I analyzed cement samples exposed and unexposed to moisture over various periods. The TGA results of these samples showed variation with each repetition. However, I consistently used calcium oxalate as a reference material, and the results were satisfactory. The TG analysis employed an 80:20 helium-to-oxygen gas mixture and was connected to a mass spectrometer.
You may use Al2O3 as the reference and purge pure argon gas instead. Purge the Ar gas for 20 min before the commencement of the measurement at a higher rate. Then, you can reduce the Ar gas flow. The ramp rate is also very important since it changes the thermogram.
How are you preparing your samples prior to TGA analysis? What temperature are you purging with Ar gas prior to the TGA run, what is your ramp cycle? What are you looking for, thermal degradation, moisture content, reaction kinetics? There are several companies that offer TGA equipment specifically for concrete and other ceramic-type or construction materials. These companies have procedures. Also, have you done a literature search? You are not the first to use a TGA with concrete.
Don't forget to subtract the baseline, which must be performed without sample and under the same experimental conditions as your experiments.
wish you good luck.
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