In simple terms, sugar acts as a retarder and delays the setting time of concrete.
This is the reason why transit mixer drivers are sometimes advised to add some soft drink to the concrete mix if the vehicle gets stuck up in the traffic for too long.
Technically speaking,
Sugars have been categorized as ‘cement destroyers’ and when sugar is added to Portland cement paste at the onset of mixing, hardening may be delayed indefinitely.
Concrete hardens due to formation of calcium silicate hydrate.
The retarding action of sugar is probably by the prevention of the formation of calcium silicate hydrate.
Sugar exceeding 0.2% by weight of concrete will slow down the reaction drastically.
Sugar increases the setting time of cement up to 1.33 hrs at dosage level of 0.06% by wt of cement. There will be no effect on workability, compaction by the use of sugar as admixture in concrete. Higher long-term compressive strength is achieved in concrete by the use of sugar as admixture.
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