To study the promotion process of cement hydration by polycarboxylate superplasticizers modified calcium silicate hydrate (C–S–H/PCE) and understand the mechanism of C–S–H/PCE seeds promotion of cement hydration. Acrylic acid-based polycarboxylate superplasticizer (PCE-1) and silane-based polycarboxylate superplasticizer (PCE-2) were used to surface modify the hydrothermal synthesized calcium silicate hydrate (C–S–H/Unmodified) seeds, resulting in the polycarboxylate superplasticizer modified C–S–H seeds (C–S–H/PCE-1 and C–S–H/PCE-2). Subsequently, these three C–S–H seeds were added to the cement paste. The compressive strength, phase composition, and heat release curve of cement paste and the surface tension of C–S–H seeds were tested. The results showed that the surface modification of PCE-1 and PCE-2 resulted in an increase in the surface contact angle of C–S–H seeds from 36.9° to 41.1° and 42.9°, resulting in lattice mismatch of the sedimentary phase (hydration product) on the surface of the substrate material (C–S–H seeds) and inhibiting the epitaxial growth of cement hydration products on the surface of C–S–H seeds. PCE modification reduced the promoting effect of C–S–H seeds on the hydration process of Portland cement. Moreover, the degree of reduction in the hydration promoting effect of C–S–H/PCE-2 on Portland cement is significantly greater than that of C–S–H/PCE-1 crystal nucleus. Tests of the adsorption equilibrium of PCE in the pore solution indicated that the C–S–H/PCE seeds did not directly introduce new crystal nucleation sites but exposed new C–S–H surfaces through the desorption of PCE on the surface of C–S–H/PCE seeds. The desorption degree of PCE on the surface of C–S–H/PCE seeds determined the promoting effect of C–S–H/PCE seeds on cement hydration.

In order to obtain stable and dispersed calcium silicate hydrate (C‒S‒H) crystal nucleus, improve its crystal nucleus-inducing effect on cement hydration, and realize the efficient utilization of cement clinker. Polycarboxylate superplasticizers (PCE) with different proportions of acrylic acid (AA) and silane group (KH570) were prepared via free radical polymerization to disperse calcium silicate hydrate (C‒S‒H) seeds. The corresponding C‒S‒H/PCE seeds were synthesized by a solution precipitation method. The grain size/size distribution, the stability of C‒S‒H/PCE seeds and the bonding mode of PCE on C‒S‒H interface were investigated. The results show that the PCE with an appropriate proportion of KH570 can effectively control the grain size of C‒S‒H/PCE seeds. The adsorption mode of PCE on C‒S‒H surface changes from Ca²⁺ complexation to a more stable Si—O—Si chemical bond, and the grain size of C‒S‒H/PCE seeds firstly decreases and then increases with the increase of KH570 ratio. At a KH570 to AA ratio of 1, the adsorption layer thickness of PCE on the surface of C‒S‒H is 2.5 nm, the grain size of C‒S‒H/PCE seeds is 60 nm and the stability is optimum. The PCE undergoes an intramolecular dehydration condensation process under alkaline condition with further increasing the proportion of KH570, forming a reticulated silicone resin structure, which is unfavorable for the regulation of grain size of C‒S‒H/PCE seeds.