Quality references for concrete

Luckily for renovation works done with MCI’s various quality measurements exist.
Below is an overview of some of the minimum/maximum requirements necessary for the renovated concrete structure to have.
For the cleaned and replaced concrete it is required that the tensile strength of concrete and the adhesive forces with the concrete and adhesive forces of the concrete to the steel are at least 1.5 N/mm2. The higher the tensile strength however, obviously the stronger the material.
Depending on the thickness of the repair mortar layer the surface roughness can be ca. 5 mm. for layers with a thickness of 10-50 mm and ca. 1 mm. for layers with a thickness of 2-10 mm.
The pH value of the concrete has to be higher than 9.
The Chloride concentration has is no limitation, however some authors do state that the chloride concentration cannot exceed 1%.
Openness of the concrete surface structure have to contain >50% visible aggregate grains, degree of coverage of the grains with the cement matrix can be ca 2/3 grain volume.
The cleanness grade of the cleaned reinforcing steel has to be minimum SA 2 resp. St3 (according to international standards ISO 8501-1, SIS 05 59 00 1967, DIN 55 928-Teil 4, ASTM D 2200-67, SSPC VIS) depending on the cleaning method: sandblasting, shot blasting, hydro dynamically, manually. Usually SA2 is achieved mechanically upon which manual finishing to a St3 finish delivers the final product. (21)

For the level of corrosion protection other factors are reviewed.
The fluids impermeability has to reach at least a gases permeability coefficient of 1x10-16m2 (EN 993-4).
Chlorides diffusion has to be at least smaller than 1x10-12 m2/s (GF).
The capillary water absorption coefficient has to be at least 10-1 kg/m2h1/2 (HRN.U.M8.300).
The anticorrosive reinforcing steel protection is expressed in corrosion current intensity/density and has to be according to ASTM STP 1065 smaller than 0,1 μA/cm2. (21)

4.3 Practical example: Renovation of reinforced concrete in a shipping wharf:

Figure 8: Wharf in Ploce, Croatia where the renovation works took place. (22)

First, as described in the above paragraphs, water-jetting the concrete surface removes the deteriorated concrete and lays bare the corroded steel rods. Simultaneously as the corroded rods are laid bare they also get cleaned as the rust is blasted off by the waterjet.
The water pressure used is > 2000 bar.
The goal is to clear an area in the concrete to such a degree that it is ready for the application of repairing mortar and that the concrete’s tensile strength is restored to bigger than 1.5 N/mm2. (21)

Because it was a wharf that was being renovated, accessibility to the affected area was challenging due to the fact it being so close to the water's’ edge.
Floating platforms were used to hold the high pressure pumps responsible for applying the repair mortar and the final protective/decorative coating.
Logistical challenges such as transportation of material and communication with the crew performing the work happened through openings in the reinforced concrete slab.(21)

Corrosion protection of the reinforcing steel was achieved through a polymer cement coating, containing MCI’s. Simple application by brush of 1-2 coatings meant a consumption of about 0,2 kg/m2 of MCI solution for the 12 mm. diameter reinforcing steel.
Secondly the structure was impregnated with a hydrophobic solution to prevent moisture and salts that are soluble in water from entering the concrete.
This solution was a (1:4) solution with water of the MCI’s in powder form. It was applied much like the polymer cement coating; just using a brush and layering on a couple of layers proved to be sufficient.
Total usage of solution: 25 kg/m2. (21)

Figure 9: Hydrophobic impregnation of the concrete surface (22)

After the removal, cleanup and coating of the reinforced steel reprofiling has to be done to encast the steel back in a concrete matrix. (21)

Figure 10: Reprofiled concrete surface (22)

This was performed using 3 layers of repair mortar containing MCI’s.
One of the dangers of applying repair mortar is that it would cure or dry to fast. Especially at the wharf, where air and moisture can freely reach the newly renovated area measures had to be taken to protect the work that had been done.
To prevent “too fast”-curing of the repair mortar a layer of soy oil containing MCI’s was applied using a brush in just a single layer, using about 5 l/m2. (21)

Finally protection from moisture and environmental reactants was achieved by applying both a hydrophobic impregnation solution and a protective/decorative coating, simply acrylic paint containing MCI’s, to the surface of the concrete. (21)

Figure 11: Finished product. (22)

Final quality testing performed by IGH-PC Split showed that the renovation works performed had a positive effect on the reinforced concrete and it was behaving according to the standardized norms and requirements discussed in the paragraphs above. (21)

Conclusion

A huge amount of structures contain steel parts which makes deterioration topic very relevant. In our report we tried to cover all aspects related to damages in structures caused by corrosion. It was found that there are many triggers of corrosion and it is very hard to avoid this process so it should be well controlled. Many factors should be taken into consideration because a small defect or shortcoming in design could lead to significant economical impact. Risk analysis on design stage, correct design and appropriate protection will help to reach the maximum lifetime of construction, and maintenance made in time will help to prolong constructions life.

References

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17 Dr. Akil Ahmed, Prof. Mehtab Alam, and Dr. Asif Husain. Investigation of Structural Defects and Renovation of a RC Residential Building. International Journal of Chemical, Environmental & Biological Sciences (IJCEBS) Volume 1, Issue 2 (2013) ISSN 2320 –4087

18 Repairing, renovating and strengthening concrete [online] http://www.kleinandhoffman.com/images/uploads/RepairRenovationStrengtheningConcrete%20Structures%20Paul.pdf
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19 Repair of corrosion affected areas in reinforced concrete [online] http://civil-resources.blogspot.fi/2010/06/repair-of-corrosion-affected-reinforced.html
Accessed 19.10.2015 at 8:42

20 "Durability of Galvanized Steel Framing in Residential Buildings", International Zinc Association [online] http://www.steelframing.org/PDF/durability/durability2011-singlepgs-final.pdf

21 Jure Franciskovic, Boris Miksic, Ivan Rogan, Mijo Tomicic, Protection and repair of reinforced concrete structures by means of MCI-inhibitors and corrosion protective materials. May 21, 2006

22 Jure Franciskovic, Boris Miksic, Ivan Rogan, Mijo Tomicic, Protection and repair of reinforced concrete structures by means of MCI-inhibitors and corrosion protective materials. May 21, 2006 [figure]

23 Epoxy coated rebar [figure] http://solutions.3m.com/wps/portal/3M/en_US/CPPD/Home/

24 Application of Corrosion inhibitors [figure] http://www.epms-supplies.co.uk/c-Corrosion-Inhibitors-(26).aspx

Date: 2015-12-18; view: 1087