Determination of the True Density of Cement Using a Pycnometer

The measurement of the fineness of cement is an important requirement for the cement industry. The standard method (ASTM–C204-Blaine) to determine the fineness of hydraulic cement requires the use of a predetermined value for the porosity of a packed bed of cement. This is because the Carman-Kozeny equation (on which the Blaine’s apparatus is based) is only valid over a limited range of porosities. Hence it is critical for the user to work in a narrow range (typically 0.5 ± 0.005) of porosity when conducting the tests. The porosity of a packed bed is given by:

where:

å = desired porosity of the bed
W = grams of sample required
ñ= density of test sample
V = bulk volume of the bed

Determination of Density Using ASTM-C188

The calculation of the porosity requires that the density of the cement sample be available to the user. The currently adopted method for density determination (ASTM-C188) uses either kerosene or naptha as the displacement fluid. The use of these fluids presents challenges due to special requirements for thermostatting, environ-mental concerns due to the necessity for the safe disposal of samples and waste solvent after analysis, and safety of the operator during testing. Also, the testing process is time consuming, rather messy, and requires great attention to detail by the operator.

Determination of Fineness of Quicklime Using ASTM-C110

Another method (ASTM-C 110) to determine the fineness of pulverized quicklime and hydrated lime by air permeability also requires the use of the C188 method to determine the density of the sample. Gas pycnometry, however, presents a viable alternative to the C188 method to determine the true density of the cement sample. The method involves displacement by the sample of a dry gas, usually helium, which penetrates all the pores of the sample (if any) to provide a quick and accurate value of the density.

Helium is inert and does not need any special requirements such as thermostatting during testing. Disposal concerns are not necessary and the same sample can be tested several times to calculate the mean, standard deviation etc. (the ASTM method requires a fresh sample for each analysis). The same dry sample can be used directly in subsequent Blaine measurements.

Determination of Cement Density Using a Pycnometer

Pycnometers manufactured by Quantachrome Corporation provide the user with a quick and clean method to determine the density of the cement sample. Both manual and automatic models are available to suit different needs and budgets. The operator requires minimal training to operate the instrument. The automatic models have easy to use operator interface (thereby reducing operator error) and also provide the capability to print reports (via a printer) that contain sample ID, date of analysis, statistics, etc. Please contact a Quantachrome representative or the authorized distributor in your country to obtain more information.

This information has been sourced, reviewed and adapted from materials provided by Quantachrome Instruments.

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