Microstructural changes of globules in calcium–silicate–hydrate gels with and without additives determined by small-angle neutron and X-ray scattering

The microstructure of calcium–silicate–hydrate (C−S−H) gel, a major hydrated phase of Ordinary Portland Cement, with and without polycarboxylic ether (PCE) additives is investigated by combined analyses of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) data. The results show that these comb-shaped polymers tend to increase the size of the disk-like globules but have little influence on the thickness of the water and calcium silicate layers within the globules. As a result, the fractal packing of the globules becomes more open in the range of a few hundred nanometers, in the sense that the mass fractal dimension diminishes, since the PCE adsorption on the globules increases the repulsive force between and polydispersity of the C−S−H units. Moreover, scanning electron microscope (SEM) study of the synthesized C−S−H gels in the micrometer range shows that the PCEs depress the formation of fibrils while enhancing the foil-like morphology.

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► Studied polycarboxylic ether’s effect on structure of calcium–silicate–hydrate gel.
► Used combined small-angle X-ray and neutron scattering data analysis.
► Basic building blocks (globules) pack into a more open fractal structure.
► Sub-structure of the globules is unchanged but the globules become larger.
► SEM shows the depression of fibril formation and enhancement of foil-like morphology.