The paper discusses the modeling of the forces of interparticle pair interaction of spheroidal agglomerate in composite cement. Based on the calculation of the autohesion forces that make up the spheroidal agglomerate, i.e. the Portland cement (“carrier particles”) and silica fume (“guest particles”), it was found that for uncharged particles the magnitude of the electric interaction forces is negligible in comparison with molecular van der Waals and capillary forces. The bipolar charging of particles in the corona discharge field at a corona electrode potential of +18 and –18 kV sharply increases the electric component of the autohesion force, which in value approaches the value of capillary forces. In this case, the Coulomb attractive forces between oppositely charged particles begin to act before the direct contact of the particles, which contributes to the agglomeration of particles. These calculations are confirmed by the results of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of composite cement samples containing Portland cement (75 %) and dry gas purification silica fume (25 %), the number of angular particles of irregular shape decreases for a mixture of these materials processed in the device for surface modification.
The aim of the research was to study the activation technology of the materials for concrete by their surface modification in a high-voltage electric field. It is noted that the mineral additives modified in a high-voltage electric field are characterized by a higher activity of the calcium hydroxide absorption. It was established that, despite the presence of a large number of crystalline compounds in metakaolin, its pozzolanic activity in the absorption of calcium hydroxide from a saturated solution is quite high. The same value of the hydration activity coefficient is also determined for the ground slag. The authors found that a characteristic feature of the dispersed mineral additives, surface-modified in a high-voltage electric field in comparison with control samples, are the lower values of bulk density and repose angle. This is due to a change in the forces balance that occurs during the mutual contact of particles. The influence of the mineral additives’ surface modification in a high-voltage electric field on interparticle interactions in the “solid – liquid” system is evaluated. It is established that in the absence of a repulsion barrier, the particles form the aggregates that increase their sedimentation rate. During unipolar or bipolar charging of particles in an electric field, the sedimentation rate slows down or accelerates accordingly. These effects are used to modify the cement surface.
With the increase in the number of finely dispersed mineral additives in concrete, their water demand increases and the effect of micro-filling weakens. To solve this problem, various methods of dry surface modification are proposed. As a result of the finely dispersed mineral powders’ surface modification, an improvement in their rheological characteristics, a decrease in wettability, a change in granulometry and other properties are achieved. This article discusses the surface modification effect’s laws in a high-voltage electric field on the autogenous properties of mineral dispersed concrete components, structure formation processes, mechanical properties, and cement stone hydration products. According to the results of the study, it was found that the surface modification of bulk materials - concrete components - in a high-voltage electric field changes autohesion properties in comparison with control samples. The data indicate lower values of bulk density and angle of repose. This is due to a change in the balance of forces that arise during the mutual contact of particles after surface modification. With a certain balance of these forces, autohesion will contribute to the dense packing of particles and thereby affect the structure formation processes. The results of changes in the plastic strength of cement pastes confirm that there is an intensification of the structure formation process. Moreover, a more intense increase in plastic strength is observed during bipolar charging of particles in comparison with unipolar charging. This is due to an increase in the number of heterogeneous charges in the system and, as a consequence, an increase in the strength of adhesive contacts, as evidenced by the data of X-ray phase analysis.
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