Calumex® XT-20 is an Amorphous Calcium Aluminate (C12A7) additive to Ordinary Portlandcement, used to accelerate setting times, compensate shrinkage and increase both early and late strength development. C12A7 is the most effective set accelerator known. Calumex® XT-20 provides roughly 4 times the working time of Calumex® SC-A based formulations, without the addition of retarders (depending on the applied dosage).
As is the case with Calumex® SC-A, the basis of Calumex® XT-20 is an amorphous clinker, making it a lot more reactive than crystalline alternatives. This means the required dosage in end formulations can be a lot lower. Between 10-20% of the binder weight should be replaced by Calumex® XT-20, depending on the desired effect.
To further optimize the working time without sacrificing strength development, Delta-20 set retarder can be applied.