Slump Test: A New Empirical Model for High Yield Stress Materials

In order to decrease the fitting deviation between rheometrical measurements and empirical parameters using slump test, this paper proposes a new analytical method to evaluate the high yield stress of materials (cement pastes).In doing so, an experimental study was performed for measuring the empirical characteristics by cylindrical mold with different water to binder ratios (w/b) by aiming to increase the yield stress. Parallelly, experimental observations showed clearly the unyielded zone at flow stoppage of high yield stress samples. Based on these results, an idea was formed to applied metallic element at inlet of mold in order to push the spreading of paste. The obtained results of the model proposed in this paper were compared with the yield stress evaluated from shear flow curves using AR2000-rheometer with plate-plate geometry at rate-controlled. In fact, this study demonstrates the applicability and novelty of the present model in the process of relating the empirical parameters to yield stress.

PERBEDAAN EFEKTIVITAS PELARUT ORANGE OIL TERHADAP SEALER BERBASIS RESIS DAN ZINC OXIDE EUGENOL

This study aims to determine the differences in the effectiveness of orange oil solvent against resin-based sealers and zinc oxide eugenol. The samples of this study were resin based sealers and zinc oxide eugenol based sealers which were molded in a cylindrical mold made of aluminum with a diameter of 10 mm and a height of 3 mm. The total sample size in this study was 60 samples, then divided into 4 groups, 2 groups for resin-based sealers with a time of 2 minutes and 5 minutes, and a sealer based on zinc oxide eugenol with a time of 2 minutes and a time of 5 minutes, after which it was put into incubator with a temperature of 370C for 48 hours, then weighed for each group. Data analysis used paired T test with the Kolmogorov Smirnov normality test. The results showed that the orange oil solvent did not have a significant difference to the resin-based sealers and the zinc oxide eugenol-based sealers. At the immersion time of 2 minutes, the solubility of resin-based sealers and zinc oxide eugenol did not have significant differences (p> 0.05). Based on the research results, it can be concluded that orange oil solvent is equally effective in both sealers, neither is more effective than the other Keywords: Orange Oil solvent, resin sealer, Zinc Oxide Eugenol sealer.

Does Self-Compacting Concrete Exert more Pressure on Formworks than Normal Vibrated Flowing Concrete?

This paper investigates lateral pressure on formwork indirectly by measuring lateral deflection using an innovative device. This device is fabricated from Polyvinyl Chloride (PVC) cylindrical mold in a fashion allowing occurrence and measurement of lateral movement at different depths using dial gauges. The lateral deflections for different systems of filling materials including water, sand, self-compacting concrete (SCC), and flowing concrete. The flowing concrete is tested under two conditions, vibrated (NVC), and non-vibrated (NCno.V). The results show that the NVC produced the largest lateral deflection which attributed to the vibration pressure. The measured lateral deflection are ranked descending in the following order: NVC, Water, SCC, NCno.V and Sand.

The effect of the temperature dependence of the heat conductivity on the physical laws of the bulk synthesis of a composite

Two-dimensional model of high-temperature synthesis of chemical compounds and alloys in a dynamic thermal explosion mode when a powder compact is heated in a steel cylindrical mold by an induction heat source are proposed. The complex of chemical reactions is described by a total reaction with effective formal kinetic parameters. The kinetic law takes into account strong retardation of the reaction by the layer of the synthesized product that prevents the interaction of the reagents. The model makes it possible to investigate the macroscopic physical laws of the synthesis of a composite with a change in the heating rate and reactor dimensions. It is made a comparison of the results obtained for a constant heat conductivity coefficient and a temperature-dependent heat conductivity coefficient. It is revealed that taking into account the temperature dependence of the heat conductivity coefficient can lead to a numerical change in the ignition delay time and to a qualitatively different temperature distribution in the reactor bulk.

Pengaruh Temperatur, Komposisi Bahan Cangkang Inti Kelapa Sawit dan Konsentrasi Perekat pada Karakteristik Briket Komersial dari Tempurung Kelapa Sawit

Briquettes are an essential product for metal mineral processing plants in Indonesia. One good alternative raw materials for briquettes that do not pollute the environment is the palm kernel shell. This research was conducted by making briquettes from palm kernel shells to find optimal variations in carbonization temperature, material mixture, and adhesive mixture. The research was conducted on a laboratory scale. The palm kernel shell and coal kernel were carbonized at various temperatures, namely 450°C, 550°C, and 650°C, then crushed and sieved to 35 mesh. The powdered palm kernel shell and coal that have become powdered charcoal are weighted based on a mixture of powder and the adhesive composition ratio of 40 g. After that, the briquettes were formed under a pressure of 100 kg/cm² on a cylindrical mold with 40 mm. The analyzes carried out were moisture content, ash content, volatile substances content, fixed carbon content, calorific value, compressive strength, density, porosity, and SEM (Scanning Electron Microscope). The results showed that the briquette from the kernel of the palm kernel shell was optimal at a temperature of 550 ° C with a starch adhesive mixture of 7.5%, a pressure of 100 kg/cm², moisture content of 5.34%, an ash content of 5.81%, a substance content. Volatile amounted to 18.77%, 71.08% for fixed carbon, heating value 7125.86 cal/g. Density of 0.78, porosity of 0.04 and strength of 72.56 kg / cm².

Surface Geometry of Four Conventional Nanohybrid Resin-Based Composites and Four Regular Viscosity Bulk Fill Resin-Based Composites after Two-Step Polishing Procedure

Objectives. The aim of the study was to determine the quantitative and qualitative surface structure of contemporary RBCs in posterior teeth reconstructions: regular viscosity bulk fill and conventional composites, obtained after two-stage polishing procedure. Materials and Methods. Four conventional nanohybrid composites (Tetric EvoCeram, GrandioSO, Filtek Z550, and Ceram·X Mono) and four regular viscosity bulk fill composites (Tetric EvoCeram Bulk Fill, X-tra fil, Filtek Bulk Fill Posterior, and QuixFil) were tested. Samples of each RBC were prepared using PMMA cylindrical mold. After two-step polishing procedure, a surface geometry was evaluated under profilometry (Turbowave v. 7.36, Hommel-Etamic) and SEM (VEGA 3, Tescan Analytics). To evaluate differences between values, the following nonparametric tests were used: Friedman’s ANOVA, Wilcoxon’s matched-pair test, ANOVA Kruskal-Wallis, and Mann-Whitney U. Results. All conventional RBCs showed Ra values in the range of 0.20-0.26 μm. Bulk fill showed higher values in range of 0.49-1.36 μm except for Filtek Bulk Fill Posterior, which achieved 0.23 μm Ra value. SEM images of conventional RBCs were described as smooth surfaces with slight damage except for TEC, which presented smooth surface with no damage. Bulk fill composites showed rough surface, except for TBF, which presented smooth surface with slight damage. Conclusions. Regular viscosity bulk fill composites do not constitute a homogeneous group regarding surface roughness after polishing. They obtain, for the most part, poorer smoothness values after polishing than conventional RBCs.

Study of the Compressive Strength of Mortars as a Function of Material Composition, Workability, and Specimen Geometry

In the present work, the statistical dispersion of the mortar compressive strength as a function of the geometric parameters of the specimens as well as the effect of the mortar workability difference on the compressive strength was investigated. For this purpose, specimens were prepared for six types of mortars: two conventional mortars in the proportions of 1 : 1 : 6 and 1 : 2 : 9 of cement, hydrated lime, and sand, respectively, two with clay replacing lime, and two with marble waste in place of lime. The results confirm the difference between the results found for the two geometries due to the differences in the heights of the molding layers and show that the workability of the mortar modifies the resistance properties, especially in the cylindrical mold where the molding of the specimens is more complex. By comparing the differences between the destructive test results and those defined by the Finite Element Modeling (FEM) for conventional mortars, it was clear that the effect of excess material in the sample during the compression tests did not change the strength properties studied. This facilitates the performance of the assay as specimens may be used excessively on the side without the need for sample rectification.

Elution Study of Three Light-Cured Orthodontic Adhesives

Objectives: The aim of the study was to evaluate monomer elution from three commercial orthodontic adhesive pastes. Methods: Three monomers BPA, Bis-GMA, and TEGDMA were observed from Green Glue (Hangzhou Westlake Biomaterials Co., Zhejiang, China), GrenGloo (Ormco Co., Glendora, CA, USA), and Transbond XT (3M Unitek, St. Paul, MN, USA). The adhesive was light-cured in a cylindrical mold with 6 mm in diameter and 2 mm thick, before immediately immerse into 10 ml extraction media of 75%ethanol in a tightly sealed container at 37°C. The solution was refreshed at four intervals of time 1, 3, 5, and 7 d. The immersion medium was determined using High-performance liquid chromatography (HPLC). Results and Conclusions: BPA were found from three adhesives. Bis-GMA was found only from Transbond XT. TEGDMA were found from both Green Glue and Grengloo. Green Glue had 10-30 times higher TEGDMA elution than Grengloo. Major elution was found from all orthodontic adhesive paste within 1 d, and decrease with time to 7 d.