American Association Of State Highway And Transportation Officials Research Articles

Dynamic load testing of a modular truss bridge using military vehicles

Determination of appropriate load factors ensures bridge assessments completed using limit states design are applicable for all potential loading scenarios. Extremely limited research has been completed to determine accurate Dynamic Load Allowance (DLA) values for military vehicle loading of bridges, specifically independent values for tracked and wheeled vehicle types. An experimental testing program was used to assess the dynamic load effects caused by these vehicle categories by subjecting a bridge to loading from multiple different vehicle types at different speeds, while controlling deck surface condition. It was found that tracked vehicles generated approximately half the dynamic bridge response of wheeled vehicles. Using this knowledge, tracked vehicle DLA value recommendations relevant for this bridge are made for use in the North Atlantic Treaty Organization (NATO) Military Load Classification (MLC) system, and in the Canadian Highway Bridge Design Code (CHBDC) and American Association of State Highway and Transportation Officials (AASHTO) bridge code. Further research in this area could lead to strategic increases in tracked vehicle mobility.

DETERMINING THE SUITABILITY OF CLAY AT ITU, AKWA IBOM STATE, NIGERIA FOR ROAD CONSTRUCTION

Incessant road failures in Nigeria have become an issue of serious concern in recent times as a large portion of states and federal budgets are dedicated to revamping road infrastructures. In this study, we examined the geotechnical properties of clay samples collected from Ntak Inyang along Calabar-Itu highway, in Itu LGA of Akwa Ibom State, Nigeria with the aim of ascertaining whether the earth material at the study location is suitable for road construction. We carried out proctor’s compaction test, sieve analysis, California bearing ratio test and Attenberg’s limit test to analyse the clay samples for moisture content, California bearing ratio, plasticity and plastic limit, dry density and particle sizes. Results obtained indicate that the clay sample has an optimum moisture content of 13.53 %, dry density value in the range: 1580 kgm-3-1650 kgm-3, plastic limit of 22.15 %, plasticity index of 23 %, liquid limit of 45.63 %, sieve of 43.36 % with particles less than 0.075 mm and no particle size up to 5.0 mm, California bearing ratios of 9.0 % at 10.0 % moisture content, 6.7 % at 12.0 % moisture content, 2.0 % at 14.0 % moisture content. Based on these results, the clay sample is regarded as a sub-grade material with the classification of A-7-6 according to AASHTO (American Association of State Highway and Transportation Officials) classification. These results make the sample unsuitable for road construction but qualify it as a potential raw material for production of ceramic wares and tiles.

Effect of Saw Dust Ash on Index and Engineering Properties of a Weak Lateritic Soil

The effect of saw dust ash on index and engineering properties of a weak lateritic soil was carried out in this study. Specimens prepared from lateritic samples were tested for its gradation (sieve analysis), unconfined compressive strength (UCS) and compaction parameters (MDD and OMC) at energy level of British Standard Light (BSL). The samples were admixed with varying percentages of saw dust ash (SDA) and the tests were repeated on the admixed samples. The general trend of the results shows that the gradation of the soil improved from A-7-5 to A-5 at 4% SDA content by American Association of State Highway and Transportation Officials (AASHTO) soil classification system, UCS values also peaked to 237.12 kN/m2 at 4% SDA content while the compaction parameters were still best at the natural stage at BSL energy level. The peak UCS value, though, shows an improvement of 26.9% when compared to that of natural soil, it still falls below the minimum specified value for base material stabilization using OPC (1710 kN/m2) as well as that for sub-base material (687-1373 kN/m2). From the work, 4% stabilization of weak lateritic soil with SDA can improve some index and engineering properties of a weak lateritic soil. It is also evident that the resulting stabilized soil should not be used for pavement construction. Nevertheless, addition of 4% SDA to weak lateritic soil should be encouraged when slight gradation improvement is the only target. Keywords: index properties; engineering properties; lateritic soil; saw dust ash; stabilization.

A Simplified Mechanistic-Empirical Flexible Pavement Design Method for Moderate to Hot Climate Regions

Flexible pavement structure design is a complex task because of the variability of design input parameters and complex failure mechanisms. Therefore, the aim of this study is to develop and implement a simplified Mechanistic-Empirical (M-E) pavement design method based on the 1993 American Association of State Highway and Transportation Officials (AASHTO), the National Cooperative Highway Research Program (NCHRP) 9-22, and NCHRP 1-37A and 1-40D projects. This simplified methodology is implemented into a computer code and a user-friendly software called “ME-PAVE”. In this methodology, only two equivalent temperatures, as per the NCHRP 9-22 project, are estimated to adjust the dynamic modulus of the asphalt layer(s) for Asphalt Concrete (AC) rutting and AC fatigue cracking prediction instead of using the hourly climatic data, as in the AASHTOWare Pavement ME. In ME-PAVE, the structural responses at critical locations in the pavement structure are determined by a Finite Element Module (FEM), which is verified by a Multi-layer Elastic Analysis (MLEA) program. To ensure that the simplified methodology is practical and accurate, the incorporated transfer functions in the proposed simplified methodology are calibrated based on the Long-Term Pavement Performance (LTPP) data. Based on statistical analyses, the built-in FEM results exhibit very similar trends to those yielded by MLEA, with a coefficient of determination, R2 of 1.0. For all practical purposes, the proposed methodology, despite all simplifications, yields acceptable prediction accuracy with R2 of 0.317 for the rut depth compared to the current practices, NCHRP 1-37A and 1-40D (R2 = 0.399 and 0.577, respectively); while the prediction accuracy for fatigue cracking with R2 of 0.382 is comparable to the NCHRP 1-40D with R2 of 0.275. Nonetheless, the standard error for both distresses is in good agreement based on the investigated data and the developed methodology. Finally, the conducted sensitivity analysis demonstrate that the proposed methodology produces rational pavement performance.

Investigation of waste clay brick as partial replacement of geopolymer binders for rigid pavement application

Waste clay brick (WCB) is identified as a feasible alternative cementitious material for producing geopolymer binders to replace ordinary Portland cement (OPC). This study investigated mechanical properties and environmental impacts of one-part geopolymer binders at ambient curing conditions, employing binary blends of WCB with fly ash or slag, while using anhydrous solid sodium metasilicate as the sole activator. WCB was replaced separately with fly ash and slag at 20%, 40%, 60% and 80% by mass to obtain the aluminosilicate precursors. Combination of the aluminosilicate precursors and the solid activator was considered as the total binder. The effect of the alkali activator content, particle size and water-to-binder ratio on compressive strength development were investigated. The strengths of the geopolymers were compared with minimum concrete strength requirements indicated in Australian pavement design guidelines and American Association of State Highway and Transportation Officials (AASHTO) guidelines. The experimental results indicated an optimum activator content of 10% by mass of the total binder for all binary geopolymer systems. Compared to WCB alone and WCB-fly ash blends, binary geopolymer systems of WCB-slag blends showed higher compressive strengths. WCB-slag blends showed high early strength gain and achieved more than 22% and 48% of its corresponding 28-day strength within 24 h and 72 h, respectively. Highest 28-day compressive strength of 81.8 MPa was achieved for the binder with 40% WCB and 60% slag in the precursor. The strength further improved to 96.8 MPa by reducing WCB particle size from 150 µm-passing to 75 µm-passing. Additionally, the environmental impacts associated with the different blends were evaluated considering carbon dioxide emission and energy consumption during their production. These values were subsequently compared with those of OPC manufacturing. The comparison showed that WCB based geopolymer binders can reduce carbon emissions up to 78% and energy consumption up to 85%.

An improved framework for volume change of shrink/swell soils subjected to time-varying climatic effects

The ability to estimate soil volume change as a function of time is a valuable tool in the design or forensic analysis of shallow foundations and pavement structures. This paper presents an improved framework for estimating the volume change of shrink/swell soils due to time-varying climatic effects using the Lytton et al. (2005) approach with the suction envelope models created by Vann & Houston (2021) and updated considerations of short-term varying climate. The procedure can be easily implemented in any country due to its mechanistic-empirical nature. The authors present an example calculation of the proposed framework using the data from an American Association of State Highway and Transportation Officials (AASHTO) Long-Term Pavement Performance (LTPP) Seasonal Monitoring Program (SMP) section, located approximately 80 miles northeast of Dallas, Texas. The volume change estimated from the proposed framework was compared to 70 measured data points from sections from the SMP study and the results look promising. The models are universal and can be used in any part of the world provided measured data is available to calibrate for local conditions. Ongoing calibration effort with the remaining LTPP SMP sections will allow obtaining calibration factors for the proposed framework that will improve the estimation of the volume change predictions under pavements and facilitate the implementation into current design procedures.

Improvement of the Shear Strength Parameters of a Granular Volcanic Soil Using Type I Portland Cement

The purpose of this research is to improve the parameters of shear strength in granular volcanic soil, by adding a percentage of Portland type I cement. The first step for this research was to classify the soil through a Granulometry test, according to the Unified Soil Classification System (USCS), the result was considered as a poorly graded sand with gravel also considered by The American Association of State Highway and Transportation Officials (AASHTO) as “A-1-b”. In addition, the compaction curve of the volcanic soil has a Maximum Dry Density (MDD) of 1.21 kg/cm2 and an optimum moisture content of 17.8%. Also, the friction angle of 33.5° and a cohesion of 0 kg/cm2, and the results of the Direct Shear Test indicate the Residual Stresses of 0.63, 1.34 and 2.65 kg/cm2 according to the Normal Stresses 1, 2 and 4 kg/cm2, respectively. The second step was to apply a Modified Proctor Test as following: one sample for natural soil and four samples adding 3%, 5%, 7% and 9% of cement. Finally, applied the Direct Shear Test: one sample for natural soil and three samples adding 3%, 5%, and 7% of cement after 7 days of curing, then three more samples are taken adding 3, 5% and 7% of cement at 14 days of curing. The results of the Modified Proctor Test of the volcanic soil with the addition of 5% cement has a maximum peak of a Maximum Dry Density of 1.33 kg/cm2 and with an Optimal Moisture Content of 22.7%, improved the MDD by 10% in regard to the natural soil. And the results of the Direct Shear Test shown in each sample an increase from 14.6% to 79.1% in the friction angle in comparison with the natural soil from 25.8% to 161.5% in shear strength. Likewise, the behavior of the volumetric deformation is shown, presenting a greater contraction when a normal stress of 1 kg/cm2 is applied and a greater expansion when a normal stress of 4 kg/cm2 is applied. Also, the volcanic soil at 7 days of curing with 7% cement addition increases its resistance by 67.34% and the volumetric variation decreases by 50% and the volcanic soil at 14 days of curing with 5% addition of cement increases its resistance by 103.40% and the volumetric variation decreases by 25%.

Effect of variations in layer thickness and resilience modulus on flexible pavement performance

A pavement mechanistic-empirical analysis is based on a pre-designed structure checked for required performance criteria. In case the latter are not met, this structure is modified and reprocessed. In this context, analyzing the effect of variations in project parameters on pavement performance prediction subsidizes a better understanding of results provided by computer programs. The objective of this study is to assess the effect of layer thickness and resilience modulus variations on flexible pavement performance. To do so, performance was estimated for the 20th project year through Elastic Layered System Model 5 (ELSYM5) software and American Association of State Highway and Transportation Officials (AASHTO) Mechanistic-Empirical method (ME). Using multiple regression models for result adjustment and through statistical assessments on regression coefficients calculated, it can be concluded that pavement lifespan consumption, predicted by simulations on ELSYM5, is sensitive to variations in coating and subbase thickness and in subgrade resilience modulus. For AASHTO ME method, predicted values for distresses were significantly sensitive to variations in coating, base and subbase thickness, and in base and subgrade resilience modulus. Comparing both approaches, it is concluded that ELSYM5 can be a viable alternative to the application of a ME pavement design method.

Stormwater Harvested from Permeable Pavements as a Means to Save Potable Water in Buildings

The main objective of this work is to analyse the potential for potable water savings in university buildings by using stormwater collected from permeable pavements. Six buildings located on the campus of the Federal University of Santa Catarina (UFSC) were selected to obtain monthly water consumption patterns and parking lot areas. The same six buildings were then evaluated considering their location in eight different cities in Brazil, with different rainfall patterns. Simulations using the computer programme Netuno were run to obtain the potential for potable water savings in each building and city combined. The structural design of permeable pavements was also assessed using two methods available in the literature, that is, the American Association of State Highway and Transportation Officials (AASHTO) and Brazilian Portland Cement Association (ABCP). The hydrological-hydraulic design of the permeable pavement was also carried out. The designed thicknesses were compared with the thicknesses obtained using the computer programme Permeable Design Pro. The potential for potable water savings between 18.4% and 84.8% was obtained, depending on the city, building and non-potable water demand considered. For the structural design, the thicknesses obtained by using both methods were similar; however, it was observed that the AASHTO method better represents the pavement model. Regarding the hydrological-hydraulic design, the differences obtained show that the simplification performed for the pavement drainage was in favour of safety. In conclusion, the use of permeable pavements in stormwater harvesting systems is promising, aligning the drainage aid, structural capacity and potential for saving potable water.

Investigating seismic behavior of horizontally curved RC bridges with different types of irregularity in comparison with equivalent straight bridges

In this paper, the seismic behavior of a total of 84 reinforced concrete bridges, including 12 straight and 72 curved bridges was studied. The bridges were designed and detailed according to the American Association of State Highway and Transportation Officials (AASHTO) regulations. To evaluate the accuracy of the seismic response predictions obtained using elastic analyses, as suggested by AASHTO, both linear and nonlinear time history analyses were performed and the results were compared. In addition, to investigate the accuracy of the code provisions regarding the limitations on the bridge subtended angle for the use of equivalent straight bridges, the results obtained for the curved bridges were compared with those obtained for the equivalent straight bridges. Furthermore, the effects of different types of irregularity on the predicted displacement demands from equivalent straight bridges were investigated. To study the effects of different types of irregularity on the results, different irregular arrangements of spans, various column heights, different abutment conditions, and different subtended angles were considered. Also the effect of combination of different types of irregularity was investigated by considering bridges with different configurations. The results indicated that the deviation of the results obtained from the linear and nonlinear analyses is significant, particularly in the transverse direction of the bridges with irregularity in columns height for different subtended angles. Also, it was shown that in bridges with restrained abutments, unlike the bridges with unrestrained (i.e., free) abutments, the equivalent straight bridges cannot be used in lieu of the curved bridges, since the differences between the results from the two models are significant and become larger with increasing the subtended angle of the bridges. It was shown that some modeling assumptions widely used for seismic analysis of bridge structures can be unrealistic and may lead to inaccurate predictions. It was shown that the AASHTO specifications regarding the use of elastic analysis for some irregular bridges and the limitations on the subtended angle for the use of equivalent straight bridges need to be reevaluated.

Quantification of Calcium Oxychloride by Differential Scanning Calorimetry: Validation and Optimization of the Testing Procedure

Abstract The American Association of State Highway and Transportation Officials (AASHTO) T 365 standard, Standard Method of Test for Quantifying Calcium Oxychloride Formation Potential of Cementitious Pastes Exposed to Deicing Salts, describes a test methodology that uses low-temperature differential scanning calorimetry (LTDSC) to quantify the formation of calcium oxychloride in cementitious systems exposed to concentrated calcium chloride solutions. AASHTO T 365 is included in AASHTO PP 84, Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, as a performance indicator for mixtures at risk of calcium oxychloride formation. During the test, the sample temperature is first dropped to −90°C, looped through a brief thermal cycle, then slowly increased to a maximum of 50°C, at a constant heating rate of 0.25°C/minute (min), for a total testing time of approximately 11 hours. The objective of this work is to modify the test to reduce its duration to facilitate wide adoption among practitioners. It is found that by increasing the minimum conditioning temperature from −90°C to −5°C, as well as by increasing the heating rate from 0.25°C/min up to 1°C/min, the test duration can be reduced from approximately 10.7 hours to approximately 1.6 hours without any statistically significant difference in the numerical test results, although an offset of the melting peak and a change in its shape were observed. This change can provide valuable savings in terms of time and energy/gas consumption and make AASHTO T 365 more competitive with other available tests for the estimation of calcium oxychloride formation, such as thermogravimetric analysis (TGA). TGA and LTDSC are compared to each other in terms of mixture classification for susceptibility to calcium oxychloride formation. It is shown that the two tests show good agreement, with 85 % of cases (out of 30 tested) receiving the same classification.

Numerical investigation of extreme wave impact on coastal bridge deck using focused waves

Horizontal and vertical impact forces on a coastal bridge deck with girders due to asymmetric and nonlinear wave loads induced by the action of focused wave groups have been investigated using open-source CFD model REEF3D. An extensive parametric study was conducted to investigate the variation of horizontal and vertical impact forces induced on bridge deck by steep focused waves. Results indicate that with increasing wave heights, while the horizontal positive force increases, the peak vertical uplift and downward forces decrease. Longer wave periods impart higher peak vertical uplift forces and horizontal positive forces. The bridge deck location at still water level, submerged and partially submerged cases are considered for the numerical study and the results are compared with the design formulae of American Association of State Highway and Transportation Officials (AASHTO). For both submerged and partially submerged scenarios, AASHTO formulae were found to highly overestimate the peak horizontal impact forces for lower wave heights and they were found to give better results for higher wave heights. In case of peak vertical impact forces, AASHTO formulae highly underestimate for lower wave heights and moderately capture the peak vertical impact force at higher wave heights and airgaps.

Measuring Instantaneous Resilience of a Highway Bridge Subjected to Earthquake Events

Bridges in a road network play a significant role in supporting the flows of people, goods, and freight during an earthquake event and are expected to maintain their functionality following the event. Thus, measuring the capability of a bridge immediately following an earthquake event is critical for understanding the post-earthquake functionalities of transportation networks and supply chain systems involving highway bridges. To this end, this paper proposes a new metric for measuring the resistant capacity of a highway immediately following an earthquake event, which is here called instantaneous resilience. The proposed metric first compares the reliability indices of a bridge before and following an earthquake event to measure the immediate earthquake impact. Although this comparison (i.e., robustness measure in this paper) indicates the remaining strength of the bridge subjected to a given earthquake event, it does not reflect collapse failure modes appropriately. Therefore, the proposed instantaneous-resilience metric combines the robustness measure with the structural redundancy measure to consider various scenarios of load path distribution. The proposed metric is computationally efficient because, in the process, it utilizes a generalized reliability-intensity (R-I) surface of a bridge which can be used to calculate the pre- and post-earthquake reliabilities of any bridge designed based on the American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD). Without developing bridge-specific fragility curves and performing structural analysis of a bridge, the proposed measure enables engineers to make a preliminary assessment of the immediate impact of the earthquake on bridges on a quantitative basis. The step-by-step calculation process of the proposed instantaneous-resilience of a bridge is presented, and its potential use in highway network performance assessment is illustrated with a simple hypothetical network system.

Earth pressure distribution around flexible arch pipes

The Canadian Highway Bridge Design Code (CHBDC), the American Association of State Highway and Transportation Officials (AASHTO) and the Swedish Design Manual (SDM) are regarded as fundamental manuals for the design of flexible corrugated metal pipes. However, these manuals do not consider properly several factors that may affect the soil-structure interaction, such as the backfill soil stiffness, the pipe burial depth, the effect of compaction loads, and the trench geometry, including the trench width and the slope of the side of the excavation. To examine these factors, this paper utilizes a detailed finite element model of a flexible corrugated metal arch pipe. The model was developed and validated by using a field case study in Sweden. In a comprehensive parametric study, the numerical analysis and the empirical methods are used to investigate the applicability and accuracy of these methods for estimating the interaction behaviour of flexible culverts installed in semi-shallow and shallow trenches.

State-of-the-art review and design of grouted duct connections for precast bridge columns

The use of prefabricated bridge columns in seismic regions is challenging since performance data on precast column connections is limited. A handful accelerated bridge construction (ABC) details to connect precast columns to adjoining members have been experimentally investigated, and some were found viable for seismic applications and field deployment. A connection consisting of ducts filled with conventional grout is the focus of the present study. In this connection type, precast column longitudinal bars are protruded out of the column and are inserted into grout-filled ducts matching the number and configuration of the column bars. A state-of-the-art review of the grouted duct connection studies and bridge component tests utilizing this connection type is presented. A preliminary design equation for duct connection filled with conventional grout is proposed based on the data collected from the literature. Subsequently, the validity of this equation is evaluated through pullout testing of 12 full-scale grouted-duct specimens. Finally, a refined design equation is proposed based on all available test data, and construction guidelines are developed to facilitate the use of grouted duct ABC column connections in high seismic regions. These design and construction guidelines were proposed to the American Association of State Highway and Transportation Officials (AASHTO) for possible adoption as national specifications.

Characterization of the fatigue behavior of asphalt mixture under full support using a Wheel-tracking Device

Most existing fatigue testing methods in the laboratory are designed to evaluate the cracking resistance of asphalt mixture only, regardless what types of structural support it is used in the field. However, literature has confirmed that fatigue cracking is a structural related distress, and the cracking potential of asphalt layer is strongly affected by its underneath structural supporting conditions. On the other hand, the Hamburg Wheel-tracking Device (HWTD) has gained popularity for characterizing the rut-resistance and moisture susceptibility of asphalt mixtures under moving loads among state Department of Transportation (DOT) and agencies, and it has the capability to be modified to specify supporting conditions. Therefore, in this study, we propose to make some modifications to the existing HWTD and to study its capability of being also utilized as a cracking device for its potential advantages in equipment availability and simulating field loading and structural conditions. The developed HWTD fatigue test was used to simulate the conditions experienced by an asphalt mixture layer paved on the flexible base and applied with a vertical moving load. Three mixtures were specially designed to have known fatigue behavior difference for evaluating the reliability of this newly developed method, and to be compared with the standard American Association of State Highway and Transportation officials (AASHTO) semi-circular bending (SCB) method (AASHTO TP 124-18). A variety of strain and pressure gauges were used to record the load responses for fatigue behavior analysis. Both the phenomenological fatigue life analysis approach and the dissipated energy based ratio of dissipated energy change (RDEC) approach were used for data analysis. It was found that the HWTD fatigue test was essentially a type of laboratory scale accelerated loading test which can simulate the fatigue cracking phenomenon under the proposed testing setup. The RDEC approach with different failure criteria were suitable and effective in analyzing the testing data and can quantify the fatigue behavior of specific mixture within reasonable time frame. The results were consistent with the standard SCB fracture test results. In conclusion, the HWTD fatigue test has the potential to be a rational and convenient method for characterizing the fatigue behavior of hot mix asphalt (HMA) materials with the consideration of supporting conditions.

Characterization and Classification of Geotechnical Index Properties of Shallow Soil Deposits at Oworoshoki Area, Kosofe Local Government, Lagos, Nigeria

The study of geotechnical index properties of soils in Oworoshoki, Kosofe, Lagos State was conducted to characterize and classify the index properties of soil samples. Disturbed and undisturbed soils were collected at different shallow depths (1m, 2m and 3m) from the study area and laboratory test was conducted. The laboratory test conducted includes natural moisture content, atterberg limits (liquid limit and plastic limit), particle size distribution, specific gravity, unit weight and hydrometer. The results of the test were gotten: natural moisture content as 23.5%, 24.5% and 25.3% , liquid limits (LL) 28.68%, 26.64% and 29.10%, Oworoshoki is non-plastic for the three depths i.e. plastic limit (PL) is 0, particle size distribution percentage passing through BS #200 (0.075mm) are 95.97 %, 97.97%, 98.10% and this shows that the soil sample contain much silt, the samples are non-plastic for all depths (1m, 2m and 3m), specific gravity as 2.61, 2.55 and 2.60, unit weight as 17.5 KN/m3, 18.1kn/m3 and 18.9KN/m3 and hydrometer percentage passing through BS #200 (0.075mm) as 95.97% at 1.0m depth, 97.97% at 2.0m depth and 98.10% at 3.0m depth. Hydrometer test was conducted because 95.97% passes sieve 0.075mm.This shows that the soil contain high amount of silt. Soils from depth 1.0m, 2.0m and 3.0m are non-plastic (NP) because the Plastic Index (PI=0) and the soil samples are classified as A – 3 according to American Association of State Highway and Transportation Officials (AASHTO) System.

Investigation of measured prestress losses compared with design prestress losses in AASHTO Types II, III, IV, and VI bridge girders

Inaccurate prediction of prestress losses leads to inaccurate predictions for camber, deflection, and concrete stresses in a bridge girder. This study aims to improve the prediction of prestress losses and provides bridge designers with insights into the differences between design and actual concrete properties. Prestress losses, compressive strength, modulus of elasticity, shrinkage, and creep were measured for several American Association of State Highway and Transportation Officials (AASHTO) Types II, III, IV, and VI girders. The investigation revealed that the measured total prestress losses at the time of deck placement were lower than the design losses calculated using the refined estimates method of the 2017 AASHTO LRFD Bridge Design Specifications. This was mainly attributed to the actual concrete compressive strength at transfer being greater than the design compressive strength. This discrepancy was as high as 73% for some girders. It was also determined that the 2017 AASHTO LRFD specifications’ refined estimates method for estimating prestress losses overestimates the total prestress losses at the time of deck placement for AASHTO Types II and III girders.

Comparative Analysis and Assessment of States’ Traffic Management Center Programs

This research presents a step-by-step guideline for traffic data collection standards set by the Institute of Transportation Engineers (ITE) and American Association of State Highway and Transportation Officials (AASHTO). This study reviews manual and automatic methods of traffic counting and provides detailed information on traffic volume and vehicle classification studies. This research also provides a detailed analysis of the Delaware Department of Transportation (DelDOT)-TMC (Transportation Management Center) websites and compares it to selected Department of Transportation websites of other states such as Vermont, Connecticut, New Jersey, Pennsylvania, California, Texas, and Virginia. The purpose of the comparison is to analyze the data sources; user friendliness, accessibility, types of data available, presentation formats, and style for each state to determine how they compared to DelDOT-TMC. Although there were some similarities, the findings suggest that two major differences are present. The overall results revealed that DelDOT-TMC provides limited traffic and roadway weather data, and presentation formats to the public as compared to the other states. Further, a unitless variable, called the Capacity Factor (Q), has been developed within this study to represent this relative comparison. This study shows that DelDOT TMC performs well within the group of selected states and better than selected states of similar size and most selected states of larger size; where only Virginia performs better then DelDOT TMC. DelDOT TMC does not perform as well as selected neighboring states; however, it performs in an acceptable range relative to neighboring states.

Assessing the Influence of Moisture Damage under Repeated Load on Multilayer Interface Bond Strength of Asphalt Concrete

The performance and durability of the asphalt pavement structure mainly depend on the strength of the bonding between the layers. Such a bond is achieved through the use of an adhesive material (tack coat) to bond the asphalt layers. The main objective of this study is to evaluate the effect of moisture in conjunction with repeated traffic loads on the strength of the bonding between asphalt layers using two types of tack coats with different application rates. Using the nominal maximum size of aggregate (NMAS), the layers were graded (25/19) and (19/9.5) mm. The slabs of multilayer asphalt concrete were prepared using a roller compactor using two types of tack coats to bond between layers, namely rapid curing cut back asphalt (RC-70) and cationic medium setting emulsion (CMS), with different application rates. Six extruded cores with a diameter of 116 mm each form the prepared slab has been obtained. Core specimens were subjected to moisture damage according to the American Association of State Highway and Transportation Officials (AASHTO), after which repeated bond shear stresses and monotonic tests are practiced. It is concluded that permanent deformation increased with moisture-induction under repeated load for both interfaces and tack coat types. The (CMS) as a tack coat had less permanent deformation values than RC-70 for both interface types and all application rates. In contrast, the interface bond strength (IBS) value was higher than that for (RC-70) in both interface types after moisture conditions. The trend of the results illustrates that (IBS) decreased with moisture conditions under repeated load, as compared to samples under repeated load only.