How does freezing and thawing damage concrete?

Water in pores expands about 9% on freezing, creating hydraulic pressure; repeated cycles crack and scale it

Ice contracts and pulls the paste apart

Frozen water reacts with C3A to form ettringite

Freezing dissolves Ca(OH)2 which leaches out

What happens to cement paste at high temperature in a fire?

Above 300 °C paste loses water and above 500 °C Ca(OH)2 decomposes, causing cracking, spalling and strength loss

It gains strength because more hydration occurs

Why does drying shrinkage cause cracks?

Shrinkage is restrained by steel or supports, producing tensile stress; the cracks let aggressive agents in

Concrete expands on drying and crushes

Shrinkage only occurs when concrete freezes

Shrinkage is caused by sulphates

What is the general effect of physical processes on later chemical attack?

They make concrete denser and slow chemical attack

They have no link to chemical attack

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Physical causes of concrete deterioration

Short answer

Physical causes include freezing-thawing (water expansion causing scaling/cracking), thermal effects (differential expansion, fire spalling), shrinkage cracking, abrasion, erosion/cavitation, salt crystallization, and wetting-drying cycles. All increase permeability; control by low w/c, air entrainment, and good curing.

Explain the physical causes of concrete deterioration.

Physical causes act by mechanical, thermal or moisture processes without changing the chemical composition of cement paste.

Cause	Mechanism	Effect and control
Freezing and thawing	Water in pores freezes, expanding by 9%, causing hydraulic pressure; repeated cycles	Scaling, cracking, D-cracking. Use air entrainment (4 to 7%), low w/c, sound aggregate
Thermal effects (temperature cycle, fire)	Differential expansion/contraction; above 300 °C paste loses water, above 500 °C Ca(OH)2 decomposes	Cracking, spalling, loss of strength. Joints, cover, insulation
Shrinkage and moisture movement	Drying shrinkage restrained by steel/supports	Cracks, which open the way for aggressive agents. Low w/c, curing, joints
Abrasion	Wear by traffic, sliding or rolling	Surface loss in pavements, floors. Hard aggregates, high strength, surface treatments
Erosion and cavitation	High velocity water with silt, or vapour bubbles collapsing	Pitting of spillways. Smooth surface, high-strength concrete
Salt crystallisation	Salt solution crystallises in pores on drying	Pressure causing scaling and efflorescence. Dense concrete, membranes
Wetting and drying	Moisture gradients cause cyclic stress	Cracking and surface deterioration

All physical processes increase permeability and speed up chemical attack, so low w/c, good curing and compaction help in all of them.

✓ Answer checked by Claude Sonnet 5.5

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