Results of laboratory carbonation experiments on Nirex Reference Vault Backfill cement

Some repository concepts envisage the use of large quantities of cementitious materials – both for repository construction and as a buffer/backfill. However, some wastes placed within a subsurface repository will contain a significant amount of organic material that may degrade to produce carbon dioxide. This will react with cement buffer/backfill to produce carbonate minerals such as calcite, which will reduce the ability of the buffer/backfill to maintain highly alkaline conditions and as a consequence its ability to limit radionuclide migration. The reaction may also alter the physical properties of the buffer/backfill. The work involved in this study investigates these processes through elevated pressure laboratory experiments conducted at a range of likely future in situ repository conditions. These will provide information on the reactions that occur, with results serving as examples with which to test predictive modelling codes. This report details a series of batch experiments to study carbonation of Nirex Reference Vault Backfil (NRVB) cement. Thirty-two static batch experiments were pressurised with either CO2, or with N2 for ‘nonreacting’ comparison tests at 20°C or 40°C, and 40 or 80 bar. Twenty-six of these were left to react for durations of between 10-40 days, with six more left to react for a year. The aim of them was to help investigate mineralogical and fluid chemical changes due to the diffusional ingress of CO2 into unconfined NRVB samples measuring 2.5 cm in diameter and 5 cm long. All the cement samples showed rapid reaction with CO2, manifested by a colour change from grey to light brown. Petrographic analysis of the reacted cement revealed that this colour change reflected the breakdown and dissolution of primary calcium ferrite and calcium alumina-ferrite (CAF) cement clinker phases (e.g. brownmillerite, Ca2(Al,Fe)2O5 to form calcium carbonates and finely-disseminated free ferric oxide (probably hematite, Fe2O3), as a result of reaction with CO2 to give a ‘rusty’ colour. It should be noted that his is not an oxidation reaction as the iron is present as Fe3+ in the original cement phases. The cement blocks remained intact, even after prolonged exposure to CO2-rich fluids. Carbonation was associated with an increase in weight of up to 8.5% during CO2 uptake, though the samples did not change in overall size. There is potential therefore, for carbonation to immobilise 14CO2 if that were present. Free-phase CO2 gave slightly more reaction than dissolved CO2, possibly because of its higher concentration and greater ability to penetrate the samples. In terms of major reactions during carbonation, these were the breakdown of portlandite, calcium silicate hydrate (CSH) phases, calcium aluminate (or calcium aluminate hydrate) phases, and ettringite-like phases, and the formation of carbonate phases and silica gel. Carbonation also revealed that heterogeneity within the cement samples had a major impact on migration pathways and extent of carbonation. This heterogeneity may have been a result of casting, and was only observed in some of the samples studied. It led to faster carbonation in some areas, and may account for some of the differences observed in the reacted cement samples. Such heterogeneity may be present within a repository, and should be taken into account when assessing repository performance

AFES Circular 80

To remain competitive, commercial vegetable producers require updated information on the performance of new vegetable varieties under the soil and climatic conditions of southcentral Alaska. Variety trials provide the opportunity to evaluate potentially adapted plant material. Although many varieties are developed in environments considerably different from that of southcentral Alaska, some may prove to be useful to commercial growers in Alaska. The information on new varieties must be collected over several growing seasons to provide sufficient confidence in the observed performance. Additionally, each year of the performance trials, new varieties are grown with traditional or standard varieties which are used to compare the quality of the new varieties. Commercial production of new varieties should be considered after several years of variety trial work with initial plantings on a small production scale.Introduction -- Overview -- Seed Source List -- Weather Summary -- Broccoli -- Cabbage -- Carrots -- Lettuce -- Potatoe

Comparison of Pitching Moments Produced by Plain Flaps and by Spoilers and Some Aerodynamic Characteristics of an NACA 23012 Airfoil with Various Types of Aileron

Sectional characteristics of airfoil having retractable slotted flap with plain, slot-lip, or retractable ailerons are presented for a large range of aileron deflections. The analysis indicated that pitching moments produced by spoilers were less positive than those produced by plain flaps of equal effectiveness, also that pitching moments created by the spoiler increased less with the Mach number than similar moments produced by plain flaps. Positive values of pitching moment decreased as devices were located nearer airfoil leading edge

An experimental and analogue study of iron release from red sandstones

The Jurassic Entrada sandstone at Salt Wash Graben, Utah, USA, a red sandstone contains significant rock bleaching. The cause of the bleaching has been thought to be associated with the modern day CO2-rich fluids in the area which present on the surface by utalising the local fractures, some of which are filled with calcite and iron rich minerals (e.g. Jarosite). An experimental study was conducted to determine the cause of the bleaching. CO2 was found not to cause sandstone bleaching. However, the CO2 was found to mobilize significant amounts of iron from the fracture minerals suggesting that this is a possible source of the iron in the modern pore fluids

Note on some observed effects of rocket motor operation on the base pressures of bodies in free light

Some measurements of the effects of rocket-motor operation on base pressure were obtained incidental to other research on some bodies in free flight. These data are presented and qualitatively analyzed. The analysis indicates that jet effects on drag are of sufficient importance to deserve consideration in the design of jet motor nozzles, especially for aircraft and missiles where the thrust and drag are of the same order of magnitude. The base-pressure changes induced by the jet should be considered in the structural design of the outer body skin on the aft portion of fuselages containing jets. (author

Residential building and occupant vulnerability to pyroclastic density currents in explosive eruptions

International audienceA major hazard during the eruption of explosive volcanoes is the formation of pyroclastic density currents (PDCs). Casualties and physical building damage from PDCs are caused by the temperature, pressure, and particle load of the flow. This paper examines the vulnerability of buildings and occupants to the forces imposed by PDCs along with associated infiltration of PDC particle and gas mixtures into an intact building. New studies are presented of building and occupant vulnerability with respect to temperature, pressure, and ash concentration. Initial mitigation recommendations are provided

Archaeological Geophysical Prospection in Peatland Environments: case studies and suggestions for future practice

Peatland environments, in contrast to ‘dry-land’ sites, preserve organic material, including anthropogenic objects, because they are anaerobic, and are therefore of great importance to archaeology. Peat also preserves macro- and micro- paleoenvironmental evidence and is the primary resource for understanding past climates and ecology. Archaeological sites often lie within or at the base of wet, deep, homogenous peat rendering them invisible to surface observers. As a result, they most often c..