Effect of mechanical activation on the properties of Portland cement

The paper deals with the mechanical activation of cement by grinding in a high-speed mill, and compares the parameters found with the commonly used grinding method in cement production, which uses grinding of cement by means of a ball mill. The aim is to verify the influence of the aging time of the ground material on the preservation of the mechanical activation effect and on the properties of the final product at different stages of hydration. It evaluates the physical-mechanical properties, the compressive and tensile strength after 1, 2, 7, 14 and 28 days, as well as the course of the hydration process. The evaluated results suggest the existence of mechanical activation, but this effect is very difficult to achieve and depends on many other factors.

Opposing Effects of Additives in Dry Milling and Tableting of Organic Particles

Applying additives and excipients during the dry processing of fine particles is a common measure to control the particle–particle interactions, to specifically influence the powder properties and to enhance the process efficiency or product quality. In this study, the impacts of a particulate lubricant, a nano-disperse flow additive and liquid grinding aids on the dry fine milling and subsequent tableting of the ground material were investigated for three different organic model compounds. It is presented that the three additive classes cause varying and partly opposing effects during these process steps. Especially the lubricant and the grinding aids were shown to increase the efficiency of the milling process as well as the product fineness of the ground material, and to avoid critical product adhesions on the machine surfaces. Thereby, stable and efficient grinding conditions were partially not possible without the addition of such additives. However, as these positive effects are attributed to a reduction of the adhesive forces between the particles, much lower tablet strengths were achieved for these additives. This propagation of powder, and in turn, final product properties over whole process chains, has not been studied in detail so far. It was further revealed that the material behavior and the microstructure of the product particles is decisive for the processing as well, which is why additive effects may be product-specific and can even be suppressed under certain processing conditions. In comparison to the process performances, the powder properties and surface energies of the product particles were less influenced by the additives. On the contrary, particle-based morphologies or deformation behavior seem to play a major role in comparison to inorganic materials. Thus, it can be stated that global bulk properties and surface energies provide first indications of powder behavior and susceptibility. However, additional specific properties need to be evaluated to more clearly understand the influences of additives.

Evaluation of the Bacteriological risk of solid Medical and Pharmaceutical waste from a Moroccan Hospital Center

Medical and pharmaceutical waste (MPW) pose a big problem in society and at the healthcare centers because they cause a bacteriological risk in the living being and the environment. Morocco, since 1991, has developed a legal arsenal on medical and pharmaceutical waste. In order to identify pathogens at the level of hospital waste, and to assess their treatment system, this study was carried out at a Moroccan hospital center. The analysis of the samples was performed at the medical biology laboratory of the same hospital. Eleven samples were done at four care units, including two at the internal storage room before treating waste with an ECODAX T300 type mill, and two after treatment from the ground material and leachate. Before crushing 63.6% (7/11) of the samples gave positive cultures. The presence of pathogenic microorganisms such as (Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas stuzerie and Pseudomonas fluorescens) have been identified and their sensitivity to antibiotics has also been determined. After the grinding cycle, the microbiological characterization of the samples on ground material and leachate revealed 100% of bacterial presence, the microorganisms (Escherichia coli and Klebsiella pneumoniae) were identified. The results show that hospital waste encloses multi-resistant pathogenic bacteria before and after their treatment, which raises a big question mark on the quality and effectiveness of the treatment of MPW.

Effect of Specimen Placement on Model Rock Blasting

Small-scale model blasting plays an important role in understanding mechanism of rock fragmentation by blasting and improving blast technology in rock and mining engineering. Because a specimen (or model) often needs to be placed on either a ground or another material in model blasting, an additional interface appears between the specimen and the ground (or material), compared with an engineering blast that does not have such an interface. In this paper, four model blasts with high-speed photography were presented. The results showed that: (1) as the impedance of a rock specimen was smaller than that of the ground material, the specimen was thrown up and a certain amount of kinetic energy was brought with such a bounce. Thus, this placement should be avoided in model blasts. (2) As a rock specimen was placed on three blocks of the same type of rock as the specimen the specimen was not bounced up during blasting. Correspondingly, no kinetic energy was induced by specimen bounce. Therefore, this placement is recommended for model blasting. If very high specific charge must be used in model blasting, the above-recommended method will not work well due to possible breakage of the base material during blasting. In this case, the rock specimen can be placed on a material with smaller impedance than that of the rock specimen so that specimen bounce can be reduced. Accordingly, such a possible specimen bounce should be estimated by stress wave analysis.

CONDITION OF THE TREATED SURFACE OF NIOBIUM-BASED ALLOY WHEN GRINDING FROM SILICON CARBIDE

The study of the surface of silicon carbide after grinding niobium was carried out on a Versa 3D electronic microscope. It is shown that as a result of the grinding, traces of the grinding wheel material are formed on the treated surface, and the ground material itself is prone to adhesion to the grinding wheel. As a result of cohesive interaction, the metal adhering to the grinding wheel is transferred, and vice versa. And, as a result of adhesion-fatigue processes, mechanical action, there is a hanging wear of the grinding wheel and the indentation of individual crystals of silicon carbide into the surface of the metal being processed. This article examines such features of the behavior of niobium, when grinding it with silicon wheels and is considered from the standpoint of the electronic structure of the metal atom.

MITIGATING TSUNAMI DAMAGE BY PROMOTING GROUND EROSION

To reduce the damage caused when a tsunami overflows coastal dikes, this study performs hydraulic experiments and numerical simulations and proposes a new method for slowing the tsunami by intentionally eroding parts of the ground. The effectiveness of the proposed method is assessed, velocity-reduction mechanism is clarified, and reduced tsunami velocity is predicted. Using crushed expanded polystyrene (EPS) as the ground material, vertical erosion is enhanced and a large depression is formed that changes the flow from supercritical to subcritical, thereby decelerating it. Assuming a constant tsunami overflow rate, the tsunami velocity after deceleration can be predicted with [Formula: see text] uncertainty.