Curing to concrete is done to maintain moisture level which is present inside of the concrete.
It gets evaporated during hydration process if the temperatures of surface are not controlled.
by the 7th or 10th day depending on the blending of cement, it achieves around 70% of its hydration process and makes a concrete much more stronger. further this the hydration process becomes slow and also the evaporation and temperature goes down, due to this most of the engineers do think that curing for a specified period is OK.
To do actual tests and arrive at the same you can do experiments at your project by curing the concrete specimens in condition of structure by putting them with structure.
at the specified period take the specimens from there and do test at lab to check the losses or gains in it.
Concrete is very interesting material and its behavior can not be predicted as to one thing which happens there are many reasons and many aspect which affects its strength property.
When we do test concrete in lab condition, we should also need to maintain a temperature of curing water which is in most of the cases not done.
This will reflect on experiment results.
Doing the curing for 28 days is not practically possible when you go for a large scale, this is why everybody tries to achieve 70% strength of the concrete up to 7 days only.
when 70% strength is formed, it becomes difficult for water from concrete to get escape out of it.
During the construction process, the curing is also an continuous activity which keeps going on for every builded structure every day.
The concrete which is in shed have less chances of getting evaporation losses compare with concrete which is directly under sunlight because in case when there is direct sunlight, the external parameter is also working on it to make evaporation out of concrete.
Curing means, to prevent the water to get out of concrete during process of hydration, you do it by pouring water, applying curing compunds or covering it with polythene sheets or whatever mean you have.
