Liquid Precursor Infiltration Processing of Powder Compacts: II, Fracture Toughness and Strength

Si₃N₄ powder compacts were infiltrated with liquid precursors which produce either Zr(Y)O₂ (3 mol% Y₂O₃) solid solution or amorphous Si₃N₄ after pyrolysis at relative low temperatures and without shrinkage. Results show that cracks which occur within a thin, surface layer of the precursor during pyrolysis can extend into the powder compact. As suggested by theory, this cracking phenomenon could be avoided either by making the powder compact stronger before infiltration or by removing the thin precursor layer before pyrolysis. The mechanical properties of these materials were studied as a function of residual porosity. It was observed that crack extension occurred within the second phase produced by infiltration and pyrolysis. The second phase appeared to govern the critical stress intensity factor ( K_c ) of the material. K_c was found to be a linear function of the change in residual, relative porosity divided by the initial, relative porosity in the powder compact. Reasonable flexural strengths (∼300 MPa) could be achieved despite considerable residual porosity.     

Influence of strain histories on liquefaction resistance of sand

The liquefaction resistance of sand increases with cyclic pre-shearing and pre-shaking as a result of earthquakes if the strain level in the pre-shearing is small. When larger shear strains are imposed, liquefaction resistance decreases. These complicated effects of pre-shearing histories on the liquefaction resistance are investigated in this study through a series of cyclic triaxial tests. Various combinations of cyclic stress amplitude and number of cycles of pre-shearing are examined. The tested sand is Toyoura Sand at 45% relative density, under a confining pressure of 50 kPa. Test results indicate that for the range of shear strain amplitude in pre-shearing smaller than 0.35%, the liquefaction resistance increases with pre-shearing. The increase in the liquefaction resistance depends strongly on the volumetric strain in the pre-shearing, and several effects of the shear stress amplitude and number of cycles can be negligible. Small volumetric strain of the order of 1% doubled the liquefaction resistance. Meanwhile, in the range of shear strain amplitude larger than 0.6%, the liquefaction resistance decreases. The liquefaction resistance decreases as the shear strain amplitude increases. Shear strain amplitude is one of the factors dominating this degrading effect, and the volumetric strain exerts beneficial effects to a certain extent. In this study, another series of tests are conducted to investigate the combined effects of small and large strain amplitude pre-shearing. It is observed that small shear strain pre-shearing cycles subsequent to large shear strain cycles erased the degrading effect of the latter. However, a large shear strain pre-shearing after small strain cycles degrades the beneficial effect of the small shear strain pre-shearing cycles previously applied to the specimens; however, the effects of the former small strain pre-shearing remains.     

Arsenic removal by iron-modified activated carbon

Iron-impregnated activated carbons have been found to be very effective in arsenic removal. Oxyanionic arsenic species such as arsenate and arsenite adsorb at the iron oxyhydroxide surface by forming complexes with the surface sites. Our goal has been to load as much iron within the carbon pores as possible while also rendering as much of the iron to be available for sorbing arsenic. Surface oxidation of carbon by HNO3/H2SO4 or by HNO3/KMnO4 increased the amount of iron that could be loaded to 7.6-8.0%; arsenic stayed below 10 ppb until 12,000 bed volumes during rapid small-scale tests (RSSCTs) using Rutland, MA groundwater (40-60 ppb arsenic, and pH of 7.6-8.0). Boehm titrations showed that surface oxidation greatly increased the concentration of carboxylic and phenolic surface groups. Iron impregnation by precipitation or iron salt evaporation was also evaluated. Iron content was increased to 9-17% with internal iron-loading, and to 33.6% with both internal and external iron loading. These iron-tailored carbons reached 25,000-34,000 bed volumes to 10 ppb arsenic breakthrough during RSSCTs. With the 33.6% iron loading, some iron peeled off.     

Influence of highway construction projects on economic development: an empirical assessment

The evaluation of transportation projects has traditionally been made by assessing changes in travel time, vehicle operating cost, and safety. The broader, long-term effects on economic development (job, income and business growth) are a concern of transportation planners and decision makers, but have often been overlooked due to the lack of a reliable impact-estimation methodology and/or data. This paper presents a quantitative tool that can be used at the project-development phase to estimate the economic-development impacts of different types of highway construction projects. Using data from Indiana, we develop models that can be used to estimate the effects of geographic location, accessibility, and other factors on the economic-development impacts of highway construction projects. Our models can also be used as a basis for programming and ranking a wide variety of highway construction projects.     

Influence of raised floor on zone design cooling load in commercial buildings

The installation of a raised floor system can change the thermal behaviour of the building by reducing the interaction between the heat gains and the thermally massive concrete slab. In this study, the influence of the raised floor on the summer design day zone cooling load profile is evaluated with EnergyPlus for an office building located in San Francisco. The effects of structure type, window-to-wall ratio and the presence of carpet on the thermal behaviour of the raised floor are also investigated. The results show that the mere presence of the raised floor largely affects the zone cooling load profile and the peak cooling load over the range of −7 to +40%. The most significant parameters are the zone orientation, i.e. the exposure to direct solar radiation, and the presence of floor carpeting. If carpeting is present, commonly used in U.S. office buildings, the overall impact on zone peak cooling load is reduced, ranging from 0 to 5% greater for the raised floor than without it. Without carpet the peak cooling load is 4% greater with raised floor than without it in the north zone, 22% in the east and west zones, and 12% in the south zone.     

Can carbon offsetting pay for upland ecological restoration?

Upland peat soils represent a large terrestrial carbon store and as such have the potential to be either an ongoing net sink of carbon or a significant net source of carbon. In the UK many upland peats are managed for a range of purposes but these purposes have rarely included carbon stewardship. However, there is now an opportunity to consider whether management practices could be altered to enhance storage of carbon in upland peats. Further, there are now voluntary and regulated carbon trading schemes operational throughout Europe that mean stored carbon, if verified, could have an economic and tradeable value. This means that new income streams could become available for upland management. The ‘Sustainable Uplands’ RELU project has developed a model for calculating carbon fluxes from peat soils that covers all carbon uptake and release pathways (e.g. fluvial and gaseous pathways). The model has been developed so that the impact of common management options within UK upland peats can be considered. The model was run for a decade from 1997-2006 and applied to an area of 550 km² of upland peat soils in the Peak District. The study estimates that the region is presently a net sink of − 62 ktonnes CO₂ equivalent at an average export of − 136 tonnes CO₂ equivalent/km²/yr. If management interventions were targeted across the area the total sink could increase to − 160 ktonnes CO₂/yr at an average export of − 219 tonnes CO₂ equivalent/km²/yr. However, not all interventions resulted in a benefit; some resulted in increased losses of CO₂ equivalents. Given present costs of peatland restoration and value of carbon offsets, the study suggests that 51% of those areas, where a carbon benefit was estimated by modelling for targeted action of management interventions, would show a profit from carbon offsetting within 30 years. However, this percentage is very dependent upon the price of carbon used.     

Effect of damping model on pre-yielding earthquake response of structures

The present paper examines differences between responses of single-degree-of-freedom (SDOF) systems with viscous and hysteretic damping to earthquake ground motions. Only responses within yield limits are considered. The structural behavior of SDOF systems with hysteretic damping is modeled by a generalized elasto-slip model of the Masing type. The model leads to a force–displacement relationship similar to that proposed by Ramberg and Osgood. The responses of the two systems are compared for a number of earthquake records. To achieve consistent comparison, parameters of the linear system with viscous damping are determined by the secant stiffness method. In many cases significant differences in the peak displacement responses and energy values have been observed between the systems. This indicates that the prediction of the response of structures to earthquake ground motions before yielding based on linear models with viscous damping may not be as accurate as used to be believed. Tentative estimates of error associated with such predictions are presented.