Abstract
The deformation of nanostructure of calcium silicate hydrate (C-S-H) in Portland cement (PC) paste under compression was characterized by the atomic pair distribution function (PDF), measured using synchrotron X-ray diffraction. The PDF of the PC paste exhibited a unique deformation behavior for a short-range order below 2.0 nm, close to the size of the C-S-H globule, while the deformation for a long-range order was similar to that of a calcium hydroxide phase measured by Bragg peak shift. The compressive deformation of the C-S-H nanostructure was comprised of three stages with different interactions between globules. This behavior would originate from the granular nature of C-S-H, which deforms with increasing packing density by slipping the interfaces between globules, rearranging the overall C-S-H nanostructure. This new approach will lead to increasing applications of the PDF technique to understand the deformation mechanism of C-S-H in PC-based materials.
Highlights
Portland cement (PC) paste is composed of various hydration products, such as calcium hydroxide (CH), ettringite, monosulphate, and calcium silicate hydrate (C-S-H), as well as several anhydrous PC clinker phases [1]
Various discussions on the mesoscale structure of C-S-H have been made regarding the basis of physical properties such as specific surface area, pore size, and density measured by a number of observation techniques [2,3,4]
Assuming that C-S-H acts as a granular material, the force transmission between globules follows the principle of the force chain network [18]
Summary
Portland cement (PC) paste is composed of various hydration products, such as calcium hydroxide (CH), ettringite, monosulphate, and calcium silicate hydrate (C-S-H), as well as several anhydrous PC clinker phases [1]. Jennings suggested that the basic model for the nanostructure of C-S-H to represent these physical parameters, which is a particle-packing model with nanoscale globules, is known as the colloid model [5, 6]. This is a useful model for understanding the physical and mechanical properties of C-S-H as in the case of Constantinides and Ulm [7] discovering the unique nanogranular behavior of C-S-H, driven by particle-to-particle contact forces, from the results of the mapping of the indentation modulus
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