Measuring the Density of Cement Powders Via Gas Pycnometry

Based on the gas displacement method, this article describes a method for determining the optimal gas type and pressure for measuring cement density, providing a reliable method to characterize porous cement density using BetterPyc 380, an automatic gas pycnometer.

Cement is an important building material frequently utilized for the production of concrete, mortar, and prefabricated components. It is of significant importance in construction, national defense, hydraulic engineering, and infrastructure, where the top priority is quality control.

Density has a major impact on the performance, quality, and application of cement materials. This means the measurement of cement density is vital.

Currently, cement density can be measured using one of two methods: namely, the LeChatelier’s flask method or the gas displacement method.

The Le-Chatelier’s flask method is limited by time consumption, clogging problems, irritating odor, high kerosene price, and cleaning inconvenience. An automatic gas pycnometer, with a design based on the gas displacement method, may be employed to measure the cement density in a friendly way.

Image Credit: Bettersize Instruments Ltd.

Additionally, in comparison to the kerosene molecules, the gas molecules can enter the pores in the cement particles, ignoring the pore size and hydrophobicity performance, which results in a more accurate measurement.

This article discusses the measurement conditions, such as pressure and type of analysis gas, for obtaining more accurate results with the automated BetterPyc 380.

Image Credit: Bettersize Instruments Ltd.

Experiment

Cement density is measured using the BetterPyc 380 automatic gas pycnometer with a resolution of 0.0001 mg/cm³ and an accuracy of ≤ 0.03%. The measuring temperature is 20 ℃. The electronic balance’s accuracy is 0.001 g.

100 g of cement powder is collected after being passed through a 0.90 mm mesh sieve. This is subsequently placed in a laboratory oven to dry at 110 ℃ for one hour to eliminate any moisture and then cooled to room temperature in a desiccator.

Helium and nitrogen are utilized as the analytical gases, with measurements being taken at pressures of 5, 10, 15, and 20 psig.

Results and Discussion

Table 1 demonstrates how the measured density increases as the pressure increases. There are numerous micropores in the cement particles, and as the pressure increases, the gas progressively displaces the air from the micropores, causing density to increase.

In this case, if the analysis pressure is greater than 10 psig, the measured density will be nearer the true value, and the standard deviation of the results will be improved. As a result, 20 psig is recommended as the analysis pressure.

Generally, gases such as nitrogen and helium are preferred for gas pycnometer measurements as they do not react with the sample and subsequently impact its properties.

As displayed in Figure 1, at analysis pressures of 15 and 20 psig, the measurement results using nitrogen are lesser than those using helium gas. This is due to the smaller molecular size of helium, which allows it to penetrate small pores and voids in the porous cement powder, leading to a more accurate density result.

Figure 1. Image Credit: Bettersize Instruments Ltd.

Table 3.1. Measured density using different analysis gases under different pressures. Source: Bettersize Instruments Ltd.

Conclusion

It is important to note that the gas type and pressure used in the gas pycnometer should be cautiously selected to confirm accurate and reliable density measurements.

Based on the measurement result, it is advised to use helium as the analysis gas for the measurement of the cement powder’s density under 20 psig pressure.

This article provides the recommended measurement conditions for the use of the BetterPyc 380 to measure the density of porous cement powders, which are detailed in Table 2 below.

Table 3.2. Suggested measurement conditions. Source: Bettersize Instruments Ltd.

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

For more information on this source, please visit Bettersize Instruments Ltd.