Abstract. As part of the 2019 Southern oCean seAsonal Experiment (SCALE) Winter Cruise of the South African icebreaker SA Agulhas II, first-year ice was sampled at the advancing outer edge of the Antarctic marginal ice zone along a 150 km Good Hope Line transect. Ice cores were extracted from four solitary pancake ice floes of 1.83–2.95 m diameter and 0.37–0.45 m thickness as well as a 12×4 m pancake ice floe of 0.31–0.76 m thickness that was part of a larger consolidated pack ice domain. The ice cores were subsequently analysed for temperature, salinity, texture, anisotropic elastic properties and compressive strength. All ice cores from both solitary pancake ice floes and consolidated pack ice exhibited predominantly granular textures. The vertical distributions of salinity, brine volume and mechanical properties were significantly different for the two ice types. High salinity values of 12.6±4.9 PSU were found at the topmost layer of the solitary pancake ice floes but not for the consolidated pack ice. The uniaxial compressive strengths for pancake ice and consolidated pack ice were determined as 2.3±0.5 and 4.1±0.9 MPa, respectively. Young's and shear moduli in the longitudinal core direction of solitary pancake ice were obtained as 3.7±2.0 and 1.3±0.7 GPa, respectively, and of consolidated pack ice as 6.4±1.6 and 2.3±0.6 GPa, respectively. Comparing Young's and shear moduli measured in longitudinal and transverse core directions, a clear directional dependency was found, in particular for the consolidated pack ice.
Abstract. Frazil ice, consisting of loose disc-shaped ice crystals, is the very first ice that forms in the annual cycle in the marginal ice zone (MIZ) of the Antarctic. A sufficient number of frazil ice crystals forms the surface grease ice layer taking a fundamental role in the freezing processes in the MIZ. As soon as the ocean waves are sufficiently damped, a closed ice cover can form. In this brief communication we investigate the rheological properties of frazil ice, which has a crucial influence on the growth of sea ice in the MIZ. Grease ice shows shear thinning flow behavior.
Cement is the strength-forming component of concrete. It has been a major building material for more than a century. However, its production is accountable for a considerable percentage of global CO2 emissions and is very energy-intensive. The Ordinary Portland Cement (OPC) production is a thermal process at around 1450 °C. This study shows that the reactivation of Hydrated Cement Powder (HCP) can be successful at a much lower temperature. Therefore, the possibility of using HCP to replace parts of OPC in concrete reduces the energy consumption and the CO2 emissions associated with OPC production. HCP, which may ultimately stem from recycled concrete, needs treatment to produce new concrete of the required mechanical strength. Using reactivated HCP in concrete, an optimum strength is achieved by heating the HCP in the range of 400–800 °C. Among other factors, the type of cement used influences the optimum heating temperature and attainable strength. This paper shows that 600 °C is an optimum heating temperature using the OPC type CEM I 52.5R. The crystalline phase transitions resulting from the thermal treatment were analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetry (TG). The heat released during hydration was investigated, and scanning electron microscopy (SEM) displays the microstructure evolution. OPC can be partially replaced by thermally treated HCP in mortar, attaining similar mechanical strength values.
Frazil ice, consisting of loose disc-shaped ice crystals, is the first ice that forms in the annual cycle in the marginal ice zone (MIZ) of the Antarctic. A sufficient number of frazil ice crystals form the surface “grease ice” layer, playing a fundamental role in the freezing processes in the MIZ. As soon as the ocean waves are sufficiently damped by a frazil ice cover, a closed ice cover can form. In this article, we investigate the rheological properties of frazil ice, which has a crucial influence on the growth of sea ice in the MIZ. An in situ test setup for measuring temperature and rheological properties was developed. Frazil ice shows shear thinning flow behavior. The presented measurements enable real-data-founded modelling of the annual ice cycle in the MIZ.
Sea ice growth in the Marginal Ice Zone of the Antarctic is one of the largest annual changes on earth with a huge impact on the global climate and ecology system. The principles of sea ice growth and melting in the MIZ of the Antarctic is yet not as well researched as its polar counterpart in the north.For this study, pancake ice, consolidated ice and floe ice were analyzed with a compression test in July, October and November 2019 in the marginal ice zone of the Antarctic. Newly formed pancake ice in July showed the highest compressive strength in the bottom layer (3 MPa), whereas consolidated ice was strongest at the top (5 MPa). Consolidated ice in October and November had the highest compressive strength in a middle layer with up to 13.5 MPa, the maximum strength at the top was 3 MPa. Floe ice, consisting of destroyed pack ice, did not show a clear strength development over sea ice depth.
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