What is chloride ion diffusion in concrete?

What is chloride ion diffusion in concrete?

In saturated state, chloride ions enter concrete by ionic diffusion due to concentration gradient between the exposed surface and the pore solution inside concrete. This process is often described by Fick’s second law of diffusion [8.

What is concrete diffusion coefficient?

Diffusion coefficient D, is considered the rate determining parameter of chloride ingress in concrete. In the paper D is defined following Crank and emphasis is made in that different D values are obtained from different testing conditions and from the units in which chloride concentration is expressed.

What is chloride intrusion?

In the presence of oxygen and water, chloride attack corrodes the steel reducing the strength of the structure drastically. WHAT IS CHLORIDE ATTACK. Chloride ion (CL-) is formed when the element chlorine gains an electron or when a compound such as hydrogen chloride is dissolved in water.

What is chloride induced corrosion?

Chloride ions do not directly attack the integrity of concrete causing degradation, but they pass through its pores until reaching the steel surface. Chloride ions then react with the oxide film causing a local breakdown – a pit, hence the name pitting corrosion – within it.

How does chloride affect steel?

Wet and humid environments containing chloride ions can cause pitting corrosion and crevice corrosion of austenitic stainless steel components. Components under an applied or residual stress can deteriorate further by stress corrosion cracking in these conditions.

What is chloride permeability?

2 Chloride diffusion coefficient. Chloride penetration refers to the depth to which chloride ions from the environment penetrate into the concrete. This can lead to corrosion in RCC structures, and thus study of chloride permeability is an important aspect that affects the durability of the concrete.

Why do chlorides increase corrosion?

The chloride ions attack the passive layer and catalyze the corrosion process. Chloride ions breakdown the passive layer and cause pitting of the steel reinforcement. Chloride is adsorbed in the protective oxide layer. The oxidized iron reacts to form soluble intermediate soluble iron complex at the anode.

How does excess chloride corrode concrete?

The chloride builds up with time, possibly leading to a condition where the concrete is no longer able to protect the reinforcement from corrosion. Chlorides can penetrate through the cracks and capillary pores.

What causes chloride shift?

The chloride shift or “Hamburger effect” describes the movement of chloride into RBCs which occurs when the buffer effects of deoxygenated haemoglobin increase the intracellular bicarbonate concentration, and the bicarbonate is exported from the RBC in exchange for chloride.

What is chloride migration test?

Chloride migration tests were developed to obtain the chloride diffusion coefficient in a much shorter test period compared to natural diffusion tests, by accelerating the chloride ingress rate with the applied electrical field.

What is rapid chloride migration test?

One of the most used methods in assessing the chloride penetration resistance of concrete is the rapid chloride migration test (RCMT). This is an expeditious and simple method but may not be representative of the chloride transport behaviour of concrete in real environment.

How do chlorides affect corrosion?

The chloride ions present in the water promote local corrosion such as crevice corrosion and pitting, and the higher the chloride content, the more corrosive the water. The chloride concentration of the water that passes through sewage treatment plants is usually lower than the chloride concentration of seawater.

How do chlorides affect concrete?

Chlorides in concrete result in the corrosion of reinforcing steel. Steel is naturally protected (passivated) from corrosion in the high pH (alkaline) environment when embedded in concrete.

Why chloride is not good for concrete?

A major contributing factor is the presence of chloride ions in the concrete, which causes the reinforcing steel inside to corrode.

What is chloride shift and why is it important?

The chloride shift is an exchange of ions that takes place in our red blood cells in order to ensure that no build up of electric change takes place during gas exchange. Within our tissues, the cells produce a bunch of carbon dioxide molecules that are ultimately expelled by the cell and travel to the blood plasma.

How does chloride shift maintain pH?

Significance of Chloride Shift The CO2 carrying capacity of venous blood increases because of the chloride shift. The unloading capacity of oxygen increases as there is a modulation in the haemoglobin tetramer. The change in pH is reduced that is caused due to metabolic byproducts.

What is chloride ion permeability?

What are the main ways in which chloride ions in the external environment penetrate concrete?

Capillary absorption, hydrostatic pressure, and diffusion are the means by which chloride ions can penetrate concrete.

What is chloride permeability test?

​ASTM C1202: Rapid Chloride Permeability (Coulombs Passed) The ASTM C1202 rapid chloride permeability test, which is widely used, quickly determines how resistant your concrete is to chloride ingress.

How does chloride affect hardened concrete?

This layer, which is self-generated soon after the hydration of cement has started, consists of 7-Fe₂O3 adhering tightly to the steel. As long as that oxide film is present, the steel remains intact. However, chloride ions destroy the film and, in the presence of water and oxygen, corrosion occurs.

What are the two types of chloride diffusion?

In this paper, a new chloride diffusion model is developed, in which the bound chloride is divided into two types. One is reversible, which is related to the physical binding. The other is irreversible, which is related to the chemical binding.

What is the diffusion coefficient of free chloride?

It was reported that, if the Fick’s second law alone is used to model the chloride transport, the diffusion coefficient was found to be 0.26 × 10 −11 m 2 /s for the free chloride and 0.729 × 10 −11 m 2 /s for the total chloride [ 41 ]. Fig. 6.

Is there a chloride diffusion model in concrete exposed to marine environment?

In this paper, we have presented a new chloride diffusion model in concrete exposed to marine environment, which considers the effects of the physically and chemically bound chlorides.

How does concrete transport chlorides?

Concrete is a porous material. The transport of chlorides in concrete involves not only the diffusion of chloride ions in pore solution but also the physical and chemical interactions between chloride ions and pore surfaces within cement matrix [ 4, 5 ]. The latter provides a “binding” function to mobile chloride ions.