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Building Defects (Concrete
Testing (Chlorides (Sources:
Accelerators -…
Building Defects
Carbonation
Coverage on Reinforcement :arrow_down:
embedded steel is protected from corrosion by virtue of the highly alkaline environment
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Repair Prescriptive specification
- Clean and prepare. Expose corroded reinforcement
- Reinforcement Corrosion Protection Coating Monotop 610
- Hand apply the Repair mortar Monotop 615 ~(wet on wet (610))
- Corrosion management - Margels (delays the start of corrosion and reduces corrosion rates,)
- Smoothing coat Sikaguard Elastofill
- Protective coat primer Sikaguard aqua primer
- Protective coating - Elastic coat
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Test Methods
Sulphate Testing involves an acid extraction and precipitation of the sulphate as barium sulphate with barium chloride solution. The resulting barium sulphate is filtered and weighed to determine sulphate gravimetrically.
H20 soluble salts enter concrete and react with it to form Ettringite, which has a greater volume, resulting in the expansion and disintegration of mortars.
Assuming that concrete contains 15% by mass of cement, sulphate content can be expressed as a percentage of the mass of cement with anything over 5% likely to be harmful. In severe cases, 10-15% has been identified.
Sulphate attack is a chemical reaction between solutions of soluble salts (such as potassium, sodium or magnesium) and a component of lime or ordinary Portland cement.
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Crazing
minor surface shrinkage in rapid drying conditions. (ie Low humidity and hot temperatures, or alternate wetting and drying.)
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Chlorides
Sources:
- Accelerators - mixing process to reduce setting time (50s-60s prevalent, used till '78) - Calcium Chloride
- Marine aggregates
- External contamination - de-icing salts, marine environments
Testing:
- Core samples
- Dust drillings tests
- silver nitrate + potassium chromate = Brown :red_cross: or yellow/white (further testing required)
- Half Cell Potential Test measures extent of corrosion
Sufficient levels of chloride ion can disrupt the passive layer and reduce corrosion protection. The risk of chlorides breaking down the passive layer increases as the chloride concentration increases or as the alkalinity of the concrete diminishes.
Treating a building for carbonation when chloride is present will increase the rate at which deterioration occurs.
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Repair Prescriptive specification
- Clean and prepare. Expose corroded reinforcement
- Reinforcement Corrosion Protection Coating SikaTop Armatec-110 EpoCem
- install Galvashield galvanic anodes
- Hand apply the Repair mortar Armorcrete, Monotop 615 ~(wet on wet (610))
- Corrosion management - Galvashield CC's & FerroGard 903+
- Pore filler/Sealer Sika Monotop 620
- Protective coat primer Sikaguard 552Waqua primer
- Protective coating - Elastic coat
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