Special Binders Research Articles

Otta Seals and Gravseals as Low-Cost Surfacing Alternatives for Low-Volume Roads: Experiences in South Africa

The geology of the northeastern part of the province of KwaZulu–Natal, South Africa, is predominantly alluvial with vast deposits of sands. Suitable gravel sources are hard to come by, which results in high graveling and regraveling costs brought about by long haul distances and accelerated gravel loss. Most gravel roads carry fewer than 500 vehicles per day of which less than 10% are heavy vehicles. The high cost of regraveling has led to consideration of upgrading such roads to surfaced standard, even though traffic volumes do not justify upgrading. Traditional chip seals are expensive and cannot be economically justified on roads that carry fewer than 500 vehicles per day. The KwaZulu–Natal Department of Transport is actively involved in efforts to identify cost-effective alternative surfacing products for low-volume roads. Field trials were conducted with Otta seals and Gravseals, which have been used successfully in other countries, as low-cost surfacing products for low-volume roads. The Otta seal is formed by placing graded aggregates on a relatively thick film of soft binder that, because of traffic and rolling, works its way through the aggregates. Gravseal consists of a special semipriming rubberized binder that is covered by a graded aggregate. Both Otta seals and Gravseals provide relatively flexible bituminous surfaces suitable for low-volume roads. Cost savings are derived mainly from the broad aggregate specifications, which allow for the use of marginal materials.

Prospects for metal injection moulding using a gamma titanium aluminide based alloy powder

Alloy powder of an advanced gamma titanium aluminide alloy (γ-TAB: Ti–47Al–4(Mn, Nb, Cr, Si, B) (at.%)) was produced by argon gas atomization. The fine powder (<45 μm) was mixed with a special binder and test specimens were moulded. The specimens were debinded and subsequently sintered at 1410 °C. The porosity after sintering was about 3.8%. Subsequent hot isostatic pressing (HIP) caused a further reduction in porosity to 0.4%. While the fine alloy powder had low oxygen and nitrogen levels (O 2: 790 μg g −1, N 2: 140 μg g −1), the sintered and HIP'ed samples are characterized by a considerable increase in O 2 and N 2. Both types of impurities vary in the depth of the samples in the range of 1600–8000 μg g −1 (O 2) and 160–890 μg g −1 (N 2). After HIP the microstructure is of duplex type. Tensile tests at room temperature resulted in a yield strength of 410 MPa, an ultimate tensile strength of 430 MPa and a plastic elongation of 0.6%.

Asphalt Pavement Design using Results of Laboratory Fatigue Tests of Asphalt Mixtures

ABSTRACT Fatigue tests with use of 4 Point Bending test were performed on conventional and innovative asphalt mixtures: typical asphalt concrete, high stiffness modulus asphalt concrete and stone mastic asphalt with conventional and special binders, multigrade or elastomer-bitumen. The results of fatigue testing were applied for development of fatigue characteristics of particular asphalt mixtures. Pavement design analysis was performed with design of thickness of asphalt layers and prediction of their fatigue life. It was shown that use of fatigue law developed from laboratory test results for asphalt mixture enabled to prove the efficiency of use of innovative materials. It is possible to reduce total thickness of asphalt layers when applying in base course high stiffness modulus asphalt with special binders without decrease in fatigue life.

A Higher-Order Calculus for Categories

A calculus for a fragment of category theory is presented. The types in the language denote categories and the expressions functors. The judgements of the calculus systematise categorical arguments such as: an expression is functorial in its free variables; two expressions are naturally isomorphic in their free variables. There are special binders for limits and more general ends. The rules for limits and ends support an algebraic manipulation of universal constructions as opposed to a more traditional diagrammatic approach. Duality within the calculus and applications in proving continuity are discussed with examples. The calculus gives a basis for mechanising a theory of categories in a generic theorem prover like Isabelle.

Carbon anodes prepared from graphite particles pretreated in a gelatine solution

A new procedure for carbon anode preparation is described. First, carbon (graphite) particles are pretreated in an aqueous solution of gelatine. Then, the slurry is directly pressed on the copper substrate without addition of a special binder. It is shown that such anodes have lower irreversible loss (13–16%) than the classically prepared anodes. Efficiency reaches values close to 100% at latest in the third cycle. Reversible capacity can be as high as 340 mA h g −1. Stability of the new anodes up to 20 cycles is satisfactory only at higher concentrations of gelatine solution used in the pretreatment. Optimization of the new anode is a subject of further investigation.

A new rapid tooling technique and its special binder study

A new rapid tooling technique named Rapid Pattern Based Powder Sintering (RPBPS) has been developed. It comprises the steps of first building a pattern made of polymer materials using a rapid prototyping machine based on a 3‐D CAD model. The pattern is positioned on a substrate in a box or frame, then a mixture of metal (ceramic or polymer) powder and binder is cast around the pattern. Next, there is a step of removing the pattern and separating the substrate to obtain a green compact that has the desired cavity. Then the green compact will be sintered and/or infiltrated to form a tool or part. The new technique has the advantages of using a variety of materials, rapidity, making complex geometry parts and low cost, compared with several existing rapid tooling techniques. Many key technical problems in RPBPS are related to the binder. In order to select a suitable binder, the heat deformation resistance and heat stabilization of some polymer materials are discussed in depth.

Gelation forming of ceramic compacts using agarose

AbstractThe development of a cast forming process for ceramics based on agarose gelation is described and the properties of green and sintered bodies are presented. For this process, a warm alumina slurry containing more than 50 vol.-% solids loading and ∼1 wt-% agarose binder (Al2O3 basis) is cast into a relatively cold, non-porous mould, resulting in a tough green body formed by gelation (37°C) of the agarose molecules. The green compacts show uniform density distribution, with precise dimensions and very smooth surfaces. After drying, they can be sintered directly without special binder burn out procedures. Complex ceramic parts with thick and thin cross-sections can be formed. The process is illustrated for the preparation of a turbine rotor component.

SiC platelet orientation in a liquid-phase-sintered silicon carbide composite formed by thermoplastic forming techniques

Thermoplastic forming techniques were used to study the alignment of the platelets ( d 50 = 14 μm, aspect ratio 8–10) and the effect on densification of a liquidphase-sintered silicon carbide composite. Several ceramic parts (test bars, tubes, discs, rings and balls) were manufactured by injection moulding, hot moulding (low-pressure injection moulding) and thermoplastic extrusion methods. Special binders for injection moulding/extrusion and hot moulding were developed. The feedstocks were characterized by torque rheometry in a sigma-blades kneader and by shear-stress-controlled rotation viscosimetry, respectively. The orientation of the platelets in the matrix material was studied by microscopy. An alignment of the platelets corresponding to the flow of the mixtures was observed. In some shapes there was a perfect alignment of the platelets preventing the formation of a platelet framework and resulting in high sintering densities of 97% of theoretical with 20% platelet content. This essentially demonstrates the opportunity of making dense, plateletreinforced composites by pressureless sintering.

The Usage of Industrialwaste Materials for the Productionof Special Cements and Binders

AbstractBy mixing various industrial wastes, as garbage combustion ashes, bottom ashes, fluidized bed ashes, lignite power station ashes, fume purification sulfates and sulfites and lime it is possible to produce cements and binders on the basis of alinite, calcium sulfoaluminate and belite depending on the chemical variety of used wastes.The fabrication process for these cements was studied by laboratory experiments and the different phases and properties were studied in detail. Alinite cement was already produced on a larger scale in a rotary kiln of 10m length. These cements can be used for application purposes in mining mortars, expansive cements, rapid hardening binders and in landfill technologies. The hydration process and workability can be controlled by using various additives. hus industrial wastes can be a secondary resource for special cement production.

Oxidation resistance of carbon-ceramics composite materials sintered from ground powder mixtures of raw coke and ceramics

Carbon-SiC-B4C composite materials were prepared from ground powder mixtures of petroleum raw coke, SiC and B4C by powder sintering, without the use of any special binder and hot-pressing process. Dense composites with a fine microtexture were obtained. Oxidation tests were carried out on the composites at temperatures from 1000 to 1300° C under an air flow. The oxidation resistance depended strongly on the SiC/(SiC + B4C) ratio and total contents of SiC and B4C in the composites, which determined the compositions of B2O3 and SiO2 in the protective film formed at the surface of the composite block during oxidation. In optimum ratios, from 63 to 87%, the composites showed such a high oxidation resistance that they were comparable with Si3 N4 at 1200° C.