Concrete

Question 1

What are the Properties in the Strength Development of Concrete ( CAWCCTT)

Answer 1

Cement Type
Admixtures
w/c ratio
Compaction
Curing
Temperature
Age

Question 2

What is the Poissons ratio for concrete

Answer 2

0.15-0.20

Question 3

What are the 4 factors that cause creep in hardened concrete ( think soil creep )

Answer 3

Humidity
W/c ratio
Cement content
Stress

Question 4

Why does drying shrinkage occur

Answer 4

Due to loss of moisture through evaporation

Question 5

How can drying shrinkage be controlled

Answer 5

Reducing movement
Adding cement
Reinforced details
Movement joints

Question 6

What does shrinkage drying cause to hardened concrete

Answer 6

Excessive cracking

Question 7

List what is drying shrinkage dependent on ?

Answer 7

Humidity
Tempeture of surrounding air
Ratio of surface area to volume of concrete
Rate of air flow
Water and cement content
Curing

Question 8

What is thermal movement and why does it occur ?

Answer 8

The expansion and contraction of concrete due to the temperature change of heating and cooling

Question 9

What does cooling cause in thermal movement in concrete and why

Answer 9

Cooling can cause cracking if restrained due to daily/seasonal temperature change and heat of hydration

Question 10

What can heating cause in thermal movement

Answer 10

Can cause the steel within concrete to start buckling

Question 11

What is the equation for expansion of material due to heating

Answer 11

LΔ = LxaxΔT

Question 12

What is the difference between diffusion and permeability in the durability of concrete

Answer 12

Diffusion involves the change in concentration of a liquid/gas, while permeability involves the flow of a liquid/gas.

Question 13

Evaporation/absorption is dependent on what in hardened concrete

Answer 13

RH
Ambient Temperature
Wind
Surface characteristics

Question 14

What types of deterioration ( loss of function over time ) is there for each material

Answer 14

Timber : wet/dry loss of strength
Concrete: sulphate or acid attack
Steel: formation of rust in the presence of oxygen and water

Question 15

What is concrete carbonisation and how fast is it

Answer 15

Carbon dioxide neutralises with calcium hydroxide, if reaction reaches reinforcement in concrete corrosion will occur.
Very slow, depending on diffusion

Question 16

What type of process is Chloride attack on reinforcements steel

Answer 16

A slow process depending on the surface absorption and diffusion within the concrete

Question 17

What causes a chloride attack on reinforcemed concrete

Answer 17

Seawater and de-icing salts

Question 18

How do you reduce the chance of a chloride attack on reinforced steel occurring

Answer 18

Keep surface absorption as low as possible through compaction process and curing
Keep diffusion low using a low w/c ratio with alternative cement materials ( admixtures )

Question 19

How does fire affect the durability of materials such as timber, steel, plastics and concrete

Answer 19

Timer: highly flammable and toxic ( char outside of thick members )
Steel: loss of strength rapidly at high tempeture
Plastics : highly flammable and toxic
Concrete: non flammable but can spall at high temp

Question 20

What are the basic materials that make up concrete ( CAWAV )

Answer 20

Cement
Aggregates
Water
Admixtures
Voids

Question 21

What are the different types of Portland cement

Answer 21

OPC - Ordinary
RHPC - Rapid Hardening
SR - Sulphate resistant
WPC - White

Question 22

What is the process of creating cement

Answer 22

1 Rock materials of limestone, silica, shale, iron oxide are quarried
2 Rocks are then crushed into smaller rocks
3 Rock material is then mixed and run through a “ Rotary Kiln”
4 Rotary Kiln mixes Rock material and calines limestone - gets rid of CO2 - forming a clicker
5 clicker ground to a fine power and mixed with gypsum

Question 23

What are the alternatives to Portland Cement

Answer 23

GGBS ( Ground Gradulated Blast furnace Slag )
PFA ( Pulverised Fuel Ash )
Metakalin
Rice ash
Silica fume

Question 24

What is GGBS

Answer 24

By product of iron smelting
Carbon footprint of 35kg per tonne of CO2
Generally is blended up to 70% in OPC
Reduced early strength and early heat of hydration
Much lower carbon footprint

Question 25

What makes up cement hydration

Answer 25

W/c ratio is important for workability , strength and durability of concrete Setting and hardening is a chemical reaction This reaction is exothermic leading to “Heat of hydration”

Question 26

Explain the heat of hydration graph and Draw

Answer 26

Strength gain is initially rapid but slows down over time Strength gain will occur indefinitely while moisture is present within concrete ( this is curing )

Question 27

What materials make up aggregates (3 materials)

Answer 27

Gravel, sand, crushed rocks

Question 28

What types of aggregated are there and what separates them

Answer 28

Coarse aggregate: cannot pass through a 5mm sieve Fine aggregate : passes through a 5mm sieve

Question 29

How much do aggregate generally make up in a concrete mix

Answer 29

50-80%

Question 30

What are aggregates used for

Answer 30

Packing efficiently Reduce spacing Costs Improving properties such as strength and drying shrinkage

Question 31

What are the requirement for aggregate?

Answer 31

Hard Durable Strength Cleanliness ( no dust , chemical impurities and organic matter )

Question 32

What are the differences of densities in aggregates and what are they used for

Answer 32

Normal : gravel and crushed rocks Lightweight : weak porous solid, thermal properties High: radioactive screening

Question 33

What water is used in concrete and what is not allowed in it

Answer 33

Water must be free from impurities and potable Must be free from (sugar sulphate chlorides)

Question 34

Name the types of admixtures there are

Answer 34

Water reducing Air entraining Superplasticisers Self-compaction Foamed

Question 35

What does the reducing water admixture do and how

Answer 35

Reduces the amount of water needed using plasticisers

Question 36

What does the air entraining admixture do

Answer 36

Evenly distributed air around concrete Improves durability to marine and frost environments

Question 37

What does superplasticisers do ?

Answer 37

Allows for water removal , creating a higher strength

Question 38

What does self compacting admixtures do

Answer 38

Concrete doesn’t require compaction

Question 39

What does the foam admixture do

Answer 39

High flowing concrete with bubbles without any stones

Question 40

What factors affect the workability of fresh concrete

Answer 40

Water content Fineness of cement Aggregates Grading Admixtures Time Temperature

Question 41

What causes segregation in fresh concrete

Answer 41

Overhandling or vibration of concrete , or poor grading

Question 42

What is laitance

Answer 42

When coarse aggregate separates and sink to the bottom leaving cement paste on the top forming a scum on the surface of the concrete

Question 43

How do you reduce segregation

Answer 43

Increase air content Increase rate of hydration Reduce w/c ratio

Question 44

What is bleeding and what occurs

Answer 44

Bleeding is when water from the concrete comes to the surface of fresh concrete Occurs when water is lighter than concrete, leaves pockets of low density in the concrete

Question 45

What are the 3 causes of bleeding

Answer 45

To much water Poor grading of aggregates Overworking concrete

Question 46

What is shrinkage

Answer 46

Shrinkage is when moisture moves from a high to low concentration in diffusion or air flow

Question 47

What is the cause of shrinkage and what happens

Answer 47

Moisture loss from the surface Cracks form when the concrete is still young Cracks form parallel to each other

Question 48

What increases evaporation which leads to shrinkage

Answer 48

Low RH High surface temp High wind speed

Question 49

How to minimize evaporation

Answer 49

Moist aggregates Concrete cover Plastic fibres

Question 50

How does honeycombing occur

Answer 50

Honeycombing occurs when void are left in concrete due to poor compaction not filling the spaces between the aggregates

Question 51

What is the definition of curing

Answer 51

Curing is the maintenance of satisfactory moisture content and temperature in concrete for a period of time