Physical Attack Presented by: Bryan Perrie (presented by Mark - - PowerPoint PPT Presentation

Presented by:

Bryan Perrie (presented by Mark Alexander)

The Concrete Institute

Main Durability Issues in SA Physical Attack

Physical Attack

• Abrasion
• Erosion
• Cavitation
• Temperature/moisture cycling
• Salt crystallisation
• Fire
• Traffic
• Freezing and freeze-thaw
• Cracking
• Abuse

Abrasion

Wearing of the surface due to repeated rubbing or friction

• Largely governed by aggregate quality but combination with paste quality
• Improve by finishing, curing

Erosion

Wearing of surface by abrasive action of fluids, suspended solids and wind borne sand Special case of Abrasion

• Improve by removing abrasive material, reducing flow and wind speed

Cavitation

Change in velocity or direction of high velocity flow

• Improve by design to reduce velocity and

direction of flow

Temperature and moisture cycling

Can cause crazing and surface degradation

Salt crystallisation

Wetting and drying in marine environments allows soluble salts ingressing in the wet cycle, to crystallise in the dry cycles resulting in expansive pressures and spalling

• Reduce permeability

Fire

Concrete strengths reduce with increasing temperature above 300º C The strength reduction is roughly linear up to 1000º C when it has lost all strength Reinforcing steel strength also reduces (also the yield) Often accompanied by spalling Most damage done by fire brigade

Traffic

Traffic results in fatigue and cracking and also loss of texture in roads, runways and industrial pavements

• Increase flexural and compressive strength with good curing

Freezing and freeze-thaw

Freezing is expansive and disruptive Freeze-thaw results in:

• D-cracking adjacent to joints
• Delamination and scaling
• Aggravated by de-icing salts

Freezing and freeze-thaw (cont.)

Factors include:

• Porosity/permeability
• Aggregate characteristics
• Moisture state
• Climatic conditions

Cracking

Includes:

• Plastic shrinkage
• Drying shrinkage
• Thermal
• Overstressing
• Deflections

Abuse

• Lack of housekeeping
• Overloading
• Lack of maintenance including joint seals

Physical Attack

• Abrasion (Concr, Const, HC?)
• Erosion (Des, Concr, Const, HC)
• Cavitation (Des)
• Temperature/moisture cycling (Des,

Concr)

• Salt crystallisation (Concr, Const)
• Fire (HC)
• Traffic (Des, Concr, Const)
• Freezing and freeze/thaw (Des,

Concr, Const)

• Cracking (Des, Const)
• Abuse (HC)

Thank You