Evaluation of Cement Content in Concrete by Measuring the Density of Suspension Using Hydrometer

A Method for the Quality Control of Fresh Concrete

Abstract

A rapid Method for the evaluation of the amount of Portland cement in fresh concrete by measuring the specific gravity of mortar suspension is described.
This method is characterized by two features, viz. (1) using three hydrometers according to cement content, and (2) measuring the height of sand sediment in mortar suspension simultaneously with the measurement of density.
A control curve was constructed through follwing procedures: As the first step the amounts of cement in 1:2 mortar were determined by experiment, which satisfy the condition that the hydrometers of different measuring range go to the same depth into the suspension. Then the specific gravities of 1:1 and 1:3 mortar suspensions containing the same amount of cement as before were measured using the three hydrometers. Lastly, the three curves as shown in Fig. 5 were drawn to corelate the 9 values of specific gravity with the cement content. Using the control curve it is thus possible to estimate the amount of Portland cement of any fresh concrete if sand content were known, which the authors estimated from the height of sand sediment.
The estimation of cement content in the fresh concrete, which had been prepared in laboratory by hand mixing (not in a concrete mixer) and with various mixing proportions have been carried out. The error as a mean was found to be 2% (-1.1, +5.3%) or 7kg/m³ concrete (-5, +25kg/m³).