The effects of colloidal nanosilica on the interfacial transition zone (ITZ) in concrete at three days are studied. Mechanical properties are investigated at macro-scale, followed by nanoindentation characterization at micro-scale. A top-down and a bottom-up modelling are carried out, respectively, at macro- and micro-scales. Macro-mechanical results show that nanosilica addition is especially beneficial for the improvement of ITZ performance. Estimates from statistical nanoindentation provide evidence, suggesting that the hydration acceleration effect of nanosilica dominates in the modification of ITZ in an early age. It is revealed by modelling at both scale levels that the ratio of the Young's modulus of ITZ to that of bulk paste increases from around 50%–80% if nanosilica is incorporated. This work further confirms that a substantial improvement on ITZ can be obtained by ultra-fine nanosilica modification.

In this paper, nanoindentation and viscoelastic modulus mapping were employed to study the influence of nanoSiO2 on the properties of the interface between C–S–H gel and cement grains. The interface width measured by modulus mapping was around 200 nm as compared to a rough estimation of less than 5 μm by nanoindentation, due to the fact that 2 orders of magnitude increase in spatial resolution can be achieved with modulus mapping. Although the influence of nanoSiO2 on the interface width was not significant, its impact on nanomechanical properties of the interface was marked. The data suggest an improvement of modulus and hardness of the interface by nanoSiO2 in early age. This interface, which could be regarded as a layer surrounding cement grains, become denser by the addition of nanoSiO2.

Investigation on the mechanical properties of cement-based materials at micron and sub-micron scales is important for understanding its overall performance. Recent progress in experimental nanomechanics opens new access to nano-engineering of cement-based composites. In this study, nanoindentation and viscoelastic modulus mapping were employed to study the interfacial properties. The interface width measured by modulus mapping was around 250 nm as compared to a rough estimation of less than 5 µm by nanoindentation, due to the fact that 2 orders of magnitude increase in spatial resolution could be achieved by modulus mapping. Both the nanoindetation and modulus mapping results indicated that the modulus of the interface falls between 60–70 GPa. The packing density in the interface was non-uniform as two peaks of value were observed for the storage modulus distribution. This interface could be regarded as a dense hydration coating around cement grains, which was less permeable and hindered the further hydration of cement.揭示水泥基材料中 C-S-H 凝胶/水泥颗粒界面的 尺寸及微观力学特性, 为从纳米尺度理解水泥 基材料的性能提供依据。采用动态模量图技术对 C-S-H 凝胶/水泥颗粒界 面微区的尺度及力学行为进行研究, 借助动态 模量图的高分辨性, 可获得该微区精确且有效 的信息。对比利用纳米压痕及动态模量图对 C-S-H 凝胶/水泥颗粒界面进行研究。纳米压痕仅能粗略估计界面微区的尺寸及力学 参量, 相比之下, 动态模量图的分辨率要高出 2 个数量级 (表2), 因此可获得更精确的测量 值。 C-S-H 凝胶/水泥颗粒界面的尺寸在 250 nm 左右, 模量值介于 60 GPa 和 70 GPa 之间。 此界 面区可认为是包覆水泥颗粒周围的一层紧密的 水化层结构, 其致密性将阻止内部水泥的进一步水化。

This paper presents a preliminary exploration on tribological properties of cement composite material at micro- and nano-scales by means of the nano-scratch technique, which is a new instrument overcoming the limitations of both the classical stylus scratch test and the atomic force microscope. Measurements were conducted on two very different types of material: cement clinker paste and polymer-based cement clinker. Mechanical parameters related to the nano-tribological performance, i.e. penetration depth, coefficient of friction, and elastic deformation ratio, were obtained from the scratching processes. By statistical deconvolution analysis, microstructure constituents with a large discrepancy in elastic modulus and hardness values can be captured as single peaks, but not for the mixture of C–S–H and Ca(OH)2 phases. A reverse tendency was observed between penetration depth and coefficient of friction of both the substrate and hard particle phase embedded in. An H/E ratio dependent elasto–plastic behavior was identified, with the elastic deformation to be dominant in high H/E ratio phases. The results confirm this new technique as a promising method for quantitative characterization of elasticity, hardness and mar resistance of heterogonous phases in cement composite.