Temperature effects on local structure, phase transformation, and mechanical properties of calcium silicate hydrates

Abstract

This study aims to elucidate the effect of heating on the local atomic arrangements, structure, phase transformation, and mechanical properties of synthesized calcium–silicate–hydrate (C–S–H). The alteration in the atomic arrangement of the synthesized C–S–H (Ca/Si =0.8) and the formation of crystalline phases that occurred in three distinct transformation stages of dehydration (105°C–200°C), decomposition (300°C–600°C), and recrystallization (700°C–1000°C) were investigated via powder X‐ray diffraction, 29Si nuclear magnetic resonance spectroscopy, and thermogravimetric analysis. Further, the deformation of the local atomic bonding environment and variations in mechanical properties during the three stages were assessed via pair distribution function analysis based on in‐situ total X‐ray scattering. The results revealed that the C–S–H paste before heating exhibited a lower elastic modulus in real space than that in the reciprocal space in the initial loading stage because water molecules acted as a lubricant in the interlayer. At the dehydration stage, the strain as a function of external loading exhibited irregular deformation owing to the formation of additional pores induced by the evaporation of free moisture. At the decomposition stage, the structural deformation of the main d‐spacing (d ≈ 3.0 Å) was similar to that of the real space before the propagation of microcracks. At the recrystallization stage, the elastic modulus increased to 48 GPa owing to the thermal phase transformation of C–S–H to crystalline β‐wollastonite. The results provide direct experimental evidence of the microstructural and nanostructural deformation behavior of C–S–H pastes after exposure to high temperature under external loading.

In situ TEM observation of calcium silicate hydrate nanostructure at high temperatures

“…C-S-H can even transform into wollastonite at a temperature of over 850 o C [13,32]. Some techniques such as high temperature XRD or neutron diffraction can be the powerful alternatives to resolve the crystallization and transformation of C-S-H during the heating process [12,13,33].…”

Evolution of C–S–H in lime mortars with nanoparticles: Nanostructural analysis of afwillite growth mechanisms by HRTEM

“…A significant increase in temperature can change its local structure, which leads to phase transformations that modify various properties, including mechanical response 106 and solubility 96 . In afwillite, Ca solubility generally decreases with increasing temperature 53 .…”

“…The maximum creep resistance achieved when the Ca/Si ratio is 1.5, similar to the Ca/Si ratio in afwillite, leading to a modification in the mechanical response of the material. 3 A significant increase in temperature can change its local structure, which leads to phase transformations that modify various properties, including mechanical response 106 and solubility. 96 In afwillite, Ca solubility generally decreases with increasing temperature.…”

Influence of the availability of calcium on the hydration of tricalcium aluminate (C3A) in seawater‐mixed C3A–gypsum system

“…Concrete is the most widely used man-made construction material in the world. [1][2][3] In the last few decades, along with the rapid urbanization, a great number of infrastructural projects have been constructed, especially in developing countries. The global cement production has been, thus, increasing rapidly from about 1.1 billion metric tons in 1990 to over 4 billion metric tons in 2020.…”

“…Concrete is the most widely used man‐made construction material in the world 1–3 . In the last few decades, along with the rapid urbanization, a great number of infrastructural projects have been constructed, especially in developing countries.…”