Composites 2 Flashcards
Is concrete a composite?
yes
What is filler is concrete made out of?
Aggregate- rock and sand
What matrix is concrete made out of
Cement
What percentage of concrete is aggregate?
70-80%
What is the purpose of sand in aggregate?
Fills voids to reduce porosity
How does concrete set
Cement undergoes a cementation reaction
What is the water used for in cement
incorporates into the structure
Main minerals (C)
CaO
Main minerals (A)
Al2O3
Main minerals (F)
Fe2O3
Main minerals (S)
SiO2
Density of concrete
2 gcm3 (dense)
(L/H) concrete fracture toughness
L
(L/H) concrete tensile strength
L
Why is concrete used?
Cheap and good compressive strength
Why does concrete get better with age
Cementation reaction still taking place
What does the strength depend on in concrete?(2)
Minerals and amount of water
Pro of adding more water to your concrete
Makes concrete more workable
Con of adding more water
As it increases shrinkage it makes cracking more likely
what is reinforced concrete
concrete with steel rods
What is pre-stressed concrete?
Steel rods under tensile stress while concrete is pored
Con of steel reinforced concrete
water rusts steel making it expand and create cracks
Why is concrete so bad for the enviroment
Only cause so much produced, actual production is quite low co2
Why would you use wood?(5)
Cheap, strong, lightweight, aesthetics, eco friendly
Structure of wood - Fibre
Lignin holds cellouse fibres and hemicellulose together in same direction
Structure of wood - cell structure
Made of cells with microfibril facing different ways in each layer
structure of wood- macrostructure
Long unidirectional polymer cells
Why is softwood less dense
Has more hollow cells for transporting water
Can wood float on water
yes
What effects wood strength
direction of cells
Does wood have good compressive strength
no
Which type of wood does wood densification use?
Soft wood
How does wood densification work?
Uses chemicals and heat to remove lignin and hemicelluloses
Why densify wood?
Outperforms in specific strength, energy to manufacture and cost
