In hot weather concreting, when the normal setting time is shortened by the higher temperature, it can lead to the formation of cold joints between successive batches.
When retarders are used in concrete, the initially poured concrete remains plastic for longer to ensure cohesivity with the next batch of freshly poured concrete layer.
Cohesion between the layers can be advantageous for achieving a desired architectural finish with exposed aggregate.
Retarders are admixtures extending concrete's setting time; this delay can be quantified using the penetration test.
The delaying of concrete setting, or retardation, can be achieved by incorporating substances like sugar, carbohydrate derivatives, soluble zinc salts, and soluble borates, among others.
Adding around 0.05 percent sugar relative to the cement's mass can extend the setting time by roughly four hours.
Retarders are believed to alter the crystal growth in concrete, creating a more effective obstacle to continued hydration.
Later, the retarder becomes part of the structure without altering the final hydration products.
