RESEARCH OF THE POSSIBILITY OF INCREASING THE QUALITY OF PREPARATION OF DRY MIXTURES IN A HORIZONTAL VANE MIXER

Paddle mixers with horizontal shafts are common at building materials enterprises for the preparation of concretes, mortars, dry mortars. A new design of a horizontal paddle mixer with rod elements located in front of the working surfaces of the blades, changing the trajectories of material particles, increasing their mobility, which leads to an increase in the degree of homogeneity of the mixed material, is considered. The aim of the study was to assess the influence of rod elements on the quality of preparation of a cement-sand mixture, to establish patterns of influence on it by the design and technological parameters of a two-shaft paddle mixer and to determine the areas of their rational values. The following tasks have been solved. A bench installation of a two-shaft horizontal paddle mixer with rod elements has been developed, on which experimental studies have been carried out on the preparation of dry cement-sand mixtures. For the criterion characterizing the quality of the mixture, the ultimate compressive strength of the prism specimens made from it is adopted. Regression equations are obtained that adequately describe the compressive strength of prism samples from the design and technological parameters of the mixer: the angle of the blades, the distance from the working surfaces of the blades to the rod elements, the rotational speed of the blade shafts, and their analysis is performed. The analysis of the change in the ultimate compressive strength of the prism specimens from the parameters under study is carried out, the rational ranges of their values are determined. It was found that a mixer with rod elements allows to obtain a dry cement-sand mixture, products from which have a higher compressive strength. During the work, the method of mathematical planning of experiments was used. As a result of the study, an assessment of the influence of rod elements on the quality of preparation of a cement-sand mixture was carried out, the regularities of the influence on it of the design and technological parameters of a two-shaft paddle mixer and the area of their rational values were established.

Carbonized Biomass as a bonding agent for Non-Load Bearing CHB Production

One‌ ‌of‌ ‌the‌ ‌most‌ ‌prominent‌ ‌construction‌ ‌materials‌ ‌for‌ ‌walls‌ ‌in‌ ‌the‌ ‌Philippines‌ ‌is‌ ‌the‌ ‌concrete‌ ‌hollow‌ ‌blocks‌ ‌or‌ ‌CHB‌ ‌due‌ ‌to‌‌ their lower cost‌ ‌than‌ ‌other‌ ‌available‌ ‌materials‌ ‌and‌ ‌the‌ ‌ease‌ ‌of‌ ‌production‌ ‌and‌ ‌installation.‌ To manage our energy and resources, including waste, carbonized‌ ‌biomass‌ ‌as‌ ‌a‌ ‌bonding‌ ‌agent‌ ‌for‌ ‌CHB‌ ‌production was studied to ‌aid‌ ‌in‌ ‌the‌ ‌country's growing‌ ‌need‌ ‌for‌‌construction materials‌ ‌. On-site fabricated CHB with several percent of carbonized biomass (CB) as substitutes for sand (0%, 20%, and 50% CB), including commercial CHB, are subjected to volume, weight, density determination, and ultimate compressive strength test. The gathered data undergo analysis through one-way ANOVA to determine the difference among the gathered compressive strength of CHB produced with different percentages of carbonized biomass. Cost analysis was also done to determine the costs and profitability of the CHB. As a result, the CHB with carbonized biomass as bonding agent produced CHB with low density, ultimate compressive strength better than commercially available CHB (with proper curing applied), and can be more profitable with increasing the carbonized biomass content.

Selective Electron Beam Melting (SEBM) of Pure Tungsten: Metallurgical Defects, Microstructure, Texture and Mechanical Properties

Effects of processing parameters on the metallurgical defects, microstructure, texture and mechanical properties of pure tungsten samples fabricated by selective electron beam melting (SEBM) are investigated. SEBM-fabricated bulk tungsten samples with features of lack of fusion, sufficient fusion, and over-melting are examined. For samples upon sufficient fusion, an ultimate compressive strength of 1.76 GPa is achieved at the volumetric energy density of 900 J/mm 3 ~1000 J/mm 3. The excellent compressive strength is higher and the associated volumetric energy density is significantly lower than corresponding reported values in literature. The average relative density of SEBM-fabricated samples is 98.93%, and no microcracks but only pores with diameters of few tens of micrometers are found in SEBM-ed tungsten samples of sufficient fusion. Properties of samples by SEBM and selective laser melting (SLM) have also been compared. It is found that SLM-fabricated samples exhibit inevitable microcracks, and have a significantly lower ultimate compressive strength and a slightly lower relative density of 98.51% in comparison with SEBM-ed samples.

Research of Physical and Mechanical Properties of Fly Ash Ceramics with SiO2 and Al2O3 Nanoparticles as Functional Addition

The article analyses the influence of SiO2 and Al2O3 nanopowders on properties of ceramics consisting of fly ash from thermal power plants, glass waste, and clay binder. Based on studies of physical and mechanical properties of the obtained ceramics (ultimate compressive strength, ultimate three-point bending strength, wear resistance, and water absorption), the paper shows the positive influence of the nanoadditives. The optimal number of SiO2 and Al2O3 nanopowders in the formulation is 0.5 wt. % that has the strongest effect on ultimate compressive strength and water absorption of the fly ash ceramics samples. The direction of further research on improving the properties of ceramic products is an application of the Al2O3 nanopowder as more perspective nanoadditive using clay dispersant.

Ultimate Compressive Strength of Steel Stiffened-Plate Structures Triggered by Brittle Fracture under Cryogenic Conditions

This chapter presents a practical method to investigate the effects of brittle fracture on the ultimate compressive strength of steel stiffened-plate structures under cryogenic conditions. Computational models are developed to analyse the ultimate compressive strength of steel stiffened-plate structures, triggered by brittle fracture, under cryogenic condition. A phenomenological form of the material model for the high-strength steel at cryogenic condition is proposed, that takes into account the Bauschinger effect, and implemented into a nonlinear finite element solver (LS-DYNA). Comparison between computational predictions and experimental measurements is made for the ultimate compressive strength response of a full-scale steel stiffened-plate structure, showing a good agreement between them.

Correction to: Study on Ultimate Compressive Strength of Aluminium-Alloy Plates and Stiffened Panels

A Correction to this paper has been published: 10.1007/s11804-021-00194-2