Sugar is mainly famous as retardant of concrete and thus is often used to help adjust the setting times, especially in emergencies. Retardants are used to slow down the setting of concrete, mainly in warm weather, to make it more plastic and provide them more time to work with the material.
Here in sugar, the setting process is slow down because it interferes with the chemical reaction that causes cement to set when water is added. Sugar is composed of carbon, oxygen and hydrogen atoms which can interfere with the hydration process by binding with the minerals and slow down the reaction. There are also some theories that the sugar-metal complexes that form can also create an insoluble layer around the cement grains that impedes the reaction necessary for hardening. All type of sugars are not efficient at this. But Glucose, a simple sugar that is mainly formed through the breakdown of starch and is the main component of corn syrup, and lactose, which is found in milk, are considered to be good cement retarders.