Curing is a process of controlling drying of concrete or mortar by continuous wetting during dehydration so as to attain its optimum strength.
Concrete should not be allowed to dry very rapidly, as it will continue gaining strength up to 28 days. It should be at least cured for 7 days, because it will have gained 3/4 of its strength.
The methods of curing include :
i] Watering or sprinkling water to the surface for at least 3 times a day.
ii] Use of plastic sheeting.
iii] Use of damp sacks or mats.
iv] Use of damp saw dust or sand.
NB The use of the last method is not preferred as it tends to stain the concrete.
So, inadequate or lack of curing can cause the collapse of a building.
In addition :
Strength of concrete
Among the properties of concrete, its strength is very important. It is important. It is comparatively strong in compression, but lower in tensile strength.
The strength is influence by several factors of which the most important are explained here below.
Factors affecting concrete strength
i] Void content
Strength decreases as the proportion of voids increases
ii] Age
The rate of gain in strength is rapid at first, but decreases progressively. At an age of 7 days, its strength is approximately 2/3 of its 28 days strength.
Type of cement
Ordinary Portland cement in 7 days it gain 2/3 strength; rapid hardening Portland cement in 3 days it gains 2/3 strength and high alumina cement gains 2/3 strength in 1 day.
iv] Water content
Optimum amount of water is needed for ease of workability and to start the chemical reaction. Too much water decreases the strength because the void content increases.
v] Grade of aggregates
Strength is increased by use of angular and rough aggregates rather than rounded and smooth. Impurities in aggregates also affect the strength.
vi] Temperature
An increase in the temperature of the concrete as it hardens; accelerates the hydration process. This increases the rate of gain of early strength, provided there is no evaporation.
vii] Segregation
This where when have fine particles at the top and larger particles at the bottom. This will result from excess compaction, transportation on rough runs and placing methods.