Study on the early crystallization of calcium silicate hydrate (C-S-H) in the presence of polycarboxylate superplasticizers

Calcium silicate hydrate (C-S-H) presents the strength-providing phase in hardened cement and concrete. Its nucleation and very early overall growth are not yet fully understood. Here, the impact of methacrylate ester-based PCEs (a common type of dispersant used to fluidize concrete) on the nucleation and crystallization of C-S-H precipitated from aqueous solutions of Ca(NO3)(2) and Na2SiO3 was investigated. It was found that in the absence of PCEs, most unexpectedly globular nanoparticles of C-S-H with a diameter of similar to 20-60 nm are favored. Thereafter, within less than 1 h the globuli convert to the well-known nanofoils of C-S-H. According to these observations, the very early C-S-H is formed following a non-classical nucleation mechanism. In the presence of PCEs, the initial globules show a core-shell morphology, presumably with PCE polymers as shell which delays the conversion to the nanofoils for several hours. The PCE polymers exhibiting higher anionicity delayed the transformation to nanofoils more than the PCEs possessing lower anionic charge. (C) 2018 Elsevier B.V. All rights reserved.