Effect of testing condition on the loss on ignition results of anhydrous granulated blast furnace slags determined via thermogravimetry

A key property influencing the quality of a blast furnace slag (GBFS) used in cements and concretes is the loss on ignition (LOI), which is associated with the amount of moisture and carbonates present. Both EN and ASTM standards describe determination of the LOI of GBFS, and thermogravimetric analysis (TGA) is also a valuable test which provides information that can be related to the LOI. However, the final mass loss obtained by TGA is influenced by the testing conditions including nature and flowrate of the gas used, the sample mass and heating rate, and there is no existing standard method for TGA of SCMs. As part of the efforts of RILEM TC 238-SCM, this study assesses the effect of the gas environment and gas flowrate on the observed mass loss from a GBFS, determined via TGA in nitrogen, argon or air atmospheres using different gas flowrates, and without correction for oxidation of sulfides to sulfates. Significant mass changes occur between 800–1000 C independent of the gas used, and are more notable under an oxidising atmosphere and at low gas flowrates. These results elucidate that it is required to standardise TGA testing parameters for analysis of GBFS to enable collection of meaningful results by this technique.