Q.
a) State the materials used in the concrete mix and explain the functions of each substance. (10 marks)
b) Explain how the following factors influence the strength of concrete:
i. Proportion and type of cements. (5 marks)
ii. Type, proportions, grading and quality of aggregates (5 marks)
iii. Method and adequacy of batching, placing and curing the concrete (5 marks)
(25 marks, 2017 Q6)
A.
a) Materials in concrete mix
In short, the materials are sand, coarse sand, gravels, cement and water.
Ref:
Earlier post.
b)
i. Proportion and type of cements
ii. Type, proportions, grading and quality of aggregates
Functions of Coarse aggregate:
· Coarse aggregate makes solid and hard mass of concrete with cement and sand.
· It increases the crushing strength of concrete.
· It reduces the cost of concrete, since it occupies major volume.
Requirements: Coarse aggregate used may be crushed stone, gravel and broken bricks.
Crushed stone: It is an excellent coarse aggregate provided. It is obtained by crushing granite, sand stone and close grained lime stone.
Crushed granite chips are commonly and advantageously used in reinforced cement concrete.
Broken bricks well burnt and over burnt bricks are broken into suitable size and used as aggregate. It should be well watered before its use. Broken bricks are used as aggregate for concrete in foundations and under floors.
But generally crushed stone is only used as coarse aggregate.
iii. Method and adequacy of batching, placing and curing the concrete
Ref:
Earlier posts.