ANALYSIS OF THE MICROSTRUCTURE OF CONCRETE FRACTURES IN STRUCTURES THAT WORK ON COMPRESSION AND ITS IMPACT ON STRENGTH
DOI:
https://doi.org/10.31650/2786-6696-2022-2-70-76Keywords:
concrete, compressive structures, ultrafine modifiers, energy-dispersion x-wave analysis, scanning electron microscopy.Abstract
Comparative microanalysis and elemental analysis of the structure of chips of concrete composites of different strength from compressive structures were used. Analysis of the microstructure of concrete chips was performed using a scanning electron microscope from Oxford SU 70 using a CCD detector. Elemental analysis of objects was performed using energy-dispersive X-wave spectroscopy (EDC analysis). The method of energy-dispersive X-wave spectroscopy is used. The character of opening of cracks of concrete samples in the course of their destruction is analyzed. From the data of X-ray and spectral analysis it follows that in a series of samples of strength of 120 MPa in the process of hydration of clinker minerals during hardening of concrete a number of chemically active substances is formed. These are primarily potassium oxide hydrate, calcium silicate hydrate (HSC) and structural gel models such as Janite and Tobermorite. Modification of the concrete composite with a complex of MK and MTK create conditions for the conversion of unstable and soluble calcium hydroxide into a strong crystalline hydrate of calcium silicate.
The structure of concrete compacted in this form gives a significant increase in strength. The influence of ultrafine modifiers on the microstructure of cement stone formed during the operation of the structure and the strength of concrete are determined. The results of the scanning electron microscopy analysis show that the phase sizes differ slightly, but are not larger than ≈20 μm. Characteristic destruction of the sample with a strength of 120 MPa occurred in the main cracks, which develop due to the greater number of phases in contrast to the nature of the destruction of the sample with a strength of 50 MPa, which broke mainly on one structure. The complex of modifiers based on microsilica and metakaolin in the concrete mixture creates conditions for the conversion of unstable and soluble calcium hydroxide into a strong crystalline hydrate of calcium silicate. When using cement with a low content of C3S less than ≈50% significantly complicates the production of high-strength concretes, in particular when using silica and metakaolin, because the effectiveness of these additives implies the presence of excess portlandite Ca (OH)2 in the curing system, while systems with low C3S content is characterized by a reduced content of Ca (OH)2.
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