Mitigation of chloride induced corrosion in reinforced concrete structures and its modeling

The paper is primarily focused on the description of transport of harmful species in concrete such as chlorides on one side and transport of corrosion inhibitors and nanoparticles used to diminish corrosion of steel reinforcement or seal the microstructure of concrete on the other side. The studied processes are helpful in reverting the chloride induced corrosion of the reinforcement in reinforced concrete structures. The transport mechanisms are summarized with the emphasis on their mathematical description and numerical solution. The paper shows modeling results of the processes including a comparison with experimental data on several typical examples. The efficiency of the methods is shown supported by experimental and numerical results. A good correlation of the models with experiments is achieved.

Anchorage length of patented wire cables in prestressed bridge girders

This paper briefly describes the methodology, performance and the obtained results of unique experiments performed on original I-73 precast bridge girders. The main objective of the experiments was to determine the actual anchorage length of corroded-through fully grouted prestressing reinforcement (prestressing wires), which is important for determination of the residual load-bearing capacity of prestressed structures. Observation probes leading all the way to the prestressing wires were drilled on selected sections of the girders along the length of the prestressing reinforcement. Optical image acquisition devices were then installed at these probes. Subsequently, controlled breakage of the patented wires (corrosion failure simulation) and observation of the changes that occurred in the prestressing wires after relief of stress were carried out. Evaluation of the experiments was then performed by analyzing the images obtained before and after the prestressing reinforcement failure.

Monitoring of the atmospheric corrosivity by resistive sensors

Atmospheric corrosivity is classified according to EN ISO 9223 Corrosion of metals and alloys – Corrosivity of atmospheres – Classification, determination and estimation. For the determination and estimation of the corrosivity category, standardized approaches are used. Monitoring of corrosivity with the application of various sensors is an actual trend. The paper gives results of verification of some types of sensors for this monitoring with standardized flat samples at atmospheric test sites in the Czech Republic. The trend of decreasing atmospheric corrosivity is evident in the last decade. Monitoring of the corrosion rate and mapping of the corrosivity become a very important step in preventing failures in long-term atmospheric exposition. This type of monitoring was used on bridge construction to estimate the seasonal effect of de-icing salts deposition, too.

Influence of conversion coatings on the resistance of adhesive joints to undercorrosion

The paper deals with the application of conversion coatings for the preparation of surfaces before adhesive bonding of galvanized and non-galvanized steels. The morphology of the coatings was monitored by electron microscopy. The corrosion characteristics of the conversion coatings were determined by linear polarization. Steels treated with conversion coatings were used to form bonded joints using three structural adhesives. The resistance of the joints to undercorrosion was determined following the change in the load-bearing capacity of the joints after exposure in the climatic chamber.

Characterization of bilayer (FeB/Fe2B) on AISI H13 work tool steel

In this work, the borided layers were produced on AISI H13 steel via solid boriding with a powders mixture containing 90 wt.% B4C and 10 wt.% NaBF4 for treatment times of 2-6 h at 900, 950 and 1000 °C. The microscopic observations revealed a less pronounced toothed interface between the borided layer and the transition zone. The XRD studies indicated the presence of a dual phase boride layer (FeB/Fe2B) besides the chromium and vanadium borides as precipitates inside it. The boronizing kinetics of AISI H13 steel was investigated by using the classical parabolic growth law. The obtained value of boron activation energy in the entire boride layer (FeB + + Fe2B) was found to be 236.34 kJ mol-1. Furthermore, this value of energy has been compared to the literature data. Finally, the nanohardness and reduced modulus of elasticity were measured for FeB, Fe2B and transition zone.

Corrosion behaviour of the NiTiX (X = Si, Mg, Al) alloy prepared by self-propagating high-temperature synthesis

The NiTi alloys are used in the biomaterial field, because of their shape memory, superelasticity, and good corrosion resistance. The influence of alloying elements on the corrosion behaviour of NiTi was studied in this research. Samples were made by the self-propagating high-temperature synthesis method, milled, and then sintered by the spark plasma sintering method. Si, Mg, and Al were used as alloying elements always in 5 wt.%. Studied materials were compared with reference cast NiTi. Polarization resistance was measured after 1 and 12 hours of stabilization in phosphate-buffered saline. It was found out that alloying elements do not have a clear effect on polarization resistance. Si increased Rp and on the other hand, Al decreased it. Measurement of cyclic potentiodynamic polarization in PBS was conducted, too. All studied samples showed signs of localized corrosion. Corrosion was probably initiated in pores, which are presented on the surface due to used manufacturing technology.

Simulation of the incubation time for the formation of (FeB/Fe2B) bilayer on pure iron

In this work, a mathematical model was used in order to study the growth kinetics of (Fe2B/FeB) bilayer during bori-ding process basing on the second Fick’s law and mass balance equation. The run of the numerical simulation allowed calculating the incubation time (τ) of each boronized layer (Fe2B or FeB), and estimating the effect of this parameter on the growth of the boronized layer. The boride incubation time for forming the FeB or Fe2B layer on the pure iron substrate was incorporated into the present mathematical model. To simulate the value of the growth rate constant and the incubation time for the bilayer configuration, the experimental data available in the literature concerning the boronizing of pure iron were considered. Based on the experimental and simulation results, it was shown that the incubation time decreases with increasing temperature in the FeB and Fe2B phases. It was concluded from this study that the thickness of each boride layer depended on its growth rate constant and on another parameter kτ which was the rate constant of incubation time.The obtained results confirmed the validity of the present mathematical model and gave a good estimate of the incubation time during the formation of each boride layer as well as formulated the variation of this parameter with a mathematical equation. Furthermore, the comparison of experimental data with the simulated results of boronized layer thickness allowed to validate the present model.

Corrosion in underground infrastructures

There is a significant loss due to corrosion of buried infrastructure. Many pipes have failed due to mistreatment happening within them all around the world. Different soil aeration leads to macro corrosion cells that cause critical levels within the path corrosion leading to a loss of structural integrity of the buried pipes underground. This review paper seeks to address and presents a predetermined model developed by using software COMSOL Multiphysics to identify and characterize the areas experiencing a high rate of corrosion beneath the surface due to differential aeration. The pipe surfaces experience electrochemical reactions and reactant transport mechanisms in the soil and the pipes. Porosity and degree of saturation make the closed-form equations used to create the mass transport properties and electrical properties that constitute three-phase medium using standard soil parameters. The current model enables the study of soil property variations and conditions from the external environment pipeline corrosion. The model results conclude and agree well with the literature and case studies done at pipeline failure sites. The model used in this review will then enable water utilities to develop forecasting tools that may be useful for assessment.

Simulation of boronizing kinetics of ASTM A36 steel with the alternative kinetic model and the integral method

In this study, two different mathematical models have been proposed for estimating the diffusivities of boron in the Fe2B layer on ASTM A36 steel in the range of 1173 to 1273 K with exposure times of 2 to 8 h. The boride incubation period required for the formation of such a layer was constant regardless of the boriding conditions. In both approaches, the boron diffusivity in the iron phase was considered in an unsaturated matrix. The first approach was derived from the mass balance equation at the (Fe2B/substrate) interface while the second approach employed the integral diffusion model. The calculated values of boron activation energies for ASTM A36 steel were found to be very comparable for the two approaches (161.65 and 160.96 and kJ mol-1). Afterwards, these values of activation energy were confronted with the results from the literature. Experimental validation of these two approaches has been done by comparing the experimental value of Fe2B layer thickness measured at 1123 K for 2.5 h with the simulated values. Finally, the predicted values of Fe2B layer thickness were in line with the experimental measurement.

Terephthalohydrazide and isophthalo- hydrazide as new corrosion inhibitors for mild steel in hydrochloric acid: Experimental and theoretical approaches

Most organic corrosion inhibitors have polar groups through which the molecule can be adsorbed strongly or specifically on the metal surface. In this investigation, terephthalo- hydrazide and isophthalohydrazide were synthesized as corrosion inhibitors, and their corrosion-inhibiting properties on mild steel were evaluated in a corrosive environment by weight loss measurements. The results of corrosion experiments revealed that terephthalohydrazide and isophthalohydrazide as inhibitors controlled or reduced corrosion through adsorption mechanism and showed inhibitive efficiencies of 96.4 % and 97.2 %, respectively, at the optimum concentration of 0.5 mM. The surface morphology of the metal was evaluated by scanning electron microscopy. The terephthalohydrazide or isophthalohydrazide molecules were adsorbed on the mild steel surface, and the process of adsorption follows chemical adsorption. Quantum chemical calculations of the tested corrosion inhibitors were consistent with the experimental observations.