Self Curing Concrete – Introduction
Self-curing in the concrete means to provide a continuous supply of water to the concrete so that during the release of the heat of the hydration process, concrete utilizes it and prevents the evaporation of water molecules within concrete mass.
Thus if curing is not done then, micro-cracks in concrete are developed due to loss of od water molecules from concrete, and the process of shrinkage occurs. The traditional curing process involves only interactions of concrete over the surface of concrete but not inside the concrete mass.
So, the advanced technology of concrete curing, named SELF CURING CONCRETE concept was introduced with the help of different research in the US by Paul Klinger in 1957 in which the internal curing inside is possible within concrete.
In the practice of self-curing concrete, the small inclusions are dispersed to entire concrete mass which holds the extra molecules of water necessary for hydration and release during the hydration process.
This curing process is thus more effective and reduces self desiccation. The practice is achieved by the use of different types of components and admixtures in concrete.
Admixture that are added in Self curing concrete
The basic principle concept of self-curing concrete is to provide the water needed for hydration within the concrete mass without affecting its water-cement ratio so that there is no alteration of strength as well as there is proper hydration to prevent the concrete micro crack.
Thus, it’s only possible by using different kinds of aggregate and admixture. The major components and admixture used in self-curing concrete are :
1. Light weight and high absorption rate aggregate
Normally, in traditional concrete, there is the use of high density and less porous aggregate like Basalt, granite, etc. But for self-curing concrete, there is the use of the lightweight with high absorption rate aggregate.
The reason behind the use of such concrete is that such aggregate doesn’t displace the water from concrete mass, in spite, it’s absorption property would store the water in aggregate and release while in process of hydration. Some of the use of aggregates in the research lab are pumice, shale, clay.
2. Super absorbent polymer
These are chemically synthesized hydrophilic polymers. As the name its self says, the chemical is used to absorb the water in the form of inclusion. The word hydrophilic means water-loving or attracting.
The hydrophilic polymers have the basic two components, one is organic Hydrophobic carbon part and the other is the inorganic part which helps to attach water molecules within it.
And thus with the help of hydrophilic radicals, they form the hydrogel with the polymer. And thus the water remains attached but in undisturbed form.
This undisturbed water inclusion is used during the hydration process providing internal curing. Some of the highly prefer super absorbent polymer are polyvalent alcohol, polyethylene glycol (PEG), poly-acrylic acid, xylitol, sorbitol, Glycerin phytosterols, hyaluronic, polyoxyethylene (POE), sodium pyrrolidone carboxylate, stearyl alcohol, and urethanes.
3. Shrinkage reduction admixture
These are the plasticizers, that are used in concrete mass in order to increase the workability without adding the extra water beyond than necessary water-cement binding ratio.
Thus such plasticizers help to decrease the shrinkage crack that happens due to loss of water from gray concrete while hardening.
Moreover, such plasticizers, help to decrease capillary action and surface tension of water within the concrete mass which is also the reason for the tensional micro-cracks in drying concrete.
The early shrinkage, as well as long term drying shrinkage, is reduced to 35- 50 percent with the use of such admixture.
These chemicals are mainly based on ethylene glycol derivatives compounds like sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate, and polycarboxylate ethers.
4. Wood polymer
This polymer hadn’t been massively using for the construction process but has been used on the research process to enhance the property of the self-curing concrete.
Self curing concrete compounds
The major compound include in self curing concrete is super absorbent polymer. The polymer forms specific compounds that seems as hydrogel with action to the water.
The polymer’s hydrophilic tails attach the water molecules within it. And the hydrophobic (hydrophobic literally means afraid of water) heads repel the water and align to form polymer chain that traps the water containg hydrophilic part inside.
This way both inclusion of water and escaping of water is prevented in concrete with the help of this gel-like compound formation. The gel water is used during hydration giving only the crystallized compound in concrete.
Preparation of Self curing Concrete
All the dry constituents are placed in the mixer and mixed for two minutes to make it the uniform mixture.
Now, add half of the water and the remaining water with a superplasticizer.
Now, a self-curing agent such as polyethylene-glycol or saturated lightweight aggregate is added gradually during the mixture of concrete.
The mixing is done for at least two minutes and keeps in mind that no segregation occurs. The workability of concrete should be proper according to the design mix.
Proper placement and should be done while casting into form-work of structure.
Application of the self curing concrete
Self-curing concrete is basically targeted to the high-performance concrete and high strength concrete by which massive megastructure like tall sky scrapper, Tunnels, Bridge, shotcrete to prevent unstable slopes are needed to be constructed.
These kinds of works need a very low water-cement ratio and less use of water. Thus there is a very high chance of the microcrack formation in such kind concrete during hydration. Thus the internal Curing is needed to apply in such works.
Self-curing concrete created uninterrupted and progressive curing thus generally more applicable to the place where the accessibility after construction is difficult.
Highly applicable where there is a scarcity of water like the desert area of the world. Moreover, the construction of rigid pavement road, where the water curing is difficult to maintain for a long time, sloping surfaces concreting, they can be applied for ease.
Self-catering is an advanced technology in the field of civil engineering performed after lots of research and hard practices. So it would be obviously targeted o achieve maximum advantage as much as possible. Some of the advantages are,
- It reduces the shrinkage and avoids micro-cracks in the concrete structure which increases the strength of concrete and reduces the permeability
- Due to the formation of less void, micro-cracks, and permeability, the water, and other chemicals can’t trap in it. And certain effects like sulfur action cause due to atmospheric sulfur dioxide, expansion and contraction of water causing expansion of cracks,etc., that Detroit concrete is prevented and thus durability increases. Also, there is the protection of the reinforcement bars.
- Reduction of the thermal expansion coefficient, so volumetric expansion and cracking are less even in radiated surfaces of concrete.
- Self-curing concrete helps in increasing strength and the hardness of concrete
There is a certain drawback of the self-curing concrete, even though it has its own advantage over certain fields.
Some disadvantages like related to economy, affordability, adaptability, risk factors always come when there is an introduction of new technologies. Some disadvantages of it can simply be listed.
- Uneconomical and cannot be used for the small projects
- The use of the lightweight aggregate decreases the density of the concrete. Moreover, such aggregate might not have high crushing strength value. This might overall might affect the strength of concrete.
- The use of different synthetic chemicals like organic polymers might show a delay effect in concrete.
- The detailed study of chemicals involved in concrete is needed to dine for a long time.
Related things to know
Like self-curing concrete, the researchers have devised new technology called SELF HEALING CONCRETE. The principle of both method and practice can be considered analogous in the sense that practice is done in order to prevent the micro-cracks and voids in concrete although it is very different in their mechanism.
The self-curing concrete is based on prevention mechanism, in which voids and cracks are avoided to create due to hydration of water. But Self healing concrete is based on the cure mechanism, which takes action for the unpredictable creation of voids.
Self-healing concrete is prepared by mixing the special bacteria to the concrete mix. Those bacteria remain dominant for a long period and on the presence of the air these bacteria consume air produces concrete or cementing agents as byproduct filling the voids and cracks.
I hope this article remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rajan Shresth