Search Results (5)

This paper deals with a method for producing gypsum concrete by vibropressing ultra-stiff concrete mixtures with a water–gypsum ratio (W/G) of 0.25–0.35 (stiffness 50–55 s according to Vebe), as well as the method of designing the composition of such concrete. The research was carried out using mathematical experimental design. Experimental and statistical polynomial models of strength and average density dependences on technological factors such as moisture content in the gypsum concrete mixture, aggregate consumption, and vibropressing parameters (dynamic punch pressure during vibration and process duration) were obtained. Models of the aggregate quantity and granulometric composition influence on the gypsum concrete strength at constant compaction parameters and changes in the mixture moisture content were obtained. Based on the obtained models, a method for designing the composition of vibropressed gypsum concrete on dense aggregate was developed. According to the proposed method, the aggregate-to-gypsum ratio (A/G) is first found, taking into account the given strength and quality of the materials. Next, the optimal W/G ratio, which ensures maximum compaction, is calculated and, after that, the residual air volume and the component consumption are obtained. The method allows determining the composition of gypsum concrete on dense aggregate, compacted by vibropressing of superhard mixtures according to a given compressive strength after 1 day of hardening in the range from 15 to 44 MPa. It also allows you to take into account the operating parameters of the molding plant, the aggregate grain composition, and determine the optimal moisture content of the gypsum concrete mixture. Full article

This work focuses on the use of municipal waste incineration bottom ash (MSWI) for the development and production of products suitable for use as construction products. The generation of these ashes is increasing every year due to the incineration of municipal waste. There are currently three incineration plants operating in major cities in Lithuania. The non-hazardous bottom ash remaining from the incineration process is stored in dedicated sorting and aging sites until it is used as an inert form of aggregate for the installation of road foundations. However, it has been observed that these ashes have a tendency to bind and cement when exposed to atmospheric precipitation at the storage site. Based on this characteristic, it was decided in this study to use alkaline activation of the ash to accelerate the bonding process and to create a dense, non-porous composite concrete structure. This activation method is known to create another problem during ash bonding, where the presence of metallic aluminum particles in the ash leads to the release of hydrogen gas and makes the structure of the cured samples porous. For the purposes of the study, it was decided to create a completely different mixture structure and not to use additional water in the mixtures tested. A very low water/solids ratio (W/S) of <0.08 was used for the alkaline activation of the mixtures. All the water required for ash activation was obtained from sodium silicate and sodium hydroxide solution. Metakaolin waste (MKW) was used to adjust the SiO₂/Na₂O/Al₂O₃ ratio of the mixtures. Vibro-pressing was used to form and increase the density of the samples. And for the formation of the concrete structure, 0/4 fraction sand was used as aggregate. The final alkali-activated sample obtained had properties similar to those of the very widely used vibro-pressed cementitious paving tiles and did not exhibit hydrogen evolution during alkali activation due to the very low W/S ratio. The best results were achieved by samples with a highest compressive strength of 40.0 MPa and a tensile strength of 5.60 MPa, as well as a density of 1950 kg/m³. It is believed that this alkaline activation and vibro-pressing method can expand the use of MSWI ash in the development of building products. Full article

The article provides a brief overview of technologies and methods for processing dispersed metallic waste generated during ferroalloy production, including high-carbon ferrochrome (HCFeCr). It is noted that the most cost-effective and rational method for reusing metallic dust is briquetting. Considering the development of briquetting technologies, as well as the latest equipment and binder materials involved in this process, aspiration dust from ferrochrome crushing can be fully utilized in metallurgical recycling. To verify this assumption, laboratory studies were conducted using polymer-based binders and liquid glass as a baseline option. The methodology of briquetting using both laboratory and industrial presses is described, along with an assessment of the mechanical properties of the briquettes. The studies indicate that the introduction of an inert filler (gas-cleaning dust) into the metallic dust composition improves the briquetting ability of the mixture by enhancing adhesion between metal particles and the binder. The obtained industrial briquette samples exhibit high mechanical strength, ensuring their further use in metallurgical processing. The study concludes that semi-dry briquetting using hydraulic vibropresses is a promising approach for the utilization of dispersed ferroalloy waste. Full article

To reduce CO₂ emissions from the building industry, one option is to replace cement in specific applications with alternative binders. The Carbstone technology is based on the reaction of calcium- and magnesium-containing minerals with CO₂ to form carbonate binders. Mixes of carbon steel slag and stainless-steel slag, with tailored particle size distributions, were compacted with a vibro-press and subsequently carbonated in an autoclave to produce carbonated steel slag pavers. The carbonated materials sequester 100–150 g CO₂/kg slag. Compressive and tensile splitting strength of the resulting pavers were determined, and the ratio was found to be comparable to that of concrete. The environmental performance of the Carbstone pavers, with an average tensile splitting strength of 3.6 MPa, was found to be in compliance with Belgian and Dutch leaching limit values for construction materials. In addition, leaching results for a concrete mix made with aggregates of crushed Carbstone pavers (simulating the so-called “second life” of pavers) demonstrate that the pavers can be recycled as aggregates in cement-bound products after their product lifetime. Full article

The concrete industry is under increasing pressure to reduce greenhouse gas emissions. An immediate solution is to minimize the amount of Portland cement used by partially substituting other supplementary cementitious materials. This article presents the results of an experimental campaign on the influence of replacing Portland cement with both calcined and uncalcined diatomites from the filtration of beer and wine in the production of elements made of vibro-pressed pre-cast concrete, such as pipes. Additionally, a natural diatomite is used. The mechanical properties, capillary water absorption, carbonation, and chloride ingress are tested. The results obtained show the possibility of using natural and recycled diatomites on an industrial scale, which can improve even the long term properties of prepared precast concrete. Full article