Investigation on the effectiveness of the repair method 8.3 “Corrosion protection by increasing the electrical resistivity” in chloride-containing concrete Part 2: Chloride redistribution in concrete after application of a system sealing surface protective coating

This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity.     

Phase behavior,density, and crystallization of polyethylene in n‐pentane and in n‐pentane/CO2 at high pressures

The phase behavior and volumetric properties of polyethylene (PE) in solutions of n‐pentane and n‐pentane/CO₂ were studied in a temperature (T) range of 370–440 K at pressures up to 60 MPa. Measurements were conducted with a variable‐volume view‐cell system equipped with optical sensors to monitor the changes in the transmitted light intensity as the P or the T of the system was changed. Lower‐critical‐solution‐temperature‐type behavior was observed for all of the liquid–liquid (L–L) phase boundaries, which shifted to higher pressures in solutions containing CO₂. The solid–fluid (S–F) phase boundaries were investigated over a P range of 8–54 MPa and took place in a narrow T range, from 374 to 378 K in this P interval. The S–F phase boundary showed a unique feature in that the demixing temperatures showed both increasing and decreasing trends with P depending on the P range. This was observed in both the PE/n‐pentane and PE/n‐pentane/CO₂ mixtures. The density of these solutions were measured as a function of P at selected temperatures or as a function of T at selected pressures that corresponded to the paths followed in approaching the phase boundaries (S–F or L–L) starting from a homogeneous one‐phase condition. The data showed a smooth variation of the overall mixture density along these paths. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2201–2209, 2003     

KINETICS FOR LOW TEMPERATURE PYROLYSIS OF BLACK LIQUOR

A kinetic study of pyrolysis of dried black liquor was performed using a Netzsch 429 Thermogravimetric Analyzer. It was found that as conversion increases from 10 to 45% the apparent pyrolysis activation energy for black liquor increases from 77.20 to 112.74 KJ/mol. For black liquor the order of reaction was found to be first-order. The reaction rate constant was found to be 2.12×10⁹ min. These results are in agreement with the data reported by other investigators on biomass pyrolysis.     

Excavation and support design of the Dicle–Kralkizi water tunnel: an overview

Tunneling projects have their uniqueness in terms of engineering problems. The expertise gained from analyzing these projects establishes a sound basis for future application. This paper conveys experiences gained during the construction and support of the design of the Dicle–Kralkizi water tunnel, Turkey. Tunnel stability problems including overbreaks and surface subsidence are evaluated. An analysis of the breakdowns, factors controlling advance rate and the overall performance of tunnel are covered. The accumulated information presented here is believed to be useful and reliable for a successful tunnel excavation in similar formations.     

Morphological changes in poly(?-caprolactone) in dense carbon dioxide

Morphological changes that take place in poly(?-caprolactone) upon exposure to carbon dioxide at high pressures have been explored as a function of pressure and temperature. SEM and DSC results point to a competition between CO₂-modulated crystallization and pressure-induced phase separation which leads to unique morphologies. At 293 K, exposure to CO₂ at pressures up to 45 MPa leads to recrystallization resulting in higher level of crystallinity and higher melting temperatures. Highest crystallinity levels along with distinct crystal morphology were observed after exposure to CO₂ at 308 K and 21 MPa. At a higher pressure at this temperature (308 K/34 MPa) polymer undergoes melting, and foaming is achieved during depressurization prior to solidification. At 323 K, the polymer is found to display unique crystal morphology with concave crystal geometry as well as porous domains. The results are discussed in terms of the crystallization and phase separation paths that are followed during exposure to CO₂ and the depressurization stages.     

Solubility of polyethylene in n-pentane at high pressures

The high pressure solubility of polyethylene standards (M_w = 2100, 16400, 108000 and 420000 and M_w/M_n = 1.14, 1.16, 1.32 and 2.66, respectively) in n-pentane has been studied. Concentrations of up to 15 wt% polymer have been investigated. For each polymer sample and concentration, pressures that are required to achieve single-phase solutions have been determined over a range of temperatures. The solutions are found to all show lower critical solution temperatures. Demixing pressures are observed to depend strongly on the molecular weight of the polymer.     

Phase behavior and density of polysulfone in binary fluid mixtures of tetrahydrofuran and carbon dioxide under high pressure: Miscibility windows

Mixtures of tetrahydrofuran (THF) and carbon dioxide (CO₂) were identified as new solvent systems for polysulfone. The miscibility and density of polysulfone in binary fluid mixtures of THF and CO₂ were investigated from 300 to 425 K at pressures up to 70 MPa. The influence of the CO₂ and polysulfone concentrations was studied, with the concentrations of the other two components kept constant. At a 4.5 wt % polymer concentration, the demixing pressures in a 10 wt % CO₂ and 90 wt % THF mixture increased with temperature (310–425 K) from 15 to 40 MPa. With increasing CO₂ concentration (from ca. 10 to 14 wt %), a significant increase (from 15 to 70 MPa at 310 K) was observed in the demixing pressures. Furthermore, with an increasing amount of CO₂, the nature of the phase boundary shifted from lower critical solution temperature behavior to upper critical solution temperature behavior. The influence of the polymer concentration was studied in the 0–5 wt % range at two CO₂ levels, with solvent compositions of 10 wt % CO₂ and 90 wt % THF and 13 wt % CO₂ and 87 wt % THF. The system with a higher level of CO₂ (13 wt %) showed highly unusual phase behavior: on pressure–composition and temperature–composition diagrams, the system displayed two distinct regions of miscibility. In the system with 10 wt % CO₂, the distinct regions of miscibility that were observed in the system with 13 wt % CO₂ partially overlapped and led to a W‐shape phase boundary. The densities of the polymer solutions were measured from the one‐phase region through the demixing point into the two‐phase region at a constant temperature. No significant change in density was found around the phase boundary; this indicated that the coexisting phases had similar densities, as is often the case with liquid–liquid phase separation in polymer solutions under high pressure. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2357–2362, 2002     

Effects of dowels produced from various materials on withdrawal strength in MDF and Pb

Wood dowels are commonly used in the construction furniture, but little information is available about the additive effects of dowels on the ultimate withdrawal strength of single or multidowel joints. This study was carried out to determine the tensile strength of 10‐mm‐diameter dowels produced from medium‐density fiberboard (MDF), plywood, scotch pine (Pinus sylvestris L.), and beech (Fagus orientalis lipsky), bonded parallel and vertical to the surface of MDF and particleboard (Pb) with poly(vinyl acetate) (PVAc) and Desmodur‐VTKA (D‐VTKA). Tensile strength was applied to the dowels according to the procedure in the ASTM‐D 1037 standard. The effects of dowel species, direction of tensile, composite material, and type of adhesive on tensile strength were determined. The results showed that the highest tensile strength was obtained in beech dowels bonded vertically with PVAc adhesive to the surface of MDF at 7.91 N/mm². If the dowels used in furniture production are subjected to great tensile strength, beech dowels bonded with PVAc adhesive on MDF should be used. However, when dowels produced from MDF and plywood waste are used, they also can produce positive results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 531–535, 2003     

Confined batch foaming of semi-crystalline rubbery elastomers with carbon dioxide using a mold

Confined foaming of poly(ethylene-co-vinyl acetate-co-carbon monoxide) using carbon dioxide as a physical blowing agent in a mold with either permeable or impermeable boundaries has been explored as a strategy to control final foam dimensions and morphology. The results are discussed in terms of comparisons to free-foaming experiments conducted at the same pressure and temperature conditions following the same pressurization and depressurization paths. Foaming experiments were carried out at 30 and 40°C and 100, 200, and 300 bar followed by rapid depressurization of the foaming cell. Confined foaming led to smaller pores with more uniform distributions across the polymer cross-section. However, bulk foam densities of the foams generated under confinement were higher than those generated under the free-foaming mode. Surface characteristics and skin layer formation were altered by expansion against both the permeable and impermeable boundaries. Confined foaming promotes uniform pore distribution and overall dimensional uniformity and may impart surface texture but the trade-off is in the degree to which the bulk foam density can be lowered.