American Association Of State Highway And Transportation Officials Research Articles

CORN-COB ASH AS PARTIAL REPLACEMENT OF CEMENT FOR STABILIZATION OF LATERITE SOIL

Properties of underlying soils and borrowed soil samples are some of the key factors that determine the performance rate of roads. Most of the underlying soils possess some characteristics that make them unsuitable for use. There are available agricultural waste products in most rural settlements which can be used to treat unsuitable soils. This research examined the use of corn cob ash (CCA) as an admixture to cement on some selected geotechnical properties of laterite soil. The choice of the A-7-5 class of laterite soil is due to its general rating as poor material for subgrade and other layers of road pavement by the classification system of the American Association of State Highway and Transportation Officials (AASHTO). Cement was gradually added to the soil sample in steps of 2% from 0% to 10% by weight of the soil sample and its effect on the plasticity of the sample was examined. The addition of cement performed optimally on the soil’s plasticity at 4% which was used to form different mixtures of cement and CCA having a total sum not exceeding 4%. The additives were added to the soil sample which was subjected to laboratory tests such as compaction, California bearing ratio (CBR) and unconfined compressive strength (UCS) compacted with the efforts of 596kN/m2 and 1192kN/m2. The combination of 2% cement and 2% CCA on the soil sample improved the plasticity index and UCS properties of the soil to its optimal level while 3-1 and 4-0 cement-CCA performed optimally for CBR and compaction respectively. Thus, it was concluded that CCA performed optimally with cement at a ratio varying between 4:0 to 3:1 total percentage not exceeding 4% of the weight of the soil sample.

Deep Learning-Based Steel Bridge Corrosion Segmentation and Condition Rating Using Mask RCNN and YOLOv8

The application of deep learning (DL) algorithms has become of great interest in recent years due to their superior performance in structural damage identification, including the detection of corrosion. There has been growing interest in the application of convolutional neural networks (CNNs) for corrosion detection and classification. However, current approaches primarily involve detecting corrosion within bounding boxes, lacking the segmentation of corrosion with irregular boundary shapes. As a result, it becomes challenging to quantify corrosion areas and severity, which is crucial for engineers to rate the condition of structural elements and assess the performance of infrastructures. Furthermore, training an efficient deep learning model requires a large number of corrosion images and the manual labeling of every single image. This process can be tedious and labor-intensive. In this project, an open-source steel bridge corrosion dataset along with corresponding annotations was generated. This database contains 514 images with various corrosion severity levels, gathered from a variety of steel bridges. A pixel-level annotation was performed according to the Bridge Inspectors Reference Manual (BIRM) and the American Association of State Highway and Transportation Officials (AASHTO) regulations for corrosion condition rating (defect #1000). Two state-of-the-art semantic segmentation algorithms, Mask RCNN and YOLOv8, were trained and validated on the dataset. These trained models were then tested on a set of test images and the results were compared. The trained Mask RCNN and YOLOv8 models demonstrated satisfactory performance in segmenting and rating corrosion, making them suitable for practical applications.

An artificial-intelligence based approach for predicting structural damages of paved-road systems under superloads

When studies on mechanistic-based pavement analysis and design are actively conducted, highly-accurate and meaningful data related to structural damages caused by traffic loads have accumulated. Although widely-used pavement design programs such as the American Association of State Highway and Transportation Officials (AASHTO)Ware Pavement Mechanistic-Empirical (M-E) Design software supports M-E pavement design for comprehensive pavement structures and traffic loadings, it is still unable to predict extrapolated mechanistic responses when pavements are subjected to superloads having non-standardized loading configurations not yet included in the software. In this study, artificial neural-network (ANN)-based surrogate models were developed and optimized to provide high accuracy in predicting critical pavement responses related to representative structural damages of jointed plain-concrete pavements (JPCPs) and flexible pavements when subjected to a single pass of various superload types, thereby extensively broadening the scope of constrained mappings in terms of loading variables. Sensitivity analysis on pavement structural and loading variables was performed using the ANN models developed in this study to identify the significance level of each explanatory variable in generating target-pavement responses.

Impact of Ball Bank Indicator on Predicting Rural Curve Crashes

The ball bank indicator (BBI) measures the lateral forces on a vehicle. It is used to establish the advisory speed limit as outlined in the American Association of State Highway and Transportation Officials (AASHTO)’s Green Book. BBI values respond to roadway geometry and driver behavior. Currently, BBI data are available from various curves across the U.S. However, the relationship between BBI and curve lane departures is unknown. Therefore, the objective of this paper is to assess the impact of BBI as an explanatory variable for curve lane departures within a safety performance function (SPF) (i.e., a crash prediction model). To accomplish this objective, a study is conducted on rural curves in Districts 1, 2, and 6 of Georgia Department of Transportation in the U.S. BBI is integrated into a negative binomial model alongside other common explanatory variables used in the Highway Safety Manual. This SPF, with BBI incorporated, is compared with a baseline SPF without the BBI. The results show BBI is a statistically significant variable under a 99.9% threshold. Additionally, it was found that the model with BBI has 2.78% and 2.83% less mean absolute error and route mean squared error, respectively. Though the improvement in the model is minor, this finding is notable because BBI data may already be available for a transportation agency to leverage to assess risk on curves. Furthermore, this data could be even more beneficial if it were crowdsourced to gauge real-world behaviors.

Assessing durability properties of ultra-high performance concrete-class materials

Ultra-high performance concrete (UHPC) is a class of concrete materials that has received significant attention from the infrastructure community due to its favorable mechanical and durability performance. As the use of UHPC in infrastructure projects is becoming more common, there is an increasing interest in identifying appropriate testing techniques to assess the durability properties of UHPC-class materials. The dense microstructure of UHPC-class materials and the presence of a high concentration of fiber reinforcement have made it difficult to rely on existing standard testing approaches for concrete durability assessment. This study explores the application of various conventional-concrete durability test methods to UHPC, including electrical resistivity (American Association of State Highway and Transportation Officials (AASHTO) TP 119-22), freeze–thaw (ASTM C666), water absorption (ASTM C1585), and rapid chloride migration test (NT BUILD 492). The selected tests are meant to qualify and quantify the microstructural penetrability of UHPC to ions and fluids, a surrogate property commonly used as an indicator of durability. The findings from this study indicate that electrical resistivity can be used as a durability indicator for UHPC-class materials. Moreover, strong correlation between electrical resistivity and the chloride migration coefficient is identified, a potential benefit given that chloride migration can be used to estimate service lives of UHPC-class materials. Other tests, including freeze–thaw and water absorption, although identifying the favorable performance of UHPC relative to conventional concrete, were unable to provide insightful information through which the performance of individual UHPCs could be differentiated.

COMPACTION CHARACTERISTICS AND WORKABILITY OF THE LATERITIC SOIL-IRON ORE TAILINGS IN PAVEMENT CONSTRUCTION

The mining waste deposit such as iron ore tailings (IOT) in Nigeria is a menace to the environment by constituting a nuisance to the mining industry, and its effect on lateritic soil as a compaction and plasticity reduction material for road pavement is considered in this study. The used natural lateritic soil was classified as A-7-6(11) or CL by the American Association of State Highway and Transportation Officials (AASHTO) and Unified Soil Classification System (USCS) respectively. Up to 16% of the soil’s dry weight was modified with iron ore tailings (IOT). Studying the effects of IOT on the altered soil focused on its cation exchange capacity, plasticity, compaction properties and California bearing ratio (CBR). British Standard Light (BSL) energy was used for the compaction process. However, the results of regression analysis showed that the optimum moisture content had a substantial impact on the soil CBR values. The results of the tests show that as the IOT content increased, plasticity and compaction characteristic values increased. Although an optimal 10% IOT treatment of lateritic soil significantly improved its strength properties, the plasticity characteristics recorded exceeded the requirement specified by the Nigerian General Specifications for direct use as a subbase or base material. Thus, reusing 10% iron ore tailings as filling materials required additional percentages of other pozzolanic materials to lessen the environmental problems associated with their deposition.

Analysis and Evaluation of Slip Base Aluminum Single-Post Sign Supports under Manual for Assessing Safety Hardware Safety Performance Criteria

Single-post sign supports are commonly used near to roadways. Signs can assume various configurations, yet few full-scale crash tests have been conducted to date to investigate crash performance of sign supports under current American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) criteria. This study investigated crash performance for aluminum, slip base, single-post signs under MASH criteria to determine critical configurations and develop prospective assessments of crashworthiness. These systems were supported by a four-bolt slip base and mounted on a 4 in. diameter aluminum post. Two full-scale crash tests were performed to evaluate performance of a system with a 4 × 4 ft sign panel under MASH test Nos. 3-61 and 3-62, in which the slip base activated and released the sign in a predictable manner. Safety concerns for the tested signs were raised by sign penetration through the rear window and excessive roof crush during MASH test No. 3-61. LS-DYNA models were developed and validated against test results. LS-DYNA simulations were conducted on four sign configurations to represent a range of sign panel sizes and design heights to analyze critical characteristics of single-post signs. Simulations were also conducted with increased design height to explore preliminary options for improving the performance of sign supports. Generally, signs with centroid heights at least 10 ft were deemed to have high potential of passing MASH Test Level 3 (TL-3) criteria, but it was recommended that the critical sign configuration be modified to raise the sign cluster centroid from a design height of 9 ft to 11.5 ft or greater.

Design and Full-Scale Testing of New MASH Test Level 4 (TL-4) Alaska 2-Tube Bridge Rail

The purpose of this project was to design and test a new Alaska multi-state 2-tube bridge rail meeting the safety-performance evaluation guidelines included in the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH), Second Edition 2016. The new 2-tube bridge rail designed and tested for this project was crash tested in accordance with MASH Test Level 4 (TL-4). Three crash tests were performed. The new bridge rail is 38 in. tall from the top of asphalt overlay and anchors to a 10 in. high by 18 in. wide curb. The curb was cast on top of a 35 ¾ in. wide deck cantilever that varied in thickness from 6 in. at the extreme field side edge to 12 in. at the exterior girder element. The posts were spaced on 10 ft centers. The posts were anchored to the concrete curb and deck using four 7/8 in. diameter A449 anchor bolts. The two-tube rail elements consisted of two HSS7 × 5 × 3/8 tubular elements. The calculated strength of the design was 77 kip at a height of 30 in. The bridge rail was considered acceptable for strength as per the AASHTO Load and Resistance Factor Design (LRFD) Section 13 Bridge Design Specifications. A test specimen of the bridge rail was constructed and crash tested per MASH TL-4. The new two-tube bridge rail met all the performance requirements of MASH TL-4. Details of the design and testing of the new bridge rail are provided in this paper.

Comprehensive Balanced Mixture Design Protocol: Design Phase through Production Quality Assurance

The objective of this study was to develop a comprehensive balanced mix design (BMD) protocol for a state highway agency (SHA) using one of the four approaches presented by both the National Asphalt Pavement Association (NAPA) and the American Association of State Highway and Transportation Officials (AASHTO). This comprehensive BMD was to ensure that a mixture design continues to be balanced from the mixture design phase to the production quality assurance (QA) phase. While existing publications by NAPA, AASHTO, and others provide a good initial framework for developing a BMD protocol, many important questions arise that are left for each SHA to answer when developing a comprehensive BMD protocol. This paper outlines these questions and how each of them was addressed. Also, a new approach for developing a pass/fail criterion for bottom-up fatigue cracking using AASHTOWare® pavement mechanistic-empirical design (PMED) predictive models is presented. Twenty-one SHA-approved plant-produced mixtures were obtained and tested to aid in the development of this pass/fail criterion. A similar approach as presented in this paper can be used by other SHAs. A comprehensive BMD protocol is presented at the end of this paper along with recommendations for future studies needed for further refinement.

Experimental and analytical approaches for load rating reinforced concrete slab bridge

Load testing of bridges is often used as a reliable method for assessing the capacity of in-service bridges with low analytical load rating factors. This paper presents a detailed load rating study of an 82-year-old concrete slab bridge with an unusually large aspect ratio of 3.73 by performing non-destructive diagnostic and proof load tests. The test-based modified rating factor is evaluated based on the American Association of State Highway and Transportation Officials (AASHTO) approach and the structural effective strip width approach which is then compared with the analytical rating factor from a simplified 1-D beam-line model. Field data is also used to evaluate the impact of the rotational stiffness of the bridge on its global response and load rating factor. The field test results based on the AASHTO approach reveal that the rating factor improves by up to 53% compared to the analytical rating factor. Monitoring the rotational residual response at the bridge supports is proven to be an effective method for assessing the global response of the bridge during field testing. The study shows that adding a rotational spring with a field-calibrated rotational stiffness to the 1-D analytical model of the bridge can significantly increase the load rating factor.

Evaluation of the Impact of Oxidation and Moisture Conditioning on Indirect Tensile Asphalt Cracking Test Parameters and the Tensile Strength Ratio

This study evaluated the effect of laboratory oxidation and testing temperature on asphalt mixtures’ moisture damage. The purpose of this study was to present a modified American Association of State Highway and Transportation Officials (AASHTO) T283 testing procedure that is more sensitive to moisture damage in asphalt mixtures. This study assessed the original test conditioning (OTC), short-term oxidative conditioning (STOC), and long-term oxidative conditioning (LTOC). Three performance grades (PGs)—PG 64-22, PG 76-22, and PG 52-34—and three test temperatures—the ambient laboratory temperature (25°C), asphalt intermediate temperature, and climate intermediate temperature (CIT)—were selected. To better understand the oxidation and moisture conditioning effects, AASHTO T283’s Tensile Strength Ratio ( TSR%) was utilized. Furthermore, additional analysis of the load–displacement curve parameters was carried out using the Indirect Tensile Asphalt Cracking Test, where an interaction diagram that included the mixture toughness ( Gf), ductile–brittle behavior ratio ( l75/ m75), and their interactions with CTindex was created. Statistical analysis was conducted using analysis of variance and Tukey’s post-hoc analysis to determine an appropriate oxidation and testing temperature where moisture damage is most sensitive. Results showed that higher oxidation and CIT had the greatest impact on TSR%. Moisture conditioning increased the CTindex and oxidation reduced the CTindex. The increase in CTindex was attributable to an increasing l75/| m75| and decreasing Gf. The CTindex decreased because of reducing l75/| m75| and increasing Gf. The statistical analyses showed that asphalt mixtures are more susceptible to moisture damage at STOC and LTOC than OTC. Overall, the findings highlight the need for an alternative oxidation conditioning and testing at the CIT to more accurately detect moisture damage in asphalt mixtures.

Updated Zone of Intrusion Envelopes in the Manual for Assessing Safety Hardware Impact Conditions

Roadside barriers are used to shield fixed objects near the roadway and are designed to mitigate the severity of run-off-road crashes near those fixed objects. The zone of intrusion (ZOI) defines the potential location of a vehicle component above and beyond the top face of the barrier during an impact, and therefore indicates if there is a potential that a fixed object located behind a barrier could interact with the vehicle during redirection. Previous ZOI envelope guidelines were based on older vehicle models and test results. Further review was required to update the guidelines for contemporary vehicles and impact conditions in accordance with the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH). A literature review of full-scale crash tests and computer simulations were used to identify the ZOI envelope shapes for MASH test levels 2–5. Simulations were calibrated using test data and were used to investigate gaps in the full-scale test data. Conservative guidelines were developed from the combined simulation and test data, and recommended ZOI envelope shapes were developed that conservatively bounded the ZOI results. Results were presented for potential revision of ZOI envelope guidelines in the AASHTO Roadside Design Guide. Future recommendations to improve ZOI measurements in test data and simulation modeling were also presented.

Proof Load Testing Method by the American Association of State Highway and Transportation Officials and Suggestions for Improvement

Because of the aging of infrastructure, methods are explored by which the reliability of existing bridges and viaducts can be assessed. In cases in which limited information of the structure is available or its condition is of concern, proof load testing may be used to demonstrate sufficient live load carrying capacity. Proof load tests in the U.S.A. are typically performed using the Manual for Bridge Evaluation (MBE) published by the American Association of State Highway and Transportation Officials (AASHTO). The proof load is expressed by the regular live load model magnified by the target proof load factor. The level of reliability obtained using the target proof load factor is not explicitly stated in the MBE, but is of particular interest. In this article, relevant background documents are investigated to uncover the underlying calculations, assumptions, and input data. Current challenges in proof load testing are described in which the considerations of time dependence, stop criteria, available information, and system-level assessment are highlighted. Subsequently, improvements to the MBE proof load testing background are suggested. An example calculation using traffic data from the Netherlands shows that the HL93 load model and Eurocode LM1 provide a reasonably constant proof load factor with span length for bending and shear. However, the HS20 load model does not scale well with increasing span length. It is found that the magnitude of the target load as specified through the proof load factor is directly related to the desired level of reliability. Although the MBE proof load testing method is practical, several challenges remain.

Effect of structural repairs on the load rating and reliability of a prestressed concrete bridge

Prestressed girders often deteriorate over time due to environmental and man-made stressors, lowering the strength and serviceability of bridge structures. Although structural repairs are implemented to improve the load carrying capacity of the structure, the presence of numerous unknowns leads to high uncertainty in estimating the adequacy of repairs. For instance, the cross-section of the remaining strands, material properties, applied external loads, and workmanship assumptions made throughout the repair process introduce ambiguities when estimating the adequacy of the repairs. This study evaluates the efficiency of re-tensioning repairs of prestressed concrete bridge span girders. The repairs include field splicing, re-tensioning, of deteriorated or damaged strands by torquing a splicing coupler. The evaluation in this study considers component, system reliability, and load ratings while accounting for several uncertainties, such as structural repair, material properties, and external loads. This paper introduces an approach to account for prestressing strands damage and repair uncertainties while also accounting for other uncertainties. In this regard, five cases are studied: as-built, repaired, and three varying degrees of damage cases. First, the distribution for structural demand and capacity accounting for uncertainty in loads, material properties, and repair process is defined for each girder in the prestressed concrete bridge span. In doing so, Monte-Carlo simulation is employed to determine the distributions. Accordingly, the limit state function of the girders is defined from the obtained distributions. Then, the component reliability of each AASHTO (American Association of State Highway and Transportation Officials) Type II girder is calculated from the obtained reliability indices based on the determined limit state functions. Finally, a system reliability model of the span is developed from the component reliability of each girder. Some advantages and disadvantages of using component and system reliability index versus load rating in damaged and repaired prestressed concrete bridge girders are also discussed. Several critical conclusions are made regarding the uncertainties in structural repair, material properties and external loads, and their impact on the load rating and the component and system reliability of the prestressed concrete bridge structure girders.

Evaluation of Single Lane Parallel-Type Entrance Ramp Terminal Using Vehicle Dynamics Model for Freeways

Abstract Providing an appropriate length of highway entrance ramps is an important feature that should be considered in freeway design. The recommended minimum acceleration lane length in the Green Book of the American Association of State Highway and Transportation Officials (AASHTO) is currently used for designing entrance ramp terminals. However, in some cases, traffic congestion and crashes are observed when heavy trucks enter freeways, which indicates they could not accelerate enough and did not reach the merge speed at the end of the acceleration lane. Therefore, several scenarios were simulated using a dynamic simulation model (TruckSim) for heavy vehicles with weight to power ratios of 61, 67, 86, and 108 (kg/kW) and grades of zero, ±3, and ±5%. Subsequently, a linear regression model was presented to calculate acceleration lane lengths. The results showed that the acceleration rate of heavy vehicles is not adequate, especially in upgrades. For example, at +5% upgrades, heavy trucks cannot accelerate to the merge speed mentioned in the AASHTO. Conversely, the acceleration rate of heavy vehicles increased in downgrades; therefore, some heavy vehicles were able to achieve merge speed along the proposed length of AASHTO.

Development of Skewed Steel I-Girder Bridge Field Monitoring Strategy through Agency Survey and Numerical Simulation

Highly-skewed steel I-girder bridges are commonly used across the US, especially in congested areas, despite complications in their analysis and design. The American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specification provides suggestions for design values of flange lateral bending stress in addition to line girder analysis when bridge skew exceeds 20° for certain cross-frame layouts. For bridges with skew exceeding 60°, a higher level of analysis is often required, with cross-frames considered primary members in design. Neither the magnitude of additional lateral stress nor the associated skew limits are particularly well understood, so more study is needed to refine and support this analysis and design approach. In addition to short-term response and load distribution, long-term bridge behavior for thermally induced stresses and deformations also needs to be more thoroughly studied. In support of an ongoing research initiative in Illinois, an agency survey was formulated and distributed across the US to understand practices used and challenges faced by state transportation agencies when designing and constructing skewed steel I-girder bridges. Findings from the responses of 23 state agencies illuminate issues, concerns, and current practice related to design, construction, and service life of those bridges. The agency survey informed selection of two bridges in Champaign, Illinois, for field monitoring, in order to provide new understanding of skew effects on bridge superstructure behavior. Three-dimensional finite-element analysis was conducted to guide field instrumentation planning, and initial measurements from the monitored bridges under traffic load confirmed good predictions compared to the planning-stage numerical study.

LRFD calibration for soil failure limit state using the Stiffness Method

The paper describes load and resistance factor design (LRFD) calibration for the resistance factor used in the Stiffness Method internal stability soil failure limit state for geogrid mechanically stabilized earth (MSE) walls. The Stiffness Method was recently adopted in the current American Association of State Highway and Transportation Officials LRFD Bridge Design Specifications in the US, and will appear in the next edition of the Canadian Highway Bridge Design Code. The paper describes the details of the calibration of the soil failure limit state which is unique to the Stiffness Method. Calibration outcomes include consideration of the concept of level of understanding in the selection of nominal load and resistance values which is unique to LRFD foundation engineering practice in Canada. A practical conclusion from these calculations is that if product line-specific creep test data are available to estimate the reinforcement secant creep stiffness used for design, then a resistance factor of 1.0 is reasonable for US practice. If only minimum average roll value tensile strength data are available, then a value of 0.95 is recommended for US practice. For Canadian practice, the corresponding values for typical level of understanding are 0.90 and 0.85, respectively.

Reclassifying Fracture Critical Members (Non-Redundant Steel Tension Members) to System Redundant Members in a Steel Arch Bridge

The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design Bridge Design Specifications define fracture critical members (FCMs) as steel primary members, which are subject to tension and whose failure would probably cause the collapse of a portion of or the entire bridge. FCMs not only lead to additional material procurement and fabrication quality requirements, but bridges with FCMs need to meet the requirements of special mandatory bi-annual hands-on inspections in additions to the routine planned bridge inspections per the National Bridge Inspection Standards. The special mandatory inspections for FCMs are a considerable budgetary constraint for asset owners while still not providing definite safety proofs within the period in between the inspections. Designation of FCMs should be carefully scrutinized in a new bridge constructed with high-quality materials and well-designed details. In 2012, the Federal Highway Administration published a memorandum introducing system redundant members (SRMs), which are identified through refined analysis and exempted from the inspection requirements for FCMs. A new AASHTO Guide Specification released in 2018 outlines a detailed procedure for the reclassification of FCMs as SRMs. This paper summarizes the analyses and results of a detailed FEA performed for a newly designed steel arch bridge. The analyses considered potential failure scenarios at the edge girder of the steel arch bridge and demonstrated the available redundancy in the system to distribute the loads by satisfying the performance criteria set forth in the AASHTO Guide Specification. Reclassification of the FCMs as SRMs could help the asset owner to reallocate their strained resources more efficiently.

Experimental Insight into the Containment of Plastic Waste in Cement-Stabilised Soil as a Road Pavement Layer Material

Plastic waste (PW) constitutes a nuisance to our environment despite several efforts to reduce, reuse and recycle it. This study experimentally explores the possibility of storing plastic waste within a cement-stabilised soil that can be used as a road pavement layer material without adversely affecting the geotechnical characteristics of the stabilised soil. The soil is an A-2-6 soil, according to classification by the American Association of State Highway and Transportation Officials (AASHTO). Compaction characteristics, the California bearing ratio (CBR) and the unconfined compressive strength (UCS) of soil with 10% cement were determined for the 0, 2, 5, 10 and 15% addition of PW. The cementing of soil particles, which played a vital role in enhancing its strength on the addition of cement, may have been activated by the pozzolanic reaction between cement and soil particles. However, the addition of PW to this cement-stabilised mix led to a decrease in strength parameters at all variations. The soil with 10% cement and 2% PW yielded higher strength when compared to other mix ratios with PW and is suitable for use as a layer material in road pavement construction. As a sustainable strategy for PW management in developing nations, the usage of PW in cement-stabilised soil layer is recommended.

A Practical Design Guide for Unbonded Jointed Plain Concrete Roads over Deteriorated HMA Roads: Realistic Traffic Loading

This study aimed to determine the material properties and the thickness of the layers of an unbonded jointed plain concrete pavement design over a deteriorated flexible pavement that lost its service capability. Maximum principal stresses occurring under the concrete pavement should not exceed the modulus of rupture of the concrete. Three-dimensional finite element analyses using ANSYS (Release 18.1 SAS IP, Inc.) software were carried out with the Taguchi method. The most reliable solution for the pavement design was investigated with whole configuration axle loading that reflects the realistic traffic situation. The stress values under the concrete slab due to the positive temperature gradient neglected in the American Association of State Highway and Transportation Officials (AASHTO) method were also investigated. The concrete slabs are exposed to these stresses for longer than the axle loads. Temperature distributions throughout the thickness of the concrete slab were calculated with the bilinear formulas suggested in the study. Axle loadings were applied on both the pavement edge and corner to reflect the most critical loading condition in the pavement design. The critical axle type was found to be 1.2. It was observed that a 0.15 m concrete thickness was appropriate for the concrete class, joint spacing and hot mix asphalt (HMA) elasticity modulus levels used for the 1.22, 1.122, and 1.2 + 111 axle types, but it was not appropriate for the 1.2 axle types. The slab thicknesses calculated with the AASHTO method, and the finite element method were found to be close to each other. It was determined that the concrete thickness significantly affected the maximum principal stress, with a performance statistic (S/N) value of 1692 for the 1.2 axle type. This was followed by the modulus of elasticity of the concrete with an S/N value of 0.356, the modulus of elasticity of the existing flexible pavement with an S/N value of 0.244, and the concrete joint spacing with an S/N value of 0.105. A practical design guide was recommended to extend the service life of a highly deteriorated flexible pavement with the construction of unbonded jointed plain concrete.