1. HYDRATION-CONTROL ADMIXTURES
Asena SİVASLIOĞLU

2. What is hydration?
A few hours after mixing the concrete components, they form a solid structure with no plastic properties. The chemical reaction caused by the reaction of cement and water is called hydration. Progress of hydration depends on water and heat. Hydration heat is important for both producer and operatör.

3. Hydration Process It starts when cement and water become together.
It has five process;
1- Mixing (Karıştırma Süreci)
2- Sleeping (Uyku Süreci)
3- Setting Period (Priz Süreci)
4- Cooling (Soğuma Süreci)
5- Condensation (Yoğunlaşma Süreci)

4. Mixing Process
C3A reacts so fast in this process so that high heat is released. False or rapid set occurs. Plaster is used to prevent this. Plaster reacts with C3A and water, gel-like water surround cement particles. This prevent C3A, decrease the heat,prevent unwanted set.
At this process, used admixtures include less C3A and sulphate ratio should be enough for reaction.

5. Sleeping Period
C-A-S-H gel controls the aluminate react. Changing of heat and physical proporties is so little. The consistence of concrete is plastic.
At this process, silicate start to decompose slowly. Ca+ and OH- make more saturated.

6. Setting Period
In the admixtures, silicates react with CH -which occurs as a result of cement reaction- and create C-S-H. Concrete gains strength through C-S-H. This reactions happens slowly. Puzolonic concretes’s reaction happens more slowly and it causes;
Setting time can be late
Increasing workability time
Decreasing heat of hydration
Speed of gaining early strength decrease

7. Cooling Period
In this period, topochemical reaction happens. Cement is saturated. Hydation starts at C3S so CSH and CH occur. Concrete starts gain strenght.

8. Condensation Period
Reaction starts to be slow. Heat decreases significantly. Concrete becomes more strength.

9. Hydration Controlling Admixtures
Hydration Controlling Admixtures (HCAs) which are sometimes refered to as hydration stabilizers (HSs) are becoming more popular with concrete producers today as a replacement for conventional set retarding admixtures.
They consist of a two-part chemical system:
Stabilizer/retarder that stops hydration
Activator that restarts hydration
The stabilizer can suspend hydration for 72 hours and the activator is added to the mixture just before the concrete is used. This admixture presently does not have a standard specification

10. Benefits
The admixture is also useful in maintaining concrete in a stabilized non-hardened state during long hauls.
By controlling hydration some HCAs reduce the rate of temperature gain in the plastic concrete and the peak temperature in hardened concrete.
Provides predictable setting. A Hydration Controlling Admixture can be used at designated dosage rates to allow you to start the hydration process when you want.
Allows returned concrete to be used that day even the next day.

11. Benefits
One of the main differences between hydration controlling admixtures and conventional set retarders is that when a conventional set retarder starts to wear off, the concrete tends to set quickly where as a hydration controlling admixture has a time release effect and wears off over time.
Can produce higher early and ultimate strenghts.
HCAs also help with temperature, air loss, and slump loss to an extent.

12. DRACO-ECOMIX Hydration control concrete admixture in powder form.
ECOMIX stops the hydration of cement and wash water and prevent the first setting. It becomes normal with addition of fresh concrete.
Reusing reduced concrete in ready-mix and wash water
Remove the water and concrete wastes

13. BASF-DELVO EASY STABILIZER
Hydration control concrete admixture in powder form.
Controls the hydration of cement and providing of reusing fresh concrete and wash water.
It creates a barrier around the cement particles so hydration of fresh concrete and wash water in the ready mix is stopped.

14. REFERANCES AKÇANSA-ÇİMENTONUN HİDRATASYONU
1. KOSMATKA, STEVEN H., VOIGT, GERALD F., TAYLOR, PETER .,”Integrated Materials and Construction Practices for Concrete Pavement: A State-of-the- Practice Manual”, Center for Transportation Research and Education Iowa State University, 2006, p
2. MEHTA, KUMAR P., MONTEIRO, PAULA J.M., “Concrete: Microstructure, Properties and Materials”, McGraw-Hill, 2006
3. SOROKO, I., “Concrete in Hot Environments”, E&FN Spon, 2004
4.ERDOĞAN, T. Y., “ Sorular ve Yanıtlarıyla Beton Malzemeleri” , THBB Yayınları, 2004