CHLORIDE ION CORROSION

• The aggression that chloride ion (Cl-) represents for the steel is known, and also the risks that the oxidation of the reinforced steel carries.

• The strongly basic pH of concrete causes that a passive layer is formed around the reinforcement. And this protect the concrete against the oxidation.

• But this layer could be broken by the chlorides.• For this reason, is very important the concrete

cover that we use according to the exposure classes.

• We must control the ion chloride amount both the project and the service life.

CHLORIDE ION CORROSION The chloride corrosion process.

CHLORIDE CORROSION ANALYSIS

• It’s important make a good report concerning the repair of concrete corroded by the effect of chloride ions.

• To do this we first try to find out what the source of ions.• Then do an inspection of the penetration of chlorides in the

concrete, in order to know the level of concentration which has. In this way we can study the following concepts are important:

• Time chloride ions take to reach the steel.• The speed of propagation of chloride ions through the

concrete. It is important to know the shelf life that our structure has.

• According to the standards the chloride concentration mustn’t be bigger than 2.6g / 100g of cement.

CHLORIDE CORROSION ANALYSIS

Lifetime calculation of a reinforcement concrete which has suffered corrosion by chloride ion. If we can establish the penetration outline of chloride ion, and we suppose that the exposure condition won’t be very different from actual, is possible to calculate the time when the process of corrosion starts. For that we use the next graphic.

We can establish the next equation system: 𝑋1ሺ𝑡ሻ= 𝐾.ξ𝑡1 ; 𝑋2ሺ𝑡ሻ= 𝐾.ξ𝑡2

For example: if we did a control study in year 10 (t1=10), and we found the critical threshold at a depth of 18mm (X1(10years) = 18mm) and the structure has a concrete cover of 25mm (X2 = 25mm). We can obtain the time when the critical threshold will be at a depth similar that a cover.

𝑡2 = (𝑋2 𝑋1ൗ� )2 .𝑡1 = (25 18ൗ� )2 .10 = 19 𝑦𝑒𝑎𝑟𝑠

CHLORIDE CORROSION ANALYSIS

• STEP 1 Possible source of chloride: Salts for the road security

• STEP 2 Determination of present of chloride ion and measurement:

Obtain concrete samples (20mg) with a drill. Samples of different depths. Study the chloride ions amount in the laboratory.

• STEP 3 Study the results and think about the best solution

CHLORIDE CORROSION ANALYSIS

And by this way we obtain the values of chloride ions measurements.

Now, we can do the outlines of chloride measurements for each crack tested.

Study of possible corroded steel in the crack where we found the highest values.

We can use the method of overage cell voltage measurement.

REPAIR METHODS

1. For the cracks with less chloride ions percent that maximum value:

- Injecting cracks according to principle 4.5. of EN-1504

2. For the cracks with higher chloride ions percent that maximum value:

- Remplacing contaminated concrete according to principle 7.2. of EN-1504

For both, increase the coating according to principle 7.1. of EN-1504.

The products and methods selected will be explained next.

INJECTING CRACKS

For the repair methods and products, we select a guide of a Spanish company - SIKA

SIKA guide for injecting cracks in principle 4.5

INJECTING CRACKS

Requirements and concrete preparation:

The concrete slab must have at least 28 days.

The concrete surface must have a clean surface around all the crack. And must be health, clean and free of loose material.

If it was necessary clean the interior of the crack with compressed air or water.

INJECTING CRACKS

First, apply the surface sealant.

Surface sealant: We use the product of SIKA – SIKADUR 31 HMG

Mix the products. Put the nozzles along the cracks. Seal the crack with SIKADUR 31 HMG. Leave it hardening during 24h. Verify that it is a open system injecting compressed air.

INJECTING CRACKS

Next, inject the product.

Sealing of crack : We use the product of SIKA – SIKADUR 52

Mix the product. Inject at constant preassure. Start injecting at the lowest point until the fluid brim in the next nuzzle. To finish, When the resin is hard, remove the surface

sealant and finish to seal the crack until the same altitude as the concrete surface.

INJECTING CRACKS

COATING INCREASE

For the process of coating increase, we select a guide of a Spanish company - SIKA

SIKA guide for injecting cracks in principle 7.1.

COATING INCREASE

Support preparation: It must be clean and without friable material. If it

was necessary, it will be prepare with mechanic methods.

Wetting the surface until saturation.

Product mix: Mix it with water according to the consistency

that you want to achieve. Mix during 2-3min.

COATING INCREASE

Application: Apply the product manually or with mechanic

projection. Its important take into account the working times,

and do the job and expansion boards.

Concrete curing: It must be protected of sun, wind and freeze

during its hardening. Avoid the formation of cracks with a good cured,

with water contributions.

COATING INCREASE

WORK TIME TABLE

24-48h

24h

24h

1. Remove concrete2. Clean Steel bars3. Coating steel bars4. Put new concrete5. Prepare cracks6. Clean surface7. Aply the surface sealant8. Injecting cracks9. Clean surface10. Wet surface11. Aply the coating product12. Cured13. Paint the lines

48h

48h

TOTAL TIME150h

48h 96h

WORK TIMES

WAITING TIMES