Concrete Mix & Cast Report - Design, Constituents, Results

Concrete Mix & Cast 1
CONCRETE MIX & CAST REPORT
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Concrete Mix & Cast 2
Purpose
The purpose of this experiment is to design a concrete mix for materials available in the
laboratory. A slump test was conducted on the fresh concrete so as to determine its workability.
Afterwards, the concrete was cast in three cylinders with a total of 6 Liters of concrete was
required for the test. The resultant concrete was supposed to achieve a target strength of 30
MPa.
Concept
Concrete is a structural material that is an aggregation of cement, aggregates (fine and
coarse), water and sometimes admixtures (Faris, 2017). Concrete begins to set immediately
mixing is stopped. Once it has began hardening, curing should be done regularly through
flooding so as to avoid the effects dehydration such as cracking. Curing should be done for 28
days after casting. At 28 days, concrete is believed to have gained the maximum strength and has
the capability of supporting loads. Concrete gains strength indefinitely albeit insignificantly
(Yglesias, 2014).
Concrete is weak in tension but good in compression i.e has high compressive stregth
(Grantham , et al., 2011). This is the reason why beams have more steel reinforcement at the
bottom than at the top. This is because beams experience tension at the bottom and tension at the
top when loaded along their horizontal axis. The concrete design mix determines the target
strength of the concrete. Concrete can be produced in different classes that differ in the
characteristic strength of the hardened concrete achieved at the 28th after casting.
Constituents

Concrete Mix & Cast 3
As stated above, cement concrete is primarily composed water, sand, aggregates, cement and
sometimes an admixture.
Water
Water used for concreting should be clean and clear and be suitable for drinking (Misra ,
2017). It should be free from impurities such as salts. The amount of water available in the
concrete mix determines it’s workability.
Portland cement
This is a binding material that results from the crushing of clinker that mainly consists of
hydraulic calcium silicates (Kurdowki, 2014). When mixed with water, an exothermic reaction
takes place. A mixture of cement and water can be cast in moulds of different shapes. Cement
moulds should be cured for 28 days after casting to avoid dehydration. Concrete is an expensive
material and hence it would be uneconomically to build structures purely out of concrete. As a
solution, both fine and coarse aggregates are used to increase the bulk of the material. The
aggregate surface bonds well with the cement in a concrete mix.
Coarse aggregates
The most common coarse aggregate is gravel. The most commonly used aggregate size in the
production of concrete is 20 mm. Normally, aggregates that pass through the 40 mm sieve but
are retained in the 4.75 mm sieve re regarded as coarse aggregates. Size 40 mm aggregates are
usually used to produce mass concrete.
Fine aggregates