Concrete Construction

Question 1

What is concrete (simple overview of what it consists of)

Answer 1

A composite material consisting of aggregate particles in a binding material

Question 2

What is the binder of concrete

Answer 2

(Portland) Cement and water

Question 3

What is fresh concrete

Answer 3

The mixture of all the aggregates and binders, before it hardens. Looks like a grey slush.

Question 4

What does workable mean

Answer 4

The concrete is wet so it can be casted.

Question 5

On the Scanning Electron Microscope what type of substances appear bright (and conversely dark)

Answer 5

Heavy and dense materials (and thus dark is low density)

Question 6

What phase of standard will be the densest (appear brightest)

Answer 6

Unreacted cement

Question 7

What phase of standard concrete will be the least dense (appear darkest)

Answer 7

Air voids and water

Question 8

What happens when cement reacts with water

Answer 8

The cement dissolves and releases ions which then recombine into hydration products (more in detail in cement)

Question 9

Where do the hydration products grow from

Answer 9

The unreacted cement

Question 10

What is the hardening of concrete a direct result of

Answer 10

The precipitation of the hydration products

Question 11

What is paste and what is mortar

Answer 11

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.

Question 12

Give an example of mortar use

Answer 12

The binder for bricks

Question 13

Give an example of paste (sometimes called grout) usage

Answer 13

Filler for gaps in prestressed concrete

Question 14

What is the annual production of concrete (tonnes per year, give an order of magnitude)

Answer 14

10^10

Question 15

What is the most consumed manmade material and what is the most consumed resource

Answer 15

Concrete and water respectively

Question 16

Advantages of concrete

Answer 16

Cheap, castable, strong compressive strength, durable, fire and water resistant, low conductivity, high thermal mass, abundant raw materials, inert, versatile through composition changes

Question 17

Service life of typical concrete

Answer 17

50 -100 years (100 or more for critical infrastructure)

Question 18

Disadvantages of concrete

Answer 18

low tensile strength, high carbon footprint, high water consumption, takes time and care to gain strength, not widely recyclable

Question 19

How can the tensile strength of concrete be improved

Answer 19

Reinforced with steel or prestressing the concrete (introducing internal stress to counteract the external load)

Question 20

How does steel complement concrete

Answer 20

Steel has high tensile strength, concrete adheres to steel allowing stress transfer

Question 21

How does concrete complement steel

Answer 21

Concrete is alkaline so can protect steel from corroding, concrete is fire resistant, concrete has a similar thermal expansion coefficient to steel

Question 22

What are the 4 concrete degradation mechanisms

Answer 22

Corrosion, alkali silica reaction, sulphate attack, acid attack

Question 23

What property of concrete causes it to degrade

Answer 23

It is very porous, which allows water to seep into the voids

Question 24

Why do air voids form in concrete

Answer 24

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

Question 25

Why do air voids form in concrete

Answer 25

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 called capillary pores

Question 26

What is the carbon footprint of concrete (percentage of total carbon footprint)

Answer 26

8%

Question 27

Why does cement/ concrete have a high carbon footprint

Answer 27

The process of burning the raw materials requires a lot of energy and the burning of limestone releases CO2 when it degrades into calcium oxide