Skip to main content

Cassie Castorena


Fitts-Woolard Hall 3233


Dr. Cassie Castorena is an Associate Professor in the Department of Civil, Construction, and Environmental Engineering at North Carolina State University. She is interested in multi-scale characterization of asphalt materials, asphalt binder modification, asphalt pavement design, and asphalt pavement distress mechanisms.


Ph.D. Civil and Environmental Engineering University of Wisconsin-Madison

M.S. Civil and Environmental Engineering University of Wisconsin-Madison

B.S. Civil and Environmental Engineering University of Wisconsin-Madison

Area(s) of Expertise

Dr. Castorena's research is focused on characterization of asphalt materials. Specifically, her work utilizes multi-scale characterization to develop a fundamental understanding of asphalt binders and their interaction with mineral aggregates. This work aims to improve our methods for asphalt pavement material selection and design. Additionally, she investigates the use of innovative alternative cement binders and asphalt modification technology for improved pavement sustainability.


View all publications 


Date: 08/01/23 - 7/31/25
Amount: $339,112.00
Funding Agencies: NC Department of Transportation

Past and on-going NCDOT research projects have provided insights on critical aspects of the performance of asphalt mixtures containing recycled asphalt materials (RAM). NCDOT RP 2019-21 found that agglomerations of RAM particles exist in asphalt mixtures. These agglomerations act as ???black rocks??? and prohibit complete recycled binder availability. However, all experiments conducted in NCDOT RP 2019-21 employed a laboratory bucket mixer to prepare asphalt mixture samples, which may not reflect mixing in an asphalt plant. Furthermore, the NCDOT does not currently specify how to preheat virgin aggregate and RAM when producing asphalt mixtures in the laboratory, which may affect recycled binder contribution. NCDOT RP 2019-21 identified three adjustments to mixture design to account for recycled binder availability, termed availability adjusted mix design (AAMD). One of the proposed changes was to use only the available recycled binder to calculate the ???effective??? rather than total recycled binder replacement percentage (RBR%). The effective RBR% is lower than the total RBR% for a given mixture. Consequently, the reliance on the total RBR% may result in an effective binder system that is softer than what was expected. Shifting to specifications based on the effective RBR% would increase the amount of RAM that can be used in a mixture without adjusting to a PG 58-28 virgin binder and increase the maximum RAM that can be incorporated into a mixture without exceeding maximum limits.

Date: 08/01/22 - 7/31/25
Amount: $322,786.00
Funding Agencies: NC Department of Transportation

Current procedures for asphalt mixture design in North Carolina require contractors to conform to volumetric requirements on the air void content, voids in mineral aggregate, and other parameters at a fixed, traffic- and layer-specific compaction effort. The presumption in this case is that the mixtures produced under the same guidelines will have similar properties. However, recent findings by NCSU suggests that this presumption may be inaccurate and may have substantial implications in the design, performance, and management of roadways. This research study will address this issue by: i) identifying the most appropriate durability related testing protocol for incorporation into mix design and quality assurance/control operations; ii) establishing initial threshold limits for the test identified; iii) developing a draft balanced mix design (BMD) procedure for North Carolina, and iv) developing a draft protocol for integrating the identified performance tests into quality assurance and quality control operations. The primary outcome of the proposed research will be a test method and procedure that the NCDOT can deploy in asphalt mixture design and production to ensure that the mixtures delivered in the state have an acceptable level of performance.

Date: 08/01/22 - 1/31/25
Amount: $307,444.00
Funding Agencies: NC Department of Transportation

The vast majority of asphalt mixtures produced in North Carolina contain recycled materials, including Reclaimed Asphalt Pavement (RAP) and/or Recycled Asphalt Shingles (RAS). This research project seeks to identify how asphalt plant processing and stockpiling variables affect the consistency of RAP and RAS materials with time in a given stockpile and across different plants in North Carolina. Furthermore, the project will assess how changes in recycled material properties affects asphalt mixture performance is needed to understand the practical implications of variability. Collectively, the results of this research will inform improved measures within the NCDOT specifications to mitigate variability of recycled material sources and, in turn, improve the reliability of asphalt mixture performance.

Date: 10/01/21 - 12/31/23
Amount: $134,995.00
Funding Agencies: Federal Highway Administration (FHWA)

This project will explore an innovative method to determine Reclaimed Asphalt Pavement (RAP) binder availability. RAP binder availability refers to the percentage of total RAP binder that is released and available to blend with virgin asphalt during asphalt mixture production. Research has shown that the primary source of unavailable recycled binder is agglomerations of adhered RAP particles. The binder bound within the agglomerations is prohibited from coming contacting and therefore, blending with virgin asphalt. The proposed innovation determines the extent of RAP agglomeration and, in turn, RAP binder availability by comparing the gradation of recovered RAP aggregates to that of the RAP itself. Quantifying the inactive recycled binder content of RAP sources using the proposed innovation offers a means to discredit unavailable recycled binder within design practices. It is expected that discrediting unavailable recycled binder will improve the design and performance of high RAP content mixtures, consequently increasing pavement service life and reducing life cycle costs. The research products may also enable the design of satisfactory asphalt mixtures with higher RAP contents, resulting in environmental and cost benefits. Preliminary results of the proposed innovation are promising. This project will rigorously optimize the innovation, evaluate the performance implications of discrediting inactive recycled binder within design procedures, and develop a provisional AASHTO standard procedure.

Date: 08/01/21 - 12/31/23
Amount: $398,171.00
Funding Agencies: NC Department of Transportation

Vehicle collisions and increases in collisions rates during wet conditions are one of the major safety concerns for the NCDOT. Collision rates increase when the surface is wet because skid resistance reduces under these conditions. The precise amount of loss is dependent on many factors, but the consensus among experts is that pavement friction and macrotexture are important factors that affect the skid resistance and changes in this resistance under wet conditions. This research will achieve three objectives; 1) characterize friction and texture performance models, 2) develop friction and texture performance thresholds, and 3) identify asphalt mixture compositional factors (gradation, asphalt content, presence of modified versus non-modified asphalt, etc.) that affect the as-constructed macrotexture and friction. The primary outcome of the proposed research will be an initial set of performance models that can be used to assess immediate and potentially long-term friction/macrotexture issues. The research will also produce a set of threshold limits for friction/macrotexture where investigatory and intervention steps need to be taken to control for safety. Finally, the research will produce information on the mixture design factors that contribute to higher or lower friction/macrotexture. These outcomes can be used by the Traffic Safety and Materials and Test Units of the North Carolina DOT to predict and manage friction and texture performance on roadways and to understand when measurements represent a potential hazard exists. It will also be used to help identify asphalt mixtures with potential friction and macrotexture issues and develop better guidelines, specifications, and operational controls (if necessary) for recently overlaid pavements. This could lead to reduced collision rates on these pavements. Thus, this research will result in overall improved procedures for flexible pavement overlay operations.

Date: 03/11/20 - 11/23/23
Amount: $374,079.00
Funding Agencies: Federal Highway Administration (FHWA)

In this research study, NCSU will design, conduct, and provide recommendations relating to a two-phase ruggedness and interlaboratory study on a test method that has been identified as critical to asphalt pavement performance and design practice. AASHTO TP 132 (2019) Standard Method of Test for Determining the Dynamic Modulus for Asphalt Mixtures Using Small Specimens in the Asphalt Mixture Performance Tester (AMPT) has been developed, refined, and recently published as an AASHTO provisional standard; a statistically sound refinement procedure is needed to facilitate widespread adoption and implementation. Not only can this standard be used to obtain inputs to the AASHTO PavementME pavement structural analysis software, the standard is being used in ongoing FHWA efforts as part of a performance-related specification framework which seeks to increase pavement life through fundamental testing and predictive relationships. AASHTO TP 132 is of interest because of its fundamental nature, determination via the AMPT standardized equipment, and its ability to model and predict material performance over a wide range of loading and climate conditions a pavement may experience; resulting in better performing, safe, quiet, durable, long lasting asphalt roadways. Additionally, a draft practice for preparing small-scale specimens has been developed and published as AASHTO PP 99 (2019) Standard Method of Practice for Preparation of Small Cylindrical Performance Test Specimens Using the Superpave Gyratory Compactor (SGC) and Field Cores. This draft practice is of significant interest to the asphalt materials community due to anticipated materials, time, and cost savings associated with preparing and evaluating smaller performance test. NCSU will carry out the following tasks. Task 1 ?????????????????? Develop final research plans and project schedule ?????????????????? The proposed plan will be revised based on feedback from the FHWA. Task 2 ?????????????????? Kickoff meeting ?????????????????? NCSU will meet with the project panel to review the statement of work and work plans. Task 3 ?????????????????? Perform work plan and document efforts ?????????????????? NCSU will carry out the approved work plan by following the appropriate ASTM standard test methods to develop a rugged test method. Task 4 ?????????????????? Ruggedness study presentations and webinar ?????????????????? NCSU will present the findings to targeted stakeholders. Task 5 ?????????????????? Publication ready final deliverables ?????????????????? the AASHTO standards will be revised into a final form. Task 6 ?????????????????? Revise work ILS work plan ?????????????????? NCSU will revise the original work plan from Task 1 based on findings from Tasks 3-5 for conducting the ILS study. Task 7 ?????????????????? Perform work plan and document efforts ?????????????????? NCSU will coordinate the ILS according to the approved work plan. This will include identifying participants, sending materials, and analyzing their results statistically. Task 8 ?????????????????? ILS study presentation and webinar ?????????????????? NCSU will present their findings to targeted stakeholders. Task 9 ?????????????????? Publication ready final deliverables ?????????????????? the AASHTO standards revised in Task 5 will be modified to include repeatability and reproducibility statements.

Date: 01/01/21 - 8/15/23
Amount: $370,363.00
Funding Agencies: NC Department of Transportation

The use of high Recycled Binder Replacement Percentages (RBRs%) in asphalt surface mixtures is increasing. The asphalt binders in recycled materials are generally hardened and embrittled from oxidization and may not fully mobilize and blend with virgin materials. Consequently, high recycled content mixtures may be prone to cracking if appropriate measures to consider this effect are not taken during the mixture design process. The objectives of the proposed research project are to: (1) modify the NCDOT??????????????????s procedures for the design of surface mixtures containing RAP and RAS to improve performance and (2) modify the NCDOT??????????????????s specifications to improve the consistency within and across RAP and RAS stockpiles within North Carolina. 1. To achieve these objectives, an operational review will be conducted to identify how contractors process, stockpile, characterize and use RAP and RAS under the current NCDOT guidelines. In addition, relationships between asphalt content and performance will be developed for recycled mixtures sourced from North Carolina. These relationships will be used to identify the maximum virgin binder content allowable and to maximize cracking performance without having the rutting performance fall below a critical performance threshold for each mixture. The collective results will be used to identify appropriate revisions to the NCDOT??????????????????s current recycled mixture design procedure to ensure reliable performance. The research results will lead improved specifications that will facilitate the design of better-performing surface mixtures containing recycled materials. These specifications will improve the durability of NCDOT pavements and consequently decrease life-cycle costs.

Date: 07/01/20 - 5/31/23
Amount: $248,113.00
Funding Agencies: US Dept. of Transportation (DOT)

In 2007, the Virginia Department of Transportation (VDOT) introduced specifications to allow higher percentages of reclaimed asphalt pavement (RAP) (i.e., up to 30%) in hot-mix asphalt (HMA) surface mixtures without adjustment of the virgin binder grade. The increased use of RAP was expected to result in a lower cost of produced asphalt mixtures given the continuous rising cost of oil and thus asphalt binders and fuel needed to produce asphalt pavements. By 2013, VDOT had begun to consider the feasibility of allowing the use of surface mixtures containing up to 45% of RAP material. Several trial sections were constructed containing mixtures with 20%, 30%, 40%, and 45% RAP for evaluation (Nair et al., 2019). In general, those trials found that mixtures containing up to 45% RAP could be designed, produced, and constructed if proper procedures are followed. In 2019, the research team at Virginia Transportation Research Council (VTRC) initiated another study to evaluate field trials of high RAP asphalt mixtures (i.e., more than 40%) designed following the Balanced Mix Design (BMD) special provision for VDOT??????????????????s surface mixtures. The primary concern with such mixtures has been that the use of high percentage of RAP will overly stiffen mixtures; making them more brittle and prone to premature cracking. The use of high percentage of RAP can lead to numerous construction and performance issues including, but not limited to, compactibility and workability in cool weather, low-temperature cracking with accumulation of thermally induced stresses, fatigue cracking and micro damage accumulation leading to crack initiation and propagation with repeated loading, reflection cracking with repeated loading and daily / seasonal thermal stresses, and raveling with subsequent aging or moisture damage. The challenges arising from the use of high RAP content mixtures can be addressed through the use of softer binders or additives such as recycling agents (RAs). These additives were utilized in HMA in the early period of widespread recycling in the 1970s and 1980s for the purpose of realizing three types of benefits: environmental, economic, and engineering. The use of RAs holds promise as long as there is a proper understanding of how effectively they restore binder rheology and how that effectiveness evolves with aging of mixtures in the laboratory, making them proper additives to be incorporated in mixtures to be placed in field. Hence, there is a need for an engineered framework to evaluate RAs in terms of their stiffness and cracking resistance when incorporated into the binder blends of corresponding mixtures. Currently, there are no unique and / or detailed handy guides or specifications that outline a framework to evaluate acceptability of RAs in the state of Virginia. Therefore, this study aims to identify and / or develop a testing protocol to evaluate the effectiveness of RAs in alleviating the brittleness of high RAP asphalt mixtures. In addition, a performance-based parameter(s) with its threshold limits / criteria will be identified or developed to accept or reject a certain product (i.e., recycling agents). Both objectives will facilitate responsible use of innovative materials as part of Virginia??????????????????s Balanced Mix Design (BMD) initiative. In this study, NCSU researchers will conduct experiments on asphalt binder, asphalt from reclaimed asphalt pavement (RAP), rejuvenator agents, mortars, and asphalt mixture.

Date: 08/01/19 - 2/28/23
Amount: $502,432.00
Funding Agencies: NC Department of Transportation

Asphalt mixtures used in pavement construction are required to meet the North Carolina Department of Transportation (NCDOT) moisture sensitivity specifications. To improve resistance to moisture damage various antistrip additives are used by the asphalt plants producing asphalt mixtures. These antistrip additives help improve the adhesion between asphalt and aggregate and thus improve the resistance of the asphalt mixtures to moisture damage. The antistrip additives are added to the asphalt mixture at the plant by various mechanisms based on the type of antistrip additive being used or they come premixed with the asphalt liquid. The additive is usually added to the asphalt liquid. A problem in the mechanism used to add the antistrip additive to the asphalt might lead to a lesser amount, or no antistrip additive being added into the asphalt mixture. This might lead to the asphalt mixture not meeting the NCDOT moisture sensitivity specifications. Since the additive is added to the asphalt liquid, any problem in the mechanism will not be noticed until the asphalt mixture is tested for its moisture sensitivity.

Date: 08/01/19 - 2/28/23
Amount: $306,668.00
Funding Agencies: NC Department of Transportation

The use of asphalt mixtures containing high Recycled Binder Replacements (RBRs) is increasing. Recycled binders are oxidized and thus, harder and more susceptible to cracking than virgin binders. Consequently, the use of higher recycled content mixtures has prompted heightened interest in recycling agents and necessitated the use of asphalt extenders to produce softer virgin binder grades. Recycling agents include a wide-range of both softening agents and rejuvenators that are intended to restore the physical and chemical properties of aged asphalt binders. Petroleum-based extender products have been in existence for a long time (e.g., Re-refined Engine Oil Bottom (REOB)). Non-petroleum based products have been more recently introduced (e.g., bio-oils).

Date: 08/01/18 - 4/30/22
Amount: $275,735.00
Funding Agencies: NC Department of Transportation

The usage of Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Shingles (RAS) in asphalt mixtures has increased significantly in recent years. While increasing recycled material usage has the potential to yield environmental and economic benefits, there is uncertainty in the validity of the current volumetric design and the associated performance of RAP and RAS mixtures. The mixture design procedure currently employed by the NCDOT assumes 100 percent binder contribution from recycled materials. However, it is currently poorly understood to what extent the recycled binder acts as ????????????????black rock??????????????? as opposed to actually blending with virgin asphalt. The erroneous assumption of complete blending will lead to an underestimation of required virgin asphalt binder content during mixture design and consequently yield mixtures with high cracking susceptibility. In addition, the recycled binder contribution is an important consideration when selecting the virgin binder grade for a mixture. Erroneous assumptions of blending may have negligible effects at low reclaimed binder contents but significant effects at higher contents. Therefore, given the increasing use of higher recycled material content mixtures in practice, an in-depth study is needed to develop an understanding of recycled binder contribution to improve the virgin binder grade selection and volumetric design of RAP and RAS mixtures.

Date: 08/01/19 - 10/31/21
Amount: $314,998.00
Funding Agencies: NC Department of Transportation

Vehicle collisions and increases in collisions rates during wet conditions are one of the major safety concerns for the NCDOT. Wet collision rates increase because skid resistance reduces under wet conditions. The precise amount of loss is dependent on many factors, but the consensus among experts is that pavement friction and macrotexture are important factors that affect the skid resistance and changes in this resistance under wet conditions. Although the NCDOT actively addresses skid resistance issues as they are identified, a recent study involving a small subset of North Carolina roadways has suggested that wet crash rates may increase after pavements are overlaid. That study concluded that NCDOT needed to consider characterization of both friction and macrotexture as part of its pavement friction measurement and management plan. While the current studies have successfully identified the potential for issues in recently overlaid projects, they did not identify whether these effects are temporary, and if so, how long they may last. In addition, past studies have not been able to identify any specific causative effects that may increase or decrease the impact of overlays on skid resistance. Since the primary change after an overlay is placed is the driving surface, there is a need to better understand how the asphalt mixture composition may affect the overall skid resistance of the roadway under wet conditions.

Date: 09/28/17 - 10/26/21
Amount: $782,309.00
Funding Agencies: Federal Highway Administration (FHWA)

AASHTO TP 107 enables the practical, mechanistic performance characterization of asphalt concrete using cyclic fatigue testing in the Asphalt Mixture Performance Tester (AMPT). AASHTO TP 107 was initially developed for the use of 100-mm diameter specimens, which yield a single test specimen per gyratory sample. Recently, a modified version of AASHTO TP 107 was proposed for the testing of 38-mm diameter small specimens that improves the efficiency of specimen fabrication and enables the testing of field cores extracted from as-built pavement layers. The objective of the proposed research is to improve AASHTO TP 107 by conducting ruggedness and interlaboratory studies using both small and large specimens. The ruggedness evaluation will identify controllable experimental factors that significantly affect the test results and to establish limits for their control. The interlaboratory study will lead to precision statements that define the repeatability and reproducibility of small and large cyclic fatigue the test results.

Date: 08/01/18 - 7/31/21
Amount: $303,135.00
Funding Agencies: NC Department of Transportation

The North Carolina Department of Transportation (NCDOT) uses the AASHTO Guide for Design of Pavement Structures 1993 to determine the minimum pavement stiffness that ensures pavement longevity. During design, this stiffness is first determined using an iterative design process, charts, or software. Then, the engineer selects materials and layer thicknesses that provide the required stiffness by summing the contributions of individual layers. The contribution from any given layer is calculated by the product of that layer??????????????????s thickness and a structural layer coefficient that captures the overall quality and structural benefit of the material. In the NCDOT procedure, the structural layer coefficient for asphalt concrete (AC) is 0.44 (surface and intermediate mixtures) or 0.30 (base mixtures), while other material types are lower, e.g., the structural layer coefficient for unbound aggregate base materials is 0.14. While the NCDOT has had success with these structural layer coefficient values, they are based on a test road constructed and evaluated in one climate zone and with one set of materials. Modern material selection and design have resulted in substantial changes in AC and aggregate base since this time. These improvements have likely resulted in different structural contributions from these materials, which means the structural layer coefficients should be reviewed and possibly changed. Proper characterization of these layer coefficients could result in substantial cost savings to the NCDOT by reducing the required pavement thickness and/or leading to pavements that require less frequent rehabilitation and reconstruction.

Date: 08/01/19 - 5/31/21
Amount: $91,309.00
Funding Agencies: NC Department of Transportation

The North Carolina Department of Transportation (NCDOT) has recently modified the asphalt mixture design procedures in part, to increase the asphalt content and address observed cracking issues with asphalt mixtures. These changes have reduced the number of asphalt mixture types, changed compaction levels and the volumetric limits for some mixtures, and adjusted how recycled materials are considered. Given the complexity of the interactions between material parameters, the procedural changes do not guarantee that the resultant asphalt mixture designs have actually achieved the intended goal of improved durability.

Date: 08/01/17 - 5/31/21
Amount: $258,427.00
Funding Agencies: NC Department of Transportation

Emulsions are used as tack coats to bond hot-mix asphalt layers and in chip seals to bind aggregates. The rate of emulsion application is critical to the performance of both tack coats and chip seals and hence, is an important design factor. Emulsion is often applied to aged flexible pavements in North Carolina. Oxidative aging embrittles asphalt binder near the pavement surface which increases top down cracking and raveling, leaving the pavement surface porous and dry. Consequently, when emulsion is applied to an aged flexible pavement, a portion of the applied emulsion will be absorbed by the existing pavement. To compensate, the current practice is to adjust the required target Emulsion Application Rate (EAR) used in the construction based on visual inspection of the existing pavement surface. This current practice is subjective and visual appearance cannot be tied directly to surface dryness. Therefore, an improved method is needed to inform adjustment of the target EAR during construction to account for emulsion lost to absorption. Improved selection of the design EAR will result in prolonged pavement service life, potentially resulting in significant economic savings.

Date: 06/15/15 - 5/31/21
Amount: $375,000.00
Funding Agencies: National Science Foundation (NSF)

The long-term goal of the proposed research is develop a sustainable alternative to asphalt binder in pavements. For an alternative binder to be viable as a replacement to asphalt cement, it must (a) be derived from renewable sources that can be produced economically in mass quantities, (b) require less energy and produce fewer emissions than the production and construction of concrete using current asphalt binder technology, and (c) demonstrate equal or superior performance over asphalt binder. To best meet these objectives, bio-binders will be produced using thermo-chemical conversion of biomass. Biomass feedstock and thermo-chemical conversion operating parameters will be varied in order to link inputs to produce a viable paving binder. Rigorous analyses of bio-binder chemical composition and properties will be conducted to assess the viability of bio-binders produced for use in pavements. In addition, preliminary trials of producing bio-binder ?????????????????? aggregate mixtures will be conducted using conventional laboratory methods for producing asphalt mixtures. Performance testing of bio-binder ?????????????????? aggregate mixtures will be conducted to assess their performance and to link critical bio-binder properties to the resultant performance of mixtures. In addition, life cycle analysis will be conducted to assess the sustainability of bio-binders compared to petroleum-based asphalts.

Date: 05/21/13 - 3/31/21
Amount: $950,000.00
Funding Agencies: US Dept. of Transportation (DOT)

The objective of the proposed research is to develop a calibrated and validated procedure to simulate long-term aging of asphalt mixtures for performance testing and prediction. The final product of the proposed research will be a laboratory aging procedure and associated models that prescribe a set of laboratory aging conditions to represent the long-term aged state of asphalt mixture in a pavement as a function of climate, depth, and air voids. The proposed research will be conducted by a research consortium led by NCSU, including Western Research Institute, Arizona State University, and Nichols Consulting Engineers.

Date: 08/01/16 - 12/31/18
Amount: $188,042.00
Funding Agencies: NC Department of Transportation

Crack sealing is a pavement preservation technique used to prevent moisture intrusion into cracked pavements, thereby preventing weakening of underlying layers and reducing the rate of pavement deterioration. However, if crack sealing covers too much of the pavement surface area, it can negatively impact skid resistance, creating a potential safety hazard. Crack sealing may cover too much of a pavement??????????????????s surface area if either excessive crack sealant is applied (e.g., overband is too wide) or if the density of cracks sealed on the pavement surface is too high. Current crack sealant specifications do not include provisions to prohibit skid loss. To develop such specifications, research is needed to determine the allowable percentage of pavement surface area that can be occupied by crack sealant without the loss of frictional properties.

Date: 03/01/17 - 6/30/18
Amount: $49,476.00
Funding Agencies: NC Department of Transportation

Emulsions are used as tack coats to bond asphalt concrete layers and as a bonding agent in pavement surface treatments. The emulsion application rate (EAR) is critical to the performance of both tack coats and surface treatments. The EAR can vary longitudinally along the length of paving as a result of fluctuations in distributor speed and flow rates. Currently, the only measure for quality control of the EAR along the length of paving is to measure the change in the volume of emulsion in the distributer tank before and after paving. This practice lacks the ability to quantify local variability in the applied EAR. In addition, the existing paving surface will absorb a portion of the applied emulsion which will be unavailable to act as a bonding agent for aggregate or asphalt concrete placed on top of the emulsion. To compensate, the current practice is to adjust the required target EAR used in the construction based on visual inspection of the existing pavement surface. The current practice is subjective and visual appearance cannot be tied directly to surface dryness.

Date: 08/01/15 - 12/31/17
Amount: $277,218.00
Funding Agencies: NC Department of Transportation

The current specification for acceptance of Aggregate Base Course (ABC) materials consists of a band-type gradation specification, which is essentially a ????????????????recipe??????????????? that dictates the mass percentages of the individual particle sizes constituting the ABC. The ????????????????recipe??????????????? specification is based on the assumption that the product will achieve the desired engineering performance as long as it meets required gradations and is placed and compacted properly in the field. However, the biggest disadvantage of the ????????????????recipe??????????????? specification is that it cannot quantify the mechanical behavior of the aggregates under different traffic and weather conditions, which will determine the stress states and moisture variations. Recent developments in mechanistic-empirical pavement design (i.e., Pavement ME Design) utilize mechanical material properties and structure to predict pavement performance, which includes properties of the unbound aggregates. Therefore, understanding the mechanical properties of ABC is critical for prediction of pavement performance, and consequently design. Unfortunately, the current ABC specification is disconnected with the design process and required parameters. A more comprehensive approach to test, evaluate, and accept aggregate base course material is needed. Understanding of the material behavior due to stress conditions and moisture variations is important to ensure adequate pavement performance. Gradation alone is insufficient to adequately capture mechanical properties of different aggregates. Incorporating easy to measure physical characteristics of the ABC (e.g., angularity, shape, and texture) and aggregate packing theory into the material specification will aid in linking easily measured ABC properties to observed mechanical properties. Developing a relationship between the material properties and the mechanical behavior will allow the new specification to be directly related to the design parameters. Additionally, the re-appraisal of the ABC specification should include tests that are practical enough to be used routinely to evaluate the necessary variables. To best meet the objectives of the proposed research, first, a literature review of current practices for ABC specification used throughout the US, identification of critical properties governing ABC mechanical behavior, and state-of-the art test methods to efficiently characterize the identified properties will be conducted. The literature review will be followed by a testing program that focuses on both physical material properties and mechanical behavior of the ABC material. The testing program will be complimented with modeling the ABC material using aggregate packing theory and the discrete element method. The material and behavioral testing and modeling results will be compiled to develop a relationship between the material properties and pavement performance, which in term will be used to propose a new specification for ABC material.

Date: 08/16/14 - 7/31/17
Amount: $294,588.00
Funding Agencies: NC Department of Transportation

The objectives of the proposed research are: (1) to provide important performance information regarding asphalt base and aggregate base pavements that can be used to update the NCDOT??????????????????s life cycle cost analysis (LCCA) procedure, (2) to identify pavement sections that have both base types in order to recalibrate ME Design for North Carolina conditions, and (3) to develop guidelines for the recalibration of ME Design and demonstrate the data collection process using new paving projects. ????????????????

Date: 01/01/15 - 6/30/17
Amount: $99,998.00
Funding Agencies: National Academy of Sciences

The specific innovation to be developed is a small specimen geometry for uniaxial asphalt mixture dynamic modulus and direct tension fatigue testing in the Asphalt Mixture Performance Tester (AMPT). Two small specimen geometries will be tried: a small cylindrical geometry consisting of 38mm diameter specimens with 100mm height and a small prismatic geometry 25mm thick, by 50mm wide, by 100mm tall. Both uniaxial cyclic, direct tension and monotonic direct tension (constant strain rate) testing for fatigue characterization will be considered. The small specimen geometry will allow for testing individual layers of as-built pavements, allowing for forensic investigations of field performance and performance-based construction quality assurance. In addition, use of small specimens can greatly improve laboratory prepared mixture testing efficiency by allowing for extraction of multiple small test specimens from a single gyratory sample. Fatigue performance evaluation will be facilitated by applying the Viscoelastic Continuum Damage (VECD) mechanics to fatigue test results.

Date: 02/03/14 - 9/30/16
Amount: $86,144.00
Funding Agencies: National Academy of Sciences

North Carolina State University (NCSU) will assist Michigan State University (MSU) in developing guidelines to facilitate development of performance ? related specifications (PRS) for asphalt pavement preservation treatments. As part of this effort NCSU will assist MSU in the planning phase of the research project, which will consist aiding MSU in reviewing literature to identify most widely used preservation treatments for asphalt pavements and corresponding design and quality assurance practices, identifying processes and an outline for guidelines for pavement preservation treatment PRS development, and identifying corresponding data needs and developing demonstration examples. The aforementioned research will be used as input for development of a research plan by MSU with aid of NCSU.

Date: 08/16/13 - 12/31/15
Amount: $197,146.00
Funding Agencies: NC Department of Transportation

Emulsions are used as bonding agents in tack coats and surface treatments. The rate of emulsion application is critical in determining the performance of both tack coats and chip seals and thus is an important design factor. It has been demonstrated that field emulsion applications rates are highly variable, which is not captured using current measures for quality control. The objective of the proposed research is to develop a test method to enable in-situ determination of emulsion application rates at specific locations along a roadway. The proposed research will result in improved quality control of emulsion application rates, which lead to prolonged pavement service life, decreased life cycle costs, and enhanced safety.

Date: 07/01/13 - 6/30/14
Amount: $7,000.00
Funding Agencies: NCSU Faculty Research & Professional Development Fund

Asphalt concrete is composite materials consisting of aggregates of varying size, asphalt binder, and air voids. Coarse aggregates in asphalt mixtures are effectively coated by a blend of asphalt binder and filler (i.e., dust), termed asphalt mastic. The mastic constitutes the weakest phase of asphalt concrete and therefore performance of asphalt pavements is highly correlated to the properties of the mastic. Thus, pavement performance can be improved if the mastic is engineered to resist damage. Such engineering requires a fundamental understanding the mechanisms of interactions between asphalt binder and mineral filler. The objective of the proposed research herein is to develop a fundamental understanding of the physico-chemical interaction between fillers and asphalt. Previous research suggests that physico-chemical interaction between asphalt and filler leads to selective adsorption of polar components of the asphalt binder by the filler particles, forming an interphase layer at the asphalt binder ? filler boundary. However, no explicit study of the properties of the interphase with respect to thickness or properties has been conducted which is needed to better understand how physico-chemical interaction affects mastic performance. The proposed research will utilize Atomic Force Microscopy (AFM) to detect and probe the properties of the interphase layer in mastics. Bulk properties of mastics and their respective binders and fillers will also be measured to link mastic response to microstructural findings.

Date: 01/01/13 - 1/31/14
Amount: $24,992.00
Funding Agencies: Federal Highway Administration (FHWA)

The purpose of the proposed work is to develop specifications for selection of the Linear Amplitude Sweep (LAS) testing temperature for ranking the relative damage tolerance of asphalt binders. Accomplishing this task requires two components: first, a comprehensive analysis of the effect of temperature on binder damage resistance must be conducted. This analysis will serve as input to the second component: development of a specification for selection of the testing temperature for ranking the relative damage tolerance of asphalt binders.

Date: 01/01/13 - 12/31/13
Amount: $20,000.00
Funding Agencies: NCSU Research and Innovation Seed Funding Program

Currently, over 90% of pavements worldwide are constructed with an asphaltic surface, which results in use of 30 million tons of asphalt annually in the US alone. Asphalt is a byproduct of refining petroleum, a non-renewable resource and thus, supplies are diminishing. There is a need for development of alternative binders from bio-renewable resources. This project will investigate the use of bio-binders produced via hydrothermal conversion of biomass as an alternative to asphalt. Both micro algae and corn cob will be evaluated as biomass feedstock for production of bio-binders. Experimental characterization of bio-binders will be conducted to assess their potential use as paving binders.

View all grants