Concrete properties

What is concrete composed of?

• aggregate

• cement paste

• aggregate paste interface (important influence on properties of hardened concrete)

• pore

• water

what is heterogeneous?

when a mixture is diverse in content

e.g. concrete consists of randomly distributed aggregates of different sizes and shapes

what is hydration?

An on going chemical reaction between cement and water leading to the progressive development of structure and strength of cement paste

Setting

When concrete goes from fluid to solid

• can cause a rise in temperature

• occurs faster at higher temperatures

• rate can be increased using chemical admixtures

Hardening

when cement gains strength after it has stiffened

• through continued hydration

• rate depends on the fineness of cement and chemical composition

• can be accelerated by heat and chemical accelerators

What does workability encompass?

• Mixability

• Mobility

• Stability

• Compactability

• Finishability

What factor can influence workability?

• Water content

• Aggregate type size and shape

• Cement fineness

• Chemical admixtures

How can we measure workability?

• Slump test

• Compacting factor test

• Vebe test

• Flow table test

What is segregation?

When solids sink while placing

• Can happen when not enough waste is in the paste to bind everything to bind together

• Can lead to a lack of uniformity and cohesion

• Bad quality concrete and loss of durability

What is bleeding?

When water rises out of the mixture - happens often in very workable mixes

Can cause a lack of uniformity and cohesion

Bad quality concrete and loss of durability

• Can create voids

When does plastic cracking occur?

Before concrete sets and hardens fully

• during rapid drying (rate of water loss > rate of bleeding)

• occurs between 1-6 hours after casting