Yang Yang

Bio: Yang Yang is an academic researcher from Zhejiang University of Technology. The author has contributed to research in topics: Cement & Shrinkage. The author has an hindex of 13, co-authored 47 publications receiving 961 citations.

Influence of colloidal silica sol on fresh properties of cement paste as compared to nano-silica powder with agglomerates in micron-scale

Abstract: Influence of colloidal silica sol (SS) with mono-dispersed nano-particles on fresh properties of cement paste was investigated as compared to nano-silica powder (NS) with agglomerates in micron-scale. The SS addition showed a much greater influence on sedimentation and rheological behavior of the paste than the NS incorporation, because the nano-particles in SS coagulate immediately once cement is mixed into water containing SS, forming loose floc and coating layer around cement particles. The loose floc cannot function as fillers to release free water, but possesses a more open microstructure, leading to a higher free water retention capacity than the agglomerates in NS. However, addition of SS presented an obviously better accelerating effect on cement hydration than that of NS, though the nano-particles in SS are nearly the same as those in NS in primary particle size and the flocs in the paste with SS addition are typically larger than the agglomerates in NS, implying that the acceleration may have nothing to do with the seeding effect. Through detecting calcium-absorbing properties of NS and SS, it is found that the accelerating effect is highly dependent on the rapid depletion of calcium ions in the paste. Finally, it was interestingly found that the CH crystals are even more prone to grow along (0001) plane with larger size in the paste with SS addition, because the coagulated gel network in the paste slows down the diffusion rate of the released ions and eliminate the convection in the system, thus the 3D nucleation and growth of the CH crystals were suppressed.

Whether do nano-particles act as nucleation sites for C-S-H gel growth during cement hydration?

Abstract: In this study, three modelling experiments were designed to investigate whether nano-particles incorporated in the cement paste act as nucleation sites for C S H gel growth during cement hydration. The nano-particles with (nano-SiO2) and without (nano-TiO2) pozzolanic reactivity were used. In the first experiment, both the cement and nano-particles were dispersed in water to prepare dilute cement paste, in which the cement and nano-particles can contact each other. In the second one, the cement particles were laid inside a filter paper funnel and immersed in tap and ultrapure water with nano-particles dispersed, in order to separate the cement particles with nano-particles by using the filter paper. In the third one, large clinker particle was embedded in resin, surface-polished and then exposed upside down in ultrapure water with and without nano-particles dispersed. After hydration for 7 days, the hydration products in the paste or the nano-particle dispersion were observed by using TEM and the hydrated surface of the embedded clinkers were detected by using SEM. Based on the experimental results and the detailed discussions by using the classic nucleation theory, it was found that there may have no nucleus function of the nano-particles for the C S H gel precipitation during cement hydration, at least in the hydrating system with nano-silica and nano-TiO2 addition. It was proposed to more reasonably explain the observations in the three modelling experiments by using the topochemical reaction instead of the through-solution mechanism for the C S H gel formation.