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

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)