Producing Heavyweight High-Performance Concrete by Using Black Sand as Newly Shielding Construction Material

Experimental work was carried out to study new fine aggregate shielding construction materials, namely black sand (BS). The BS effect on the mechanical, durability, and shielding characteristics of heavyweight high-performance concrete (HWHPC) was evaluated. This study aimed at improving various HWHPC properties, concertedly. Fifteen mixtures of HWHPC were made, with various variables, including replacing 10% and 15% of the cement with fly ash (FA) and replacing normal sand by BS at various contents (15%, 30%, 45%, 60%, 75%, and 100%). The test specimens were subjected to various exposure conditions, including elevated temperatures, which ranged from 250 °C to 750 °C, for a duration of 3 h; magnesium sulfate (MS) exposure; and gamma-ray exposure. The effects of elevated temperature and sulfate resistance on concrete mass loss were examined. The results revealed that BS is a promising shielding construction material. The BS content is the most important factor influencing concrete compressive strength. Mixes containing 15% BS demonstrated significantly better strength compared to the control mixes. Exposure to 250 °C led to a notable increase in compressive strength. BS showed a significant effect on HWHPC fire resistance properties, especially at 750 °C and a significant linear attenuation coefficient. Using 10% FA with 15% BS was the most effective mixing proportion for improving all HWHPC properties concertedly, especially at greater ages.

Study on Stem Cutting Propagation of Gynostemma Pentaphyllum (Thunb.) Makino in Hoa Binh Province

Gynostemma pentaphyllum (Thunb.) Makino is a medicinal plant distributed mostly in the mountainous areas of Vietnam. G. pentaphyllum contains more than 189 types of saponin which can be used for the treatment of various diseases. Currently, due to over-exploitation, this plant species is under threaten. Our research aimed to study a suitable method for plant propagation by stem cutting techniques to promote the growth and development of G. pentaphyllum. Six experiments were conducted to (i) evaluate the established seedling rates of different G. pentaphyllum varieties, and choose the best variety to (ii) evaluate the established seedling rate influenced by different factors, viz. stem cutting position, cutting season, growing in the selected substrates, stem cutting length, number of buds per stem, and application of α-NAA. The results showed that among five varieties, G2 which was collected in Mai Chau district disclosed the highest ability to shooting, the highest number of roots per stem cutting, the shortest nursery days, the highest shooting rate, and the highestestablished seedling rate. We also determined that using middle-aged plants for stem cuttings, at 15-20cm in length, with 2 nodes and grown in Spring and Winter cropping seasons, using growing substrates with a mixture of 50% of black sand and 50% of soil, and plus α-NAA 50ppm in 3-5min produced the highest explant rate. The established seedlingsat the time of explant were 15-20cm in height, containing 4-5 leaves and at least 9-10 roots per cutting, and were 30-32 days.

Platinum and gold placer from Tugidak Island, Alaska: Platinum-group minerals and their inclusions, gold, and chromite mineralogy

ABSTRACT Black sand beach placers from Kodiak, Sitkinak, and Tugidak Islands, Alaska, have been mined intermittently for gold and minor platinum-group alloys for more than 100 years. High-grade platinum-rich magnetic separate and accompanying black sand from the southern beach placer of Tugidak Island were studied using electron microprobe WDS and scanning electron microscope EDS; mineral classification and identification were based on these techniques. The major platinum mineral is isoferroplatinum, followed by minor tetraferroplatinum and tulameenite, and rare ferronickelplatinum. Two types of alteration were identified in about 3–4% of the alloy grains: rim formation involving Pt loss and increased Fe, Ni, and/or Cu, and fracturing and vein filling by Cu-rich alloy. Ruthenium-Ir-Os-Pt alloys occur as inclusions and veins as well as form part of composite grains. Ten percent of the alloy grains contain a large variety of platinum-group minerals (PGM). Inclusions of cuprorhodsite, malanite, cuproiridsite, laurite, erlichmanite, cooperite, braggite, bowieite, kashinite, miassite, hollingworthite, irarsite, sperrylite, stillwaterite, genkinite, stibiopalladinite, keithconnite, zvyagintsevite, and probable palladodymite and vincentite were identified. Two unidentified inclusion phases also occur. Most of the PGM inclusions are primary and were trapped by a growing crystal from a melt; some inclusions exhibit textures that suggest trapping of an As,Te,S-rich immiscible melt. Secondary inclusions and evidence of deformation were observed in a few alloy grains. Associated with PGM inclusions or as separate inclusions are various base-metal sulfides. Two silicate-melt inclusions in one isoferroplatinum grain have an andesite–shoshonite composition. Minor gold and Ag-rich gold in the high-grade magnetic separate contain magnetite, pyrrhotite, and chromite inclusions. The gold composition suggests that their sources are the numerous quartz veins and apophyses related to granitoids on Kodiak Island. The composition of the placer chromite is similar to chromite from the Border Ranges mélange fault system and suggests that the Uyak Complex ultramafic and mafic rocks are part of a supra-subduction-zone ophiolite and are the source of the platinum-group minerals.

Organic matter in black sand soils related to alkyl carbon and organo-mineral structures at the microscale

<p><span>Agricultural sandy soils with high organic matter (OM) contents are generally unexpected under the current paradigm of organic matter formation and stabilization. These so-called black sand soils occur in North-Western Europe and have been related to historical heathland vegetation. The properties and mechanisms of the high OM sequestration in these soils are not clear as they exceed common observations of OM stored in coarse-textured soils. In this study, we analyzed a subset of samples with ‘black sand’ properties from the European soil database “Land Use/Cover Area frame statistical Survey” (LUCAS). Through particle size fractionation, we isolated the fine fraction <20 µm which contained, on average, 55 % of the total soil organic carbon (OC), in only 8 % of the corresponding soil mass. The fine fraction <20 µm contained 301 mg OC g<sup>-1</sup> with a C:N ratio of 17.4 on average and was positively correlated with the bulk soil OC. The characterization of OM composition in the fine fractions by solid-state <sup>13</sup>C nuclear magnetic resonance (NMR) spectroscopy revealed that the share of alkyl C increased with OC concentrations whereas O/N-alkyl C decreased. To analyze the distribution of OM at the microscale, we analyzed five samples from the <20 µm fraction containing a gradient of 245-378 mg OC g<sup>‑1</sup> with nanoscale secondary ion mass spectrometry (NanoSIMS) at a spatial resolution of 120 nm. These microscale measurements revealed fine mineral particle structures associated with heterogeneously distributed OM. Using image analysis, we found that the proportion of OM-dominated area (indicated by <sup>12</sup>C<sub>2</sub><sup>-</sup> and <sup>26</sup>CN<sup>-</sup>) increased from 52 to 80 % on average with increasing OC concentration of the fine fractions. A majority of OM-dominated area was correlated with higher <sup>42</sup>AlO<sup>-</sup> counts, which might suggest a preferential co-localization. In turn, the particle area which was dominated by minerals (indicated by <sup>16</sup>O<sup>‑</sup>, <sup>28</sup>Si<sup>‑</sup>, <sup>42</sup>AlO<sup>‑</sup> and <sup>72</sup>FeO<sup>‑</sup>) contained less Al and more Si. This shows that the more alkylated and OM-rich fine fractions are related with distinct patterns of organo-mineral structures at the microscale.</span></p>

A Review on the Negative Impacts of Black Sand Mining on the Ecosystem of Kerala

India having coastline of in excess of 6000 km, has likely the greatest and most luxurious coastline placers. India's beach sand stores and rises contain weighty minerals like ilmenite,zircon, rutile, monazite, and sillimanite, the world necessity of garnet. Kerala has a 570 km long coastline as one of world's most potential fishing ground with exceptional biodiversity and furthermore as the plentiful wellspring of probably the most extraordinary minerals that can be found in the world. The most expected wellspring of these mineral stores is the coastline of the stretch of Kollam and Alappuzha that extends around 150 km. The dark sand mining has influenced the biodiversity of the zone consequently absolutely influencing the lives of the rural communities bringing about an ecological constrained movement and occupation misfortune. This paper critically reviews the negative impacts of the black sand mining on the ecosystem of Kerala.

Properties of High-Performance Concretes made of Black Sand at High Temperature

To modify high-performance concrete (HPC) fireproofing properties, black sand (BS) was partially substituted as fine aggregate at various levels. This study aims at evaluating the BS reliability in improving HPC durability properties for various construction applications based on its unique heavy minerals. To achieve this, five HPC series blends were setup to substitute fine aggregate independently with BS. Substitution percentages ranged from 15 to 100% with consistent supplementary cementing materials (SCMs) proportion for each gathering. Tests were performed to assess compressive strength before and after fire exposure under various temperatures of 250, 500 and 750 °C at different curing age. Generally, blending FA with BS was better than using SF with BS. Utilizing BS in the range of 15 to 60% as fine aggregate with 10% FA improves HPC fire-insulating properties. Besides, Z1 SEM analysis observed homogenously and compacted HPC microstructure at 250 and 500 °C. Doi: 10.28991/cej-2021-03091634 Full Text: PDF