It is important to determine the correct content of admixture required for the concrete to get the desired results. The dosage of the admixture can be determine with help of Marsh cone test for particular brand of cement and brand of plasticizer, at particular w/c ratio.
Marsh cone
It is known that cement and water mixture is the main reason behind which the flow and the workability of concrete depends. Therefore, in the marsh cone test sample of mixture of cement and water along with the admixture is taken .
Marsh cone is conical brass vessel with smooth aperture at the bottom of diameter 5mm.
Procedure:
Take 2 kg of cement along with 1 litre of water(w/c ratio=0.5) . Add 0.1% by weight of cement of admixture to the cement and water mixture. Mix water, cement and admixture for some time. Now, take 1 litre of the mixture and pour it in the marsh cone. Place finger on the aperture of the cone before pouring the mix. Remove the finger from the aperture and start a stopwatch. The total time required by the slurry to flow out of marsh cone is called as Marsh cone time. Same procedure can be tried with different w/c ratio or different brand of cement/admixture or different dosage of admixture , but one of them should be kept constant. The mix which gives lowest marsh cone time is optimum dosage for that cement and brand of admixture at that w/c ratio.
The above method is normally use for finding the amount of plasticizer and superplasticizer.