Multiscale analysis on microstructural changes in hardened cement paste dried under different relative humidity levels: A comparison with cement paste containing water-dispersible polyurethane ether compound

This study investigated microstructural changes in hardened cement paste with and without a water-dispersible polyurethane (PU) ether compound under varying relative humidity (RH) levels. The small-angle X-ray scattering technique was used to analyse the agglomeration, piling, and densification of calcium silicate hydrate (C-S-H) units. Mercury intrusion porosimetry and water vapour sorption isotherms were used to further characterise pore structures and surface areas, focusing on the C-S-H unit changes across different RH levels and the influence of PU. The presence of PU reduced variation in scattering profiles and subsequent calculated disc thickness at each RH, indicating the inhibition of C-S-H structural evolution during drying. These findings indicate less variation in the pore structure and surface area during the drying process than in the paste without PU. The length change isotherm of the cement paste with PU confirmed reduced shrinkage and hysteresis, which can be attributed to microstructural stabilisation.