Quantification of the degree of hydration in complex cement systems by hyphenated TGA-FTIR

Introduction

While TGA has long been used to quantify DOH in simple hydrated cement mixes, it cannot readily account for effect of novel additives when determining chemically bound water from the weight loss curve of the thermogram alone. Taking advantage of the FTIR to determine the contents of the gas evolved from the TGA during analysis allows for a more accurate quantitation of DOH for cement mixes made up of more complex additives. Evolved gases can be identified by their IR spectra and by using the Beer’s law principle a linear calibration can be established for both H2O and CO2 allowing quantitation without relying on defined temperature ranges to identify decomposition gases. Directly calculating a sample specific WB∞ using a representative 100% hydrated sample with the TGA-IR method allows for less reliance on method specific mathematical models. As such DOH calculation accuracy can be enhanced by more specific IR gas measurement in combination with the mass loss calculations from the TGA.