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

his work focuses on microwave (MW)-dehydration and clinkering of hydrated cement paste, by studying the intrinsic MW-material interaction during heating to 1100 degrees 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 degrees 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 degrees C, at CH breakdown at 400-450 degrees C, and during continuous CSH breakdown up to 750-800 degrees C. The dielectric properties, epsilon' +i epsilon, of dehydrated cement above 750 degrees 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.

Automated summary

This study focuses on the microwave (MW) dehydration and clinkering of hydrated cement paste, specifically investigating the MW-material interaction during heating to 1100 degrees C. The dielectric properties of various cement components were measured, and their changes were correlated to phase changes detected through different analysis methods. The research shows that ordinary Portland Cement (OPC) can be effectively MW heated, and the dielectric properties of hydrated cement contribute to its efficient heating process. The recovery of clinker phases demonstrates the potential for cement retrieval from hydrates.