SET ACCELERATION ADMIXTURES BERKAN BOZKUŞ 26338304672

WHAT IS THE SET ACCELERATING ADMIXTURE? A cement accelerator is an admixture for the use in concrete, mortar, rendering or screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier. This allows concrete to be placed in winter with reduced risk of frost damage. These are used in cold weather conditions(below 5 °C)

WHY DO WE USE ? If a contractor is using an accelerator, the odds are good that the weather is wintry. Accelerators counteract the influence of cold weather, which slows down the curing and setting process. But accelerators aren't just for cold weather. A contractor can use one anytime a curing process needs a kick. The admixture may allow a concrete worker to remove forms earlier, get onto a concrete surface earlier for finishing, and sometimes even put loads on it earlier, such as when diverting foot traffic to do patching.

Calcium Chloride  A number of chemicals qualify as accelerators, but the most common is calcium chloride. It's cheap, plentiful, and readily available from huge chemical companies. However, while calcium chloride may be the cheap favorite for concrete in general, it is not necessarily the best option for decorative concrete.

Calcium chloride slightly increases workability and reduces the water required to achieve a given slump in a mix.  It reduces initial and final setting times, and it improves compressive and flexural strengths of concrete at early ages. Excessive amounts of calcium chloride may cause rapid stiffening and shrinkage while drying, creating cracks in the cured surface. Calcium chloride may promote corrosion in steel reinforcements and increase the potential for scaling.

In any case, contractors who want to accelerate their concrete aren't forced to use calcium chloride. There are four of the most common: 1) Calcium formate 2) Triethanolamine 3) Calcium nitrite 4)Calcium nitrate

1.Mindess, S. and Young, J.F, Concrete, Prentice Hall Inc., 1981. REFERENCES 1.Mindess, S. and Young, J.F, Concrete, Prentice Hall Inc., 1981. 2.Hawkins, P., Tennis, P., and Detwiler, R., The Use of Limestone in Portland Cement: A State-of-the-Art Review, EB227, Portland Cement Association, Skokie, IL, 44, 2003 3.Pera, J., Hussonb, S. and Guilhot, B., Influence of Finely Ground Limestone on Cement Hydration, Cement and Concrete Composites, 21, 99-105, 1999. 4.De Belie, N., Grosse, C.U., Kurz, J., Reinhardt, H.W., Ultrasound Monitoring of The Influence of Different Accelerating Admixtures and Cement Types for Shotcrete on Setting and Hardening Behavior, Cement and Concrete Research, 35, 2087–2094, 2005