Concrete 3

Compressive stength vs water-cement ratio

tension test

Coupon test

What is creep

Time-dependent strain – movement
under a constant load over time

What is creep dependent on

Humidity
• Cement content
• Water/cement ratio
• Stress

How can shrinkage be controlled

reduced moisture, cement, reinforcement
details, movement joints or fibres

What is shrinkage dependent on

Humidity
• Temperature of surrounding air
• Rate of air flow over surface
• Ratio of surface area to the volume of
concrete
• Water & cement contents
• Curing

What is thermal movement

Expansion and contraction on heating or cooling

Permeability

Evaporation/Absorption
• Loss or gain of liquid or gas from/into a surface
• In concrete, it depends on ambient temperature, wind
sunshine, relative humidity, surface characteristics

Diffusion

Liquid or gas movement from a high concentration to
a low concentration
• Diffusion involves a difference in concentration of a
gas or liquid

Deterioration

loss of function over time,

concrete- sulphate or acid attack

how can reinforced concrete deteriorate

Corrosion - concrete carbonation, chloride attack

fire

what is concrete carbonation

Reinforcement is protected by highly
alkaline pore water in the hardened
concrete
• Carbon dioxide in the air neutralises the
Calcium Hydroxide
• If the reaction reaches the
reinforcement, corrosion will occur
• Very slow process dependent on
diffusion

What is chloride attack

a process where chloride ions penetrate the concrete, destroy the steel's protective passive layer

Slow process dependent on surface absorption and
diffusion inside concrete
• Attacks steel quickly if chloride ions can permeate
concrete cover
• Sources are sea water and de-icing salts
predominantly
• Keep surface sorptivity- how easily moisture can penetrate surface- as low as possible through
compaction and curing and keep diffusion low
using low water cement ratio with alternative
cement materials

how can fire reduce reinforced concrete’s durability

steel rapidly loses strength at high temperatures