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Are retarding admixtures reliable as to the time of setting?

Q. Are retarding admixtures reliable as to the time of setting?


A. Yes, unless they are grossly overdosed. In addition to variation in the dosage of the retarding admixture and properties of the cement, initial and final times of setting of the concrete depend on the w/cm, temperature of the concrete, and ambient conditions. Changes in these conditions will alter time of setting with or without a retarding admixture. When other admixtures are used in combination with the retarding admixture, care should be exercised to avoid unexpected extension in time of setting. Large dosages of water reducing admixtures may also extend the setting times. Lowering the temperature of concrete and making use of some of the pozzolans also extend the time of setting (ACI 207.1R).


References: SP-1(02); E4-12; ACI 212.3R-16; SP-288; ACI 207.1R-05; ASTM C494

Topics in Concrete: Admixture; Concrete Fundamentals; Hot Weather; Pozzolan

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