Rimvydas Stonys

Investigating the hydration of deflocculated calcium aluminate cement-based binder with catalyst waste

The hydration of the binder, consisting of calcium aluminate cement (CAC) with Al2O3 >70% and with or without the additives of the FCC catalyst waste and polycarboxylate deflocculant Castament FS-20, is investigated. The methods of calorimetry, thermal analysis, XRD, electrical conductivity, SEM, as well as ultrasonic wave velocity measuring and bending strength evaluation are used. The results of the investigation show that the FCC catalyst as well as polycarboxylate deflocculant, are active additives, influencing the CAC binder’s hydration process. In the structure of the hardened binders, certain amounts of unhydrated CAC minerals, CA, and CA2, and the hydration products, such as CAH10, C2AH8 and the amorphous AH3, are found. However, in the binder with a deflocculant, there are smaller amounts of CAH10 and the amorphous AH3, though the amount of C2AH8 is higher than that in the binder without a deflocculant additive. It has been found that in the case, when the FCC catalyst and deflocculant are simultaneously used, the FCC catalyst produces a positive effect on the formation of the CAC binder’s structure, increasing its mechanical strength. The results obtained in this article allow to predict that the FCC catalyst and deflocculant simultaneously used as the additives to the CAC binder, will enable to control the hydration process of the binder.

Reuse of ultrafine mineral wool production waste in the manufacture of refractory concrete

The paper deals with the mineral wool production waste (cupola dust - CD), presents CD characterization and aims to reuse CD in production of refractory concrete with calcium aluminate cement. The study of CD covers its chemical, phase and thermal analyses along with the morphological study and determination of particles size distribution. Zeta-potential, electrical conductivity and pH values of CD suspension are presented in the paper as well. Commercial microsilica additive in refractory concrete has been replaced with cupola dust. Compositions of refractory concrete have been prepared by incorporating 1%, 2% and 3% of CD. The bulk density, ultrasonic wave velocity, cold crushing strength and thermal shock resistance of the created refractory concrete have been determined. Based on experimental results, it has been found that cupola dust may be used for the production of refractory concrete. The environmental impact related to the CD reuse in refractory concrete production has been evaluated as well.

Investigation of influence of nano-reinforcement on the mechanical properties of composite materials

AbstractThe present work studies the possibility to decrease the formation of micro and nano cracks around short fibres in fibre-reinforced concrete (FRC) composite with the help of nano-reinforcement, which is carbon nanotubes, or micro reinforcement, which is carbon short fibres and nano-fillers. Tensile and bending strength of FRC depends on the spatial distribution of fibres inside a material, type of fibre and cement matrix, as well as an effective micromechanical work of each fibre while pulling out of the concrete matrix. Shrinkage stresses, acting in the matrix in the vicinity of a fibre, lead to the formation of micro-cracks. Such micro-cracks were observed experimentally and were investigated numerically performing broad modelling based on the finite element method (FEM). The investigation was focused on the micromechanical behaviour of a single steel fibre in a cement matrix. Numerical modelling results demonstrated a high level of shrinkage overstresses around steel fibres in concrete. The rol...

Action of the Products of Biofuel Combustion on the Phase Composition and Structure of Refractory Material

The changes occurring in the phase composition and microstructure of aluminum-silicate refractory material which disintegrated during operation in a solid-biofuel combustion unit were investigated. The main reasons for the disintegration of the material were determined on the basis of investigations performed by using modern methods and analyzing the results in comparison with published data on the chemical composition of volatile products of biofuel combustion and their physical-chemical properties.

Study of Alkali Resistance of Refractory Materials Used in Boilers Operating on Wood Fuel

Using the ASTM C 454–83 method alkali resistance is studied for various refractories (chamotte brick, traditional and medium-cement chamotte concrete) used most often in power generation boilers operating on wood fuel. Resistance to alkali of medium-cement concrete developed by the authors with a filler prepared from sinter grade Gorkal-50 (produced by the Gorka Plant, Poland) is also studied. It is established that use of milled quartz sand additive improves resistance of the test cement significantly towards the action of alkaline salt (K2CO3 is used in the work) at 1100°C. It is shown that the test additive during action of alkali facilitates formation of a protective layer that prevents penetration of K2CO3 decomposition products into the material structure.

Effect of short fibers orientation on mechanical properties of composite material – fiber reinforced concrete

AbstractTraditional fiberconcrete structures have fibres in the mix oriented in all spatial directions, distributed in the structural element volume homogenously, what not easy to obtain in practice. In many situations, structurally more effective is the insertion of fibres into the concrete structural element body by forming layers, with a predetermined fibre concentration and orientation in every layer. In the present investigation, layered fibre concrete is under investigation. Short steel fibres were attached to flexible warps with the necessary fibres concentration and orientation. Warps were placed into the prismatic mould separating them by concrete layers without fibres. Prisms were matured and tested under four-point bending. The bending-affected mechanical behaviour of cracked fibre concrete was simulated numerically by using a developed structural model. Comparing the simulation results with experimental data, material micromechanical fracture mechanisms were analysed and evaluated.

The effect of carbon and polypropylene fibers on thermal shock resistance of the refractory castable

AbstractThis work investigates medium cement refractory castable with additives of carbon and polypropylene fibers. The peculiarities of microstructure changes in the fiber and castable matrix contact zone, channel formation, and changes of cold crushing strength of fiber additives, which have a refractory castable matrix under temperature treatment, were investigated. The investigation results allowed to predict that using a mix of fibers more effective than using them individually. The influence of fiber additives on the mechanical characteristics and thermal shock resistance of the refractory castable with fiber additives was tested. It was found that the addition of carbon fiber has a positive impact on the thermal shock resistance of the investigated castable, which is confirmed by the results obtained by thermal cycling, as well as by the values calculated for thermal shock resistance R4 and Rst. In addition, the results of the investigation of thermal cycling show that the value of the thermal shoc...

The Investigation of Properties of Insulating Refractory Concrete with Portland Cement Binder

The present work contains the results of experimental study on properties of insulating refractory concrete created on the basis of Portland cement (PC) binder and modified with microsilica (MS). The experimental compositions were made using Portland cement, lightweight aggregates (expanded clay and vermiculite) and microsilica additives. It was established that MS additives enable significant improvement of mechanical properties and thermal shock resistance of PC-based insulating concrete with values comparable to insulating refractory concrete based on calcium aluminate cement.