Retarder and retarding water-reducing admixture have different retarding effects in slurry and concrete. The retardation effect increases with the increase in dosage, and excessive addition will cause cement hydration to completely stop.
Various retardants and retarding water-reducing agents mainly delay and inhibit the hydration of C3A minerals and C3S mineral components. They have a relatively small impact on C2S, so they do not affect the later hydration and long-term development of cement slurry. Strength increases with age.
The setting time of the retarder is the main indicator. The initial setting is required to be delayed by more than 90 minutes compared with the benchmark concrete, that is, the setting time difference is >+90 minutes. However, the final setting time difference is not uniformly specified, because the super retarder and ordinary retarder are The indicators of coagulants vary greatly.
A good retarder should not reduce the strength of concrete within the normal dosage, so the compressive strength ratio should not be less than 90-100% at each age.
The air content is required to be no more than 5.5%. Because ordinary water-reducing agents have retarding properties and certain air-entraining properties, they should not be over-mixed.
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