Enhanced Integrated Climatic Model Research Articles

Detailing an Improved Heat Transfer Model for Pavements

Temperature profiles are a fundamental input into mechanistic-empirical pavement analysis and design, and the enhanced integrated climatic model (EICM) is the state-of-the-practice for calculating those profiles. The EICM has also been used in other applications, such as analysis to evaluate the effects of climate change on pavements and to estimate the effects of pavements on urban heat islands. The calculations in the EICM for pavement temperatures can be viewed as having two primary components that together act as a system: the thermal model describing conductance of temperatures throughout the pavement, and the boundary conditions that include the convective terms at the pavement surface, an energy balance model to predict the solar radiation at the surface of the pavement and a specified lower boundary condition (generally constant temperature at defined depth). As is shown in this paper, the current EICM models overpredict temperatures during hot times and in no-wind conditions, while also underpredicting (albeit to a lesser magnitude) during cold conditions. This result implies that the increases in pavement temperatures predicted to occur with climate change are likewise overestimated. Conversely, because the convection coefficient is incorrect, the predicted amount of energy contributing to urban heat islands will also not be correctly predicted using the current EICM models. Although improvements to the solar model are noted, this paper focuses on improvements to the thermal model and convective boundary condition using modern heat transfer principles and data from the Long-Term Pavement Performance database.

Relating gradation parameters to mechanical and drainage performance of unbound granular materials

Abstract The drainage performance of unbound granular material (UGM) is an important consideration in pavement design because premature failures can occur due to the presence of excess moisture in UGM layers. Recently, transportation agencies have been evaluating their granular base and subbase drainage and mechanical performance to ensure sufficient drainage capacity while maintaining adequate structural support to produce more sustainable pavement structures. Relating performance to UGM construction specification requires accurate characterization of physical and gradation parameters and their effects on the mechanical and drainage performance of UGM. These evaluations led to an update of the specification requirements of UGM in many jurisdictions including Manitoba. In this study, resilient modulus and constant head hydraulic conductivity tests were performed to characterize the mechanical and drainage performance of nine UGM samples. The laboratory test results were also used to investigate the reliability of the estimated hydraulic conductivity from the Moulton prediction model, and from the Enhanced Integrated Climatic Model (EICM). Test results showed an improvement in resilient modulus and drainage quality for samples in gradation bands that specify larger maximum aggregate size and limited fines. A statistical analysis of the test results showed that D10 larger than 0.2 mm and D60 larger than 8 mm would guarantee higher stiffness and better drainage performance with a time-to drain of less than 5 days for typical pavement cross-sections and a resilient modulus value exceeding 200 MPa. The Moulton prediction model was found to provide a better approximation of hydraulic conductivity of the materials included in this study, while the EICM model was found to significantly overestimate the hydraulic conductivity for most of the samples.

Winter temperature prediction for near-surface depth of pervious concrete pavement

ABSTRACTPervious concrete pavement (PCP) consists of a highly porous concrete slab, placed on a permeable base layer. This permeable pavement system allows storm water runoff to infiltrate through the pavement and percolate into the subdrainage system or directly into the subgrade soil. PCP is gaining popularity in municipal applications across the United States, including the cold climate regions. The focus of this study was to investigate frost durations at PCP near-surface depths for use in winter maintenance operations. Also, tools are recommended for predicting the near-surface temperature of PCP during winter months. A PCP sidewalk was placed and instrumented on Washington State University’s campus in Pullman, WA. First, temperature measurements at various depths of the PCP sidewalk and frost periods at the respective depths were presented during one winter season. Second, the Enhanced Integrated Climatic Model (EICM) was used to predict the PCP’s near-surface temperature during the winter. Using each layer’s thermal properties, the EICM estimates the heat transfer between the pavement and the surroundings. Heat conductivity and capacity were defined for the PCP using the parallel model, based on PCP porosity and the volumetric proportions of the mixture constituents. Meteorological indices for the model were obtained from a local weather station and an on-site pyranometer for solar radiation. Comparison of the predicted temperature for the top three-inch (76 mm) depth of the pervious concrete layer showed agreements with the field data during the winter. A multiple linear regression model was developed to predict PCP’s temperature at 0.5 inch (13 mm) depth.

Local Calibration of EICM Using Measured Temperature Gradients and Numerical Analysis

Due to the daily and seasonal fluctuation of temperature gradients, accurate temperature gradients under local climatic conditions are imperative to correctly predict the performance of PCC pavements. In this study, temperature sensors were installed at various depths (0-, 6.4-, 12.8-, 19.2-, and 25.6-cm) in a PCC pavement section to monitor temperature gradients. Based on the measured daily and seasonal temperature data, correlations between air temperature and surface temperature, as well as surface temperature and slab temperature difference, were developed. A finite element analysis was performed to simulate the temperature variation in a PCC pavement, and the analysis results were compared to the field measurement. A local calibration of the enhanced integrated climatic model (EICM) was conducted by comparing the field-measurements with the EICM-predicted temperature gradients. The conclusion demonstrated that surface temperature, rather than air temperature, would better predict temperature gradient in PCC pavements for the input data in EICM.

Unsaturated Soil Modeling for Airfield Pavement Design

This study presents results of one of the first in situ assessment studies on the use of the Mechanistic-Empirical Pavement Design Guide (M-EPDG) methodology applied to the design of airfield pavements. The M-EPDG’s Enhanced Integrated Climatic Model (EICM) introduces unsaturated soil modeling techniques into the prediction of moisture changes in the unbound materials throughout the life of pavements for highway conditions. Field soil moisture content changes measured at several Air Force bases in the U.S. were collected from historic studies and compared to MEPDG predictions. Details and outcomes from this comparative study are presented herein. Despite significant differences in structural dimensions and geometric design, this study showed that the EICM promises to be a suitable predictive methodology to be adapted for airfield pavement conditions and has the potential to become a tool for the incorporation of unsaturated soil modeling for the design of airfield pavements, provided that several enhancements are made to the model applied to highway design. Also, a discussion on possible sources of uncertainty in the predictions of the MEPDG and a series of alternative revisions and enhancements required to incorporate the EICM with current airfield pavement design methodologies are presented.

Field-Monitoring System for Suction and Temperature Profiles under Pavements

The purpose of this paper is to describe the development of and typical results from a new field-monitoring system to evaluate changes in matric suction and temperature profiles in subgrade soil layers beneath constructed pavement systems over an extended period of time. This monitoring system involves the placement of sensors capable of inferring the volumetric water content and temperature of soils into a borehole in the shoulder of an existing pavement. High-permeability silica flour is used to backfill the borehole around the sensors so that changes in matric suction with depth in the subgrade can be inferred through the soil-water retention curve of the silica flour. The monitoring results from a pavement site in Arkansas with low-permeability clay subgrade are compared with predictions from the Enhanced Integrated Climatic Model (EICM). The measured and predicted temperature distributions match well, but the EICM did not capture the fluctuations in matric suction inferred from the monitoring system. This can be attributed not only to the fact that the monitoring system captured the two-dimensional water flow near the pavement shoulder but also to the possibility that the EICM may not have adequately represented the water-flow process through the asphalt and base-course layers. Profiles of matric suction and temperature obtained using the monitoring system provide real-time, site-specific feedback on interactions between the atmosphere and pavement systems. Comparison of results from multiple pavement sites with clay subgrades across Arkansas demonstrates the variability in matric suction and temperature changes in different climatic settings.

Thermal Stresses of PCC Pavements Containing Fly Ash and Slag

With the current demand for portland cement concrete (PCC) sustainability, supplementary cementitious materials (SCMs) are often used in concrete mixtures to improve the mixture properties in both fresh and hardened concrete. In this research, sixteen concrete mixtures (one control mixture, three binary mixtures, and twelve ternary mixtures) with various combinations of fly ash, slag, and portland cement were fabricated. The thermal and mechanical properties of the selected ternary mixtures were measured at various ages, and the critical temperature gradient through the slab thickness was generated by using the enhanced integrated climatic model (EICM). By using the measured mechanical properties, nonlinear temperature gradients obtained from EICM, and CTE gradients throughout the slab thickness, Westergaard-Bradbury solution was used to calculate the critical tensile stress on the PCC pavements. The analysis results show that all the ternary mixtures with the replacement of 30% slag and 30% fly ash, and replacement of 50% slag and 20% fly ash did not exceed 100% tensile stress-to-strength ratio at all ages.

Modification of Mechanistic–Empirical Pavement Design Guide Procedure for Two-Lift Composite Concrete Pavements

Modifications made to the Mechanistic–Empirical Pavement Design Guide (MEPDG) to accommodate the design of a newly constructed composite pavement system featuring a thin portland cement concrete (PCC) layer placed over another PCC layer (PCC–PCC pavement) are described. In previous versions of the MEPDG, a newly constructed PCC–PCC pavement project was considered a bonded PCC overlay of an existing PCC pavement. As a result of this simplification, the MEPDG was not consistent in its predictions for a newly constructed PCC–PCC pavement and its structurally equivalent single-layer analogue. To remedy this inconsistency, researchers suggested modifications to the Enhanced Integrated Climatic Model (EICM) used by the MEPDG in terms of (a) number of locations through the slab used by EICM to determine the thermal gradient and (b) EICM calculation of the subgrade spring stiffness (or k-value). Before-and-after MEPDG sensitivity analyses are included to justify the modifications developed and implemented into the MEPDG with the assistance of the MEPDG development team. This research was conducted under SHRP 2 R21, Composite Pavement Systems.

Minnesota Road Research Data for Evaluation and Local Calibration of the Mechanistic–Empirical Pavement Design Guide's Enhanced Integrated Climatic Model

This paper describes research to evaluate modeling of the thermal behavior of concrete and composite pavements by the Enhanced Integrated Climatic Model (EICM), the climate-modeling package used in the Mechanistic–Empirical Pavement Design Guide (MEPDG). First, the study uses temperature data collected at the Minnesota Road Research Project (MnROAD) facility from portland cement concrete (PCC) and asphalt concrete (AC)–PCC pavements to investigate benefits of AC overlays on the thermal characteristics of PCC slabs. Furthermore, the study validates EICM predictions of thermal gradients through the slabs and investigates the effect of MEPDG-user inputs for thermal conductivity of PCC. Overall, the paper examines measured data from MnROAD for AC-PCC pavements and their single-layer PCC counterparts and attempts to explain how similar pavement systems and their thermal characteristics are taken into account in the MEPDG. The paper concludes that evaluation of the material thermal inputs should be part of a process of local calibration and adaptation of the MEPDG.

Verification of Virtual Climatic Data in MEPDG Using the LTPP Database

The Enhanced Integrated Climatic Model (EICM) integrated in the Mechanistic-Empirical Pavement Design Guide (MEPDG) allows users to select adjacent weather stations to generate a virtual weather station (VWS), whose data are further used to predict environmental impact on pavement performance. It is essential that the derived virtual data be accurate and representative of the actual climatic conditions. To evaluate the accuracy of the MEPDG generated VWS data, climatic data from corresponding automated weather stations (AWS) in the long-term pavement performance (LTPP) database are obtained to conduct the comparison analysis. It is observed that most VWS climatic data estimate the actual weather data reasonably well. However, in some cases, significant differences are observed. The potential factors resulting in the discrepancies are investigated. MEPDG analyses are conducted to quantify the climate data differences on predicted pavement performance. Finally, the paper presents recommendations when using the MEPDG software to generate VWS so as to help establish more accurate key climatic inputs.

Incorporation of Environmental Effects in Pavement Design

ABSTRACT Environmental conditions have a significant effect on the performance of both flexible and rigid pavements. External factors such as precipitation, temperature, freeze-thaw cycles, and depth to water table play a key role in defining the bounds of the impact the environment can have on the pavement performance. As part of the new US Mechanistic-Empirical Pavement Design Guide (MEPDG) being developed under the overall project sponsored by the National Cooperative Highway Research Program (NCHRP project 1–37A), a climatic modelling tool called the Enhanced Integrated Climatic Model (EICM) was implemented to incorporate the changes in temperature and moisture of unbound materials into the design process. Currently a new independent review project (NCHRP 1–40) is reviewing this model to correct errors and to develop further enhancements to produce a final methodology ready for approval/disapproval vote by AASHTO in 2006. This paper reflects the methodology used for the MEPDG and present the models incorporated by Arizona State University into the EICM, the input needed and the outputs generated by the program. A discussion on how EICM determines the temperature and moisture distribution within the pavement system is also presented.

Incorporation of Environmental Effects in Pavement Design

ABSTRACT Environmental conditions have a significant effect on the performance of both flexible and rigid pavements. External factors such as precipitation, temperature, freeze-thaw cycles, and depth to water table play a key role in defining the bounds of the impact the environment can have on the pavement performance. As part of the new US Mechanistic-Empirical Pavement Design Guide (MEPDG) being developed under the overall project sponsored by the National Cooperative Highway Research Program (NCHRP project 1–37A), a climatic modelling tool called the Enhanced Integrated Climatic Model (EICM) was implemented to incorporate the changes in temperature and moisture of unbound materials into the design process. Currently a new independent review project (NCHRP 1–40) is reviewing this model to correct errors and to develop further enhancements to produce a final methodology ready for approval/disapproval vote by AASHTO in 2006. This paper reflects the methodology used for the MEPDG and present the models incorporated by Arizona State University into the EICM, the input needed and the outputs generated by the program. A discussion on how EICM determines the temperature and moisture distribution within the pavement system is also presented.

Investigations of Environmental and Traffic Impacts onMechanistic-Empirical Pavement Design GuidePredictions

The Mechanistic-Empirical Pavement Design Guide (MEPDG) represents a major improvement on its predecessors, particularly in its comprehensive coverage of environmental impact on pavement performance. Another improvement is the approach introduced to assess and accumulate damage created by traffic. A major strength of the MEPDG is the consideration given to the interaction between environmental, material, and traffic parameters, rather than consideration of only the parameters themselves. The process through which these interactions are considered sounds very comprehensive; however, is it practical? The Enhanced Integrated Climatic Model (EICM) is a core component of the MEPDG; it controls the material properties used in the analysis to a great extent. As a result, EICMpredictionshaveasignificantimpactonMEPDG-accumulateddamage and therefore on predicted service life. In a previous study, an effort was made to validate EICM predictions with field-measured temperature and moisture profiles outside the MEPDG....

Part 4: Pavement Subsurface Drainage: Estimation of Expected Moisture Contents for Pavements by Environmental and Soil Characteristics

Expected moisture contents were evaluated for pavements on the basis of climatic and soil characteristics with the use of the Enhanced Integrated Climatic Model (EICM). Subgrade moisture content varies with environmental and soil conditions and has significant influence on pavement performance. Thus, it is important to establish realistic estimates of expected subgrade moisture contents to account for the effects of this variable on predicted pavement performance during the design stage properly. To predict expected moisture contents, researchers examined regional variations in climatic and soil-water characteristic curves in Texas. Through cluster analysis, seven climatic and nine soil regions were established that captured the variations in climatic and soil characteristics across the state. Typical pavement structures and groundwater table data in different regions were used to reflect regional characteristics and to estimate the initial boundary soil suction profile for a given pavement, which is a cr...

Investigations of Environmental and Traffic Impacts on Mechanistic–Empirical Pavement Design GuidePredictions

The Mechanistic–Empirical Pavement Design Guide (MEPDG) represents a major improvement on its predecessors, particularly in its comprehensive coverage of environmental impact on pavement performance. Another improvement is the approach introduced to assess and accumulate damage created by traffic. A major strength of the MEPDG is the consideration given to the interaction between environmental, material, and traffic parameters, rather than consideration of only the parameters themselves. The process through which these interactions are considered sounds very comprehensive; however, is it practical? The Enhanced Integrated Climatic Model (EICM) is a core component of the MEPDG; it controls the material properties used in the analysis to a great extent. As a result, EICM predictions have a significant impact on MEPDG-accumulated damage and therefore on predicted service life. In a previous study, an effort was made to validate EICM predictions with field-measured temperature and moisture profiles outside the MEPDG. However, this effort was not successful. Therefore, the potential impacts of the accuracy of EICM predictions on MEPDG-predicted damage and hence on expected pavement service life were investigated. Eight weather stations closest to New Jersey's Long-Term Pavement Performance Specific Pavement Study 5 site were analyzed. In addition, to address the interaction between environment and traffic in the MEPDG, analyses were run with two traffic input levels: first with Level 3 traffic data and then with Level 1 traffic data.

Estimation of Expected Moisture Contents for Pavements by Environmental and Soil Characteristics

Expected moisture contents were evaluated for pavements on the basis of climatic and soil characteristics with the use of the Enhanced Integrated Climatic Model (EICM). Subgrade moisture content varies with environmental and soil conditions and has significant influence on pavement performance. Thus, it is important to establish realistic estimates of expected subgrade moisture contents to account for the effects of this variable on predicted pavement performance during the design stage properly. To predict expected moisture contents, researchers examined regional variations in climatic and soil–water characteristic curves in Texas. Through cluster analysis, seven climatic and nine soil regions were established that captured the variations in climatic and soil characteristics across the state. Typical pavement structures and groundwater table data in different regions were used to reflect regional characteristics and to estimate the initial boundary soil suction profile for a given pavement, which is a critical factor in determining expected moisture variations in the subgrade for given pavement and climatic and soil conditions. The limited verification of the EICM analysis showed realistic predictions of moisture contents when compared with field measurements and confirmed that the results of the regional characterizations are reasonable. Accordingly, researchers evaluated the expected moisture variations across different regions. The results indicate that in most pavements the predicted moisture contents reach an equilibrium stage at some time after construction. From these results, researchers established expected moisture contents that reflect the variation in environmental and soil characteristics across Texas.

Validation of Enhanced Integrated Climatic Model Predictions with New Jersey Seasonal Monitoring Data

Environment is one of the essential factors that influence pavement material behavior and consequently its performance. The variation of climatic patterns from region to region, coupled with the variation of site-specific conditions across North America, makes it difficult to develop standard models to account for seasonal variation in material properties that apply for all regions. Consequently, the need to develop regional models becomes an essential requirement for most transportation departments. The enhanced integrated climatic model (EICM) was evaluated to determine its suitability in predicting subsurface temperature and moisture conditions within New Jersey sites. The validation of the model used environmental data collected through pavement instrumentation of a large-scale research study under the sponsorship of the New Jersey Department of Transportation. Site-specific data were input to the model, and the model output parameters were compared against field-measured values. The results of the validation for two of the instrumented sites are reported. Results of the study do not indicate a high correlation between field-measured values and EICM-predicted temperature and moisture profiles for the various pavement layers.

Validation of Enhanced Integrated Climatic Model Predictions with New Jersey Seasonal Monitoring Data

Environment is one of the essential factors that influence pavement material behavior and consequently its performance. The variation of climatic patterns from region to region, coupled with the variation of site-specific conditions across North America, makes it difficult to develop standard models to account for seasonal variation in material properties that apply for all regions. Consequently, the need to develop regional models becomes an essential requirement for most transportation departments. The enhanced integrated climatic model (EICM) was evaluated to determine its suitability in predicting subsurface temperature and moisture conditions within New Jersey sites. The validation of the model used environmental data collected through pavement instrumentation of a large-scale research study under the sponsorship of the New Jersey Department of Transportation. Site-specific data were input to the model, and the model output parameters were compared against field-measured values. The results of the va...