Solid State Phenomena Vol. 352

Abstract: Computational modelling of quasi-brittle fracture in cement-based composites needs to cover both i) the damage caused by micro-fractured zones, referring to some nonlocal strain-stress relations, respecting quite different behaviour of such composites in tension and compression, and ii) the initiation and propagation of macroscopic cracks, exploiting the cohesive zone model, handled by some modification of the finite element technique, together with the discretization in time. A fundamental issue for such model is the introduction of a traction-separation (stress-displacement) relationship. This contribution pays particular attention to the design, identification and estimation of material parameters for the traction separation law suitable for predicting the deformation behaviour of samples of materials and structures.

Abstract: Cement production is currently very energy-intensive, with the grinding process consuming the majority of the total energy in cement production. Therefore, there is a constant search for ways to reduce this amount of energy while maintaining the same grinding efficiency. The main goal of the article is to investigate the effect of grinding intensifiers, which should reduce the energy needed to grind raw materials. Potentially usable technologies in the field of mechanochemical activation are investigated, i.e., high-speed grinding through grinding in a laboratory planetary mill and disintegrator. High-speed disintegrator grinding technology is much more efficient than planetary grinding technology. Already during the first passage through the disintegrator, an increase in the specific surface area from 200 m²/kg to 280 m²/kg was recorded, with an estimated stay of the particle in the grinding space for 3-5 seconds. Using a planetary mill, the particles would have to remain in the grinding chamber for approximately 2 minutes to achieve such an increase in specific surface area. However, with further drops, the efficiency decreases, which is due to the high tendency to aggregation and agglomeration in this milling technology.

Abstract: Lightweight refractory materials are most used as a second layer in the lining. Many techniques can be used to their production depending on their final application. This manuscript is focused on utilization of sol-gel method as the replacement of hydraulic or ceramic bond in the manufacturing process of grog and castable preparation. The results show possible ways to produce high quality lightweight refractory grog with very high purity and also lightweight refractory castable, which performs good results in terms of bulk density, apparent porosity, cold crushing strength, cold modulus of rupture and permanent linear changes.

Abstract: The paper deals with the production of fibre-cement and the use of limestone cement in its production. The paper describes the basic properties of final products, the basic raw materials and the Hatschek production technology used for the production of corrugated sheets. The attention is paid especially to the wet part of the production when describing the production process. The emphasis was mainly placed on the preparation of fibre-cement slurry and the gradual formation of a layer of fibre-cement on the surface of the cylindrical sieve. The paper describes the possible use of limestone cement in the production of corrugated sheets. Trial recipes were designed with using limestone cement CEM II with and without separately dosed limestone. The fibre-cement corrugated sheets were produced with using Hatschek technology. Mainly was investigated the influence of limestone dosing on the strength characteristics and the volume weight of the final products. The produced sheets were tested according to EN 494+A1: 2016 Fibre-cement profiled sheets and fittings - Product specification and test methods. The tested samples reached comparable results like sheets produced according to standard recipe. No negative effect on the strength characteristics of final products was proven between the standard and the trial recipes.

Abstract: The burning process of limestones is an important process in the modern industries, which can be described in two parts, CaCO₃ decarbonation due to the thermal stress and formation of CaO crystalline structure. It was already observed that the different composition and structure of a raw material influence the transformation process and has affect on the chemical and mechanical properties on the formed lime. This study is focused on the characterization of the raw material (porosity, chemical composition, geological age and origin) and its effect on the burning process and the formation of CaO and its properties. The microstructure of studied material burnt at different times of isothermal load was observed by SEM and the reactivity test was measured and analyzed. The limestone with a more porous inner system was burnt faster and is inclinable to overburn at longer thermal load.