Evaluation of methods for characterizing cement types in residual cementitious fines (RCF) from end-of-life concrete

Abstract

Concrete production is a major contributor to global CO₂ emissions, responsible for approximately 80% of the emissions in the construction sector. This high emission level is primarily due to the use of clinker, an energy-intensive component of cement. Reducing the environmental impact of concrete therefore depends on producing and reusing high-quality residual cementitious fines (RCF) derived from End-of-Life (EoL) concrete. The process of obtaining high-quality RCF begins before concrete demolition, where identifying the cement type in existing concrete is crucial for high-value downstream processing. This study explores the suitability of currently available methods for identifying binder types in (destructively obtained) RCF and evaluates which of these methods could potentially be suitable for non-destructive identification of binder types in the original concrete. The methods investigated include handheld X-ray fluorescence (HXRF), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), titration and selective dissolution. To assess their binder type identification potential, RCF powder samples obtained from concretes of known composition were analysed first. Results show that all five methods can distinguish and identify three binder types (Portland cement, blast furnace slag cement and fly ash cement) based on variations in the chemical and mineralogical properties of the RCFs derived from their respective concretes. HXRF currently shows the greatest potential for rapid, non-destructive, in-situ identification of binder types present in EoL concrete, while XRD and FTIR also show potential.