Thin Pavement Structures Research Articles

Assessment of flooding impact on thin pavement structure in Texas coastal region

Over the recent years, transportation infrastructure in the United States have experienced numerous hurricanes or tropical storms usually accompanied with heavy rainfalls. This may lead to flooding on pavements and higher groundwater levels, causing soil erosion, slope instability, reduced pavement strength, and lowering pavement’s load-bearing capacity, subsequently shortening pavement service life or increasing rehabilitation and maintenance costs. This study focuses on the impact of flooding on thin pavement structure with surface-treated pavements in Texas coastal region, which contains 6,277 lane miles of roads. First, at a project level, a Mechanistic-Empirical pavement design tool is used to analyze pavement performance under flooding and non-flooding/normal conditions. Pavement life is estimated for different flooding timing cases. Second, simulations are run to evaluate the impact of flooding on the pavement life at a network level. Three flooding frequencies are highlighted: low, 100-year; medium, 50-year; and high, 20-year. By a comparison with non-flooding baseline, it is found that the pavement life for the entire weak pavement network in the coastal region can be reduced at varying degrees due to the flooding impact. The quantified pavement life reduction can serve to enhance pavement design practice and system management decision making in a proactive manner.

Layered Viscoelastic Analysis with Moving Loads of Low-Volume Roadway Pavement Response

Low-volume roads (LVRs) are typically not expected to withstand large amounts of traffic, consequently they have relatively thin pavement structures. However situations can occur when traffic loading rapidly increases, resulting in rapid structural deterioration of the pavement. Examples include resource exploration and production, new industrial facilities, and military operations. Improved evaluation procedures, including computation of pavement structural responses, are needed to accommodate these scenarios. This paper reports recent advances in methods for computing the structural response of LVRs that incorporate viscoelastic asphalt material behavior and accommodate moving loads. Application of layered elastic analysis, using a Hankel transform with numerical integration methods, is popular in several mechanistic-empirical pavement design procedures. This paper describes an application of the collocation method for approximating the creep compliance and viscoelastic solution, which removes the necessity for approximating the Laplace transform inversion. This was coupled with Boltzmann’s superposition principle for moving loads. Comparisons showed that the proposed approximate method matched well with the viscoelastic solution, and with the full-scale instrumented test data of highway pavements. The measured near surface response of a thin LVR test pavement subjected to military truck loads was then modeled to determine the suitability of the approach for LVR. The modeled results for asphalt strain and vertical pressure in the granular layers showed generally good agreement with the measured instrumentation data. The developed structural response model provided a more realistic simulation of flexible pavement viscoelastic material behavior and accommodation of moving loads with similar computational speed to a conventional layered elastic approach.

Evaluation of the structural response of two in-service thin flexible pavements under heavy vehicle loading during different seasons by built-in sensors

ABSTRACT Long Heavy Vehicles (LHV) are considered more efficient and environmentally friendly transportation of goods compared to conventional trucks. Thus, the maximum allowable gross vehicle weight (GVW) in Sweden was increased on part of the road network from 64 to 74 tons in 2018 by increasing the vehicles’ length and the number of axle groups per vehicle but not the axle load limits. This change in loading conditions is expected to lead to changes in the structural response and degradation rate of thin pavements on the low-volume road network. To improve our understanding of thin pavements behaviour exposed to multiple axle loadings two thin pavement structures located in the north of Sweden were instrumented with road response and climate sensors. Four measurement campaigns were carried out within one year by in-situ stress and strain measurements from the built-in sensors as LHV passes over at normal speed. The recorded response was compared with numerical calculations based on multilayer elastic theory (MLET). Values of stresses and strains showed a generally good agreement with high values of coefficient of determination R 2 during different seasons when the asphalt stiffness values were adjusted based on temperature and granular layer stiffness values based on moisture.

Damage investigation of thin flexible pavements to Longer Heavier Vehicle loading through instrumented road sections and numerical calculations

Longer Heavier Vehicles provide an improvement in energy efficiency and environmental performance compared to traditional Heavy-Duty Vehicles. In Sweden, the maximum permissible vehicle gross weight has been increased from ∼64 to ∼74 tonnes without increasing the axle load limits. The consequence of this is investigated in this study. Response from two instrumented thin flexible pavements subjected to loading from three types of heavy vehicles (∼64, ∼68 and ∼74 tonnes) has been measured and the recordings were compared with numerical calculations based on 2D multilayer elastic calculations. Pavement damage contribution by the three vehicles was thereafter investigated. As long as the number of axles is increased to compensate for the increased vehicle loading and dual wheels are used, ∼74 tonnes vehicle are not more aggressive to the two thin pavement structures compared to the lighter vehicles with fewer axles but higher average axle loads and tyre pressure.

Cyclic plate testing of geosynthetic-reinforced airfield pavements

Numerous cyclic plate load tests have been performed over the past several years to investigate the potential performance benefits of including geosynthetics in paved and unpaved applications. A majority of these studies have focused on relatively thin pavement structures subjected to highway loads. Airfield pavements can be substantially thicker and include multiple aggregate layers, and data are needed to quantify geosynthetic contributions under high contact pressures (CPs). Eleven representative airfield pavement structures (four unreinforced sections, four containing geosynthetics at the subbase−subgrade interface and three containing geosynthetics at the base−subbase interface) were constructed in a laboratory containment facility and subjected to cyclic loading under 1750 kPa simulated aircraft CP. Permanent surface deformation and vertical pressure response data were collected to determine relative improvement when compared with an unreinforced pavement structure and to evaluate the influence of geosynthetics. Some geosynthetics increased the number of cycles to failure, and it was found that some level of permanent deformation (e.g. 25 mm) may be required to engage reinforcing benefits when placement occurs at the subgrade−subbase interface. Changing subbase material from a California bearing ratio of 15–18 to 55 resulted in 1·5 orders of magnitude more cycles to 25 mm of permanent deformation than any of the geosynthetic-reinforced sections evaluated.

Effects of layer interface conditions on top-down fatigue cracking of asphalt pavements

Different types of responses have been considered in the past as the driving forces of the top-down cracking (TDC). The horizontal tensile strain at the surface is the most appropriate response of pavement structures for analysing TDC. In computing the horizontal strains, most of the mechanistic design methods of asphalt pavement consider that pavement layers are fully bonded and bottom-up cracking is the critical type of fatigue distress. The bonding condition between pavement layers is one of the significant factors influencing pavement performance. In this research, the effects of interface bonding conditions on top-down fatigue cracking are investigated based on the horizontal tensile strain at the surface. Analysis procedures are conducted using of Lucas algorithm and integration, summation and extrapolation (ISE) methods to determine the horizontal strain responses of asphalt concrete (AC) layer at the surface accurately. The results reveal that the AC layer thickness, type of base layer material and temperature affect the horizontal strains at the surface and debonded locations significantly. When the layers of thick pavement with cement-treated base (CTB) are fully bonded, the TDC is a dominant type of distress at different temperatures analysed, while for the thick pavement with granular base (GB) the surface-initiated cracking occurs only at high temperature. Due to the interface debonding in the thick pavement, the maximum horizontal strains vary at different locations and failure may appear simultaneously at the top and bottom of AC layers or only at one of those regions. For the thin pavement structure, the layer interface bonding conditions hardly influence the mechanistic response at the surface and the pavement with GB is more vulnerable to bottom-up cracking, whereas the likelihood of TDC increases at high temperature for the thin pavement with CTB.

Prediction of Subgrade CBR using FWD for Thin Bituminous Pavements

Deflection based models developed by Jameson, Roberts et al and Queensland Department of Transportation and Main Roads are commonly used for predicting the subgrade CBR of asphalt pavements. The models utilise Falling Weight Deflectometer (FWD) deflection D900 recorded at 900 mm from the centre of the loading plate. The principal aim of the study is to enhance the prediction of the in-situ subgrade CBR using FWD for granular pavements with thin bituminous layers. The scope of the study included the comparison of subgrade CBR predictions from the three deflection based models and the predictions were verified using the in-situ CBR values derived from Dynamic Cone Penetrometer (DCP) from eleven pavement test sites. The study shows that the three models over predict the subgrade CBR because the deflections recorded at sensor D900 are consistently small. It is observed the impact load has little influence on the deflection at D900 for pavements with asphalt layer less than 50 mm. The inherent non-linearity behaviour of the thin pavement structure is also the reason for the discrepancies in the predictions. Consequently, a new predictive model is developed utilising the FWD deflection D450 observed at 450 mm from the impact load.

Quantitative Assessment of the Effect of Wide-Base Tires on Pavement Response by Finite Element Analysis

Various studies have shown that the new-generation wide-base tire (WBT) for trucks causes more damage to pavement than does the dual-tire assembly (DTA). However, there is no substantive approach that quantifies the difference in pavement responses produced by WBTs and the DTA. This study filled this gap by developing linear equations that connect pavement responses produced by these two tire types. Equations were developed for 10 different pavement responses through 480 finite element method simulations (240 for the DTA and 240 for WBTs) that were run in ABAQUS with the same material properties and pavement structures. The only difference was the contact stresses and contact areas that were measured under the same axle load for WBTs and the DTA. The cases modeled in simulations were selected to capture extreme conditions, that is, thick and thin pavement structures with strong and weak material properties. The equations will help pavement researchers to understand quantitatively the effect of WBTs on pavement responses as compared with the DTA. The low resultant prediction error, 10%, allows linear equations to be implemented through the application of adjustment factors on mechanistic pavement design guides such as the Mechanistic–Empirical Pavement Design Guide, which are unable to simulate WBT loading realistically. To predict pavement damage accurately, the pavement analysis should consider the WBT market penetration in the United States (approximately 10%) and the partial use of WBTs on truck axles. The impact of WBTs on pavement should be evaluated in the context of economic and environmental benefits.

Pavement Maintenance Prioritization Tool for Effects of Hydraulic Fracturing

Every year, millions of taxpayers’ dollars are spent maintaining roads. The money is used to repair damage that occurs to pavements, bridges, and other elements of the roadway system. The service life of a pavement can be greatly reduced by unexpected heavy loading, which is one consequence of hydraulic fracturing (fracking) activity in rural areas. This paper describes a tool that can potentially lengthen the service life of pavements, especially thin pavement structures, by predicting unusually heavy loading. Predicting activities that cause increased truck loading can help agencies plan preventive measures to reinforce pavement structures before they fail. The goal of this study was to develop a tool, an early warning system (EWS), that can help to predict locations where damage from heavy truck traffic will occur. Truck travel related to the oil and gas industry is predictable and has recently had significant effects on pavement deterioration. The study focused on well permitting activity in the Austin, Texas, Department of Transportation district. ArcGIS software was used to find route assignments by using trip origins and destinations for fracking activity, truck volume, and vehicle weights. Several road segments that would be at risk for heavy loading and shortened service life were successfully identified. This tool can provide information needed to prioritize proactive pavement maintenance for more effective use of tax dollars. This tool could potentially also be used to determine a roughly proportional cost of damage from fracking activity to be levied on the oil and gas industry, thus alleviating the burden on taxpayers.

A Comparison of Uniform and 3-D Tyre Contact Pressure Representations Using a Finite Element Method

In pavement engineering a crude uniform contact pressure over a circular contact area is used to generate key strains for an analytical design method. The use of a more advanced tyre contact pressure measurement device has led to a situation where there is more information that is available to generate a more accurate uniform representation of contact pressure. This measurement device also offers the ability to measure non-uniform 3-D tyre contact pressure. That is to say the vertical, transverse and longitudinal components of pressure generated by a tyre in contact with a pavement. A comparison of the key strains generated by this improved uniform contact pressure representation and the measured 3-D contact pressure is of great interest. Of course a tyre does not display the same contact pressure for different combinations of axle loading and inflation pressure. The combination of these two factors greatly affects the nature of the contact pressure observed. A finite element mesh of a 3-layer thin pavement structure was created in CAPA-3D. This was used to model the uniform and 3-D contact pressure representations of a wide based tyre. This was done for 3 inflation pressures and 3 tyre loads. The inflation pressures were for a recommended inflation pressure and then plus and minus 200kPa. The tyre loading was for a maximum European axle loading and then greater and lower than this value. This gave a good spread of conditions that are relevant to the tyre operating conditions. The key strains at different locations in the pavement relevant to the major distresses of a pavement were assessed. The main distress mechanisms being top down cracking, asphalt cracking/rutting, traditional bottom up cracking and subgrade rutting. These gave a good spread of possible distresses that tyre contact pressure can contribute to. The results showed that there was a large effect on surface strains caused by 3-D contact pressure in comparison to uniform contact pressure for all combinations of inflation pressure and tyre loading. The difference between the two contact pressure representations diminished with depth in the pavement. Therefore, it was clear that 3-D contact pressure has an effect on the distress of a pavement surface. This means to accurately understand the deterioration of a pavement surface, 3-D contact pressure must be considered. In the case of the other distresses the uniform contact pressure generated greater strains and would give a conservative pavement design. Both methods generated greatly different key strains depending on the combination of inflation pressure and tyre loading. If a complex highly accurate analysis is required, then a fully 3-D representation in combination with finite element analysis is the best option. However, if a more routine analysis is required then the improved uniform contact pressure representation could be used with a simple modelling tool (e.g. BISAR) to get good results for a traditional analytical design.

On Forecasting the Resilient Modulus from the CBR Value of Granular Bases

ABSTRACT The unbound granular materials (UGM), base and subbase layers, play an essential role in the overall structural performance of thin pavement structures. They show complex stress dependent elasto-plastic behaviour under external loading. Therefore the UGM are commonly tested using the Repeated Load Triaxial (RLT) testing method to estimate the stiffness of the material by applying haversine loading pulses. The RLT testing method represents the actual stress situation quite adequately and gives satisfactorily estimates of the stiffness characteristics of UGM. A simple test that has been used for a long time in structural design of flexible pavements is the CBR (California Bearing Ratio) test. In the CBR test, the load-deformation curve is acquired while a plunger is penetrated into the material at a constant rate. In the literature one can find a number of relationships for UGM where the CBR value is used to predict the stiffness. These connections usually do not take into account that stiffness of UGM is both stress and moisture dependent. To investigate if a relationship between the two tests exists, twenty materials have been tested with both methods and the test results compared. The materials were of varying quality and were tested at four different moisture contents. The results indicate that a simple power law can be used to forecast the stiffness if the CBR-value is known.

On Forecasting the Resilient Modulus from the CBR Value of Granular Bases

ABSTRACT The unbound granular materials (UGM), base and subbase layers, play an essential role in the overall structural performance of thin pavement structures. They show complex stress dependent elasto-plastic behaviour under external loading. Therefore the UGM are commonly tested using the Repeated Load Triaxial (RLT) testing method to estimate the stiffness of the material by applying haversine loading pulses. The RLT testing method represents the actual stress situation quite adequately and gives satisfactorily estimates of the stiffness characteristics of UGM. A simple test that has been used for a long time in structural design of flexible pavements is the CBR (California Bearing Ratio) test. In the CBR test, the load-deformation curve is acquired while a plunger is penetrated into the material at a constant rate. In the literature one can find a number of relationships for UGM where the CBR value is used to predict the stiffness. These connections usually do not take into account that stiffness of UGM is both stress and moisture dependent. To investigate if a relationship between the two tests exists, twenty materials have been tested with both methods and the test results compared. The materials were of varying quality and were tested at four different moisture contents. The results indicate that a simple power law can be used to forecast the stiffness if the CBR-value is known.

Analytical Study of Effects of Truck Tire Pressure on Pavements with Measured Tire–Pavement Contact Stress Data

Truck tire inflation pressure plays an important role in the tire–pavement interaction process. As a conventional approximation method in many pavement studies, tire–pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and to be simply equal to the tire pressure. However, recent studies have demonstrated that the tire–pavement contact stress is far from uniformly distributed. Measured tire–pavement contact stress data were input into an elastic multilayer pavement analysis program to compute pavement immediate responses. Two asphalt concrete pavement structures, a thick pavement and a thin pavement, were investigated. Major pavement responses at locations in the pavement structures were computed with the measured tire–pavement contact stress data and were compared with the conventional method. The computation results showed that the conventional method tends to underestimate pavement responses at low tire pressures and to overestimate pavement responses at high tire pressures. A two-way analysis of variance model was used to compare the pavement responses to identify the effects of truck tire pressure on immediate pavement responses. Statistical analysis found that tire pressure was significantly related to tensile strains at the bottom of the asphalt concrete layer and stresses near the pavement surface for both the thick and thin pavement structures. However, tire pressure effects on vertical strain at the top of the subgrade were minor, especially in the thick pavement.

Analysis of the wavelength content of the longitudinal profiles for C-LTPP test sections

A new approach for pavement longitudinal profile analysis is described in this paper. In this approach, based on a simple moving average filtering technique, the results are expressed in terms of the proportion of the calculated international roughness index associated with different wavelengths of pavement surface deformations. The new approach has been successfully used in the assessment of the performance of Canadian Long-Term Pavement Performance (C-LTPP) test sites. The proposed analysis approach can help in identifying the source of problems causing pavement roughness. It can thus help in identifying the proper pavement rehabilitation technique. The new analysis approach has also helped in assessing the performance of the different rehabilitation techniques used in C-LTPP. It was found that 80–130 mm thick overlays give the best results in reducing roughness associated with short wavelength deformations. The benefit of these overlays is, however, limited to several years. Moreover, overlays do not have any significant impact on long wavelength deformations. It has also been found that long wavelength distortions tend to dominate the longitudinal profiles of thin pavement structures or pavements built on soft fine grained soils. Short wavelength distortions are dominant in longitudinal profiles of cracked thick pavement structures or that are built on strong soils.Key words: pavement, performance, longitudinal profile, wavelength, IRI, roughness, deformations.

Areawide Performance-Based Rehabilitation and Maintenance Contracts for Low-Volume Roads

To address internal inefficiency and accountability issues, a number of Latin American countries have moved decisively and successfully over the last decade from force-account (direct labor) to contract maintenance. Also, there has been considerable progress in the region in transferring to the private sector, through concessions, the responsibility for improving, maintaining, and operating high-traffic-volume roads, the cost of which is recovered from tolls. Argentina, Brazil, and Chile are among the most advanced countries in this respect. More recently, some countries—particularly Argentina—have switched from the traditional quantities and unit price–based short-term maintenance contracts to long-term performance-type or results-based contracts. The new approach encompasses either routine maintenance activities alone or integrated contracts involving both the rehabilitation and routine maintenance of road networks. The latter form, the so-called CREMA system (Contrato de Recu-peración y Mantenimiento), is now being implemented in Argentina and covers approximately 12 000 km (i.e., about 40 percent of the national paved road network). Such contracts comprise the rehabilitation and subsequent maintenance over a 5-year period of 200-km- to 300-km-long subnetworks. A framework for extending the CREMA concept to low-volume roads is presented. The means by which this newly developed system could be extended to cover both the paving and future maintenance of low-volume roads is explained. Reasons are analyzed as to why this type of contract, which extends the contractor’s share of responsibility over a relatively long period of time, would be well suited to the specific design and construction features of low-cost, low-volume paved roads—in particular, in the risks related to uncertain traffic projections and in the use of local or nontraditional materials in thin pavement structures. Finally, issues related to the use of the CREMA system—especially the need to prepare adequate contract bidding documents, conduct proper bid proposal evaluations, and monitor contractor’s performance during the rehabilitation/paving and maintenance phases—are explored.

Long-Term Oven-Aging Effects on Fatigue and Initial Stiffness of Asphalt Concrete

An investigation of the effects of long-term oven aging (LTOA) on initial stiffness and fatigue of asphalt concrete was made using two typical California asphalts, known to have different aging characteristics, in mixes with one aggregate. Asphalt content, air-voids content, and days of LTOA were varied independently. Stiffness and fatigue were evaluated using the controlled-strain flexural beam test developed by the Strategic Highway Research Program Project A-003A. The results indicated that both mixes exhibited an increase in initial stiffness with LTOA periods of up to six days. The sensitivity of beam fatigue life to LTOA depended on the asphalt. Beams containing Valley asphalt had virtually no change in fatigue life due to LTOA, whereas beams with Coastal asphalt showed some sensitivity to LTOA. For both asphalts, the average reduction in fatigue life from 6 days of LTOA was less than that caused by a 3 percent increase in air-void content or a 1 percent decrease in asphalt content. Simulations of thick and thin pavement structures were performed to reconcile the effects of LTOA, asphalt content, and air-void content on mix fatigue life and stiffness by evaluating their combined effects on predicted pavement fatigue life. The simulations indicated that aging, as induced by LTOA, increased fatigue life for all cases except one.