How are the relatively small dosages of an admixture measured reliably and placed in the mixer?

Q. How are the relatively small dosages of an admixture measured reliably and placed in the mixer?

A. Admixtures are usually dispensed as liquids on a volumetric basis, which enables additions in small quantities. Most admixture manufacturers supply equipment for accurate dispensing of their products. Such equipment should include a visual method of verifying that the admixture has been properly batched and dispensed into the concrete. When two or more admixtures are being used in the same concrete, care should be taken to avoid intermixing of the admixtures before introduction into the concrete. Because the time of addition of chemical admixtures can influence their effect on setting of the concrete, it is important to add them at the same point in the batching cycle of each batch. Discharging the admixture into the stream of mixing water as it enters the mixer is generally recommended. Dispensers and visual gauges should be cleaned frequently.

References: SP-1(02); E4-12; ACI 212.3R-16; SP-288; ASTM C260; ASTM C494; ASTM C1017

Topics in Concrete: Admixture; Quality Assurance