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Environmental Effects on Concrete

Why does reinforced concrete infrastructure weaken over time? Is there a solution or coating that can block any deleterious factors and prevent further degradation?

“Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonation of hardened cement paste or chloride attack under wet conditions.” [1]  

The Wikipedia quote above summarizes the factors that often contribute to the structural damage of reinforced concrete.

  1. Firstly, it needs wet condition inside the concrete along with CO2 and other acidic agents to change the chemistry of the concrete and/or corroding the steel rebars. That is, buildings in tropic zone and sea facing area are more susceptible to larger amount of water penetrating inside the concrete and the concrete-rebar interfaces.
  2. Sea facing and chemically more active areas where salts dissolving in moisture-water penetrating into the concrete pores and interstitials that stored the water pockets will accelerates the chemical reactions such as carbonation and alkali reactions.
  3. Secondly, if there are more sources of corrosive gases such as H2S, SO2, CO2, NO, CL2 in the airs that can penetrate into the concrete that reacts with the water within the concrete and concrete-rebar interfaces, corrosions of steel rebars forming spaces between rebars and concrete will also weaken the reinforced concrete. Parking garage and/or environments where such gases are more abundant is more vulnerable. 
  4. Thirdly, for those buildings and infrastructure that situated in a temperate and colder zone where daily temperature fluctuate above and below freezing temperature, the expansive force from the trapped water going through freezing will also cause the microfracture and thus weakening the reinforced concrete.

Depending on the geo-zone and the environment that the building is exposed to, different degrees of carbonations, alkali and other chemical reactions, and corrosion of reinforcing rebars happened over the years and weakened internally with some or not so much exterior observable damages. Even with obvious signs of structural damages, to assess the degree of damage for immediate remedial actions are often not so obvious.

There are different COMBINATIONS of deleterious elements for the three major weather zones.

  1. The TROPIC zones buildings and infrastructures are exposed to:
    1. STRONGEST UV EXPOSURE that break downs most organic protective coatings
    2. HIGHEST AMOUNT OF MOISTURE AND RAINS that corrodes exposed metal facades and penetrate into concrete and coatings to reach the rebar and support metals
    3. No freezing of water and relatively minor daily and seasonable temperature swings
    4. Corrosive gases factor depends on the industrial and commercial environments. More vehicle traffics produces more exhaust corrosive gases. More industries typically produce more exhaust corrosive gases.
  2. The TEMPERATE zones buildings and infrastructures are exposed to:
  3. The COLD zones required different considerations and are typically less populated with people and infrastructure. They can be considered similar to the TEMPERATE zone for lesser daily changes of temperature and less UV exposure.

Life-Time Protection of Reinforced Concrete Building Infrastructure Required Shielding Ingress Against: Moisture-Water, Moisture Laden with Acidic Gases, Corrosive Gases, and UV Stability and Blocking. 

The above table summarizes the critical properties of FLUOROSEAL® Concrete Protection Coating CRC-V-7150 and CRC-H-7280 in comparison to silicone and acrylic that are sometimes used.

  • Direct coating over exposed concrete surfaces will protect the concrete and rebar from moisture, moisture laden with ions and corrosive gases.
  • Applying the FLUOROSEAL® CRC-V-7130 and CRC-H-7280 to the existing concrete structures that may be in existence for years, will “arrest” further damaging effects from the weathering.
  • The most important part of the protection is to apply onto the columnar supports and parking garages that are exposed to CO2 and Sulfide exhaust are more prominent corrosive elements.
  • Those building and infrastructure near the seas with high salt-spray carrying the ionics will also prevent further damages.

Those in infrastructure and building in temperate zones that are subjected to possible water trapped inside the concrete from freezing expansion stresses is also important.

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[1] https://en.wikipedia.org/wiki/Concrete_degradation