Novel use of TG-IR to quantify the degree of hydration in complex cement systems

Thermogravimetric analysis (TGA) is commonly used to quantify cement hydration by attributing mass loss to decomposing hydration products or carbonates. However, as binder systems become more complex, assuming a single gas evolves within a temperature range becomes unreliable. This work introduces a novel method for calibrating and directly measuring chemically bound water quickly in complex cementitious systems by coupling TGA with infrared spectroscopy (TG-IR). Type IL and ordinary portland cement (OPC) pastes were examined, including OPC blended with 20% fly ash (FA) or slag (SL), or 5% biochar (BC). For OPC, SL, and FA, TG-IR and the Bhatty TGA-only method agreed within 1%; however, TGA-only methods were found unreliable for high-LOI BC and IL pastes, deviating by 5–20% compared to TG-IR. TG-IR thus provides more broadly applicable framework for quantifying decomposition products in modern blended cements where the assumptions of TGA-only methods become invalid. • A method is proposed for quantifying IR absorbance to determine bound water. • TG-IR can deconvolute and quantify simultaneous gas release during thermal decomposition. • TG-IR can quantify products of complex systems without relying on prescriptive assumptions.