Calcium Nitrite Research Articles

Effects of corrosion inhibiting admixtures and supplementary cementitious materials combinations on the strength and certain durability properties of HPC

This paper reports a study carried out to evaluate the effects of corrosion inhibiting admixtures, calcium nitrite and disodium tetrapropenyl succinate, in combination with supplementary cementitious materials, fly ash and silica fume Portland cement, on the compressive strength and certain durability properties of high performance concrete. Mixture formulations, including binary and ternary combinations of these admixtures were evaluated. Chloride profiles after 91 and 365 days of exposure and the compressive strength and electrical resistivity at 1, 7, 14, 28, 180, and 365 days of age were estimated. Also, results of corrosion evaluation after five-year exposure to a natural marine environment at Treat Island Maine, USA are presented and discussed. Results indicate that the use of corrosion inhibitors in combination with supplementary cementitious materials was beneficial, albeit to various degrees, in enhancing the strength and durability properties of high performance concrete with no noticeable adverse effects.

Performance of cactus mucilage and brown seaweed extract as a steel corrosion inhibitor in chloride contaminated alkaline media

PurposeThis paper aims to present experimental results related to the performance of cactus mucilage (CM) and brown seaweed extracts (SEs) to inhibit reinforcing steel bar (rebar) corrosion in saturated calcium hydroxide alkaline solutions (pH = 12.5).Design/methodology/approachElectrochemical cells were prepared using CM solutions at 0.5, 1 and 1.38 per cent concentration (w/v), SE solutions at 0.5, 1, 1.38, 2 and 3 per cent concentration (w/v), sodium alginate at 1 per cent concentration (w/v) and calcium nitrite at 11.3 per cent (v/v). Each cell contained six deformed reinforcing steel bars of 9.5 mm nominal diameter. The experiments were performed at 23 ± 2°C in two stages. The first stage was aimed at stabilizing the rebar until passivation was reached. The second stage included adding NaCl in six steps from 0.5 to 16 g/L. Half-cell potential, linear polarization resistance and electrochemical impedance spectroscopy measurements were monitored during both stages.FindingsThe electrochemical test results indicated that both additions reduce the corrosion rate of rebars and pitting in an alkaline media with chloride ions (16 g/L NaCl). Electrochemical impedance spectroscopy results for rebars in natural-added solutions showed higher charge transfer resistance and double layer capacitance values, indicative of the formation of a second interface between the rebar and the electrolyte.Research limitations/implicationsThe information obtained was for alkaline solutions only. Further investigation is performed using concrete as the alkaline electrolyte.Practical implicationsCM and SE may be suitable low-cost corrosion inhibitors for steel in concrete.Social implicationsThe use of botanical or algae products for this application will encourage people to consider its production for this particular application. Also, the possible harvest in an environmental friendly way will diminish in the future the use of biohazards and toxic inhibitors.Originality/valueThis investigation is a continuation of a one presented in 2007, which uses only nopal mucilage. This new investigation corroborates what was concluded in the early investigation and incorporates a new natural by product, algae, as a possible corrosion inhibitor product.

Shrinkage and cracking behavior of high performance concretes containing chemical admixtures

Modern concretes often incorporate several chemical admixtures to alter the properties of fresh or hardened concrete. In this work, the influences of three types of chemical admixtures; calcium nitrite inhibitor (CNI), retarder (D − 17) and superplasticizer (W − 19) on free shrinkage and restrained shrinkage cracking of high performance concrete were experimentally investigated. The test results showed that, with the same water to binder ratio (0.4), mixtures containing D − 17 of 0.25 percent or higher ratio of W − 19 (2.76 percent) all exhibited a reduction in free shrinkage and shrinkage cracking width. However, the incorporations of various ratios of CNI into mixtures led to an increase in free shrinkage and shrinkage cracking width as compared to control mixture. In order to study the influence of CNI, the microstructure of concrete mixture containing CNI were investigated by Mercury Intrusion Porosimetry as well as Scanning Electronic Microscopy (SEM) technique.

A short-term test method to determine the chloride threshold of steel–cementitious systems with corrosion inhibiting admixtures

Now-a-days, multiple types of corrosion inhibiting admixtures (CIAs) are being used to enhance the chloride threshold (Clth) of steel–cementitious systems. However, due to the application of external potential to drive chlorides, some existing short-term test methods are not suitable to assess the Clth of S–C systems with CIAs containing anions. This paper presents the development of a Modified Accelerated Chloride Threshold (mACT) test to determine the Clth for S–C systems with CIAs. The test specimens consisted of a mortar cylinder with an embedded steel piece and electrodes forming a 3-electrode corrosion cell. The specimens were exposed to chloride solution and the linear polarization resistance tests were conducted every 3.5 days. The corrosion initiation was detected using statistical analysis of the repeated R p measurements. After corrosion initiation, the chloride content in mortar adjacent to the embedded steel piece was determined and defined as Clth. The time required to complete mACT test for an S–C system with CIAs is about 120 days. The Clth of eight specimens each with S–C system containing (i) without inhibitor, (ii) anodic inhibitor [calcium nitrite] and (iii) bipolar inhibitor [both calcium nitrite and amino alcohol] were determined. Both anodic and bipolar CIAs showed enhanced corrosion resistance. Also, the bipolar inhibitor performed better than anodic inhibitor. It was concluded that the use of CIAs could significantly delay the initiation of chloride-induced corrosion. The mACT test can be used to determine the Clth and estimate the service life during the planning and design stages of a project and help select durable materials.

Effect of steam curing condition on the strength gain of mortar containing calcium nitrite based accelerator admixture

Effect of steam curing condition on the strength gain of mortar containing calcium nitrite based accelerator admixture

Influence of calcium nitrite on the passive films of rebar in simulated concrete pore solution

PurposeThis paper aims to study the influence of the addition of calcium nitrite on the passive films of rebar to reveal what causes calcium nitrite to further prolong the durability service life of the reinforced concrete structures.Design/methodology/approachA comprehensive experimental study of the passive films, such as components, surface morphologies, electric structure and compactness, was carried out in a saturated calcium hydroxide solution which is normally used to simulate concrete pore solution by using X-ray photoelectron spectroscopy, atomic force microscopy, Mott–Schottky and potentiostatic polarization, respectively.FindingsThe results showed that the passivation behavior of rebar has been changed dramatically by the addition of calcium nitrite. That is, the passive film formed in the solution with the addition of 10 g/L Ca(NO2)2 had less donor density (Nd), more positive plat potential, smoother surface and lower content of Fehydrox than that formed in the solution without Ca(NO2)2.Originality/valueThe study focuses on the passive films and provides a more clear cognition of the durability service life extension of the reinforced concrete structures caused by the addition of calcium nitrite.

Experimental Studies on Effects of Sodium Citrate, Calcium Nitrite and Hexamine as Corrosion Inhibitor in Concrete

In the present study the effect of sodium citrate, calcium nitrate, and hexamine on corrosion of steel was analyzed. The effect of inhibitor on normal consistency of cement, initial and final setting time of cement, compressive strength of cement, soundness of cement and compressive strength of concrete were also analyzed. The results of the study also concluded that hexamine and calcium nitrite are more efficient inhibitor. It showed 45% and 25% inhibitor efficiency at the denseness of 0.5% hexamine and 0.5% calcium nitrite by weight of cement respectively. Further, sodium citrate also prevents the hydration of cement, but it is not suitable as an inhibitor. The addition of Inhibitor acts as retarder for the initial and final setting period of the cement and retard the compressive strength at initial days. After 180 days strength is improved significantly.

An Electrochemical Study to Evaluate the Effect of Calcium Nitrite Inhibitor to Mitigate the Corrosion of Reinforcement in Sodium Chloride Contaminated Ca(OH)2Solution

The effect of calcium nitrite (Ca(NO2)2) was assessed by electrochemical means such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic studies in saturated Ca(OH)2solution contaminated with 0.99 and 7.91 g/L NaCl. The preliminary results of OCP showed that the potential is shifted towards positive (noble) side as content of inhibitor increased. The EIS results indicate that Ca(NO2)2works effectively in reduction and initiation of corrosion of steel rebar in NaCl contaminated Ca(OH)2solution. Potentiodynamic studies revealed the pitting tendency of steel rebar exposed in 0.99 g/L NaCl at [Cl−/NO2-] = 1.2 attributed to low conductivity of passive film which causes interference for Cl−ions attack during anodic polarization. The 85.75% efficiency is found in 0.99 g/L at [Cl−/NO2-] = 1.2. The Ca(NO2)2inhibitor transformed the unstable iron oxides/hydroxides into stable and protective oxides/hydroxides due to its strong oxidizing nature. Therefore, this inhibitor is sufficiently and significantly reducing the corrosion of steel rebar at even its low concentration with 0.99 and 7.91 g/L NaCl solution.

Effect of LiNO2 inhibitor on corrosion characteristics of steel rebar in saturated Ca(OH)2 solution containing NaCl: An electrochemical study

It is proved that inhibitors control or reduce the onset time of corrosion of steel rebars. The nitrite based i.e. sodium or calcium nitrite corrosion inhibitor is very popular and significantly reduces the corrosion of steel rebars. In this study, the effect of LiNO2 was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic studies. This inhibitor showed 63.67% efficiency at [Cl−/NO2−]=0.6 in Ca(OH)2 solution contaminated with 0.99g/L NaCl. LiNO2 works as mixed type corrosion inhibitor by stabilizing the iron oxides/hydroxides in their stable form and stifle the corrosion of steel rebar.

Autogenous Shrinkage in High Performance Concrete with Chemical Admixtures

Durability in High Performance Concrete have resulted in the development of admixtures to mitigate several concrete deterioration mechanisms. Due to the low water/binder, HPC enables autogenous shrinkage that could lead to cracks at early ages. Superabsorbent polymers, shrinkage reducing admixtures and corrosion inhibitor based on calcium nitrite were used in HPC with silica fume to evaluate autogenous shrinkage. SAP was added with an amount of intenal curing water determined by the modification proposed by Jensen to the Power’s Model. Results showed that admixtures could improve or aggravate autogenous shrinkage.

Development of a New Concrete Marine Exposure Site on the Arabian Gulf-East Coast of Saudi Arabia

A concrete durability site in the Eastern Province of Saudi Arabia that exposes Saudi concrete to harsh marine conditions on the Arabian Gulf and salty air conditions was constructed. The site contains 32 concrete blocks formed from eight different mixtures made with Cement Type I, Cement Type V, Cement Type I with 6% silica Fumes, 25% fly Ash, 70% Ground-granulated blast-furnace slag (GGBFS), Migrate Corrosion Inhibitors (MCI), Calcium Nitrite based inhibitors (CNI) and Caltite. Each mixture formed 4 blocks; 2 were reinforced with black steel and two were plain concrete. The concrete blocks were 1200 mm high, 460 mm wide and 230 mm thick placed vertically. The concrete blocks were placed at three zones to achieve different exposure conditions which are atmospheric, splash or spray zone and tidal zone. Samples will be taken periodically to measure the rate of chloride ingress in each concrete mixture under the different exposure conditions. Embedded steel reinforcement in specimens in atmospheric zone have not recorded corrosion activities at six months of exposure. The steel bars in three zones will be monitored for corrosion activity through linear polarization test. The measured chloride profiles in the exposure site will be compared to the measured concrete transport properties from the companion laboratory specimens. Standard compressive test and bulk diffusion test were conducted for 150x300 mm and 75x150 standard cylinders, respectively. All of the cylinders’ strength exceeded the designed compressive strength of 28 MPa. Whereas for 35 days standard bulk diffusion test, mix contained 100% cement type I had the least chloride concentration, and mix 5 that had 70% GGBFS and 30% cement type I had the highest surface chloride concentration. Overall chloride profiles for all the mixes were within ranges reported in literature. Further tests of chloride binding capacity and bulk diffusion for different intervals will be undertaken.

Development of Toscana sausage with lemon flavor and sodium reduction

The high sodium intake has been related to the increase of non- transmissible chronic diseases, especially hypertension. As in Brazil sodium consumption is still above the recommended, it is necessary to develop food products with low addition. The aim of this study was produce Tuscan sausage with lemon flavor with reduced content of sodium, evaluate the microbiological and physico-chemical quality and sensory acceptance. Three formulations were developed, one control (T1), one with 20% (T2) and one with 30% (T3) of sodium reduction, based on the partial substitution of sodium chloride by PuraQ Arome NA4. Sodium content in formulation T1 was 976 mg /100g, while the formulation T2 was 835 mg/100g and T3 761 mg/100g. The samples produced met the microbiological criteria for research of Salmonella, count of coagulase-positive Staphylococcus, sulfite-reducing Clostridium and Coliforms at 45 °C. The parameters of humidity, lipid, calcium and residual nitrite were in accordance with the legislation for all formulations, but the protein content was attended only by T3 formulation. Hedonic scale test showed no difference between the samples and all were accepted for the sensory attributes color, aroma, texture, flavor and overall acceptance. Acceptability levels were greater than 78.9%, indicating that consumers appreciate the Toscana sausage with lemon flavor, and it is possible to reduce sodium maintaining the sensory quality of the product.

Effective Chloride Removal in Reinforced Concrete Using Electrochemical Method in the Presence of Calcium Nitrite

Effective Chloride Removal in Reinforced Concrete Using Electrochemical Method in the Presence of Calcium Nitrite

Corrosion resistance of strain-hardening steel-fiber-reinforced cementitious composites

This study investigated the corrosion resistance of strain-hardening steel-fiber-reinforced cementitious composites (SH-SFRCs) in a chloride environment. Two types of steel fibers, hooked and twisted, were added (2% by volume) to a high-strength mortar matrix (90 MPa). All the specimens were exposed to cyclic wetting in a 3.5% chloride solution followed by drying. The corrosion resistance of SH-SFRCs was then evaluated by measuring the direct tensile resistance after the chloride cycles. The strain capacity and toughness of all the SH-SFRCs decreased significantly after 105 chloride cycles, whereas a slight reduction was observed in their post-cracking strength. The corrosion resistance of SH-SFRCs after the chloride cycles was strongly dependent on the width of multiple microcracks when the SH-SFRCs were pre-cracked by tensioning until 0.1% tensile strain. The addition of calcium nitrite (CNI) was successful in improving the corrosion resistance of the pre-cracked SH-SFRCs in the chloride environment.

Effectiveness of inhibitors in increasing chloride threshold value for steel corrosion

This investigation was aimed at evaluating the effectiveness of corrosion inhibitors in increasing the chloride threshold value for steel corrosion. Three types of corrosion inhibitors, calcium nitrite (Ca(NO2)2), zinc oxide (ZnO), and N,N′-dimethylaminoethanol (DMEA), which respectively represented the anodic inhibitor, cathodic inhibitor, and mixed inhibitor, were chosen. The experiment was carried out in a saturated calcium hydroxide (Ca(OH)2) solution to simulate the electrolytic environment of concrete. The inhibitors were initially mixed at different levels, and then chloride ions were gradually added into the solution in several steps. The open-circuit potential (Ecorr) and corrosion current density (Icorr) determined by electrochemical impedance spectra (EIS) were used to identify the initiation of active corrosion, thereby determining the chloride threshold value. It was found that although all the inhibitors were effective in decreasing the corrosion rate of steel reinforcement, they had a marginal effect on increasing the chloride threshold value.

Impact of aggressive exposure conditions on sustainable durability, strength development and chloride diffusivity of high performance concrete

The main objective of this study is to evaluate the long-term performance of various concrete composites in natural marine environment prevailing in the Gulf region. Durability assessment studies of such nature are usually carried out under aggressive environments that constitute seawater, chloride and sulfate laden soils and wind, and groundwater conditions. These studies are very vital for sustainable development of marine and off shore reinforced concrete structures of industrial design such as petroleum installations. First round of testing and evaluation, which is presented in this paper, were performed by standard tests under laboratory conditions. Laboratory results presented in this paper will be corroborated with test outcome of ongoing three years field exposure conditions. The field study will include different parameters of investigation for high performance concrete including corrosion inhibitors, type of reinforcement, natural and industrial pozzolanic additives, water to cement ratio, water type, cover thickness, curing conditions, and concrete coatings. Like the laboratory specimens, samples in the field will be monitored for corrosion induced deterioration signs and for any signs of failureover initial period ofthree years. In this paper, laboratory results pertaining to microsilica (SF), ground granulated blast furnace slag (GGBS), epoxy coated rebars and calcium nitrite corrosion inhibitor are very conclusive. Results affirmed that the supplementary cementing materials such as GGBS and SF significantly impacted and enhanced concrete resistivity to chloride ions penetration and hence decrease the corrosion activities on steel bars protected by such concretes. As for epoxy coated rebars applications under high chloride laden conditions, results showed great concern to integrity of the epoxy coating layer on the bar and its stability. On the other hand corrosion inhibiting admixtures such as calcium nitrite proved to be more effective when used in combination with the pozzolanic additives such as GGBS and microsilica.

Assessment of high performance concrete containing fly ash and calcium nitrite based corrosion inhibitor as a mean to prevent the corrosion of reinforcing steel

This research analyses the effectiveness of the water-to-cement ratio (w/c), fly ash and a calcium nitrite based corrosion inhibitor to prevent the corrosion of reinforcing steel embedded in high performance concrete. The interactive effect between the inhibitor and fly ash was evaluated because the occurrence of a negative effect when both ingredients are added together in a concrete mixture has been reported. All the concrete mixtures studied in this investigation had 8.2% of silica fume. Twenty seven prismatic concrete specimens were fabricated with dimensions of 55 × 230 × 300 mm each containing two steel rods embedded for the purpose of corrosion monitoring. The specimens were exposed to a simulated marine environment with two daily cycles of wetting and drying for one year. To evaluate the deterioration of the specimens corrosion potentials and linear polarization resistance tests were carried out. The results indicate that the use of a low w/c, the addition of fly ash and the addition of the corrosion inhibitor contributed to the reduction of the corrosion of steel in the concrete specimens. The results further suggest that the combination of fly ash and corrosion inhibitor does not promote the deterioration of the concrete matrix.

Comparison of the effect of organic and inorganic corrosion inhibitors on the rheology of self-compacting concrete

This paper reports on the effects of using an organic and an inorganic corrosion inhibitor in self-compacting concrete (SCC). The respective organic and inorganic inhibitors used were of a migrating corrosion inhibitor (MCI) and a calcium nitrite inhibitor; the former inhibitor was used in a fly ash and a silica fume SCC and the inorganic inhibitor was used only in a fly ash SCC. It was shown that the use of the inhibitors in the traditional SCC powder pastes, at temperatures in the range of 20–40°C, extended the initial setting times of the cementitious mixtures. From this research, the relationship between the initial and final setting times of the traditional and inhibited-SCCs was developed for the first time. Indications are that the inhibitors reduced the viscosity and the segregation resistance of the traditional SCCs but there were differences in the effects of each inhibitor on the deformability and the workability retention of each type of SCCs. The greatest effect was from the use of the organic MCI in the fly ash SCC where the setting times and the deformability were appreciably impacted.

Durability of Concrete Incorporating Corrosion Inhibitors Exposed to a Salt Solution of CL - +SO 4 -2

Laboratory investigations were performed in order to assess the effectiveness of three types of inhibitors, calcium nitrite, ethanolamine and Sika ferro gard 901(commercial inhibitor) with 1%, 2% and 3% concentration by weight of cement for each inhibitor to retarding corrosion of steel embedded in concrete. Concrete specimens were used to assess the effects of corrosion inhibitors on the compressive and tensile strength of concrete and corrosion of reinforcement.Some of the specimens were subjected to wetting and drying cycles and reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density. Other concrete specimens were immersed in the salt (Cl-+So3-2) solution and reinforcement corrosion was accelerated by impressing an anodic potential of +12 V from a DC power supply and measuring the time-to-cracking of the concrete specimens.The results indicated that the concrete specimens incorporated corrosion inhibitors of calcium nitrite and Sika ferro gard 901 did not adversely affect the compressive and tensile strength of concrete. Furthermore, the time-to-cracking in specimens contains those two inhibitors (calcium nitrite and Sika ferro gard 901) were higher. Two percent of calcium nitrite followed by three percent of Sika ferro gard 901 were efficient in delaying the initiation of reinforcement corrosion and reducing the rate of reinforcement corrosion current density in the concrete specimens, while all the percentages of ethanolamine corrosion inhibitor were ineffective to delay corrosion of the rebar under the conditions of the study and it's adversely affect the strength.

Durability of Concrete Incorporating Corrosion Inhibitors Exposed to a Salt Solution of CL - +SO 4 -2

Laboratory investigations were performed in order to assess the effectiveness of three types of inhibitors, calcium nitrite, ethanolamine and Sika ferro gard 901(commercial inhibitor) with 1%, 2% and 3%concentration by weight of cement for each inhibitor to retarding corrosion of steel embedded in concrete. Concrete specimens were used to assess the effects of corrosion inhibitors on the compressive and tensile strength of concrete and corrosion of reinforcement.Some of the specimens were subjected to wetting and drying cycles and reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density. Other concrete specimens were immersed in the salt (Cl-+So3-2) solution and reinforcement corrosion was accelerated by impressing an anodic potential of +12 V from a DC power supply and measuring the time-to-cracking of the concrete specimens.The results indicated that the concrete specimens incorporated corrosion inhibitors of calcium nitrite and Sika ferro gard 901 did not adversely affect the compressive and tensile strength of concrete. Furthermore, the time-to-cracking in specimens contains those two inhibitors (calcium nitrite and Sika ferro gard 901) were higher. Two percent of calcium nitrite followed by three percent of Sika ferro gard 901 were efficient in delaying the initiation of reinforcement corrosion and reducing the rate of reinforcement corrosion current density in the concrete specimens, while all the percentages of ethanolamine corrosion inhibitor were ineffective to delay corrosion of the rebar under the conditions of the study and it's adversely affect the strength.