4: Concrete Flashcards
1
Q
What is produced when limestone decomposes?
A
calcium oxide and carbon dioxide
2
Q
How is concrete made?
A
- Cement is made by heating powdered limestone with clay.
- Cement is mixed with sand and water to make mortar.
- As it sets, it absorbs carbon dioxide from the air, forming tiny crystals of calcium carbonate, which lock together with other ingredients.
- Cement is mixed with sand, aggregate and water to make concrete.
3
Q
Equation for thermal decomposition of limestone/ marble
A
calcium carbonate = calcium oxide + carbon dioxide
CaCO3 = CaO + CO2
4
Q
What is reinforced concrete?
A
Concrete can be strengthened by letting it set around a supporting mesh of solid steel. Such reinforced concrete is a composite material
5
Q
Why use reinforced concrete?
A
It has useful properties from both the materials it contains:
- concrete is hard and strong in compression (when squashed)
- steel is flexible and strong in tension (when stretched)
6
Q
Limestone in water
A
calcium oxide + water = calcium hydroxide
CaO + H20 = Ca(OH)2
7
Q
What is calcium hydroxide used for?
A
Neutralising acids
eg. spread in farmers fields to reduce excess acidity in the soil, helping the soils grow.
Also used as treatment in lakes damaged by acid rain
