MARSH CONE TEST

• Marsh cone test is reliable and simple method to study the rheological properties of cements and mortars.

• Flow time of cement/mortar through marsh cone is indicator of viscosity, which depends upon cement super plasticizer compatibility.

• It is widely used to study cement super plasticizer compatibility and to determine optimum super plasticizer dosage of a specific cement-super plasticizer combination

Apparatus  It’s consist of a conical brass vessel held on a wooden stand with an orifice of 8mm at its bottom.  A stop watch is needed to measure the time taken by 1 litre of cement or mortar to pass through the vessel.  A mortar mixer is also needed to prepare the cement paste with desired w/c ratio

PROCEDURE  1L of cement paste is prepared in mortar mixer using 2 kg of cement and w/c ratio of 0.32-0.35.High strength Concrete designs typically have w/c ratios less than 0.35.

Water is added in two steps- 70% of water is added in beginning of mixing and rest 30% of water is mixed with super plasticizer, and added afterwards. Cement slurry is prepared with the w/c ratio of 0.32 and admixture dosage of 0.5 %.1 litre of cement slurry is made to flow through marsh cone after 5 min and 60 min of mixing and time in seconds is measured using a stopwatch. The procedure is repeated gradually increasing the S.P. Dosage in steps of 0.2%. Similar tests are conducted for rest of super plasticizers and graphs are plotted with time as Y axis and S.P. dosage as X-axis.

Significance  The saturation dosage of super plasticizer can be defined as that point beyond which there is no significant decrease in the flow time. Saturation point can be taken as the maximum super plasticizer content to be used in concrete. We can implement to use specially recommended admixtures at recommended dosages for given mix design.