Temperature dependency of the dielectric properties of hydrated and ordinary Portland cement and their constituent phases at 2.45 GHz up to 1100 ºC

Abstract

[EN] This work focuses on microwave (MW)-dehydration and clinkering of hydrated cement paste, by studying the intrinsic MW¿material interaction during heating to 1100 °C. The dielectric properties of C3S, C2S, C3A, C4AF, CSH, CH and ettringite were measured using the cavity perturbation method at 2.45 GHz, and their evolution was correlated to phase changes identified using (Q)XRD, TGA and DSC. Ordinary Portland Cement (OPC) can be MW heated from room temperature onwards, mainly due to C4AF, and couples better at 650 °C, the onset MW absorbing temperature of C3A, C3S and C2S. Hydrated cement heats well due to good dielectric properties of H2O, released up to 200 °C, at CH breakdown at 400¿450 °C, and during continuous CSH breakdown up to 750¿800 °C. The dielectric properties, ¿¿ + i¿¿, of dehydrated cement above 750 °C are close to that of C3S, mixed with C2S and small amounts of C3A and C4AF. Recovery of clinker phases shows full potential of recovering cement from hydrates.