concrete retarder admixture is used to delay the setting time of concrete without harming the strength or durability. It also delays the formation of cold joints in large construction projects and makes concrete workable during pouring.

Retarders slow the hydration process by inhibiting the formation of silicate hydrates. This is achieved by adsorption of the retarder on the surface of cement particles.

They also prevent the precipitation of aluminate hydrates. These hydrates form in solution as a reaction of the water with hydrated calcium ions.

The retarder adsorbs on the cement surface and binds to the hydrated calcium ions in solution. Eventually, the adsorption forms a layer on the cement particle surface that prevents direct contact with water.

This prevents hydration from occurring, and thus prolongs the set time of concrete.

These admixtures can also reduce the amount of water required for adequate workability in concrete by slowing the hydration process.

They can be purchased in straight retarders or as mixed admixtures with water reducing and retarding properties.

Typical dosage is less than 5% on the cement.

Dosage will vary depending on the type and strength of the admixture.

The dosage of a retarder is usually determined by its water-cement ratio, the type and amount of C3A from the concrete, and its degree of dispersing property.

Retarders can help to mitigate the dangers of long-distance concrete delivery in hot climates by offsetting the hastening effect of temperature on the initial setting time. They can also be applied on site to control concrete’s set time.