Influence of Sand Casting Waste as Substitutor of Quartz Sand in Mortar

Sand casting waste has the potential to replace quartz sand in mortar manufacture because it contains high silica. This study uses sand casting waste from the steel industry in Gresik, Indonesia to observe how it affects the quality of the mortar. Initial characterization were carried out to determine the properties of the material, including; magnetic test which results are not attracted by magnets, moisture content test with a value of 0.328%, XRD test to determine the crystallinity content which results contain 99.52% Silica Quartz, and XRF test to determine the content of the compound in which results are 81.25% Silica dominant. Then observations were made by making mortar with the replacement of quartz sand by sand casting with variations of 0% wt, 25% wt, 50% wt, and 100% wt and then tested its compressive strength at 3 days, 7 days, and 28 days. Based on the research that has been done, the optimum result using sand casting is at 25% wt with a compressive strength of 251.15 kgf/cm2 at 28 days of age which is higher than the standard.

Effect of Reinforcement Fiber Arrangement on Thermal and Mechanical Properties of High Silica/Phenolic Resin Insulation Layer

The failure of the high silica/phenolic resin insulation layer under extreme thermal conditions has become an important reason for the trouble of solid rocket motors. A great number of studies have shown that the arrangement of reinforcement fibers is a significant factor in the failure of fiber-reinforced plastic. In this paper, the thermal and mechanical properties of the high silica/phenolic resin insulation layer with different arrangements were analyzed, and the causal relationship between the failure of the insulation layer and the arrangement of reinforcement fibers was given. Two types of heat-insulating layers with strong arrangement and weak arrangement were designed. After the SRM firing test, it is concluded that the essential reason for the failure of the insulation layer is the strength anisotropy caused by the weak arrangement of reinforcement fibers. Besides, the reinforcement fibers of strong arrangement are distributed in all directions, which compensates for the axial strength defects of the weakly arranged insulation layer.

Microstructural evidence for convection in high-silica granite

High-silica (>70 wt% SiO2) granites (HSGs) are critical carriers of tin, copper, and other melt-incompatible elements, yet much remains unknown about the mechanisms responsible for their formation. One of the key issues is the apparent lack of evidence for crystal-melt segregation (e.g., modal layering), without which little can be inferred about the dynamics (or lack thereof) of crystallizing HSGs. We examined the crystallographic orientation relationships of clustered quartz crystals from the 300-m-thick Bobbejaankop sill, Bushveld Complex, South Africa. We report an inward increase in the number density and size of quartz clusters toward the central horizon of the sill, coinciding with a significant increase in concentrations of tin, copper, and tungsten. The majority of crystal pairs within each cluster exhibit coincident-site lattice orientation relationships, representing low grain-boundary energy configurations. These clusters must have formed by synneusis in a magmatic environment where crystals could have moved freely, rotating into low-energy orientations on contact. We argue that this not only demonstrates that 100-m-scale crystal-poor and liquid-rich regions can be present in bodies of HSG, but also that such bodies can undergo long-lived convection during crystallization, driven by downwards movement of crystal-rich plumes at the roof, without significant crystal-melt segregation. This dynamic behavior provides a mechanism to homogenize major-element distribution across HSGs and to concentrate highly incompatible and economic elements into central mineralized horizons.

Identifying crystal accumulation and melt extraction during formation of high-silica granite

High-silica (<70 wt% SiO2) magmas are usually believed to form via shallow crustal–level fractional crystallization of intermediate magmas. However, the broad applicability of this model is controversial, because the required crystal-melt separation processes have rarely been documented globally up to now. The ca. 50 Ma Nyemo composite pluton of the Gangdese batholith belt in southern Tibet, which comprises intrusive rocks with intermediate- to high-silica compositions (65–78 wt%), offers a unique opportunity for substantiating the coexistence of extracted melts and complementary silicic cumulates in one of Earth’s most complete transcrustal silicic magmatic systems. The Nyemo pluton intrusive rocks exhibit similar zircon Hf isotopic compositional ranges (mean εHf(t) = +5.7 to +8.3), suggesting a common, non-radiogenic magma source with crustal assimilation in the deep crust. Yet, these rocks have distinct geochemical characteristics. High-silica miarolitic and rapakivi granites are strongly depleted in Ba, Sr, and Eu, and their zircon trace elements show extremely low Eu/Eu* and Dy/Yb. In contrast, monzogranite is relatively enriched in Ba and Sr with minor Eu anomalies, and the zircon trace elements are characterized by relatively high Eu/Eu* and Dy/Yb. Therefore, we propose that the high-silica granites represent highly fractionated melt extracted from a mush reservoir at unusually low storage pressure (~99–119 MPa), and that the monzogranite constitutes the complementary residual silicic cumulates.