Concrete Degradation Causes Quiz

Concrete Degradation

• Concrete degrades due to various factors, including chemical, physical, and mechanical causes, as well as poor concrete quality.

Causes of Degradation

• Chemical Causes:

  • Carbonation: A chemical reaction between lime (created during cement hydration) and carbon dioxide in the air, forming calcium carbonate. This reduces the pH of concrete.
  • Chlorine ion (CaCl₂) attack: Chlorine salts, used as de-icing agents, cause corrosion of reinforcing steel, particularly in cold climates.
  • Sulphate salt attack: Sulphate salts in the ground and water react with cement paste, leading to expansion and disintegration, producing compounds like ettringite and thaumasite.
  • Alkali-aggregate reaction: Reaction between cement alkalis (sodium and potassium) and reactive silica in aggregates can cause expansion and cracking in concrete.
  • Acid attack: Acids can damage concrete through chemical reactions.

• Physical Causes:

  • Freeze-thaw cycles: Repeated freezing and thawing of water in concrete pores expands the water, leading to cracking and deterioration.
  • Shrinkage: As concrete dries, it shrinks, leading to internal stresses and surface cracking.
  • High temperatures: Extreme heat can damage concrete and weaken its mechanical properties.

• Mechanical Causes:

  • Abrasion: Surface wear due to friction and impact.
  • Impact: Damage from physical impacts.
  • Erosion: Removal of concrete due to water movement.
  • Cavitation: Damage from high-speed water flow in channels with irregular surfaces.

• Bad Quality of Concrete:

  • Incorrect concrete composition: Variations in water-cement ratio, gravel-cement ratio, and cement type.
  • Workability problems: Impact on the properties of fresh concrete.
  • Incorrect curing time: Insufficient curing or interrupted curing can result in reduced strength and durability and improper curing.

Carbonation

• Carbonation is a chemical reaction between lime and carbon dioxide present in the air.
• The chemical reaction forms calcium carbonate.
• The reduction of pH of the concrete is a consequence of this reaction.

Thickness of Carbonation

• Measurement is done using a colorimeter system.
• Phenolphthalein diluted with ethyl alcohol is used to assess the reaction.
• The absence of a colour change indicates that the concrete has been affected by the carbonation phenomenon.

Damages due to Carbonation

• Oxidation of the roads due to pH reduction from a high level (12.5-13) down to a lower value (≤ 9).
• Damage affects mainly the concrete's cover.

Alkali-aggregate Reaction

• This occurs when alkalis in cement react with certain types of aggregates.

Sulphate Attack

• Sulfate attack is a chemical deterioration mechanism.
• Ground water intrusion, sea water and construction materials.
• Chemicals reacting with cement paste.
• Swelling composites, Ettringite, and Thaumasite are produced

Chloride Attack

• Two main types: Sodium Chloride and Calcium Chloride.
• Important during winter for de-icing.
• Different types of aggression on the concrete.

Concrete Deterioration

• Deterioration due to the use of de-icing salts.
• Damage may include corrosion pitting, cracking, and spalling.
• The presence of chlorides in aggregates can lead to an alkali-aggregate reaction.

Causes of Concrete Degradation (Summary)

• Chemical: Carbonation, chlorine, sulfates, alkali-aggregate reaction, acid attack
• Physical: Freeze-thaw, shrinkage, high temperatures.
• Mechanical: Abrasion, impact, erosion, and cavitation
• Quality: Water/cement ratio, gravel/cement ratio, cement type, aggregate quality, and admixture quality.

Concrete Restoration Approach

• Identify the causes of degradation.
• Determine the extent (depth) of damage.
• Select the most appropriate restoration procedure.
• Prepare the substrate by removing damaged concrete.

Concrete Restoration Methods

• Manual demolition: Using hand tools to remove deteriorated concrete.
• Mechanical tool demolition: Using mechanical tools like sandblasting, hydrosandblasting, hydroscarification, and milling.

Reinforcement Protection

• Protective action is based on water, carbon dioxide, etc., permeability.
• Corrosion inhibitors protect the metal against oxidation.
• High alkalinity of restoration mortar promotes good adhesion to metal.

Concrete Restoration Mortars

• High adhesion
• Mechanical compatibility with existing concrete
• Controlled shrinkage
• Protection against chemical agents (carbon dioxide, chlorides, sulfates)

Crack Repair

• Crack sealing by epoxy resins injection.
• Elastic protective coverings.

Epoxy Resin Injection

• Material injection is carried out using various methods.
• Low pressure injection systems include membrane pumps or pressure vessels.
• High-pressure injection systems may require specialized cylindrical piston pumps.

MAPEI's Products for Concrete Restoration

• EPOJET
• EPORIP
• MAPELASTIC
• MAPEGROUT
• MAPEWRAP
• Additional product types include primers, waterproofing and finishing materials.

Specific Product Characteristics (Example)

• EPOJET: Features low viscosity, workability time, and application temperature ranges. Provides high tensile, compressive strength, and modulus of elasticity.

• EPORIP: Exhibits a different viscosity, workability time, and application temperature compared to EPOJET. Strength figures are also different in each product.

Application Examples : Different projects with various techniques for concrete remediation.

• Different projects, varied techniques: These include projects like wharf constructions, tunnel repairs, and dam restorations.