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A common perception of plasma arc treatment systems for municipal solid waste incineration ash is that the resulting vitrified slag is inert from an environmental perspective. Research was conducted to examine this hypothesis and to... more
A common perception of plasma arc treatment systems for municipal solid waste incineration ash is that the resulting vitrified slag is inert from an environmental perspective. Research was conducted to examine this hypothesis and to assess whether reduced pollutant release results from pollutant depletion during the process of the ash with plasma, or encapsulation in the glassy vitrified matrix. The concentrations of four discrete municipal solid waste incineration ash samples before and after plasma arc vitrification in a bench-scale unit were compared. Slag and untreated ash samples were leached using several standardized approaches and mobility among the four metals of interest (e.g. As, Cd, Pb and Sb) varied across samples, but was generally high (as high as 100% for Cd). Comparison across methods did not indicate substantial encapsulation in the vitrified slag, which suggests that reduced pollutant release from plasma arc vitrified slag is due to pollutant depletion by volatilization, not encapsulation. This has significant implications for the management of air pollution control residues from waste-to-energy facilities using plasma arc vitrification.
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Since 1987 when dry-point-contact (DPC) transducers were invented in the USSR, ultrasonic shear wave devices based on those transducers have been commercialized and have become one of the most effective technologies for imaging concrete.... more
Since 1987 when dry-point-contact (DPC) transducers were invented in the USSR, ultrasonic shear wave devices based on those transducers have been commercialized and have become one of the most effective technologies for imaging concrete. That said, the objectives of this paper are (1) to provide a brief review of the historical development of these powerful devices and (2) to provide a comprehensive assessment of their capabilities in imaging internal entities and structural defects. Regarding the former, the paper presents the context that gave birth to DPC technology and different generations of ultrasonic shear wave devices for concrete inspection. For the latter, one of the state-of-the-art ultrasonic shear wave devices (MIRA 3D) was used to collect data on concrete specimens with different built-in flaws/defects. Those data are then visualized with a commonly used data processing algorithm, the so-called synthetic aperture focusing technique (SAFT). Finally, based on the result...
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Research Interests: Engineering and Cement
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AbstractBottom and combined ash samples from municipal solid waste incinerator (MSWI) facilities in Florida were compared with industry aggregate standards to determine suitability for use as a roa...
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Observations by engineers throughout Florida revealed that traditional materials used for the repair of concrete pavements and structures often succumb to premature failure after relatively short service lives. A previously existing... more
Observations by engineers throughout Florida revealed that traditional materials used for the repair of concrete pavements and structures often succumb to premature failure after relatively short service lives. A previously existing standard specification for repair materials was based solely on hardened physical properties, specifically compressive strength and length change. A more rigorous testing program was needed, in which the qualification process for repair materials evaluated both physical and durability properties. A testing regimen was devised to evaluate the capacity of each material for use in the repair of structural concrete. The objective of this analysis was to determine the performance of each material type and to properly assign it a repair application category. The testing regimen also evaluated the tests themselves to determine their applicability to evaluate specific material properties, and the potential usage for product acceptance. The sampling, testing, and evaluation procedures are discussed and resultant specification changes are described.
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Measurements of thickness using acoustic methods such as ultrasonic pulse-echo or impact-echo become relevant whenever components are accessible from only one side and the design thickness needs to be verified or the geometry of... more
Measurements of thickness using acoustic methods such as ultrasonic pulse-echo or impact-echo become relevant whenever components are accessible from only one side and the design thickness needs to be verified or the geometry of structures need to be determined. While thickness measurements with acoustic non-destructive testing (NDT) methods are relatively easy and straightforward to conduct on test objects with simple geometries and wide dimensions, they can become quite challenging when the geometry of the test object is more complex or when the dimensions of the test object are rather compact. In such cases, geometry effects, i.e. misleading additional reflections at the geometrical boundaries of the structure other than the intended backwall reflection, can severely interfere with the actual measurement, which applies especially for impact-echo. Measurements have been performed on test blocks with different geometries using an automated test frame, thus providing dense scan grids and therefore good statistical significance. 2D and 3D imaging techniques are applied to the data. In particular, a combined data acquisition and real-time imaging software is presented, which integrates the measurement data into pictures showing test object, thus enhancing the interpretation of the results. Inverse thickness measurements, i.e. measurements where the thickness is known and the velocity is being determined in the test, reveal the elastic material properties, especially when longitudinal and shear wave measurements are combined.
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This research program was designed to provide the groundwork for future research aimed at using nondestructive testing to monitor new structures for compliance with Florida Department of Transportation performance specifications, and lead... more
This research program was designed to provide the groundwork for future research aimed at using nondestructive testing to monitor new structures for compliance with Florida Department of Transportation performance specifications, and lead to the understanding necessary to successfully devise nondestructive testing regimes which can be used to monitor new structures to ensure adequate performance and detect defects or damage present in existing structures. The project included a survey aimed at identifying the deterioration mechanisms and defects most relevant to bridge structures in Florida and review of previously published literature to assist in identifying specific nondestructive techniques, or combinations of techniques, which would be most effective for evaluating the damage mechanisms expected in Florida bridges. The identified deterioration mechanisms were then reproduced in the laboratory and evaluated using the recommended nondestructive techniques. Recommendations were made concerning the use of nondestructive testing technologies in the evaluation of concrete bridge structures in the State of Florida.
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Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values... more
Slag from the high temperature arc gasification (HTAG) of municipal solid waste (MSW) was tested to evaluate its material properties with respect to use as a construction aggregate. These data were compared to previously compiled values for waste to energy bottom ash, the most commonly produced and beneficially used thermal treatment residue. The slag was tested using gradations representative of a base course and a course aggregate. Los Angeles (LA) abrasion testing demonstrated that the HTAG slag had a high resistance to fracture with a measured LA loss of 24%. Soundness testing indicated a low potential for reactivity and good weathering resistance with a mean soundness loss of 3.14%. The modified Proctor compaction testing found the slag to possess a maximum dry density (24.04kN/m(3)) greater than conventionally used aggregates and WTE BA. The LBR tests demonstrated a substantial bearing capacity (>200). Mineralogical analysis of the HTAG suggested the potential for self ceme...
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Current Situation Standard concrete is, at minimum, a combination of the portland cement, limestone aggregate, sand, and water. Additives such as supplementary cementitious materials (SCMs) like fly ash and water reducers enhance the... more
Current Situation Standard concrete is, at minimum, a combination of the portland cement, limestone aggregate, sand, and water. Additives such as supplementary cementitious materials (SCMs) like fly ash and water reducers enhance the strength and durability of concrete, and the exact proportions of these materials that produce desired results have been the subjects of much research. Further additives like reactive powders, fibers, and finely ground quartz or limestone have also been used to increase the strength and durability of concrete. The resulting product is called ultrahigh performance concrete (UHPC), which can be five or more times a strong as standard concrete. When UHPC is used in structural designs, it is important to verify that it performs as expected. This is easier for precast materials, but when UHPC is cast in the field, reliable tests are needed.
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Portland cement concrete is a heterogeneous, composite material composed of coarse and fine granular material embedded in a matrix of hardened paste. The coarse material is aggregate, which is primarily used as inexpensive filler and... more
Portland cement concrete is a heterogeneous, composite material composed of coarse and fine granular material embedded in a matrix of hardened paste. The coarse material is aggregate, which is primarily used as inexpensive filler and comprises the majority of the volume of concrete and can be obtained from a variety of different sources. The physical properties of concrete are heavily influenced by the aggregate properties. Most of the coarse aggregate produced in Florida is a limestone material that is more porous, less dense, and softer than limestone produced from other areas of the U.S. To differentiate between limestone produced in Florida and limestone produced elsewhere, limestone from the geologic formations in Florida is typically referred to as “limerock.” The coarse aggregate produced in Florida and used in structural concrete require special consideration with regard to relative strength, thermal, and physical properties. The structural design of concrete is based on ser...
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The Florida Department of Transportation (FDOT) would like to implement nondestructive test and evaluation (NDT/NDE) technologies to assess quality of concrete constructed in the field as means to reduce flaws introduced by faulty... more
The Florida Department of Transportation (FDOT) would like to implement nondestructive test and evaluation (NDT/NDE) technologies to assess quality of concrete constructed in the field as means to reduce flaws introduced by faulty construction. Toward this aim, the primary objective of the project was to design, construct, and implement a facility for calibrating and validating methodologies for the NDT/NDE of structural concrete materials and members. Four concrete test blocks have been designed and built in which specific testing problems (e.g., concrete cover, concrete thickness, and tendon ducts) were implemented to investigate them under defined conditions in the laboratory. The specimens were designed to challenge NDT techniques, and serve to demonstrate their capabilities as well as their limitations. An automated test frame has been designed, built, and implemented, and a software platform for scanner control, data acquisition with different sensors, real-time imaging and da...
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This research was initiated following reports of high incidence of cracking on Florida Department of Transportation (FDOT) concrete pavement replacement slab projects. Field slabs were instrumented for data acquisition from... more
This research was initiated following reports of high incidence of cracking on Florida Department of Transportation (FDOT) concrete pavement replacement slab projects. Field slabs were instrumented for data acquisition from high-early-strength concrete pavement replacement slabs placed on projects funded by FDOT. Data were collected for three slabs located in Jacksonville, Florida, and Gainesville, Florida. A battery of laboratory tests was simultaneously conducted on the FDOT-approved concrete mixture designs used in the instrumented field slabs in addition to mixtures with variable chloride-based accelerator dosage. Temperature and strain data, as well as physical and thermal data, were acquired from slabs from the construction projects. The physical and thermal data acquired from the field were used for modeling description and verification. Subsequent to the field testing and data acquisition, the slabs were inspected for the presence of cracking. Laboratory testing included as-...
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There are ongoing research efforts directed at addressing strength limitations of compressed earth blocks (CEB) that inhibit their deployment for structural applications, particularly in areas where masonry systems are regularly subjected... more
There are ongoing research efforts directed at addressing strength limitations of compressed earth blocks (CEB) that inhibit their deployment for structural applications, particularly in areas where masonry systems are regularly subjected to lateral loads from high winds. In this paper, the authors focus specifically on the extent to which polypropylene (PP) fibers can be used to enhance the flexural performance of CEB. Cementitious matrices used for CEB production exhibit low tensile and flexural strength (brittle) properties. This work investigates plain (unreinforced) and fiber-reinforced specimens (short flexural beams) with fiber mass content of 0.2, 0.4, 0.6, 0.8, and 1.0% and ordinary Portland cement (OPC) content of 8%. The influence of the inclusion of fiber was based on tests conducted using the Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (ASTM C1609). Material properties that were quantified included first-peak strength, peak strength, equiv...
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Research Interests: Cement and Durability
One of the biggest benefits of using supplementary cementitious materials (SCMs) in concrete is the large reduction in the concrete chloride ion diffusion coefficient with age. The formation factor calculated from electrical resistivity... more
One of the biggest benefits of using supplementary cementitious materials (SCMs) in concrete is the large reduction in the concrete chloride ion diffusion coefficient with age. The formation factor calculated from electrical resistivity measurements is proportional to the concrete effective chloride diffusion coefficient. Traditionally, the aging factor used in service life modeling has been determined from examination of the apparent diffusion coefficient calculated from concrete bulk diffusion experiments, lumping chloride binding and with diffusion. This study proposes to use the formation factor determined from electrical resistivity tests to quantify the concrete aging parameter for service life modeling. To determine the effect of cement chemical composition, four types of cement were tested including type I/II low alkali cement, type IL cement, type V cement and type I/II high alkali cement. Silica fume, slag cement, Class F fly ash, and metakaolin were used as supplementary cementitious materials (SCMs) in binary and ternary blends with different replacement ratios to evaluate the effect of SCMs on the concrete electrical properties with age. The electrical properties were determined at 28, 56, 91, 182 and 365 days. A discussion about the advantages and disadvantages of this method over traditional methods to quantify aging are presented.
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Abstract The durability of portland cement concrete is strongly influenced by the penetrability of the concrete matrix. This research investigated the relationships between penetrability tests (electrical resistivity, porosity, and bulk... more
Abstract The durability of portland cement concrete is strongly influenced by the penetrability of the concrete matrix. This research investigated the relationships between penetrability tests (electrical resistivity, porosity, and bulk diffusion) and four types of portland cement specimens: cementitious paste, mixed mortar, sieved mortar, and concrete. The coarse and fine aggregate components, which are mostly non-conductive and impermeable, increased electrical resistivity. Therefore, the testing demonstrates that concrete generally had the highest resistivity, followed by mortar and paste. Porosity results from mercury intrusion porosimetry were used to explore the viability of Gaussian process regression modeling to predict the electrical resistivity of concrete. Regression modeling was able to predict surface resistivity using porosity data and thus may be a valuable concrete mixture screening tool.
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AbstractVarious filler materials were evaluated to identify and differentiate chemical reactions from physical particle reactions during hydration within a portland cement system. Laboratory teasti...
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A series of roadway tests strips were paved on-site at a landfill in Florida, U.S. Waste to energy (WTE) bottom ash was used as a partial course aggregate replacement in a hot mix asphalt (HMA) and a Portland cement concrete (PCC)... more
A series of roadway tests strips were paved on-site at a landfill in Florida, U.S. Waste to energy (WTE) bottom ash was used as a partial course aggregate replacement in a hot mix asphalt (HMA) and a Portland cement concrete (PCC) pavement, along with control HMA and PCC sections. This allowed for a comparison of the relative degree of leaching between both materials (HMA and PCC) as well as between the ash-amended and control pavements. Batch and monolithic tank leaching tests were conducted on the pavements. Testing of the PCC samples demonstrated that Mo and Al were elevated above regulatory thresholds for both the control and ash amended samples. Further leach testing demonstrated that the release of Mo was likely from the PCC and not a result of the inclusion of the BA into pavement. Batch leach testing of ash-amended HMA samples revealed Sb as a constituent of potential concern. The results of the monolith leaching test displayed leaching of Sb within the same order of magnitu...
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Oak Ridge National Laboratory (ORNL) comparatively evaluated the ability of a number of NDE techniques to generate an image of the volume of 6.5′ X 5.0′ X 10″ concrete specimens fabricated at the Florida Department of Transportation... more
Oak Ridge National Laboratory (ORNL) comparatively evaluated the ability of a number of NDE techniques to generate an image of the volume of 6.5′ X 5.0′ X 10″ concrete specimens fabricated at the Florida Department of Transportation (FDOT) NDE Validation Facility in Gainesville, Florida. These test blocks were fabricated to test the ability of various NDE methods to characterize various placements and sizes of rebar as well as simulated cracking and non-consolidation flaws. The first version of the ultrasonic linear array device, MIRA [version 1], was one of 7 different NDE equipment used to characterize the specimens. This paper deals with the ability of this equipment to determine subsurface characterizations such as reinforcing steel relative size, concrete thickness, irregularities, and inclusions using Kirchhoff-based migration techniques. The ability of individual synthetic aperture focusing technique (SAFT) B-scan cross sections resulting from self-contained scans are compared with various processing, analysis, and interpretation methods using the various features fabricated in the specimens for validation. The performance is detailed, especially with respect to the limitations and implications for evaluation of a thicker, more heavily reinforced concrete structures.
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Acoustic as well as electromagnetic methods can provide a valuable tool for the quality assessment of concrete bridges. For the efficient application in the field, the capabilities of the different methods in solving a specific testing... more
Acoustic as well as electromagnetic methods can provide a valuable tool for the quality assessment of concrete bridges. For the efficient application in the field, the capabilities of the different methods in solving a specific testing problem have to be known. In a research project funded by the Florida Department of Transportation (FDOT) a first stage facility for the calibration
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ABSTRACT Researchers investigated the applicability of various nondestructive testing (NDT) methods on full-scale concrete bridge structures, including ultrasonic pulse velocity tomography and the impact-echo method. The combination of... more
ABSTRACT Researchers investigated the applicability of various nondestructive testing (NDT) methods on full-scale concrete bridge structures, including ultrasonic pulse velocity tomography and the impact-echo method. The combination of the two methods enabled researchers to three-dimensionally evaluate material consistency and locate flaws or regions of deterioration within structural members with a new level of efficiency. Although research involving NDT methods has been conducted for many years, the use of NDT methods for primary investigation of full-scale structural elements is not typically performed. In this study, the investigation of bridge structures for flaws and damage resulted in the discovery of a previously undetected yet recurring form of damage, which led investigators to suspect a design flaw. The results of the ultrasonic pulse velocity tomography enabled researchers to assess the actual cause of the damage, which allowed the formulation of recommendations for the repair and redesign of the defective structural elements.