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How the concrete is cured by steam at atmospheric pressure?
Curing of brick or block is accelerating the hydration of cement with control of temperature and moisture movement form and into the concrete. For better quality concrete the mix of concrete and appropriate curing at the beginning of hardening. We can get quality of concrete as required by using concrete ingredients and by different curing methods.
The curing is used to prevent the loss of moisture from the concrete and keep it saturated or make it saturated as possible till the water-filled space in fresh-made cement product fills with.
Now, What is Steam Curing?
In the curing, the product is a cure at water vapor at atmospheric or high pressure. The curing is used when the strength is required in beginning and heat is required for hydration in cold weather. The main reason for using steam in curing of concrete for high early strength. The steam curing is applied at very high pressure or at atmospheric pressure. Here we will discuss concrete steam curing at atmospheric pressure.
What is the difference between Steam Curing at High Pressure and Normal Pressure?
The steam temperature is below 100 degrees Celsius is used for curing the concrete at atmospheric pressure. As the steam will be converted into water, it is also called the hot water curing and this process is done in an open atmosphere. The high-pressure concrete curing is performed in a closed chamber with high pressure about 80 to 170 psi and a high temperature of about 325o F to 375o F. The process is called Autoclaving.
Cycle of the Steam Curing
The steam curing has various phases and each phase has a different time frame that has to set.
First is an Initial delay prior to steaming
In this phase, the concrete is held at ambient temperature for about 180 minutes.
Increasing the Temperature
The curing temperature is increased to 60 degree Celsius for about 120 minutes
Hold at Maximum Temperature
The concrete is held at a maximum temperature about 70 degree Celsius for 120 minutes
Lower the Temperature
The concrete is cool down for 120 minutes
Now understand these processes in detail.
Steam curing is used to reduce heat loss and moisture. The tarpaulins are used to make the enclosed space.
Steam is applied for at least 3 hours after to get hardened the concrete. The 3 to 5 hours prior to steaming get the maximum strength.
The process is carried about by precast concrete elements which are specially prestressed concrete sleepers that are used in Indian Railway.
The bridges are built with precast prestressed girders and these girders are steam cured to increase the speed of construction.
It is hard to steam cure concrete at the site is not easy and at some sites, it is made by a steam jacket with tarpaulin or thick polyethylene sheets. The onsite steam curing is not suggested as the required strength is not achieved.
In the curing, the steam temperature is enclosed at 60 degrees Celsius until to reach the required strength. The desired strength will not be achieved if the temperature is raised from 60 to 70 degrees Celsius. The steam curing above 70 degrees Celsius is not suggested as it may damage the product. The internal temperature should not exceed to 70 degree Celsius and if so, there is expansion inside the concrete which reduce the overall strength.
In the steam curing the type of cement used, time and temperature are very important.
The use of excess heat and cooling avoid for preventing the damage of the volume changes. The temperature should not increase or decrease more than 22 to 33 degrees Celsius per hour according to the size and shape of concrete.
The curing temperature inside should maintain until it reaches to require strength. The curing time depends on the concrete and steam temperature.