Paul J Cosentino

Shear and Deformation Characteristics of Municipal Waste Combustor Bottom Ash for Highway Applications

Municipal waste combustor (MWC) bottom ash from mass-burn (MB) and refuse-derived-fuel (RDF) facilities was evaluated for potential use as highway fill material. MWC bottom ash exhibits acceptable shear and deformation characteristics for many highway applications. RDF ash contains a lower metals percentage than MB ash. The specific gravity of both ashes was found to be a function of metals content. Moisturedensity relationships and unconfined compressive strengths were found to be a function of compaction energy and moisture content. Allowing compacted ash to age increased its unconfined compressive strength. Stress-strain characteristics of both ashes are similar to those of sands. Cohesion exists possibly because of pozzolonic reactions in the bottom ash. The angle of internal friction increased with compacted density. Elastic moduli are a function of density and confining pressure. RDF ash was found to be twice as stiff as MB ash. California bearing ratio results greater than 100 indicated that MB ash could be utilized as road base, and values between 25 and 95 indicated that RDF would be acceptable for use in subgrade and subbase. Bearing ratio results were highly dependent on moisture conditions. Both ashes exhibit little to no swell and should not cause field problems during saturation.

Improving Properties of Reclaimed Asphalt Pavement for Roadway Base Applications Through Blending and Chemical Stabilization

Finding innovative ways to incorporate reclaimed asphalt pavement (RAP) into highway base course applications will provide both environmental and economic benefits by allowing in situ recycling of material for projects such as widening or shoulder addition. RAP is a well-drained granular material; however, 100% RAP has low bearing strength and creeps under load. The objective of this research is to develop methods to improve RAPs strength while reducing creep to an acceptable level through blending with high-quality crushed-limestone aggregate, by chemical stabilization with asphalt emulsion or portland cement, or both. RAP–aggregate blends with and without chemical stabilization were compacted by the modified Proctor method, cured, and tested for strength and creep. Strength was tested by the limerock bearing ratio (LBR), a variant of the California bearing ratio test. Specimens were tested dry and soaked to evaluate retained strength. One-dimensional creep testing was performed with 7-day oedometer tests. RAP–aggregate blends have the potential to be used successfully as base course material. Blends of RAP with 50% limerock base material attained acceptable LBR strength and creep with the addition of 1% of either asphalt emulsion or cement. Blends of RAP with 75% or more limerock attained close-to-acceptable LBR and low levels of creep without any chemical stabilizer. Significant variability was noted between results with different blends and stabilizing agents. Performance testing should be conducted to establish the suitability of a specific RAP–aggregate blend.

Towards the development of a complex structural inspection system using small-scale aerial vehicles and image processing

Inspections of structures such as bridges and high mast lightning (HML) and support poles are crucial to the maintenance and safety of transportation infrastructures. Government agencies rely on inspections to estimate the health of structures and make decisions-such as allocation of human resources and funds to maintain\repair the structures - that significantly affect public safety and costs. This paper describes a work-in-progress towards the development of a highly complex system capable of assisting structural inspectors during the inspection process. The authors present the conceptual design of a complex system capable of acquiring and processing image data of structures in near real-time efficiently and in a cost-effective manner. The completion of this highly complex system requires a robust systems engineering approach that integrates the software engineering, mobile technology, small-scale aerial vehicles, and transportation engineering disciplines.

THREE-DIMENSIONAL STRUCTURAL STRAIN MEASUREMENT WITH THE USE OF FIBER-OPTIC SENSORS

Three-dimensional strain sensing inside a structure is not feasible with conventional strain sensing techniques such as electrical strain gauges, which are limited to surface measurements. Three-dimensional strain measurement inside a structure would find uses in a variety of new applications: enhanced understanding and detection of composite failure modes, such as delamination; sensing for adaptive structural control; intelligent vehicle highway systems; and structural health monitoring systems for civil structures. The latter application could involve remotely monitoring structural integrity during and after an earthquake, for example. A fiber-optic strain sensor array (FOSSA) in a planar, patch-like configuration was developed, and accurate measurement of the three principal strains inside a simple structure was demonstrated. The planar configuration was chosen to avoid the difficulty and structural degradation of embedding optical sensors in three planes. Two extrinsic Fabry-Perot interferometric (EFPI) sensors and one polari-metric sensor form the planar sensor array. The two EFPI sensors were placed perpendicular to each other in the sensor plane to extract the two normal strain components along the x and y axes. The polarimetric sensor embedded in the plane was used to extract the third normal strain acting on the z axis. The sensor array was embedded in an epoxy resin cube and loaded to 454 kg (1,000 1b) with a loading machine. The strains that were measured correlated well with the external strains measured with surface-bonded electrical strain gauges. The variation in measured strain between the two sensor systems was less than 4 percent for all three principal axes.

Fiber optic pore water pressure sensor for civil engineering applications

Low cost, rugged and reliable fiberoptic sensors are being developed to meet the needs of geotechnical engineers. The primary emphasis has been on load and pressure sensors, including pore water pressure sensors. The microbend sensors developed have been tested in the laboratory up to water pressures of 100 psi and loads of 50 lb. Accuracy of sensor measurements are within 5% and is being improved upon. Sensors with larger range or more sensitivity can easily be built without changing the basic sensor design. A semi-automated calibration and testing system was developed to characterize the sensors. In this paper we describe some of the applications for the sensors, their construction, characterization system, and experimental performance.

Development of the Miniaturized Pressuremeter Test to Evaluate Unbound Pavement Layers

The development of a reliable field test that can be utilized to determine in situ pavement characteristics is discussed in this work. The developed device, which is a modified version of the PENCEL pressuremeter has a 6-in. inflatable probe capable of measuring field stress–strain response of the soils without worrying about edge effects of thin unbound granular layers. A roadway project was selected to conduct some preliminary field measurements in its subgrade layer. The PENCEL pressuremeter (PPMT) along with the miniaturized pressuremeter (MPMT) were used during the testing program to check the performance of the new device, and to validate its results. The results indicated that strength and stiffness properties of poorly graded sand subgrade, measured from running the miniaturized pressuremeter, compare well with those measured from the PENCEL pressuremeter. The MPMT data can be employed as essential inputs to evaluate existing pavement structures as part of a pavement-management system, and as critical inputs in empirical design methods of new flexible pavements and/or pavement overlays.

Evaluating Laboratory Compaction Techniques of Reclaimed Asphalt Pavement

Reclaimed asphalt pavement (RAP) is a byproduct of roadway resurfacing. A limited amount of RAP can be recycled into new hot-mix asphalt; the rest is stockpiled. Some states allow the use of RAP–aggregate blends as base course material. Because of RAPs low strength and susceptibility to creep deformation, the Florida Department of Transportation (DOT) excludes RAP from being used as pavement base course for high-traffic areas. The research objective was to determine whether the strength characteristics of RAP could be improved through compaction and thereby make its base suitable in high-traffic areas. Modified Proctor, vibratory, and gyratory compaction data were compared. Four RAP sources were used. Specimens compacted by the three methods were tested with the limerock bearing ratio (LBR), unconfined compressive strength, and indirect split tensile strength. LBR is Floridas variation of the California bearing ratio. Specimens were compacted to either a density or a compaction energy level. Vibratory compaction produced the lowest densities and strengths. Modified Proctor produced higher densities and strengths than vibratory, but the LBR strengths for all RAP types were consistently below Florida DOT standards. Gyratory compaction produced the highest densities and strengths. Gyratory RAP specimens were two to four times as strong as modified Proctor specimens at the same density. The compaction method did not have as significant an effect on creep, although gyratory-compacted samples produced less creep than modified Proctor–compacted samples.

Instrumenting Pencel Pressuremeter Control Unit to Simplify Data Collection, Reduction, and Analysis

The Pencel pressuremeter control unit was instrumented to simplify digital recording, data reduction, and analysis of soil parameters. Digital signals from the instrumentation were collected through a commercially available data acquisition package, known as an automated pressuremeter (APMT), which produced reduced stress-strain data and allowed operators to determine the critical parameters. The instrumented system saved significant time. Data from numerous tests were evaluated for accuracy. Both clays and sands were included in the comparison. A digital pressure transducer was plumbed into the control unit, and a linear potentiometer was connected directly to the piston to produce digital volumes. The digital equipment improved the accuracy of the pressures more than ten-fold and eliminated gear backlash associated with the existing volume counter. The backlash affects the moduli more than the limit pressures, especially those associated with unload-reload loops of stiffer soils. Pressure-versus-time data for each injected volume increment were evaluated to determine when the pressures stabilized. APMT indicated that the pressure stabilized between 10 and 80 s for the sands and clays evaluated. The volume increment stabilization period was defined as the time required for the pressures to stabilize.

Development of microbend sensors for pressure, load, and displacement measurements in civil engineering

We are developing low cost, rugged, and reliable fiberoptic sensors to meet current and future needs in civil engineering, including those of smart civil structures. Our work has concentrated on load, pressure, and displacement sensors, including pore water pressure sensors. We have built and demonstrated sensors in the laboratory with loads up to 50 lb., water pressures of 100 psi, and displacements up to 1 mm. Repeatability of sensor measurements are within 5% and are being improved with continued development. The range and sensitivity of the sensors can be easily changed without changing the basic sensor design. We also have multiplexed two water pressure sensors on a single fiber. We describe the sensor construction and experimental performance.

Characterizing Structural Performance of Unbound Pavement Materials Using Miniaturized Pressuremeter and California Bearing Ratio Tests

Comparative analyses were implemented between the miniaturized pressuremeter (MPMT) test and the California bearing ratio (CBR) test to assess the capability of the MPMT stress-strain data for predicting structural performance of unbound pavement layers. Fifty-four MPMT tests and 108 CBR tests were performed on both base and subgrade soils in Brevard County, Florida. These comparative analyses were conducted in two stages. First, statistical correlations were established by comparing MPMT parameters with structural coefficients and structural numbers obtained from CBR data and the corresponding correlations. The results indicated that initial elastic moduli and limit pressures from MPMT correlate well with structural coefficients and structural numbers. Comparing them with results reported by AASHTO validated the quality of the correlation models. Secondly, finite element analyses were carried out to predict CBR as a function of MPMT data reduced to the strain-level model. The elastic moduli from the MPMT strain level model were input into the finite element simulation. To capture actual soil behavior, six strain levels were utilized during numerical simulations. For base course materials, strain evaluation points were selected at the top, middle, and bottom of the layer. For subgrade soils, strain evaluation points were selected at the top of the subgrade, 15 cm and 30 cm below subgrade surface. The results indicate that strain level moduli at the top of the base course layers provide the best CBR estimation, with the ratio of finite element CBR to measured CBR equal to 0.91. The results of subgrade show that strain level moduli determined at the depth of 15 cm below subgrade surface yield the best CBR prediction. The ratio of finite element CBR to measured CBR was 1.00.