Laboratory Performance Tests Research Articles

Cemented carbides from WC powders obtained by the SHS method

Microstructure and properties of WC–Co cemented carbides from WC powders obtained by the self-propagating high-temperature synthesis (SHS) were examined. The microstructure and properties of a submicron carbide grade with 5% Co made from the near-nano SHS WC powder and a standard submicron grade are similar. Microstructure of a medium-coarse WC–6%Co grade made from the medium-coarse SHS WC powder and its properties are comparable with those of the standard medium-coarse carbide grade for percussive drilling. Results of laboratory performance tests on percussive drilling of the medium-coarse WC–6%Co grade obtained from both the SHS powder and conventional WC powder indicate that their wear-resistance and performance toughness are very similar.

Determination of displacement distributions in welded steel tension elements using digital image techniques

It is known that material properties, connection quality and manufacturing methods are among the important factors directly affecting the behavior of steel connections and hence steel structures. The possible performance differences between a fabricated connection and its computer model may cause critical design problems for steel structures. Achieving a reliable design depends, however, on how accurately the material properties and relevant constitutive models are considered to characterize the behavior of structures. Conventionally, the stress and strain fields in structural steel connections are calculated using the finite elements method with assumed material properties and constitutive models. Because the conventional strain gages allow the measurement of deformation only at one point and direction for specific time duration, it is not possible to determine the general characteristics of stress-strain distributions in connections after the laboratory performance tests. In this study, a new method is introduced to measure displacement distribution of simple steel welded connections under tension tests. The method is based on analyzing digital images of connection specimens taken periodically during the laboratory tension test. By using this method, displacement distribution of steel connections can be calculated with an acceptable precision for the tested connections. Calculated displacements based on the digital image correlation method are compared with those calculated using the finite elements method.

Laboratory performance tests on natural prefabricated vertical drains in marine clay

Consolidation of soil by surcharge loading with prefabricated vertical drains is an effective ground improvement technique in saturated cohesive soils such as marine clay. Four types of band-shaped drains made from single-layer woven and non-woven jute geotextile filter fabric wrapped around a core of coir ropes or mats, designated as natural drains, were newly developed and fabricated. Laboratory marine clay confined discharge capacity and large-scale consolidation tests were conducted on the natural drains and commercially available polymer-based drains. The effect of compressive stress on the discharge capacity of the natural drains was studied and compared with the polymer-based drains. The consolidation performance of the drains in remoulded marine clay was studied with consolidation tests on marine clay with and without the drains. It was observed that the rate of settlement of marine clay was almost identical in all the marine clay samples with the drains. All the drains accelerated the consolidation in marine clay. Numerical simulations of experimental consolidation tests were carried out using Plaxis. The magnitude and rate of settlement obtained from numerical consolidation analysis matched closely with the experimental results. It is concluded that eco-friendly and easily fabricated natural drains help in accelerating consolidation in marine clay.

Novel Application of Carbonate Fuel Cell for Capturing Carbon Dioxide from Flue Gas Streams

To address concerns about climate change resulting from emission of CO2 by coal-fueled power plants, FuelCell Energy, Inc. has developed the Combined Electric Power and Carbon-dioxide Separation (CEPACS) system concept. The CEPACS system utilizes Electrochemical Membrane (ECM) technology derived from the Company’s Direct FuelCell® products. The system separates the CO2 from the flue gas of other plants and produces electric power using a supplementary fuel. FCE is currently evaluating the use of ECM to cost effectively separate CO2 from the flue gas of Pulverized Coal (PC) power plants under a U.S. Department of Energy contract. The overarching objective of the project is to verify that the ECM can achieve at least 90% CO2 capture from the flue gas with no more than 35% increase in the cost of electricity. The project activities include: 1) laboratory scale operational and performance tests of a membrane assembly, 2) performance tests of the membrane to evaluate the effects of impurities present in the coal plant flue gas, in collaboration with Pacific Northwest National Laboratory, 3) techno-economic analysis for an ECM-based CO2 capture system applied to a 550 MW existing PC plant, in partnership with URS Corporation, and 4) bench scale (11.7 m2 area) testing of an ECM-based CO2 separation and purification system.

Relationship between fractal, viscoelastic, and aging properties of linear and radial styrene–butadiene–styrene polymer-modified bitumen

The present study is aimed at evaluating the morphological and interfacial properties of the polymer and bitumen (BIT) in linear styrene–butadiene–styrene (SBS-L) block copolymer and radial SBS (SBS-R) block copolymer-modified BIT (PmB) by fractal analysis. Fluorescence microscopy technique coupled with image analysis was used to measure the particle size distribution and fractal dimension of PmB morphology formed in mixtures. Fractal analysis approach was proposed as quantitative description method to evaluate nonuniformity of phase-separated SBS polymer particles/fibrils in PmB. Fractal-like structures in fluorescence micrographs of PmB morphology with the polymer phase-separated particles/fibrils were quantified using interface D[BW], BIT-rich phase D[B+BW], and SBS-rich phase D[W+BW] box-counting fractal dimensions. The overall morphological structure became more compact or more fibril organized as the polymer content attained overcritical values. The relatively high values for the BIT-rich phase D[B+BW] fractal dimension suggests that the PmB mixtures have a structure with extremely high space-filling capacity. Polymer-BIT mixture properties by the conventional laboratory performance tests and by the rheological measurements before and after the Rolling Thin Film Oven Test have been correlated with the PmB mixtures fractal dimensions.

Laboratory performance of warm mix asphalt containing recycled asphalt mixtures

This study aims to evaluate the laboratory performance of warm mix asphalt containing reclaimed asphalt pavement (WMA–RAP) materials. The WMA mixtures containing 0% and 40% RAP were produced using Evotherm-DAT and S-I WMA additives. The laboratory performance tests included rutting, bending, freeze–thaw splitting, Marshall immersion, aging, freeze–thaw cycles splitting, and fatigue tests. The moisture and low temperature cracking resistance were evaluated for aged mixtures. The results showed the WMA mixtures without RAP performed better moisture and low temperature cracking resistance, and lower rutting resistance than the WMA–RAP mixtures. The WMA mixtures suffered from the short-term aging exhibited a slight increase as compared to the unaged mixtures, whereas the long-term aging resulted in a distinct reduction in terms of the moisture resistance. After the short- and long-term aging, the WMA mixtures exhibited a greater decrease than the unaged mixtures in terms of the low temperature cracking resistance. The tensile strength ratio (TSR) results of the WMA–RAP mixtures generally decreased with the increase of freeze–thaw cycles, while the TSR results showed an obvious increase after three freeze–thaw cycles. The addition of RAP significantly reduced the fatigue resistance of the WMA–RAP mixtures in comparison with the WMA mixtures without RAP. Based upon the study findings, the moisture resistance under freeze–thaw cycles conditioning remains an issue to be considered in the WMA–RAP mixtures.

Wear damage of cemented carbides with different combinations of WC mean grain size and Co content. Part II: Laboratory performance tests on rock cutting and drilling

In the present work we carried out laboratory performance tests of cemented carbides with very different WC grain sizes varying from nearly 0.2μm to 5μm and Co contents varying from 6 to 33wt.% in rock cutting and drilling. These tests are determined to well simulate the real operation of cemented carbides in mining and construction applications, particularly in road-planing and rock-cutting as well as in percussive drilling and rotary drilling. The major objective of the present work was to examine the wear damage, wear behavior and wear mechanisms of cemented carbides having a similar hardness but greatly varying with respect to their WC mean grain size and Co content in rock evacuation.Phenomena of micro-fatigue, micro-fracturing and micro-chipping of cemented carbides are found to play the decisive role in rock-cutting. As a result, the wear-resistance of the near-nano carbides having a reduced fracture resistance is significantly lower than that of the medium and coarse grades having similar hardness values. The major wear mechanism of the near-nano grade in rock-cutting is related to micro-cracking and micro-chipping leading to the detachment of huge WC–Co agglomerates. This is presumably a result of reduced fracture toughness of the near-nano cemented carbides containing much grain growth inhibitors, which is caused by the segregation of grain growth inhibitors at the WC–Co and WC–WC interfaces. In contrast to the near-nano grades, the major wear mechanism of the coarse grade in rock-cutting is related to wearing off the binder interlayers among the large WC grains and their micro-chipping and fragmentation.Phenomena of micro-fatigue, micro-fracturing and micro-chipping of cemented carbides also play a very important role in rock-drilling. The wear-resistance of the near-nano grade is noticeably lower than that of the corresponding straight coarse-grain grade having nearly the same hardness but significantly higher fracture resistance. As in the case of rock-cutting, the major wear mechanism of the near-nano grade in rock-drilling is related to micro-cracking and micro-chipping caused by micro-fatigue phenomena, which leads to the detachment of huge WC–Co agglomerates. In contrast to that, the following wear mechanisms take place on the surface of the medium and medium-coarse grades during percussive drilling: (1) wearing the binder among WC grains, which leaves them unsupported, (2) abrasion of the surface of the WC grains, (3) micro-chipping the WC grains, (4) detachment of separate WC grains, and (5) detachment of relatively small WC–Co fragments. There are some regions on the worn surface of the medium and medium-coarse grades, where the WC grains were presumably in direct contact with the rock during drilling (first regions), and there are some regions lying slightly below the first regions (second regions). The worn surfaces in the first regions are characterized by a significantly lower Co content (less than 1wt.%) than on average. The Co contents on the surface of the second regions, which were not presumably in direct contact with the rock when drilling, are noticeably greater and even slightly higher than the average Co content in the bulk of the medium and medium-coarse grades, therefore, the binder was not predominately worn out from the carbide surface in these regions. The second regions presumably comprise Co interlayers on the surface on underlying WC grains after the detachment of WC–Co fragments due to micro-fatigue, as there are no traces of abrasive wear on their surface. Therefore, the presence of the first and the second region on the worn surface with various Co contents is a clear indication of the completely different wear mechanisms in these two regions.

Evaluation of permanent deformation of asphalt mixtures using different laboratory performance tests

The laboratory tests were conducted to evaluate the effects of polyester fiber on permanent deformation of asphalt mixtures. The results indicate the fibers improve the deformation resistance of mixtures. The confinements in the partial triaxial test (PTT) have significant effects on the permanent strain of mixtures. The varying confinement in the PTT better simulates the actual confinements in pavements. A stronger correlation of test results from the PTT and the wheel tracking test was found. It is concluded that the addition of polyester fibers improves the mechanical performance of mixtures, and the PTT method is a reliable new test method.

Laboratory Investigation of Biochar-Modified Asphalt Mixture

The United States is promoting the establishment of a bio-based economy, generating energy and fuels from renewable organic matters rather than fossil fuels. Byproducts such as fractions of biochar not suitable for biofuel production are drawing extensive attention. (“Biochar” is defined by Oxford's online dictionary as “charcoal produced from plant matter and stored in the soil as a means of removing carbon dioxide from the atmosphere.”) Recently, biochar produced with different production parameters was tried as an asphalt modifier owing to its carbon origin and proved to be positive in binder modification. This study evaluated the performance of hot-mix asphalt modified by one type of pyrolytic biochar with controlled production parameters. Typical carbon black powder pellets and microsized carbon fiber were selected as the reference additives. Multiple laboratory binder and performance tests were conducted to evaluate the rheological properties of the modified binder, rutting resistance, moisture susceptibility, and cracking resistance of asphalt mixtures. On the basis of test results, the biochar evaluated in this study proved to be an effective modifier in reducing the temperature susceptibility of the binder and thus increased the rutting, moisture, and cracking resistance of hot-mix asphalt. In addition, biochar proved to be a better asphalt modifier than did carbon black and carbon fiber.

STUDY OF A ROAD TEST TRACK WITH AND WITHOUT CRUMB RUBBER. SOLUTIONS FOR NOISE POLLUTION

End-of-life tires are waste materials that pollute landscapes when they are disposed of in tire dumps. However, its life cycle is not finished when they are scrapped. The rubber of end-of-life tires could be used for new purposes as construction material in road rehabilitation. A gap-graded mix characterization was carried out in this work by means of laboratory and field performance tests. The mixture has a high content of crumb rubber (CR) by weight of bitumen. Crumb Rubber was added to the binder by a wet process. Close proximity methodology has been used in in-situ characterization of the acoustic behaviour. Moreover, absorption and dynamic stiffness tests were also conducted to determine the noise generation mechanisms involved in noise. According to the results achieved, a reduction of the noise emitted by the tire/pavement interaction could be accomplished with the construction of roads with mixture with CR added by a wet process. In addition, this would result in a decrease of the amount of waste tires in landfills.

Infrared spectra and rheological properties of asphalt cement containing waste engine oil residues

This paper presents a study in which the engineering properties of asphalt binder containing waste engine oil residues were evaluated through laboratory performance testing. The infrared spectra and rheological properties of asphalt binder were evaluated with Fourier transform infrared (FT-IR) spectroscopy and dynamic shear rheometer (DSR). Asphalt binder specimens containing different concentrations of waste engine oil were fabricated with two types of binder, PG64-22 and PG76-22, and were blended with two types of laboratory aged binders to simulate the inclusion of reclaimed asphalt pavements (RAP). The results from this laboratory study indicated that the inclusion of waste engine oil up to 5% significantly altered the infrared spectra and rheological properties of asphalt binder, which may lead to the improvement of low temperature performance, but would also compromise many other performance indices, such as rut resistance at high temperature, certain aspects of fatigue resistance and elastic recovery of the binder.

Effects of New Generation Large Aircrafts on Flexible Runway Pavement

In this paper, influences of New Generation Large Aircrafts (NGLA) on the runway rutting were analyzed and the importance of combining laboratory performance tests and suitable analytically-based methodology was emphasized. Based on the multilayered elastic theory, the vertical compression stress distributions under different airplanes including NGLA were studied. Then the dynamic creep test was conducted to obtain the visco-plastic characteristics of pavement including three mixture types. Furthermore, the rutting depth under different airplane was predicted by employing the Shells method and the dynamic creep test results. The results showed rutting depth would be more significant by loading cycles of NGLA, compared with that by ordinary airplane. Suggestions composed of both the structural and material considerations were proposed for runway pavement design.

Research on Performance of a Mercury Continuous Emission Monitoring System

The environmental pollution caused by coal-fired mercury emission has received worldwide attention, because of hazards for human health. Its significant to monitor mercury emission accurately in flue gas for mercury pollution control. In this paper, a detailed description of a mercury continuous emission monitoring system (Hg CEMS) built for the detection of mercury in flue gas is presented. The key performance parameters of the Hg CEMS were discussed in detail. The Hg CEMS was installed in a power plant to monitor mercury emission in flue gas continuously. Results from a series of laboratory performance tests and field application prove that the Hg CEMS is reliable and capable for mercury detection in flue gas. The Hg CEMS can meet the requirement of mercury monitoring in China well.

Alkali–silica reaction (ASR)—performance testing: Influence of specimen pre-treatment, exposure conditions and prism size on concrete porosity, moisture state and transport properties

Whether or not concrete prism tests (CPTs) developed for assessment of alkali–silica reactivity of aggregates might be suitable for general ASR performance testing of concrete has been evaluated. This paper presents the background for the choice of test procedures and results on how variations in specimen pre-treatment, ASR exposure conditions and prism size influence concrete porosity, moisture state and transport properties. Results from measurements of alkali leaching and prism expansions during the ASR exposure are presented in a separate paper, together with discussion of consequences for ASR test procedures.For ordinary Portland cements and with water-to-cementitious-materials ratio (w/cm) 0.45 and higher it was found that the internal moisture state is sufficiently high in all the assessed procedures to produce ASR expansion. However, for less permeable concretes lack of internal moisture and lower rate of diffusion can significantly reduce the rate and extent of ASR expansion during laboratory performance testing.

Comparative evaluation of warm mix asphalt containing high percentages of reclaimed asphalt pavement

This paper compared rut resistance, fatigue resistance and moisture susceptibility of plant-produced asphalt mixtures paved in different structural layers, in which the combined effects of warm–mix asphalt (WMA) technologies and high percentages of reclaimed asphalt pavement (RAP) were evaluated through multiple laboratory performance tests. WMA technologies included foaming process and the addition of surfactant based Evotherm additive into asphalt binder. A total of fifteen WMA and control HMA mixtures were evaluated with RAP content ranging from 0% up to 40%. Laboratory performance tests included asphalt pavement analyzer (APA) rutting, Hamburg Wheel-tracking, flow number, tensile strength ratio (TSR), resilient modulus (MR) ratio, dissipated creep strain energy (DCSEf) method from Superpave indirect tension (IDT) tests, 50% stiffness reduction method and plateau value method from beam fatigue tests. The results showed that WMA-high RAP mixtures generally exhibited less rutting and moisture resistance than HMA-high RAP mixtures but better than WMA-low RAP. On the contrary, WMA-high RAP mixtures expressed better fatigue resistance than HMA-high RAP or HMA-low RAP regardless of WMA technology and pavement layer. In summary, rutting might still be a concern for WMA-high RAP mixtures while fatigue concern may not exist, and WMA-high RAP mixtures showed satisfactory moisture resistance with only one exception of foamed base WMA mixture.

Slewing Mirror Telescope optics for the early observation of UV/optical photons from Gamma-Ray Bursts

We report on design, manufacture, and testing of a Slewing Mirror Telescope (SMT), the first of its kind and a part of Ultra-Fast Flash Observatory-pathfinder (UFFO-p) for space-based prompt measurement of early UV/optical light curves from Gamma-Ray Bursts (GRBs). Using a fast slewing mirror of 150 mm diameter mounted on a 2 axis gimbal stage, SMT can deliver the images of GRB optical counterparts to the intensified CCD detector within 1.5~1.8 s over ± 35 degrees in the slewing field of view. Its Ritchey-Chrétien telescope of 100 mm diameter provides a 17 × 17 arcmin² instantaneous field of view. Technical details of design, construction, the laboratory performance tests in space environments for this unique SMT are described in conjunction with the plan for in-orbit operation onboard the Lomonosov satellite in 2013.

Effectiveness of Antistrip Agents in Asphalt Mixtures

Since the late 1970s there has been much research performed to understand better the stripping phenomenon in asphalt mixtures. As a result, there have been changes in both materials and technology over the past 30 years to improve the resistance to moisture damage and the ability to test for performance under adverse moisture conditions. Because of the changes in materials and technologies related to the development and improvement of antistrip agents, this research study was conducted to evaluate the effectiveness of current antistrip agents used in hot-mix asphalt pavements. The objectives of this project were to construct a field test section that used three different antistrip agents in a conventional Superpave® surface mixture and conduct a series of laboratory performance test comparisons using different aging periods to make long-term comparisons of the effectiveness of hydrated lime, liquid additive, and warm-mix asphalt antistrip additives. Multiple freeze–thaw cycles of zero, one, five, and 10 cycles were used for a portion of the research study. The results showed that hydrated lime had the highest tensile strength and highest tensile strength ratio (TSR) values and was the only additive treatment to meet the minimum of 80% TSR for all freeze–thaw cycle combinations. Both five and 10 freeze–thaw cycles were significantly more discriminating for moisture susceptibility than one freeze–thaw cycle alone. Warm-mix asphalt treated mixtures produced low initial tensile strengths, but the strength of these mixtures improved with time.

Evaluation of Warm Mix Asphalt Mixtures Containing Reclaimed Asphalt Pavement through Mechanical Performance Tests and an Acoustic Emission Approach

Reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) have become the primary methods for enhancing sustainability in the asphalt industry in recent years. To further enhance sustainability benefits, asphalt producers have begun using RAP and WMA in combination. Research to date has focused on evaluating WMA-RAP mixtures in terms of moisture sensitivity and permanent deformation characteristics as measured in laboratory performance tests. In the present paper, the authors investigate a set of WMA mixtures that encompass a variety of variables, including four WMA additives (Evotherm 3G, Rediset LQ, Sasobit, and Advera) and three RAP contents (0, 15, and 45%). A common belief among practitioners is that the reduced aging in the asphalt binder associated with lower production temperatures in WMA mixtures leaves additional headroom for the incorporation of higher amounts of RAP, which is generally a stiffer, more brittle material. To fully characterize the performance of WMA-RAP mixtures, the authors evaluated the low-temperature, cracking behavior of these mixtures in conjunction with moisture and rutting resistance characterization. They achieved the low temperature testing of WMA-RAP mixtures through the disk-shaped compact tension [DC(T)], indirect tension (IDT) creep compliance, and acoustic emission (AE) tests. Test results showed that chemical additives improved moisture susceptibility according to the AASHTO T 283 standard test and fracture and bulk stress relaxation characteristics using the DC(T) and IDT tests, respectively. The organic Fischer-Tropsch wax-modified WMA mixtures performed the best among the WMA mixtures in terms of rutting resistance. The introduction of RAP led to the increased resistance to permanent deformation and moisture damage. Conversely, RAP reduced thermal cracking resistance according to the low-temperature performance tests in both HMA and WMA. The authors observed the same trend in AE test results as WMA-RAP mixtures exhibited warmer embrittlement temperatures as compared with control mixtures and are therefore expected to be more prone to thermal cracking. On the basis of these findings, thermal cracking resistance remains an issue to be considered in WMA mixtures containing RAP. Additionally, performance testing has shown to be a valuable tool for the evaluation of RAP and WMA mix designs to avoid performance issues in the field.

장경간 강바닥판 교량용 에폭시 아스팔트 혼합물의 적용성 평가

The main objective of the research is to evaluate the laboratory performances of epoxy asphalt mixtures for long-span steel bridge decks. The aggregate gradations were recommended for field applications. The laboratory performance test results showed that the durability of epoxy asphalt mixtures was more noticeable than that of conventional ones. The structural analysis was conducted using resilient modulus and bond-shear test results. The analysis results revealed that just 9% out of total bond-shear stress was enough for the entire required bond-shear stress in the pavement system. The tensile stresses in the bridge decks were within limits compared to the laboratory test results from the Nanjing Grand Bridge in China. As a result, the laboratory performances of the epoxy asphalt mixtures for long-span steel bridge decks were better than those of conventional asphalt mixtures. However, the laboratory performance tests of epoxy asphalt mixtures for long-span steel bridge decks should be conducted precisely since the strengths of the mixtures are sensitive to the temperatures and curing times.

Effect of Phase-Change Materials on Thermal and Mechanical Properties of Asphalt Mixtures

Abstract The use of phase-change materials (PCMs) in asphalt mixture is expected to solve some problems related to asphalt-pavement temperature, such as rutting behaviors and urban heat island effect. This study mainly evaluated the thermal and mechanical properties of asphalt mixtures with and without various PCMs (PCM-L, PCM-Z) using laboratory performance tests. The experimental tests included thermal conductivity and diffusivity, volumetric heat capacity, indoor temperature changes versus time when heated or cooled, indirect tensile strength, high-temperature rutting, and low-temperature cracking. In addition, a hot disk thermal constants analyzer was used to measure the thermal constants of asphalt mixtures. The results showed that different PCMs had different effects on the thermal constants of asphalt mixtures. Compared with control sample, the sample with PCM-L showed a higher thermal conductivity, whereas the sample with PCM-Z had a lower thermal conductivity. Moreover, PCM-Z exhibited a more-significant phase-change adjusting-temperature effect on asphalt mixtures than PCM-L. However, the addition of PCM to asphalt mixtures resulted in a decreased indirect tensile strength and a weakened rutting resistance, but the effect of PCM-Z was smaller than that of PCM-L. In addition, the asphalt mixture with PCM-Z exhibited better cracking resistance than the mixture with PCM-L and control mixture. Therefore, it is recommended to use PCM-Z in asphalt mixtures to solve the problem of pavement at high temperatures.