Calcium Nitrite Research Articles

Inhibiting Sulphate Attack on Concrete by Hydrophobic Green Plant Extract

Organic base (Amine) and inorganic base (Nitrite) have been known for protection of concrete structures but are not commercially indigenous to most developing economies due to manufacturing difficulties and are toxic to the environment. Also inhibitors are not known to stop sulphate attack in concrete. Hence, the objective of the present investigation was to study a novel, eco-friendly and hydrophobic green plant extracts inhibitor and compares its effectiveness with established calcium nitrite and ethanolamine inhibitors. Bambusa Arundinacea (Green plant extracts), calcium nitrite and ethanolamine corrosion inhibitors were selected for the present investigation. Compressive strength of 100×100×100mm concrete cubes after 7, 28 and 90 days of curing test was used. The results of the inhibitors studied showed that Bambusa Arundinacea has superior compressive strength compared to calcium nitrite and ethanolamine. Bambusa Arundinacea may be considered a better substitute for nitrite and amine- based corrosion inhibiting admixtures for durable concrete structures due its pore blocking effects.

Anodic corrosion inhibitors against chloride induced corrosion of concrete rebars

The effect of anodic inhibitors [calcium nitrate Ca(NO3)2, calcium nitrite Ca(NO2)2 and potassium nitrate NaNO2] has been evaluated using cylinders with steel rebars exposed to the following environments: in the marine tidal zone, at roof top and in air of 38°C and 90% relative humidity for 4 years. The experiments showed that the half cell potentials were more negative than the visual inspections proved when anodic inhibitors are used. Inhibitor dosage on 3–4% of cement weight seems sufficient to protect the rebar against corrosion. Capillary absorption experiments showed that the concrete porosity was unaffected by the inhibitors. The concentration profiles of chloride, nitrite and nitrate were investigated with respect to leaching. However, it was difficult to find the background level of nitrite due to possible chemical alteration.

Calcium Nitrite Corrosion Inhibitor in Portland Cement: Influence of Nitrite on Chloride Binding and Mineralogy

The binding of nitrite and chloride in cement paste occurs mainly as a consequence of reaction with the AFm phase. The reaction has been modeled with the aid of new thermodynamic data on the stability of nitrite–AFm and by focused experiments performed on key compositions. The success of nitrite as a corrosion inhibitor for the protection of embedded steel arises from the “smart” behavior of the AFm phase; it normally stores and sequesters nitrite in preference to sulfate, carbonate, and hydroxyl ions so that the nitrite concentrations of pore fluid are low. However, if chloride ingress occurs in service, the AFm undergoes ion exchange, gaining chloride and forming Friedel's salt, while releasing soluble nitrite ions to the pore fluid. As a result, the aqueous ratio of [NO2−]/[Cl−] is maintained and remains within the passivation range for steel, even though chloride increases. The exchanges are automatic and rapid, equilibrium being reached within days at ∼25°C. Thus, theory and experience can be reconciled with respect to the action of nitrite as an inhibitor of chloride‐induced corrosion and the impacts of changing conditions, e.g., adding calcium carbonate or carbonation on the [NO2−]/[Cl−] ratio can be predicted.

Impedance study on calcium nitrite as a penetrating corrosion inhibitor for steel in concrete

Penetrating corrosion inhibitors are thought to be able to penetrate through the capillary structure of concrete to reinforcing steel and to reduce the already initiated corrosion of steel. In this work the ability of calcium nitrite to inhibit the chloride induced corrosion of steel was studied. The test protocol was adjusted to simulate the performance of penetrating corrosion inhibitors in concrete structures. Steel samples were first prepassivated in saturated solution of Ca(OH) 2 and then exposed to the same solution with 1% NaCl addition, simulating pore liquid in chloride contaminated concrete. After the initiation of steel corrosion, the first dose of calcium nitrite was added, and then its concentration was gradually increased and the inhibition effect was related to the molar ratio of chloride to nitrite ions [Cl −]/[NO 2 −]. Different rates of the increase in the inhibitor concentration were applied. Electrochemical impedance spectroscopy was used to follow the behaviour of steel at different stages of the corrosion process. The evolution of acquired spectra reflected the initiation of localized corrosion of steel and then the gradual inhibition with increasing concentration of the inhibitor. It was found, that calcium nitrite is able to inhibit the initiated corrosion (pitting) of steel and the optimum inhibitor efficiency was observed for the [Cl −]/[NO 2 −] ratio below 1. The inhibition efficiency was larger, when this value of the [Cl −]/[NO 2 −] ratio was reached in early stages of the corrosion development. Calcium nitrite can be effective as a penetrating corrosion inhibitor for steel in concrete, if it will be present in the sufficient concentration at the steel surface in early stages of the corrosion development.

Compatibility of a polycarboxylate-based superplasticiser with different set-controlling admixtures

The compatibility of specific combinations of chemical admixtures for cement pastes and mortars have been investigated. The consistency, setting time and compressive strength of cement pastes and mortars incorporating a polycarboxylate-based plasticizing admixture (PCA) with four different set-controlling admixtures (SCA); calcium formate (CF), tri-ethanolamine (TEA), mixture of calcium nitrite and nitrate salts (CNN blend) and sodium aluminate (SA) have been determined within the scope of this study. Fifty-two mortar and paste specimens with different amounts of PCA and SCA combinations have been prepared. Water/cement ratios of cement paste and mortar mixtures were 0.24 and 0.50, respectively. The paste mixtures have been prepared to determine the setting time data and the mortar mixtures have been used to determine the consistency and compressive strength values. Test results indicated that the PCA employed in this study, retards the setting time, improves consistency and reduces the early strength development of all paste and mortar mixtures at dosages greater than 0.4% by mass of cement. However, the use of different set-controlling admixtures in combination with PCA caused drastic changes in the performances of the mixtures depending on the type and amount of SCAs. It was concluded that, in order to reduce the setting time and increase the early strength of PCA incorporated mortars without causing consistency loss, the combination of PCA, and SCA should be optimized according to their types. A new 3D box-plot method has been used to determine the optimum admixture combinations for the desired properties. Maximum flow, shortest setting time and highest early strength criterion were the targets of the optimization. The most effective combination to obtain desired set acceleration and high early strength values was 1.8% PCA with 1.6% nitrite and nitrate salts based SCA by mass of cement. If consistency lost is in secondary importance, 1.8% PCA based plasticiser with 1% sodium aluminate based SCA may be an alternative combination. The proposed method can be used to optimize the targeted properties for a specific combination of cement, PCA and SCA.

Electrochemical chloride removal in reinforced concrete structures: Improvement of effectiveness by simultaneous migration of calcium nitrite

Electrochemical Chloride Extraction (ECE) is becoming a common methodology for repairing reinforced structures. Also the application of corrosion inhibitors on the concrete surface for its penetration its getting more and more interesting as protective method against corrosion of reinforcements. In this sense, the migration of corrosion inhibitors can be promoted by the application of an electric field, enhancing in this way the transport of the inhibitor. In present work, the simultaneous application of both technologies is proposed. The migration of nitrite to the rebar is promoted during the application of an ECE treatment by modifying the classical configuration through the connection of an external cathode to the rebar. The electrochemical response of the rebar after the treatment has been evaluated by corrosion potential and polarization resistance measurements. The efficiency of the treatment was confirmed by the visual inspection of the rebar and the analysis of chloride and nitrite at the level of the rebar.

Corrosion performance of steel in composite concrete system admixed with chloride and various alkaline nitrites

Composite concrete systems consist of both binary and ternary cements were designed. The corrosion performance of steel in composite concrete systems admixed with sodium chloride (3%NaCl) and different alkaline nitrites (0·5%NO2–), namely sodium nitrite (NaNO2), potassium nitrite (KNO2) and calcium nitrite [Ca(NO2)2] were studied by conducting various electrochemical and non-electrochemical techniques. Open circuit potential and weight loss measurements were carried out for 180 days of exposure. The permeability characteristics of the composite concrete systems were studied using impressed voltage technique and rapid chloride permeability test. Linear polarisation studies showed better corrosion resistance properties of steel in binary and ternary cement concrete even in the presence of 3% sodium chloride. Chloride diffusion studies revealed that the diffusion coefficient was found to be much less for (OPC+PSC) and ternary systems. Nitrites of sodium, potassium and calcium act as anodic inhibitors and they compete with chloride ions for the ferrous ions at the steel surface to form a film of ferric oxide. Ternary systems and (OPC+PSC) performed better even in the presence of a higher amount of aggressive chloride ions. The reduction in the corrosion rate of steel in composite concrete systems follows the order: (OPC+PPC+PSC)>(OPC+PSC)>(OPC+PPC)>(PPC+PSC).

Reactivities of NaOH Enhanced Iron Blast Furnace Slag/Hydrated Lime Sorbents toward SO2 at Low Temperatures: Effects of the Presence of CO2, O2, and NOx

The effects of the addition of NaOH on the reactivities toward SO2 of iron blast furnace slag/hydrated lime (BFS/HL) sorbents were studied without and with the presence of flue gas components, CO2, O2, and NOx, under the conditions prevailing in the bag filters of dry and semidry flue gas desulfurization processes. The reactivities of sorbents were markedly enhanced by the addition of NaOH when CO2, O2, and NOx were not present in the gas mixture. The enhancement effect mainly resulted from the deliquescent property of NaOH. With the presence of CO2, O2, and NOx at their typical concentrations in the flue gas, the sorbent reactivity was greatly increased due to the oxidation of bisulfite and sulfite ions to sulfate ions as well as the formation of deliquescent salts, calcium nitrite and nitrate, being enhanced by the presence of NO2 during the sulfation of a BFS/HL sorbent. The addition of NaOH in this case promoted the formation of sulfates but became less important in raising the sorbent reactivities for sorbents except BFS. Without the presence of CO2/O2/NOx, the BFS/HL sorbents with ratios ≤70/30 had higher reactivities than HL, but with the presence of CO2/O2/NOx, HL had the highest value of SO2 capture among the BFS/HL and BFS/HL/NaOH sorbents tested. Placing the SO2 removal unit before the NOx removal unit in practical operations can take advantage of the enhancement effect of CO2/O2/NOx on increasing the Ca utilization and SO2 capture of the sorbent.

Experimental Study on the Development of New Corrosion Inhibitor Contained a lot of Ca(No<sub>2</sub>)<sub>2</sub> Using Concrete Structure

The purpose of this research is to evaluate the effectiveness of nitrate as a corrosion inhibitor in mortar containing chloride. In the experiment, test specimens of mortar to which chloride and nitrite had been added, were subjected to accelerated corrosion by means of repeated drying and wetting on condition of high temperature. This study concerns the assessment of the inhibition effect of nitrite-based corrosion inhibitor using a polarization method and its influence on the chloride transport, compressive strength and setting time of concrete. From the results of the experiments, it was confirmed that the lithium, calcium nitrite corrosion inhibitor and new corrosion inhibitor over dosage 0.6 (NO2-/Cl-) molar ratio is very effective in protecting reinforcement from corrosion in mortar in which chloride ions have contained.

The electrochemical assessment of corrosion inhibition effect of calcium nitrite in blended concretes

This study examined the corrosion inhibition effect of a calcium nitrite-based corrosion inhibitor (CN) by assessing an electrochemical way together with a strength development of concrete containing CN. As binders, ordinary Portland cement (OPC) alone, a mixture of OPC with replacement of pulverised fuel ash at 30% (30% PFA), and a mixture of OPC with ground granulated blast furnace slag at 65% (65% GGBS), respectively were used for testing of the strength development, rate of chloride transport and corrosion behaviour. As a result, CN was significantly effective in increasing the resistance to corrosion risk and thus an enhancement of chloride threshold level for corrosion was achieved with no detrimental effect of CN on the compressive strength of blended concrete. For transport properties of chloride ions, PFA and GGBS were effective in lowering chloride ionic diffusion through concretes, but an increase in the content of CN in concretes resulted in an increase in the diffusivity of chloride ions. Then, the corrosion-free life of concretes exposed to a salt solution was varied with the content of CN and binder type. For OPC concretes, an increase in the CN content resulted in an increase in the time to corrosion, due to increased threshold value, while the time to corrosion for 30% PFA and 65% GGBS concretes was less dependent on the content of CN. It is due to the fact that the beneficial effect of CN in inhibiting corrosion could be offset by the increased rate of chloride transport in concretes containing pozzolanic materials.

Wallkill River Arch Bridge - Precast Concrete Ensures Bridge Durability

Adjacent prestressed concrete box beams with a composite deck slab provide the superstructure of the open-spandrel Route 52 arch bridge crossing over Wallkill River, about 50 miles (80 km) northwest of New York, N.Y. To create an overall span of 225 ft (68.6 m), precast concrete components are used efficiently and economically in both the substructure and superstructure of the bridge. This article describes some of the innovative design features—including self-consolidating, high-performance concrete with a design compressive strength of 10,000 psi (69 MPa), a calcium nitrite corrosion inhibitor, and grouted splice sleeves—that are used to increase the structure’s durability. The successful completion of the Route 52 bridge demonstrates the triumph of new technologies over traditional methods of construction.

The effect of calcium nitrite on the chloride-induced corrosion of steel in concrete

Laboratory tests were undertaken to assess the effect of calcium nitrite-based corrosion inhibitors in raising the chloride threshold level (CTL) for the corrosion of steel embedded in concrete and hence the time to corrosion initiation. Specimens with a centrally located steel rebar were cast with 0, 1·23, 2·5 and 5·0% nitrite by weight of cement and were cured for 4 weeks. Then they were immersed in 4M sodium chloride solution and the galvanic current between the embedded steel and an external cathode was monitored. The CTL of nitrite-free specimens was typically doubled and trebled by 2·5% nitrite and 5% nitrite, respectively. With and without nitrite, the CTL was reduced with an increase in the air void content at the steel–concrete interface. The time to corrosion depended on the cement content. Use of low cement content (282 kg/m3) increased the CTL as the dosage of nitrite in concrete increased, but did not extend the time to corrosion because it accelerated chloride penetration. For a richer mix (350 kg/m3) the time to corrosion increased with the dosage of calcium nitrite. After corrosion initiation, the corrosion rate for specimens containing calcium nitrite was typically two to three times higher than for nitrite-free specimens.

Effects of Flue Gas Components on the Reaction of Ca(OH)2 with SO2

A differential fixed-bed reactor was employed to study the effects of the flue gas components, H2O, CO2, NOX, and O2, on the reaction between Ca(OH)2 and SO2 under conditions similar to those in the bag filters of a spray-drying flue gas desulfurization (FGD) system. The presence of CO2 with SO2 in the gas phase enhanced the sulfation of Ca(OH)2 only when NOX was also present. When either NOX (mainly NO) or O2 was present with SO2, the enhancement effect was slight, but became great when both NOX and O2 were present, and was even greater when CO2 was also present. The great enhancement effect exerted by the presence of NOX/O2 resulted from the rise in the NO2 concentration, which enhanced the oxidation of HSO3- and SO32- to SO42- in the water layer adsorbed on Ca(OH)2 surface and the formation of deliquescent salts of calcium nitrite and nitrate. The enhancement effect due to the presence of NOX/O2 was more pronounced when the relative humidity was above that at which the salts deliquesced; the extent of sulfation was more than twice that obtained when SO2 alone was present. The presence of H2O, CO2, NOX, and O2 in the flue gas is beneficial to the SO2 capture in the low-temperature dry and semidry FGD processes. The presence of NOX/O2 also enhanced CO2 removal when SO2 was absent.

Evaluation of organic based corrosion inhibiting admixtures for reinforced concrete

PurposeAdmixtures are materials that are added to concrete at some stage in its production to give concrete new properties whether in fluid or plastic conditions. The admixtures used in the construction industry are broadly classified into Mineral and Chemical admixtures. In recent years, the use of mineral and chemical admixtures in producing high performance concrete has increased significantly. The chemical reaction of cement with admixtures differs from material to material. Calcium nitrite based corrosion inhibiting admixtures have gained popularity for protection of reinforced and pre‐stressed concrete structures but calcium nitrite is not commercialized indigenously in India due to manufacturing difficulties. Hence, the objective of the present investigation was to study a novel corrosion inhibiting admixture system and to compare its effectiveness with sodium nitrite.Design/methodology/approachDi‐sodium phthalate, sodium orthophosphate and sodium nitrite‐based corrosion inhibiting admixtures were selected for the present investigation. The critical quantities of corrosion inhibiting additives were determined by accelerated laboratory tests. The following types of tests were conducted to evaluate the efficiency of the corrosion inhibiting admixtures: compressive strength of 100 × 100 × 100 mm concrete cubes after 3,7,14 and 28 days of curing, linear polarization resistance measurements, electrochemical impedance spectroscopy measurements, an accelerated 12 V controlled potential test.FindingsFrom the above tests, the inhibitor admixtured concrete not only improved in compressive strength but also increased its corrosion resistance properties. Of the inhibitors studied, di‐sodium phthalate showed superior corrosion resistance properties, compared to sodium nitrite.Originality/valueDi‐sodium phthalate may be considered a better substitute for calcium nitrite‐based corrosion inhibiting admixtures for durable concrete structures. This fulfils the objective of the investigation.

Corrosion Evaluation of Epoxy-Coated Bars in Chloride Contaminated Concrete Using Linear Polarization Tests

Five slab specimens with predefined cracks are examined to evaluate the corrosion behavior of epoxy-coated bars in chloride contaminated concrete, using linear polarization method. The test specimens were subjected to alternating weekly cycles of ponding in a salt solution and drying for 48 weeks. Test results show that the current density of the specimen of normal steel bars becomes 0.715 <TEX>${\mu}A/cm^2$</TEX> indicating that the steel bars are in moderate or high corrosion condition. However, the corrosion rates of the specimens with damaged epoxy-coated bars are significantly below 0.1 <TEX>${\mu}A/cm^2$</TEX> and the bars appears to be in passive condition. The damaged epoxy-coated bars with a corrosion inhibitor of calcium nitrite showed a corrosion rate of 0.110 <TEX>${\mu}m/year$</TEX> or 56 percents of the corrosion rate of damaged epoxy-coated specimen without such an inhibitor, 0.195 <TEX>${\mu}m/year$</TEX>. However, the corrosion rates of specimens containing the other two corrosion inhibitors, a combination of amines and esters or mixtures of organic alkenyl dicarboxyl acid salts are quite equivalent to the control specimen. The research technique of linear polarization resistance method has proven itself to be useful in measuring corrosion rates of reinforcement in concrete.

Enhancing the Reliability of Evaluating Chloride Ingress in Concrete Using the ASTM C 1202 Rapid Chloride Penetrability Test

Abstract The rapid chloride penetrability test (RCPT-ASTM C 1202) is commonly used to evaluate the resistance of concrete to chloride ions ingress owing to its simplicity and rapidity. However, it has been criticized for various shortcomings such as giving favorable results to supplementary cementitious materials (e.g., silica fume), and bias against calcium nitrite corrosion inhibitors (CNI). Based on the ASTM C 1202 induced voltage concept, this study aims at enhancing the reliability of rapidly evaluating concrete resistance to chloride ions ingress. It is proposed that upon test termination, not only the passing charges are recorded, but the depth of chloride front migrating into concrete is also measured. Concrete mixtures herein were prepared incorporating selected materials (silica fume and CNI) that have been known to cause misleading results for the RCPT test. The effects of silica fume and CNI dosages on RCPT results were investigated and correlated to porosity trends evaluated by mercury intrusion porosimetry (MIP). The study reveals that measuring the migrating chloride front in concrete subsequent to the ASTM C 1202 test can eliminate the bias induced by electrolysis conductivity resulting from silica fume and/or CNI. This improves the reliability of assessing concrete resistance to chloride ions penetration using the RCPT procedure.

The Use of Chemical Admixtures in Concrete. Part II: Admixture-Admixture Compatibility and Practical Problems

Different combinations of admixtures can produce concretes having high flow, good cohesion, and self-leveling properties; they can be placed underwater, can expand and induce compressive stresses or reduced shrinkage, and can be placed and cured at sub-zero temperatures. Thus, correct combinations of admixtures produce custom-made concrete for particular jobs. This article, the second in a series, explores admixture-admixture compatibilities; the first article in this series discussed admixture-cement compatibilities. Topics include compatibility problems with viscosity-enhancing admixtures, compatibility problems with water reducing admixtures (WRA) or damproofing admixture combinations, shrinkage compensating concretes for flat slab applications, accelerated setting in concrete containing calcium nitrite and superplasticizers, and decreased air contents in silica fume concrete. The authors also consider problems caused by admixture side effects and poor practice, including surface finishing problems, plastic shrinkage, and the effect of retempering of concrete on the air void system. The authors conclude that it is vital to understand both admixture-cement and admixture-admixture interactions so that the best use of materials can be achieved, field problems are avoided, and more accurate prediction of concrete properties is made possible.

Effect of calcium nitrite-based corrosion inhibitor in preventing corrosion of embedded steel in concrete

Due to the corrosion inhibition effect and compatibility with concrete properties, calcium nitrite solution has been widely used, in North America and Asia,. However, investigation has often been restricted to tests using a macrocell corrosion monitoring or measuring corrosion rate in an aqueous condition. This study concerns the assessment of the inhibition effect of calcium nitrite-based corrosion inhibitor using a polarisation method and its influence on the chloride transport, compressive strength and setting time of concrete. The calcium nitrite-based corrosion inhibitor significantly reduced the corrosion rate of steel in chloride contaminated mortar and raised the chloride threshold level, ranging from 0.22% to 1.95% by weight of cement, while nitrite-free specimen produced the threshold level ranging from 0.18% to 0.33%. It was observed that concrete specimens containing the corrosion inhibitor produced the higher total charge passed in a rapid test for chloride ion permeability. An increase in the dosage of corrosion inhibitor resulted in a decrease in the concrete setting time. In addition, the compressive strength at early ages was increased by corrosion inhibitor, but in a long term (900 days), decreased to the level for 28 days.

Field Evaluation of Marine Structures Containing Calcium Nitrite

A field study of corrosion of reinforcing bars in existing concrete pier structures is presented in this paper. The objective of the research was to evaluate the effectiveness of calcium nitrite for combating corrosion in marine structures. Five sites were selected for field evaluation of reinforcement corrosion in cooperation with the Harbors Division of the Hawaii Department of Transportation. The concrete for each of these sites included a calcium nitrite-based admixture as a corrosion inhibitor. Each site was tested for permeability, chloride ion concentration, half-cell potential, polarization resistance, and pH. Corrosion activity identified by half-cell potential measurements, polarization resistance measurements, and visual inspection of bars taken from cores indicated that high dosages of calcium nitrite, 19.8 to 22.3 L/m³, provided the steel with significantly greater protection than lower dosages, 12.4 L/m³. This occurred despite the fact that the sites with higher dosages were older and usually more permeable than the structures with lower dosages.

Effectiveness of corrosion inhibiting admixture combinations in structural concrete

A long-term corrosion study was conducted to determine the effectiveness of calcium nitrite, silica fume, fly ash, ground granulated blast furnace slag, and DSS in reducing corrosion of reinforcing steel in concrete. Mixture proportions included single, double, and triple combinations of these admixtures. Non-cracked and pre-cracked slab specimens were evaluated by visual inspections, macrocell readings, half-cell potentials, and autopsies. Triple combinations of calcium nitrite, silica fume, and either fly ash or ground granulated blast furnace slag, as well as a double combination of calcium nitrite and ground granulated blast furnace slag, performed very well and are recommended in concrete mixtures exposed to severe corrosive environments. DSS outperformed the other admixtures for corrosion prevention in this study; however, it resulted in somewhat lower compressive strengths and had not been fully tested for effects on other concrete properties.