Concrete Construction Flashcards
What is concrete (simple overview of what it consists of)
A composite material consisting of aggregate particles in a binding material
What is the binder of concrete
(Portland) Cement and water
What is fresh concrete
The mixture of all the aggregates and binders, before it hardens. Looks like a grey slush.
What does workable mean
The concrete is wet so it can be casted.
On the Scanning Electron Microscope what type of substances appear bright (and conversely dark)
Heavy and dense materials (and thus dark is low density)
What phase of standard will be the densest (appear brightest)
Unreacted cement
What phase of standard concrete will be the least dense (appear darkest)
Air voids and water
What happens when cement reacts with water
The cement dissolves and releases ions which then recombine into hydration products (more in detail in cement)
Where do the hydration products grow from
The unreacted cement
What is the hardening of concrete a direct result of
The precipitation of the hydration products
What is paste and what is mortar
Paste is formed from cement, water and in modern times admixtures. Mortar is paste with fine aggregates. Note that concrete is mortar with the addition of coarse aggregates.
Give an example of mortar use
The binder for bricks
Give an example of paste (sometimes called grout) usage
Filler for gaps in prestressed concrete
What is the annual production of concrete (tonnes per year, give an order of magnitude)
10^10
What is the most consumed manmade material and what is the most consumed resource
Concrete and water respectively
Advantages of concrete
Cheap, castable, strong compressive strength, durable, fire and water resistant, low conductivity, high thermal mass, abundant raw materials, inert, versatile through composition changes
Service life of typical concrete
50 -100 years (100 or more for critical infrastructure)
Disadvantages of concrete
low tensile strength, high carbon footprint, high water consumption, takes time and care to gain strength, not widely recyclable
How can the tensile strength of concrete be improved
Reinforced with steel or prestressing the concrete (introducing internal stress to counteract the external load)
How does steel complement concrete
Steel has high tensile strength, concrete adheres to steel allowing stress transfer
How does concrete complement steel
Concrete is alkaline so can protect steel from corroding, concrete is fire resistant, concrete has a similar thermal expansion coefficient to steel
What are the 4 concrete degradation mechanisms
Corrosion, alkali silica reaction, sulphate attack, acid attack
What property of concrete causes it to degrade
It is very porous, which allows water to seep into the voids
Why do air voids form in concrete
When the water reacts with cement to form hydration products, the volume originally occupied by the water is not filled up by the hydration products leaving voids
