Multiscale structural changes and drying shrinkage of Portland cement pastes: effects of a fatty-alcohol-based shrinkage reducing agent

Investigation of the multiscale structural development of cementitious materials plays an essential role in understanding their drying behavior. Portland cement pastes with a fatty-alcohol-based shrinkage reducing agent (SRA) under practical hydration and evaporation conditions were used instead of ultimate states, which have already been reported. The results of small-angle X-ray scattering (SAXS) analysis showed that fractal disc-shaped agglomeration units of the calcium silicate hydrate (C-S-H) increased in size with the addition of the SRA. Water vapor sorption isotherms (WVSI) revealed that mesopores were formed between and/or within the agglomeration units of C-S-H, and the volume of mesopores increased with increasing SRA content. The agglomeration units containing mesopores were stable and reduced the drying shrinkage. This explanation may be extended to the macroscale structure, which predominantly contributes to drying shrinkage at very early ages. In addition, the first reported results of WVSI at extremely low relative pressures and SAXS indicated that the pore structure at the atomic level was not affected by the presence of the SRA.