It is generally accepted that fine particles could accelerate cement hydration process, or, more specifically, this accelerating effect can be attributed to additional surface area introduced by fine particles. In addition to this view, the surface state of fine particles is also an important factor, especially for nanoparticles. In the previous study, a series of nano-SiO₂-polycarboxylate superplasticizer core-shell nanoparticles (NS@PCE) were synthesized, which have a similar particle size distribution but different surface properties. In this study, the impact of NS@PCE on cement hydration was investigated by heat flow calorimetry, mechanical property measurement, XRD, and SEM. Results show that, among a series of NS@PCE, NS@PCE-2 with a moderate shell-core ratio appeared to be more effective in accelerating cement hydration. As dosage increases, the efficiency of NS@PCE-2 would reach a plateau which is quantified by various characteristic values. Compressive strength results indicate that strength has a linear correlation with cumulative heat release. A hypothesis was proposed to explain the modification effect of NS@PCE, which highlights a balance between initial dispersion and pozzolanic reactivity. This paper provides a new understanding for the surface modification of supplementary cementitious materials and their application and also sheds a new light on nano-SiO₂ for optimizing cement-based materials.

In this paper, the size and shape characteristics of desert sand particles were quantitatively investigated via a combination of X-CT scanning and spherical harmonics functions. The size characteristics of the desert sand particles were evaluated via the Length (L), Width (W), Thickness (T), and Volume equivalent spherical diameter (VESD). The average value of the VESD for the desert sand particle is 118.2 μm, which is much smaller than that of commonly used fine aggregate, and more than 90% particles are smaller than 150 μm. The overall shape of the desert sand particles was assessed with two aspect ratios: elongation (EI) and flatness (FI). Desert sand particles were classified into four categories: spheroid-shaped, oblate-shaped, prolate-shaped, and blade-shaped. The sphericity (S) values of the desert sand particles were distributed in a wider range, with an average sphericity of 0.85, much larger than that of commonly used fine aggregates. Through a combination of aspect ratios and sphericity analysis, it can be roughly concluded that the desert sand particles appear in more irregular shapes, but with relatively smooth surface morphology and less convex or concave parts.