consumption in the Balanced School Day (BSD) (two 20 min eating periods) versus the Traditional Schedule (TS) (one 20 min lunch). Foods consumed during school were assessed by direct food observation in 321 grade 3 and 4 students, aged 7–10 years, at 9 BSD and 10 TS elementary schools in Ontario. Packed lunch contents in the BSD were significantly higher than the TS in energy (3128.14 ± 1100.36 vs. 2658.98 ± 951.34 kJ, p < 0.001, respectively). Similarly, carbohydrates, total sugar, protein, fat, saturated fatty acids (SFA), calcium, iron, and sodium were significantly higher in the BSD versus TS packed lunches. Correspondingly, students in the BSD consumed significantly more energy, carbohydrates, total sugar, and SFA compared to the TS. Overall, lunches brought by students in the BSD schedule provided more energy across all macronutrients, with only a few micronutrients showing increased amounts, suggesting two 20 min eating opportunities could contribute to excess caloric intake during school, potentially contributing to the prevalence of childhood overweight and obesity in Canada. Furthermore, packed lunches in both schedules had excess amounts of nutrients of concern and much work is needed to ensure that children in Canada receive nutritious lunches at school.

Effect of macropores at the steel-concrete interface on localized corrosion behaviour of steel reinforcement

The steel-concrete interface determines the steel corrosion and the durability of concrete structures. In this paper, the relationship between macropores and localized corrosion is quantified, based on the natural deterioration of 5 wt% Cr steel reinforced mortar and laboratory tests of 5 wt% Cr steel in the saturated calcium hydroxide solution. The results show that, considering environmental factors with the same chloride content and water saturation, large interfacial macropores are always the weakest zones at which both corrosion initiation and propagation preferentially take place. The localized rate of steel corrosion (mm/year) increases linearly with the logarithm of the macropore volume (μL), and the slopes are in the range of 0.05–0.11 depending on the chloride level. The weakened pH buffering effect of solid Ca(OH)2 at interfacial macropores is not the only reason for this phenomenon; the impacts of macropores and their volume on the electrochemical corrosion process are also significant. In small macropores, both cathodic and anodic polarizations are strengthened, and the thermodynamic driving force of the iron dissolution reaction is reduced.

Composition of Corroded Reinforcing Steel Surface in Solutions Simulating the Electrolytic Environments in the Micropores of Concrete in the Propagation Period.

In the present work, the composition of a corroded reinforcing steel surface is studied at different pH values (related to different degrees of development in the corroding zones of the corrosion process) in solutions simulating chloride-contaminated environments. The media considered consist of saturated calcium hydroxide solutions, progressively neutralized with FeCl2 or by adding 0.5 M NaCl to the solution. The results found in present work confirm higher levels of acidity in the solutions with higher concentrations of Fe2+.In the present work, emphasis is given to the composition of the oxides in solutions that simulate the conditions that exist inside of a localized corrosion pit as a consequence of the reaction of chloride on reinforcing steel. The oxides were studied using Raman and XPS techniques; the results obtained with both techniques are mutually coherent. Thus, in the passive state, the oxides found are those reported previously by other authors, while in the corroding state, the present results are more comprehensive because the conditions tested studied a variety of pore solution composition with several pH values; we tried to reproduce these values inside the pits in conditions of heavy corrosion (very acidic). The oxides found are those typically produced during iron dissolution and seem not the best route to study the corrosion process of steel in concrete; the electrochemical tests better characterize the corrosion stage.

Atherogenic Index of Plasma and Its Association with Risk Factors of Coronary Artery Disease and Nutrient Intake in Korean Adult Men: The 2013-2014 KNHANES.

Coronary artery disease (CAD) has been linked to one of the highest death rates globally. The atherogenic index of plasma (AIP) may be an important predictor of atherosclerosis and cardiovascular disease, superior to the standard atherosclerotic lipid profile. This study investigated the relationship between AIP and obesity indices, blood glucose, lipid profile, and nutrient intake status in Korean adult men. The study included 1292 males aged ≥19 years old who participated in the Korea National Health and Nutrition Examination Survey, 2013–2014. Participants were divided into four groups according to AIP quartiles, calculated as log (triglyceride (TG)/high-density lipoprotein cholesterol (HDL-C)). Body mass index, waist circumference, fasting blood glucose, hemoglobin A1c, total cholesterol, TG, and low-density lipoprotein cholesterol levels increased as AIP levels increased, whereas HDL-C level declined. As the level of AIP increased, intake of saturated fatty acid, calcium, phosphorus, riboflavin, milk, and dairy product decreased significantly, and the contribution rate of milk and dairy products to fat intake decreased. AIP was linked to obesity indices, blood glucose, and blood lipid profile in Korean men, suggesting that it could predict CAD.

Growth of calcium carbonate crystal on various substrates from a saturated calcium carbonate solution utilizing difference in solubility

Crystalline calcium carbonate was deposited on various substrates (substrate temperature of 80 °C) from a saturated calcium hydrogen carbonate solution (solution temperature of 10 °C). A single aragonite phase deposited on the Al substrate, whereas a mixed phase of aragonite and calcite grew on the soda lime glass, borosilicate glass, silica glass, and polycarbonate substrates. With increasing deposition time, the crystal size and the proportion of calcite on the soda lime silicate glass substrate increased. Furthermore, calcite crystals were preferentially deposited on an Al substrate with a thin film of Au as a buffer layer (Au/Al substrate).

Action mechanism for improving water impermeability of concrete surface based on deep penetrating sealer

Deep penetrating sealer (DPS) is water-based permeable crystalline waterproofing coating, and it is widely used to improve the impermeability and durability of cement-based materials. This study investigated the action mechanism of DPS on cement-based materials, especially the microstructure of the newly generated substances and pore evolution in concrete that DPS treated. To explore the action mechanism and permeability of DPS on cement-based materials, experimental specimens were fabricated in this experiment. The specimens included concrete, cement paste, dried DPS, and the product reacted by DPS mixed with saturated calcium hydroxide solution. To test the microstructure, chemical composition, pore structure, and macroscopic permeability of the specimens, scanning electron microscopy, x-ray diffraction, energy dispersive spectrometer, nitrogen absorption, and AutoClam equipment were employed. The experimental and analytical results showed that the calcium silicate hydrate content was increased by the chemical reaction between DPS and cement-based materials. The microstructure of concrete surface then became more densified. The volume of pore with a pore size ranging from 20 to 130 nm inside concrete was decreased, and the water penetration of the concrete was reduced by approximately 75%. This study revealed the action mechanism of DPS and cement-based materials, providing reference for the improvement of DPS and practical engineering application.

A study on effectiveness of inorganic and organic corrosion inhibitors on rebar corrosion in concrete: A review

Reinforced concrete is the most extensively used building material in the construction industry. Generally, well-made concrete provides good physical and chemical protection to the embedded steel bar against an aggressive environment. The highly alkaline concrete pore solution protects the steel reinforcement from aggressive ions by forming a passive oxide layer over the steel surface. However, the passive film can be destroyed, and corrosion of steel reinforcement can be initiated either due to carbonation or due to the presence of a sufficient amount of chloride ions at the rebar level. Chloride induced corrosion of steel reinforcement affects the durability and decreases the service life of reinforced concrete structures exposed to aggressive environments, which results in huge repair and maintenance costs. By keeping in view, the substantial economic loss incurred due to corrosion of steel reinforcement in reinforced concrete structures, it is necessary to adopt adequate measures to minimize the corrosion of steel reinforcement in concrete. The most common corrosion prevention technique is the use of corrosion inhibitors in concrete. Several research works have been reported in the literature to evaluate the efficiency of corrosion inhibitors against chloride-induced corrosion of steel reinforcement in concrete. Corrosion inhibitors are typically introduced either as an admixture during the preparation of fresh concrete mixes or as a surface application on the hardened concrete to prevent the onset of corrosion of steel reinforcement or extend the corrosion initiation time in reinforced concrete structures. This review article summarizes the reported research works on inhibiting the behaviour of organic and inorganic corrosion inhibitors against chloride-induced corrosion of steel reinforcement in simulated concrete pore solution such as saturated calcium hydroxide solution containing varying concentrations of chloride ions as well as in cementitious composites. Further, the reported research works on the effect of corrosion inhibitors on the mechanical properties of cementitious composites are also are reviewed and discussed.

Structural evolution during corn stalk acidic and alkaline hydrogen peroxide pretreatment

Oxidative pretreatment is a promising strategy for biomass utilization due to its excellent performance and economic costs. Insights into lignocellulose recalcitrance are essential to further develop biomass manufacture. To understand structural recalcitrance, we performed systematic characterizations after mild hydrogen peroxide pretreatment in alkali or Lewis acid environments, followed by enzymatic hydrolysis to obtain higher glucose yields than raw materials. Results indicated that hydrogen peroxide pretreatment in saturated calcium hydroxide solution effectively removed lignin through cleavage of the lignin-carbohydrate complex and part C-C linkages in the middle lamella. The ferrous sulfate solution induced hemicellulose solubility, and the partially oxidized lignin was depolymerized under hydrogen peroxide pretreatment. The solvent could then be used for subsequent hydrolysis and cellulose conversion. It was demonstrated that hydrogen peroxide pretreatment is an effective and promising method for refining lignocellulose under an alkaline environment and is suitable for subsequent cellulose conversion in ferrous sulfate solution.

Consumption of Free Sugar Predicts Nutrient Intake of Saudi Children.

Data concerning the association between free sugar intake and nutrient intake in children in the Middle East are not available. This study aimed to explore the association between the consumption of free sugar and nutrient intake among Saudi children. A cross-sectional study included 424 Saudi children ages between 6 and 12 years old and their mothers. An online survey collected sociodemographic data from mothers. Trained data collector personal contacted mothers to arrange for a phone interview in order to collect 24-h dietary recall to assess the dietary intake of children. Only 0.90% of children consumed free sugar within the recent recommendation of the World Health Organization (WHO) of <5% of total energy intake, whereas 10.6% of children consumed free sugar <10% of total energy intake. The percentage of free sugar intake was negatively associated with total energy intake. Multiple linear regression analysis of free sugar consumption and nutrient intake adjusted for children's age and sex indicated that a higher percentage of free sugar intake significantly predicted lower intake of saturated fat, fiber, sodium, potassium, calcium, iron, zinc, and vitamin B12. Excessive intake of free sugar predicted a lower intake of many essential nutrients. Interventions that aim to reduce the intake of free sugar are urgently needed in order to improve diet of growing children. Future research to explore top food sources of free sugar is needed to establish effective interventions that aim to limit free sugar intake among children.

Effect of sodium carbonate and sodium phosphate on hydration of cement paste

Both sodium carbonate (NC) and sodium phosphate (NP) could immediately precipitate in the presence of calcium ions (Ca2+), and these precipitates would deposit on the surface of cement as one layer in cement paste. However, these precipitates have different effects on the hydration of cement. In this study, effect of NC and NP on cement hydration was discussed, and the different effect between these two was investigated. Setting time, hydration heat, conductivity of cement suspension, and compressive strength of cement paste were examined, and the hydrates were analyzed with XRD and TG-DTG. The precipitates synthesized in saturated calcium hydroxide solution were characterized with XRD, TEM, and SEM. Then one model was proposed to illustrate the mechanism of the effect of NC and NP on cement hydration. The results indicated that NC accelerated cement hydration, but NP retarded it. And the results of TEM and SEM showed that calcium carbonate (the precipitate formed by NC and Ca2+)) could well crystalize with directional growth, there is a large amount of interspace in the calcium carbonate-based layer, which would benefit the transports of water molecules and dissolved ions. However, the calcium phosphate precipitate (the precipitate formed by NP and Ca2+)) seemed to have a large amount of amorphous structure with a much more compact layer structure than calcium carbonate. The difference in composition and structure of the layer was responsible for the effect of NC and NP on cement hydration. The mechanism behind accelerating effect of NC was due to the interspace in the calcium carbonate based layer which facilitated the ion dissolution of system, while that for retarding effect of NP was because the calcium phosphate-based layer formed on the surface of cement grains seemed compact enough to restrict the transports of water molecules and dissolved ions. Such consequences were expected to give deeper insight into the effect of the surficial structure of cement grains on early hydration of cement paste.

Removal and recovery of phosphate using a novel calcium silicate hydrate composite starch cryogel

Phosphate is a major pollutant that deteriorates water quality and causes eutrophication, a novel calcium silicate hydrate composite cryogel (Cry-CSH) was thus successfully prepared for phosphate removal and recovery in this work. Calcium silicate hydrate (C–S–H) was mixed with the gel precursor (7.5% w/w) prepared from native starch and limewater (saturated calcium hydroxide solution as the cross-linker). The mixture was frozen and thawed for 3 cycles giving an interconnected macroporous composite. This had C–S–H nanoparticles (75 mg) immobilized on a monolithic floatable cryogel network (2.5 cm diameter × 1.0 cm height) enabling an easier recovery and without the losses that occur when using C–S–H nanoparticles. The phosphate adsorption reaches equilibrium at 120 min with adsorption capacity of 2.50 mgPO43−/gCry-CSH (65.42 mgPO43−/gC–S–H) under optimum conditions. Adsorption equilibrium data were well fit by the Freundlich isotherm model, while kinetic results were well fit by the pseudo second-order model. The calculated activation energy (Ea) of 43.9 kJ/mol indicates chemical adsorption, while a positive change in enthalpy (ΔH0, 19.3 kJ/mol) indicates the endothermic nature of phosphate adsorption. Cry-CSH can remove phosphate from wastewater and effluent samples with excellent removal efficiency (>98%). It can float on water surface for at least 105 days without damage, while its phosphate adsorbed form can be biodegraded within 10 days under soil buried conditions. Thus, this work demonstrated the significant potential of Cry-CSH for practical and environmentally friendly phosphate removal and recovery.