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By Abdelmalek Bouazza, Aamir Mahawish, Will P. Gates

Bio-grouting by means of microbial induced calcite (calcium carbonate) precipitation (MICP) to improve mechanical properties of granular soils has gained much attention in recent years. The biogrouting process offers an alternative and environmentally friendly approach to conventional soil improvement techniques, such as cement. Bio-grouting by urea hydrolysis has been extensively applied to tackle various geotechnical problems. However, it has yet to be applied to improve engineering properties (compressive strength) of a coarse cohesionless material with the aim using it as sand/stone columns within soft and very soft soils. This paper investigates the effect of using light, moderate and heavy biochemical treatments on the unconfined compressive strength (UCS) of coarse sand columns. In addition, the microstructure of the bio-cemented coarse material has been analysed by X-ray computed tomography (XRCT). The experimental results revealed that the UCS could reach up to 200kPa, 1000kPa and 5500kPa for light, moderate and heavy bio-cemented coarse sand columns, respectively. The microstructure investigations showed that the deposited calcium carbonate can be identified using XRCT imaging and can be associated with the gain in UCS values. Various microstructure properties, such as void ratio, dry density and porosity were also identified and compared with the laboratory data.

Jan 1, 1900

By Henry Rawdon

THE METHOD of demonstrating the structure existing in a metal or alloy at high temperatures, by etching a polished sample after it has been heated to the desired temperature, is quite familiar to metallographists. The usual procedure1,2 is to heat the specimen, previously polished for microscopic examination, to the desired temperature, in a neutral atmosphere (hydrogen or nitrogen), then admit the etching gas. (chlorine, hydrochloric acid or similar gas) for. a few seconds, and finally, after flushing out the etching gas with the neutral one, cool the specimen in the neutral atmosphere. The pattern produced by etching at a definite temperature is usually taken as a record of the microstructure prevailing at that temperature. It has frequently been pointed out that changes in composition of the surface metal occur during the preliminary heating in the neutral atmosphere, so that the appearance produced' by the etching at high temperature may not exactly represent the condition of the interior of the specimen. To overcome this uncertainty, the heating has sometimes been done in vacuo,3 the etching gas being ad-mitted when the desired temperature was reached, then pumped out and the specimen cooled in vacuo.

Jan 2, 1920

By George Comstock

THESE notes should be considered as a further discussion of Mr. S. W. Miller's paper on "Some Structures in Steel Fusion Welds."1 In that paper and the resulting discussion; several conflicting opinions were expressed as to the identity of the needles or small crystals present in oxyacetylene and electric welds. An interesting specimen of an electric weld examined by the writer seems to afford new evidence regarding the needles, that may be worth presenting at this time. The specimen consisted of a piece of 3/8 -in. (9.5-mm.) steel plate, about 2 ¼ by 1 ¾ in. (5.7 by 4.5 cm.) in size, on which some iron had been deposited by arc-welding to a depth of about 3/16 in. (4.7 mm.). The weld appeared to be a very good one, with no noticeable break or boundary between the plate and the deposited iron. Sections for microscopic examination were cut in three planes at right angles to each other through the deposited metal, two of these sections also extending through the steel base. After polishing in the usual way, the microscope showed that the deposited metal was full of very small, round, gray, oxide spots, while the steel plate contained quite a number of alumina inclusions and a little slag. The sections were etched with nitric acid in ordinary alcohol, and structures similar to those described by Mr. Miller were then displayed. Fig. 1 shows the typical appearance of the deposited metal, which was quite uniform in all three of the planes examined. The round dark-gray spots are oxides, and the pale angular crystals are evidently what, Mr. Miller called cementite and Mr. Jeffries martensite, while Dr. Ruder and Prof. Boylston suggested that they might be nitride. The boundary between this structure and the steel base was sharply defined under the microscope. Fig. 2 shows the structure of the plate just under the weld; this is almost martensitic and resembles a coarse-grained casting. This coarse cast structure soon became finer as the distance from the weld increased, finally, becoming very fine, with numerous small particles of sorbite. This very fine structure, shown in Fig. 3, became coarser in turn and finally merged into the original normal structure of the steel plate, shown

Jan 1, 1919

E. E. THUM,* Salt Lake City, Utah (written discussion?).-While the present paper is confined exclusively to the microstructure of fusion welds, it may be of interest to draw attention to certain appearances existing in resistance welds such as spot or butt-welded joints produced by the Thomson process. For instance, a butt weld between two pieces of carbon tool steel (carbon about 0.90 per cent.) will show concentric ellipsoids of the various materials from pearlite to martensite. The surfaces of demarcation are quite well defined, the center of the ellipsoid being at the intersection of the axis of the piece and the plane of the weld. Often these unannealed welds show a troostitic center; evidently this core was not quenched as rapidly as the surrounding shell. Such specimens are beautiful samples for instruction purposes. An annealed butt weld of this kind will show a very well defined central ellipsoid of decarburized, materials. It is interesting to consider the reason why this change takes place. It must be understood that the heat is on the metal for a very short time, possibly 30 sec. It is therefore evident that the decarburization, or migration, of the carbon takes place with extreme rapidity. Since no blowholes are evident in a well-made butt weld, the deoxidizing air and the products of combustion must migrate with the highest speed; second, the carbon might migrate back into the stock; or, last, a large proportion of the pearlite may be extruded with the hot metal, which forms a fin at the plane of weld. Examining these possibilities in detail, it is not probable that such deep-seated decarburization, extending with maximum effect to the very center of a 2-in. round bar, is done by reaction with the oxygen of the air. This would postulate entrance of oxygen and egress of carbon oxides in large quantity without leaving behind traces in the form of oxides or

Jan 5, 1919

By Ravi Vancheeswaran

The consolidation of ceramic fiber reinforced metal matrix composites is a key process step in the synthesis of high performance composite systems. A simulation tool has recently been developed for predicting the evolution of the composites internal state microstructural variables (eg. relative density, fiber microbendinglfracture, and chemical reaction layer thickness at the fiber-matrix interface) during the consolidation processing of spray deposited composite mono-tapes. A Generalized Predictive Control (GPC) scheme is used in conjunction with the simula-tion tool to design near optimal process paths that minimize fiber damage and reaction product thickness while simultaneously maximizing the composites relative density. The microstruc-tural evolution depends nonlinearly on the process conditions and therefore the scheme uses a constantly updated linearization of the model to optimize the input process variable vector. A control simulation is presented to illustrate the performance of the design scheme and to assess the feasibility of its use for the achievement of goal state microstructures at the completion of consolidation cycles.

Jan 1, 1996

By Qiang Yu

This paper reports on a research project supported by NSF, which aims at developing a multi-scale methodology for systematic microstructure prediction in thermo-mechanical processing of metals. This methodology is based on combining mesoscopic microstructure models with macroscopic process formulations and involves the following three main steps: (I) based on the given global processing conditions, the gross deformation patternof the entire workpiece is modeled using a continuum-based algorithm, (2) the resulting parameters are then extracted from the continuum-based simulation, post-processed and passed on to the mesoscopic numerical module, and (3) the microstructural changes are finally modeled at the mesoscopic scale. This approach is expected to overcome the disadvantages of current microstructure prediction practice employing empirical relationships between microstructural features and processing parameters. Keywords: Thermo-mechanical processing, Microstructure, Grain growth; Recrystallization; Mesoscopic models; Finite Element Method

Jan 1, 2003

By S. Becker, M. Gruner

"Microstructure stabilized crushed rock salt is a newly developed backfill material for infrastructural openings in HAW repositories. The motivation for this research is based on the fact that the microstructure stabilized crushed rock salt is considered to be superior to the currently used crushed rock salt. The avoiding of settlements with a simultaneous 100% backfilling of openings, early stabilization of the geological barrier and low permeability (< 10-14 m²) are the main improvements. With the newly developed backfill material, the gap between the crushed rock salt and the saliniferous composite backfill materials is closed. Due to the minimized amount of a binding agent, the material will still be easy to handle like a bulk material, yet guarantees close to 100 % backfill success without any settlements. This is accomplished with a long-term stable re-mineralization that is formed by the components of the binding agent. INTRODUCTION The permanent storage of high active waste in underground geological formations (HAW-repository) is the labored method in Germany as well as internationally. Experiences have been made over the last decades, e.g. in the Waste Isolation Pilot Plant (USA) and the mines Morsleben and Asse (Germany). For this purpose salt formations are preferred as host rock due to the adequate heat conductivity, creep capability, and low permeability. In order to maintain the low permeability of the host rock and to avoid any contact of the stored waste with the biosphere, the formation of flow paths has to be prevented. The cavities which have been mined for the purpose of waste storage have to be backfilled with material that is alike to the host rock. Therefore crushed rock salt is considered as an appropriate backfill material. Crushed rock salt is a bulk material that is produced by mining saliniferous formations. This material is mainly used in underground repositories as a dry backfill that is brought into the cavities by the use of mechanical (loading machine, slinger machine or scraper) or pneumatic energy (pneumatic stowing). In Germany it is intended to use dry crushed rock salt with a maximal grain diameter < 64 mm for backfill in a future repository in saliniferous formations. With this method applied, the porosity of the backfill is up to 35 % [1]."

Jan 1, 2015

Rapidly solidified TiAl-Cr-xNb-Y(x=2,4,6, at.%) alloys have been produced using a single roller melt spinning method. The microstructure of alloy ribbon was refined and component became more homogeneously by rapid solidification technology. There were two phases in alloy ribbons, including -TiAl and 2-Ti3Al phases, yet the amount of 2-Ti3Al phase in matrix obviously increased by rapid solidification than cast alloys. The micro-hardness testing also carried out. Compared to the cast alloys, the alloy ribbons have much higher hardness.

Jan 1, 2009

By S. Amira

In the last two decades, many new creep-resistant magnesium alloys have been developed for high temperatures applications. Their mechanical performance and corrosion behaviour were reported for various experimental conditions. However, these conditions often led to uneven comparison basis. In the present study the microstructure, mechanical properties and corrosion performance of four of these newly developed creep-resistant magnesium alloys were systematically compared. Specimens were obtained from experimental box-like components that were die-cast and thixocast in comparable conditions. Their mechanical and corrosion properties were compared using similar testing conditions. Results show that the creep resistance, strength and impact resistance of specimens are comparable but systematically lower compared to specimens cast under optimized conditions. The reduced concentration of elements such as Al, Ca, Sr and Ce lead to a decrease of the corrosion resistance of the magnesium alloys in 3.5% NaCI solution.

Jan 1, 2007

By D. Sethuram, P. G. Koppad, S. Iyengar, R. Shobha

TiB2 and CeO2 particle-reinforced Al6061 hybrid composites were manufactured using stir casting and hot rolling techniques. The base alloy and composites were hot-rolled at 500ºC and a 50% reduction was achieved through 12 passes. The effect of varying TiB2 and CeO2 particle additions on the microstructure and mechanical properties of the Al6061 matrix was studied. Scanning electron microscopy showed uniform dispersion of both the reinforcements, with good interfacial bonding. Microhardness and tensile properties like yield and tensile strength were found to be higher for hybrid composite with 2.5% TiB2 and 2.5% CeO2 compared to Al6061 alloy and other hybrid composites. The increased tensile strength is attributed to good dispersion and interfacial bonding between the particles and Al6061 matrix. Fracture analysis using a scanning electron microscope revealed ductile fracture for the Al6061 alloy and mixed characteristics of ductile-brittle fracture for hybrid composites

Oct 1, 2021

By Burrows. A.

Temperature profiles in the lead smelter sinter bed at Xstrata Zinc Mount Isa sinter plant have been measured using a wireless temperature probe. Corresponding sinter samples have been collected for characterization. The sinter peak bed temperatures were found to be in the range of 1000 - 1200 °C. Microstructures and softening temperatures of these sinters have been characterised. Strong correlations have been observed between peak bed temperature and peak hood temperature, and between mean sinter softening temperature and peak bed temperature. It was found that higher peak bed temperature results in higher sinter softening temperature. For the feed material used in the trials, to obtain sinters with mean softening temperatures above 1050 °C, peak bed temperatures above 1130 °C are required. There appears to be a direct correlation between granule size distribution in the feed and peak bed temperature attained. High peak bed temperatures are observed in sinters with narrow granule size distribution.

Jan 1, 2008

By S. K. Varma, Miriam Regalado, Daniel Salas, Erica Corral, Erika Esquivel

"Age hardenable 2014 aluminum alloys and composites containing 0.10 and 0.15 volume fractions of alumina particles (VFAP) have been solutionized at 540 and 550°C for up to 20 hours. The solutionized samples, heat treated for 5 and 20 hours, have been subjected to room temperature rolling until cracking develops. The work hardening curves have been compared to determine the effect of solutionizing time on the rolling characteristics from both hardness and the microstructural evolution points of view. Solutionizing at two different temperatures results in differences in the extent to which the composites can be rolled until fracture. The microstructural characterization by TEM has been performed to understand the room temperature rolling behavior.IntroductionThe effect of solutionizing on the age hardening response of 6061 and 2014 aluminum alloys and composites reinforced with 0.10, 0.15 and 0.20 volume fractions of alumina particles (VFAP) have been reported in the literature [1-4]. A comparison of the monolith and composites indicates that particles promote the aging process through differences in the microstructures in solutionized condition. The first effect of solutionizing is to produce a grain growth process which follows a grain growth law (square of grain diameter as a function of solutionizing time). It appears that it is possible for vacancies to be emitted during grain growth period as they try to minimize the total grain boundary surface area by increasing their diameter. This may be common to both the monolith and the composites. However, the second effect must be exclusively considered for the composites. The particles generate dislocations during the solutionizing process due to the differences in the values of the coefficient of thermal expansion (CTE) between the particles and aluminum base metal. It has been determined [1] that the dislocation density increases with increase in solutionizing time in the composites of 6061 aluminum alloys reinforced with 0.10, 0.15 and 0.20 VFAP. The improved bonding between particles and matrix can give rise to additional generation of dislocations due to curvature effects [1] with the result that the dislocation density continues to increase with increase in solutionizing time even after the CTE effect is considered to have been stabilized."

Jan 1, 1998

By Strathmore R. B. Cooke, Thomas E. Ban

MUCH experimental work has been performed on the mechanism of agglomeration and pelletizing of moist ore and concentrates and on the process of firing agglomerates, but except for the work of Tigerschiöld and Ilmoni1 much of the published information is empirical, and the literature contains no information concerning the structure of fired pellets. Results of a preliminary study of the microstructures occurring in pellets produced both in the laboratory and on a pilot-plant scale are presented in this paper. Most of the results were obtained from pellets prepared from Mesabi magnetic taconite, but through the courtesy of the staffs of the Minnesota Mines Experiment Station and the Bethlehem Steel Co., fired pellets produced from limonite and hematite ores and from Lebanon magnetite have also been examined. The work has been restricted almost entirely to pellets produced without additives, the exceptions being those in which coal was. added to the filter cake before rolling. Schwartz has described the microstructures occurring in ore sinters produced under reducing conditions.2 Many of the structures and constituents he describes are common to fired pellets, but the constituents normally occur in markedly different proportions. His statement that "in all satisfactory sinter the amount of hematite is small, perhaps not over 2 or 3 per cent" is inapplicable to pellets produced by pilot plant operation or by any process in which air is not deliberately excluded. Pilot plant pellets contain over 90 pct by weight of hematite, and those produced in the smaller furnaces of the Minnesota Mines Experiment Station contain more than 80 pct of that constituent. Preparation of Specimens It is difficult to examine unfired pellets microscopically because of their insufficient coherency to withstand sectioning and polishing. Fired pellets sometimes lack coherency and frequently contain holes which are troublesome during polishing. Impregnation of both air-dried and fired pellets is readily accomplished by the use of methyl methacrylate monomer.3 The dry pellets are covered in a test tube with excess monomer, to which a small amount of accelerator has been added. When the test tube is placed in a cooling bath and evacuated with an aspirator, most of the entrapped air is removed, and disruption of weak pellets by boiling of the monomer is reduced to a minimum. Polymerization is then effected by immersion of the test tube in a water-bath at about 45°C, this temperature being held for 4 or 5 days. The test tube may then be broken away from the solidified mass and the pellets sectioned by a carborundum wheel or a diamond saw. Where time is important, impregnation is carried out at a higher temperature by Meyer&apos;s method.4 Air-dried pellets must be impregnated with especial care; otherwise swelling occurs and the solids are displaced. It is more important to be certain that the monomer forms a reasonably complete network throughout the specimen than that all entrained air is removed, and for this reason the vacuum technique may be omitted. Impregnated agglomerated products and pellets are extremely coherent, section well, and may be polished either by hand or by machine. Hand polishing is not satisfactory for the examination of conditions existing at the boundaries of grains, and for this machine polishing must be used. The Graton-Vanderwilt machine gives excellent results, provided that pressure on the specimen is considerably in excess of that recommended by the manufacturer. Mineralogy of Fired Pellets Only two opaque iron minerals, magnetite and hematite, have been recognized in pellets. The complete identity of these artificial minerals with their corresponding natural counterparts is shown by their mineralographic characteristics and their X-ray structures. Wüstite has not been found. Slag is the most common transparent constituent of fired pellets. Occasionally conditions have been appropriate for the crystallization of fayalite from the slag, and at other times another crystalline sil-

Jan 1, 1952

By Timothy E. LaTour, Robert Kerrich

Microstructures and mineral chemistry of amphiboles and plagioclases from two spatially related mylonite zones at the Grenville front are significantly different, suggesting different physical conditions (including temperature) for the formation of the two zones. Oxygen isotopes indicate multiple episodes of fluid-rock interaction, consistent with previously determined mylonitization temperatures and postulated tectonic evolution of the area.

Jan 1, 1982

By Lucy Villena

El presente trabajo se detalla los resultados más importantes de los estudios realizados de la mineralogía (mena y ganga) y microtermometría con el objetivo de caracterizar los flujos mineralizantes y la dirección de la migración de los fluidos mediante los paleoisotermas de la veta 1. La veta polimetálica es comprendida Pb-Zn-Ag compuestas por rocas volcánicas (andesita a basáltica), cuyo control estructural principal está dado por fallas tensionales de dirección NE-SO, causadas por el movimiento sinestral de fallas Chonta y Huachocolpa- Huancavelica. La composición de las menas reconocidas en la veta 1 corresponde a esfalerita, galena, tetraedrita, bournonita, acantita-argentita y calcopirita, en una ganga conformada por cuarzo, calcita, barita, adularia y yeso. En las muestras de la veta estudiada, los estudios microtermométricos fueron realizados en los cristales de baritina, calcita, cuarzo y esfalerita asociada a la mineralización. Se observan inclusiones fluidas bifásicas acuosas (LH2O + v H2O) las cuales poseen al menos tres eventos mineralizantes según temperaturas de homogeneización y salinidad % equivalente en peso, los fluidos mineralizantes son moderadamente salinos, sugeriendo un ambiente de tipo epitermal.

Sep 21, 2015

By James Carroll, Lance Heyer

This paper describes the shaft design and construction for a 72-inch microtunnel under 14 active railroad tracks in Avondale, Louisiana. Initial shaft design for a deeper tunnel alignment considered secant piles with a jet grout plug. Final design for a shallower tunnel alignment included contractor input with support consisting of braced sheet piles with a jet grout plug. The authors further elaborate on jet grout implementation in very soft organic clay soils and the practical limitations of jet grouting. This paper emphasizes how all project participants worked together to utilize value engineering and alternative delivery on a unique tunneling project with a focus on temporary shaft support.

Jun 23, 2024

By Steven W. Hunt, Gregory C. Baker, Glen J. Rorison

Microtunneling methods were utilized beneath pile-supported clarifier basins to replace settlement damaged sludge drain lines at the Jones Island Wastewater Treatment Plant in Milwaukee, Wisconsin. To minimize the risk of blockage and expensive recovery of a microtunnel boring machine against pipe piles or construction debris, a Soltau RVS 80 was utilized. This machine allowed the alignment to be initially bored with guided 114-mm diameter rods to ensure proper alignment and lack of obstructions. Casing pipe was then installed by jacking 1-m long, 305-mm diameterclay pipe along the rods and behind an auger head. This case history also discusses how 2.4-m diameter precast concrete pipe was used as a one-pass sinking caisson for workshafts and new cleanout manholes.

Jan 1, 2001

By William Bergeson

This paper presents the challenges of the Homestead Avenue Interceptor Extension (HAIE) project in downtown Hartford, Connecticut. The new 72-inch (1,830 mm) sewer pipeline project consists of installing approximately 3,010 linear feet (920 m) of PVC lined reinforced concrete pipe using pressurized face microtunneling. The entire alignment is located within soft to very soft, varved silt and clay. To the extent possible, the alignment was selected to avoid bedrock, glacial till, miscellaneous fill,buried steel piles, and utilities. Challenges for this project include low ground cover, crossing major transportation routes, and limiting settlement to prevent damage to historical buildings and critical utilities. The machine was selected for the ground conditions. Design calculations were performed for selecting the reinforced concrete pipe class and for evaluating settlement. The potential for settlement damage was evaluated using both conventional analysis and finite element analysis

By William Reininger

Microtunneling provides a necessary solution for multiple utility crossings associated with the New York Metropolitan Transportation Authority Capital Construction Company?s (MTACC) Eastside Access Project for the Long Island Rail Road. Construction of four TBM tunnels and their approach structures at the eastern end of the project in Sunnyside, Queens required significant modification and expansion of the railroad infrastructure at this location. Maintenance of railroad traffic during project construction is a principal requirement. As a consequence fourteen (14) utility crossing segments are being installed under active traffic by microtunneling methods. Microtunnels were installed in a variety of conditions including depths, types of soils and construction restraints.

By Amanda Powers, Brian Glynn, Robert Sauceda, Daniel Huffines, Mike Garbeth

This paper will review the evaluation performed for the Cottonwood & Hackberry Creek Wastewater Interceptor Improvements Project to replace two separate aging and undersized interceptor sewers by either open cut construction or trenchless construction methods. A case study will be discussed for the utilization of microtunneling to avoid a deep open cut excavation within a landscaped roadway median to construct nearly a mile of new 60-inch interceptor sewer in an urban area adjacent to an environmentally sensitive riverine area, while minimizing the permitting and environmental impacts of construction, and minimizing the impacts to residents and vehicular trafc and restoration reuirements.

Jun 23, 2024