Nano-mechanical Behavior of Calcium Silicate Hydrate and Calcium Hydroxide in Cement Paste: Elevated Peak-Force Study

In this paper, the mechanical behavior of calcium–silicate–hydrate (C–S–H) and calcium–hydroxide (CH) was investigated at the nano-level. This study aims to propose a new method of evaluating nano-mechanical behavior of the two main cement paste components of C–S–H and CH. Nano-mechanical behavior of cement paste components is assessed, utilizing novel peak-force tapping mode of atomic force microscope and new proposed technique of elevated peak-forces. Another aim of this study is to investigate the early age properties of cement during the initial setting time by atomic force microscope. As a result, it is indicated that mostly C–S–H colloids treated as ductile materials comparing to brittle behavior of CH mono-layer sheet. However, multilayer of CH behaves like semi-ductile and plastic materials in very small increments of deflection. It was found that the trend of Young’s modulus is divided to three major intervals. Preliminary, the values were decreased within 20 min after the beginning of hydration and then it seems to be constant up to about 45 min after hydration (the initial setting time of cement). After that, Young’s modulus gradually increased up to 2 h after hydration to a relatively higher value. The roughness trend can be divided into three different phases as well as the Derjaguin, Müller, and Toporov modulus. First, at early 10 min, the values are increased drastically. Second, the average values are decreased sharply at 20 min after hydration and also reduced gradually up to around 60 min after hydration.