X-ray diffraction investigations of deformations and dislocation configuration in calcium hydroxide crystallites of concrete

Abstract

On the bases of proposed theoretical approach for analysis of X‐ray diffraction spectra the peculiarities of morphology, deformations, stresses and dislocation configuration of calcium hydroxide crystallites of interfacial transition zone in high‐strength concrete (the water‐cement ratio is about 0.35) are investigated. It is determined that the (0001) dislocation slip planes dividing the calcium hydroxide crystallites into coherent domains are arranged in them quasi‐periodically along c‐crystallographic axis. For dislocation configuration in crystallites the so‐called multilayer dislocation multipole configuration is proposed. From the reconstructed strain distribution function of coherent domains it was concluded that the most part of them are subjected to compressive strain caused most probably due to drying shrinkage phenomenon. The intrinsic stresses of crystallites are estimated for uniaxial compressive, hydrostatic compressive, and shear types of deformation. A possibility for dislocation pile‐ups formation in (0001) atomic planes (domain boundaries) is considered theoretically as well. From comparative analyses of intrinsic stresses of crystallites with their ultimate stresses it is assumed that the main mechanism leading to failure of calcium hydroxide both in interfacial transition zone and cement paste of concrete are dislocation pile‐ups which form against phase inclusions because of action of external shear stresses. The results are obtained and compared for two samples with granite and smoky quartz aggregates. It is assumed that the proposed theoretical approach for analysis of X‐ray diffraction spectra could be perspective especially for investigations of nanostructured polycrystalline materials with a columnar structure. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

X‐ray Diffraction Investigations of Microstructure of Calcium Hydroxide Crystallites in the Interfacial Transition Zone of Concrete

“…For comparison, Table II lists the parameters l a and ε d determined based on the Williamson-Hall plot. 10,12 There was a certain correlation between results obtained for parameters l a and ε d by the Williamson-Hall plot and our approach.…”

Deformation Mechanism of Hardened Cement Paste and Effect of Water

“…This finding indicates that the movement and removal of dislocation, or a similar mechanism, occurred in HCP. Dislocation can be formed in calcium hydroxide (Harutyunyan et al 2003), which occupies approximately 25% of cement hydrates by volume, in concrete by the stress induced by drying shrinkage. Each data set, except for the saturated sample tested at P c = 50 MPa, was fitted with one line (exponential approximation), and their slopes were approximately three (Fig.…”

“…This result shows the ductile deformation by dislocation and twinning at room temperature. The dislocation is observed in calcium hydroxide in concrete (Harutyunyan et al 2003). However, a large part of HCP is composed of C-S-H, which is generally regarded as a gel.…”

Nucleation of CaCO3 polymorphs from a colloidal alcoholic solution of Ca(OH)2 nanocrystals exposed to low humidity conditions

“…The calcium carbonate or carbonation reaction, obtained spontaneously from the reaction of calcium hydroxide (portlandite) is a process that concerns to research and application fields as diverse as biomineralization processes [1], [2], medical and pharmacological applications [3], [4], or as a product binder to improve the cohesion of highly porous materials [5]. Furthermore, its stability is very useful in the paper industry [6], in the restoration and conservation of paintings and sculptures [7], [8], or in the concrete and Portland cement industry [9].…”