Els nous materials s'inspiren en taurons i flors

Els nous materials sintètics, els més revolucionaris, s"inspiraran en la natura, capaç de crear per ella mateixa estructures amb propietats úniques

Demonstration and Field Evaluation of Alternative Portland Cement Concrete Pavement Reinforcement Materials, HR-1069, 2003

Transverse joints are placed in portland cement concrete pavements to control the development of random cracking due to stresses induced by moisture and thermal gradients and restrained slab movement. These joints are strengthened through the use of load transfer devices, typically dowel bars, designed to transfer load across the joint from one pavement slab to the next. Epoxy coated steel bars are the materials of choice at the present time, but have experienced some difficulties with resistance to corrosion from deicing salts. The research project investigated the use of alternative materials, dowel size and spacing to determine the benefits and limitations of each material. In this project two types of fiber composite materials, stainless steel solid dowels and epoxy coated dowels were tested for five years in side by side installation in a portion of U.S. 65 near Des Moines, Iowa, between 1997 and 2002. The work was directed at analyzing the load transfer characteristics of 8-in. vs. 12-in. spacing of the dowels and the alternative dowel materials, fiber composite (1.5- and 1.88-in. diameter) and stainless steel (1.5-in. diameter), compared to typical 1.5-in. diameter epoxy-coated steel dowels placed on 12-in. spacing. Data were collected biannually within each series of joints and variables in terms of load transfer in each lane (outer wheel path), visual distress, joint openings, and faulting in each wheel path. After five years of performance the following observations were made from the data collected. Each of the dowel materials is performing equally in terms of load transfer, joint movement and faulting. Stainless steel dowels are providing load transfer performance equal to or greater than epoxy-coated steel dowels at the end of five years. Fiber reinforced polymer (FRP) dowels of the sizes and materials tested should be spaced no greater than 8 in. apart to achieve comparable performance to epoxy coated dowels. No evidence of deterioration due to road salts was identified on any of the products tested. The relatively high cost of stainless steel solid and FRP dowels was a limitation at the time of this study conclusion. Work is continuing with the subject materials in laboratory studies to determine the proper shape, spacing, chemical composition and testing specification to make the FRP and stainless (clad or solid) dowels a viable alternative joint load transfer material for long lasting portland cement concrete pavements.

Development of In Situ Detection Methods for Materials-Related Distress (MRD) in Concrete Pavements: Phase 2, HR-1081, 2005

This project utilized information from ground penetrating radar (GPR) and visual inspection via the pavement profile scanner (PPS) in proof-of-concept trials. GPR tests were carried out on a variety of portland cement concrete pavements and laboratory concrete specimens. Results indicated that the higher frequency GPR antennas were capable of detecting subsurface distress in two of the three pavement sites investigated. However, the GPR systems failed to detect distress in one pavement site that exhibited extensive cracking. Laboratory experiments indicated that moisture conditions in the cracked pavement probably explain the failure. Accurate surveys need to account for moisture in the pavement slab. Importantly, however, once the pavement site exhibits severe surface cracking, there is little need for GPR, which is primarily used to detect distress that is not observed visually. Two visual inspections were also conducted for this study by personnel from Mandli Communications, Inc., and the Iowa Department of Transportation (DOT). The surveys were conducted using an Iowa DOT video log van that Mandli had fitted with additional equipment. The first survey was an extended demonstration of the PPS system. The second survey utilized the PPS with a downward imaging system that provided high-resolution pavement images. Experimental difficulties occurred during both studies; however, enough information was extracted to consider both surveys successful in identifying pavement surface distress. The results obtained from both GPR testing and visual inspections were helpful in identifying sites that exhibited materials-related distress, and both were considered to have passed the proof-of-concept trials. However, neither method can currently diagnose materials-related distress. Both techniques only detected the symptoms of materials-related distress; the actual diagnosis still relied on coring and subsequent petrographic examination. Both technologies are currently in rapid development, and the limitations may be overcome as the technologies advance and mature.

Crushed Stone Granular Surfacing Materials, HR-2046 and MLR-90-07, 1990

This project included the following tasks: (1) Preparation of a questionnaire and survey of all 99 Iowa county engineers for input on current surfacing material practice; (2) County survey data analysis and selection of surfacing materials gradations to be used for test road construction; (3) Solicitation of county engineers and stone producers for project participation; (4) Field inspection and selection of the test road; (5) Construction of test road using varying material gradations from a single source; and (6) Field and laboratory testing and test road monitoring. The results of this research project indicate that crushed stone surfacing material graded on the fine side of Iowa Department of Transportation Class A surfacing specifications provides lower roughness and better rideability; better braking and handling characteristics; and less dust generation than the coarser gradations. It is believed that this material has sufficient fines available to act as a binder for the coarser material, which in turn promotes the formation of tight surface crust. This crust acts to provide a smooth riding surface, reduces dust generation, and improves vehicle braking and handling characteristics.

Field Evaluation of Pavement Marking Materials, MLR-79-02, 1979

Pavement marking materials other than conventional paint must be evaluated as environmental standards become more restrictive. The new EPA classification for solvents states that all oil paints are photochemically reactive and, therefore, contribute to smog. This will eventually result in the elimination of organic solvents from all paints, which may occur in Iowa by 1985. The Special Investigations Section of the Office of Materials field reviewed all urban and rural applications of pavement marking materials in the spring of 1979. The field review consisted of a visual estimation of percent marking missing, percent satisfactory, and percent non-satisfactory; reflective readings by ERMA; and notation of special conditions which may have impacted performance. ERMA was not effective in evaluating the reflective quality of pavement marking materials. No pavement marking materials evaluated have been successful enough to date to totally replace conventional painting methods.

Optimization and Management of Materials in Earthwork Construction, TR-501, 2010

As a result of forensic investigations of problems across Iowa, a research study was developed aimed at providing solutions to identified problems through better management and optimization of the available pavement geotechnical materials and through ground improvement, soil reinforcement, and other soil treatment techniques. The overall goal was worked out through simple laboratory experiments, such as particle size analysis, plasticity tests, compaction tests, permeability tests, and strength tests. A review of the problems suggested three areas of study: pavement cracking due to improper management of pavement geotechnical materials, permeability of mixed-subgrade soils, and settlement of soil above the pipe due to improper compaction of the backfill. This resulted in the following three areas of study: (1) The optimization and management of earthwork materials through general soil mixing of various select and unsuitable soils and a specific example of optimization of materials in earthwork construction by soil mixing; (2) An investigation of the saturated permeability of compacted glacial till in relation to validation and prediction with the Enhanced Integrated Climatic Model (EICM); and (3) A field investigation and numerical modeling of culvert settlement. For each area of study, a literature review was conducted, research data were collected and analyzed, and important findings and conclusions were drawn. It was found that optimum mixtures of select and unsuitable soils can be defined that allow the use of unsuitable materials in embankment and subgrade locations. An improved model of saturated hydraulic conductivity was proposed for use with glacial soils from Iowa. The use of proper trench backfill compaction or the use of flowable mortar will reduce the potential for developing a bump above culverts.

Biofuel Co-Product Uses for Pavement Geo-Materials Stabilization, TR-582, 2010

The production and use of biofuels has increased in the present context of sustainable development. Biofuel production from plant biomass produces not only biofuel or ethanol but also co-products containing lignin, modified lignin, and lignin derivatives. This research investigated the utilization of lignin-containing biofuel co-products (BCPs) in pavement soil stabilization as a new application area. Laboratory tests were conducted to evaluate the performance and the moisture susceptibility of two types of BCP-treated soil samples compared to the performance of untreated and traditional stabilizer-treated (fly ash) soil samples. The two types of BCPs investigated were (1) a liquid type with higher lignin content (co-product A) and (b) a powder type with lower lignin content (co-product B). Various additive combinations (co-product A and fly ash, co-products A and B, etc.) were also evaluated as alternatives to stand-alone co-products. Test results indicate that BCPs are effective in stabilizing the Iowa Class 10 soil classified as CL or A-6(8) and have excellent resistance to moisture degradation. Strengths and moisture resistance in comparison to traditional additives (fly ash) could be obtained through the use of combined additives (co-product A + fly ash; co-product A + co-product B). Utilizing BCPs as a soil stabilizer appears to be one of the many viable answers to the profitability of the bio-based products and the bioenergy business. Future research is needed to evaluate the freeze-thaw durability and for resilient modulus characterization of BCP-modified layers for a variety of pavement subgrade and base soil types. In addition, the long-term performance of these BCPs should be evaluated under actual field conditions and traffic loadings. Innovative uses of BCP in pavement-related applications could not only provide additional revenue streams to improve the economics of biorefineries, but could also serve to establish green road infrastructures.

Evaluation of Deicing Materials and Corrosion Reducing Treatments for Deicing Salts, TR-471, 2007

Effective winter maintenance makes use of freezing-point-depressant chemicals (also known as ice-control products) to prevent the formation of the bond between snow and ice and the highway pavement. In performing such winter maintenance, the selection of appropriate ice-control products for the bond prevention task involves consideration of a number of factors, as indicated in Nixon and Williams (2001). The factors are in essence performance measurements of the ice-control products, and as such can be easily incorporated into a specification document to allow for selection of the best ice-control products for a given agency to use in its winter maintenance activities. Once performance measures for de-icing or anti-icing chemicals have been specified, this allows the creation of a quality control program for the acceptance of those chemicals. This study presents a series of performance measurement tests for ice-control products, and discusses the role that they can play in such a quality control program. Some tests are simple and rapid enough that they can be performed on every load of icecontrol products received, while for others, a sampling technique must be used. An appropriate sampling technique is presented. Further, each test is categorized as to whether it should be applied to every load of ice-control products or on a sampling basis. The study includes a detailed literature review that considers the performance of ice-control products in three areas: temperature related performance, product consistency, and negative side effects. The negative side effects are further broken down into three areas, namely operational side effects (such as chemical slipperiness), environmental side effects, and infrastructural side effects (such as corrosion of vehicles and damage to concrete). The review indicated that in the area of side effects the field performance of ice-control products is currently so difficult to model in the laboratory that no particular specification tests can be recommended at this time. A study of the impact of ice-control products on concrete was performed by Professor Wang of Iowa State University as a sub-contract to this study, and has been presented to the Iowa Highway Research Board prior to this report.

Investigation of Materials for the Reduction and Prevention of Corrosion on Highway Maintenance Equipment, TR-472, 2009

The issue of corrosion of winter maintenance equipment is becoming of greater concern because of the increased use of liquid solutions of ice control chemicals, as opposed to their application in solid form. Being in liquid form, the ice control chemicals can more easily penetrate into the nooks and crannies on equipment and avoid being cleansed from the vehicle. Given this enhanced corrosive ability, methods must be found to minimize corrosion. The methods may include coatings, additives, cleansing techniques, other methods, and may also include doing nothing, and accepting a reduced equipment lifetime as a valid (perhaps) trade off with the enhanced benefits of using liquid ice control chemicals. In reality, some combination of these methods may prove to be optimal. Whatever solutions are selected, they must be relatively cheap and durable. The latter point is critical because of the environment in which maintenance trucks operate, in which scrapes, scratches and dents are facts of life. Protection methods that are not robust simply will not work. The purpose of this study is to determine how corrosion occurs on maintenance trucks, to find methods that would minimize the major corrosion mechanisms, and to

Selective ablation of photovoltaic materials with UV laser sources for monolithic interconnection of devices based on a-Si:H

Lasers are essential tools for cell isolation and monolithic interconnection in thin-film-silicon photovoltaic technologies. Laser ablation of transparent conductive oxides (TCOs), amorphous silicon structures and back contact removal are standard processes in industry for monolithic device interconnection. However, material ablation with minimum debris and small heat affected zone is one of the main difficulty is to achieve, to reduce costs and to improve device efficiency. In this paper we present recent results in laser ablation of photovoltaic materials using excimer and UV wavelengths of diode-pumped solid-state (DPSS) laser sources. We discuss results concerning UV ablation of different TCO and thin-film silicon (a-Si:H and nc-Si:H), focussing our study on ablation threshold measurements and process-quality assessment using advanced optical microscopy techniques. In that way we show the advantages of using UV wavelengths for minimizing the characteristic material thermal affection of laser irradiation in the ns regime at higher wavelengths. Additionally we include preliminary results of selective ablation of film on film structures irradiating from the film side (direct writing configuration) including the problem of selective ablation of ZnO films on a-Si:H layers. In that way we demonstrate the potential use of UV wavelengths of fully commercial laser sources as an alternative to standard backscribing process in device fabrication.

Library-instructional materials center skills, 1968

The School Library-Instructional Materials Center should be designed to serve the total curriculum of a school. Much of a teacher's learning comes when he works with a librarian to provide his students wit the necessary and appropriate skills for a unit of s study.

SAP Control del balanç de materials

L'empresa fícticia EcsCables S.A., que està destinada a la fabricació de cables d'energia de mitja i alta tensió, té uns desviaments en el balanç de materials. L'objectiu d'aquest projecte és la de resoldre les anomalies derivades per mitjà del programari SAP, que serà l'eina imprescindible per poder saber amb certesa que està passant. Amb les dades extretes i amb l'ajuda d'un segon ERP intern anomenat Planifer s'intentarà esbrinar les causes del desviament.

Materials de suport a l'ensenyament/aprenentatge per competències

Aquest article presenta el projecte de Millora de Qualitat Docent que ofereix un disseny d’intervenció i materials de suport per a l’ensenyament i aprenentatge de competències en l’espai de seminari. Els eixos en els que es fonamenta la nostra proposta són: la identificació de les competències a assolir, l’autoavaluació com a eina formativa i la tutoria com a espai de suport en aquest procés d’aprenentatge. La intervenció s’adreça als estudiants de Grau i als professors tutors. Els materials de suport elaborats fan referència a: qüestionari online d’autopercepció del nivell de competències genèriques, qüestionari tutorial de detecció de necessitats i disseny del procés tutorial. En base a la reflexió derivada de l’elaboració d’aquest treball i en relació a l’experiència docent universitària com a professors tutors, podem constatar que l’adquisició de les competències és un procés perceptible que requereix d’un temps variable segons cada estudiant, que implica la conscienciació i participació activa del mateix i, que aquest procés requereix de l’espai de tutoria per a poder-lo dur a terme.