Deflection Basin Parameters Research Articles

Structural condition assessment of asphalt pavement semi-Rigid bases using FWD deflection basin parameters

Assessing structural conditions of semi-rigid bases in asphalt pavements is essential for effective base treatment in reconstruction and expansion (R&E) projects. Although various falling weight deflectometer (FWD) parameters have been developed for this purpose, field-validated parameters are still missing. This study identifies the appropriate FWD deflection basin parameter (DBP) through sensitivity analysis, correlation examination, and on-site milling and inspection. Findings indicate D20-D60 as the most suitable DBP, with 23 µm and 40 µm thresholds for warning and severe conditions, respectively. The correlation between D20-D60 and cracking rate suggests that high cracking rates suggest base weakness, whereas low rates may not guarantee structural integrity due to maintenance masking effects. On-site milling further confirmed this finding, demonstrating the alignment between D20-D60 assessments and field observations. The outcome of this study is anticipated to provide a practical DBP for evaluating semi-rigid base conditions and to inform base treatment strategies in R&E projects.

Fatigue cracking prediction of cobblestone interlayer pavement using non-destructive testing and mechanistic-empirical analyses

Several non-destructive testing (NTD) methods have been used to measure surface deflection, which makes to determine the elastic moduli of pavement layers through the back-calculation process and assess the structural capacity of asphalt pavements. In this study was evaluated the back-calculated moduli of the cobblestone interlayer pavements and the load capacity of this type of pavement related to the fatigue cracking criterion based on a mechanistic-empirical analysis. The employed methodology included the performance of on-site trials using non-destructive testing with the Falling Weight Deflectometer (FWD) devices on 84 test points in granular and cobblestone interlayer pavements, determination of deflection basin parameters (DBP), back-calculation layers’ moduli, and estimate of the fatigue cracking performance of the pavements by mechanistic-empirical analyses in MeDiNa software. The pavements with a cobblestone base layer displayed greater deflection measurements on the load application point compared to those measured on pavements with a granular base layer, indicating that conventional pavement displayed more stiffness. Cobblestone interlayer pavement displayed greater amounts of cracked area compared to granular base layer pavements showing lower load capacity based on the fatigue criterion. The DBP-based method by FWD test was able to identify the structural differences between the layers of pavements evaluated and identify the cracking evolution.

Comparative Evaluation of Falling Weight Deflectometer, Traffic Speed Deflectometer and Rapid Pavement Tester in Deflection Measurement

This study intends to compare deflections obtained from traffic speed deflection devices (TSDDs) with the deflections of the falling weight deflectometer (FWD). For this purpose, deflections were measured on five sections of three roads in the Norwegian road network using traffic speed deflectometer (TSD) and rapid pavement tester (Raptor). Deflections were also measured using FWD at three different temperatures and the curves of FWD deflections versus temperature (FWD temperature-dependent deflection curves) were obtained. These curves were used to correct the effect of temperature difference. It was shown that both TSD and Raptor have the potential to detect structural deficiencies; however, TSD had better consistency with FWD with regard to deflection values and deflection basin parameters. A refinement was then made to make the Raptor data more consistent with FWD data. Calculating bearing capacity before and after refinement revealed that refining Raptor data can substantially increase the consistency between Raptor and FWD.

Relationship between deflection basin parameters and backcalculated pavement layer moduli

In the case analysed, a glass fibre mesh was applied under the asphalt layer during a rehabilitation treatment. Because only one lane was reinforced, the test section can be used to observe the influence of glass fibre mesh on the relationship between the selected deflection basin parameters (RoC, BLI, MLI, and LLI) and back-calculated pavement layer moduli. The FWD measures were used to determine the bowl of deflection indicators and to back-calculate the layer’s moduli. The values of DBP-s allowed confirmation of the technical condition of pavement construction. The first measures were carried out in 2019 and repeated in 2021; the results were then compared and analysed. Influence was observed on the relationship between the deflection basin and moduli, especially for the base course and subgrade. The reinforced lane showed a better coefficient of determination between DBPs and moduli in 2019, but in 2021 relationships were observed only for LLI and subgrade moduli. The unreinforced lane, however, showed the mentioned relationships in both 2019 and 2021. Because of a relatively small number of measurement points, the presented analyses and observations should be considered as preliminary. Presented results and relationships are another step into developing an alternative approach to determining the initial pavement moduli i.e. to use as a seed moduli.

Factor analysis evaluation of asphalt pavement performance considering structural strength and hidden cracks

At present, the maintenance work is mainly based on the performance of the asphalt pavement, but the structure distresses inside the pavement is easily overlooked. Therefore, in view of the shortcomings of the evaluation system, this study carried out road nondestructive testing, and obtained performance, deflection basin parameters, and structure distresses of the asphalt pavement and using factor analysis to extract common factors of all indicators, which considers evaluation of performance is more comprehensive and determining the weights according to the contribution rate makes the evaluation results more unbiased. Can provide some guidance for the determination of pavement maintenance time.

Evaluation of the influence of the glass fiber mesh on the deflection basin parameters of a flexible pavement located in the area of mining activity

Evaluation of the influence of the glass fiber mesh on the deflection basin parameters of a flexible pavement located in the area of mining activity

T-shaped arrangement of geophones for rapid quantification of asymmetric behaviour of concrete slabs in central FWD tests

ABSTRACT The assessment of asymmetric slab behaviour is out of reach in standard Falling Weight Deflectometer (FWD) tests, because deflections are measured along the driving direction only. Herein, a new T-shaped arrangement of the geophones is proposed. It allows for rapid quantification of asymmetric slab behaviour in central FWD testing of concrete slabs. One geophone is positioned at the centre of impact (= centre of the slab), six along the driving direction, one right and one left of the centre. The ‘Lateral Asymmetry Index (LASIX)’ is introduced as a corresponding dimensionless deflection basin parameter. Its value increases with increasing asymmetric behaviour of the slab. The main research challenge tackled herein is to optimise the radial distance of the lateral geophones from the centre of the slab, such as to maximise the expressiveness of LASIX for the quantification of asymmetric slab behaviour. In this context, FWD tests with measurement of deflections in eight different directions are carried out, and the ‘effective asymmetry index ( A 28 )’ is introduced as another new dimensionless deflection basin parameter. It summarises the asymmetric behaviour based on deflection differences quantified for all 28 pairs of directions which can be combined out of the eight available measurement directions. The optimal radial distance of the lateral geophones from the centre of the slab is found as 1.20 m. Corresponding values of LASIX larger than 8 % refer to coefficients of directional variation of the AREA7 parameter larger than 5%. This indicates directional degradation of the pavement structure resulting from eccentric traffic loads. T-shaped FWD testing requires in situ efforts equivalent to those of standard testing, while allowing for a rapid and reliable quantification of asymmetric behaviour. It allows for the assessment of whether the standard evaluation of uniform moduli of subgrade reaction is realistic or questionable.

Fast prediction of the mechanical response for layered pavement under instantaneous large impact based on random forest regression

The layered pavements usually exhibit complicated mechanical properties with the effect of complex material properties under external environment. In some cases, such as launching missiles or rockets, layered pavements are required to bear large impulse load. However, traditional methods cannot non-destructively and quickly detect the internal structural of pavements. Thus, accurate and fast prediction of the mechanical properties of layered pavements is of great importance and necessity. In recent years, machine learning has shown great superiority in solving nonlinear problems. In this work, we present a method of predicting the maximum deflection and damage factor of layered pavements under instantaneous large impact based on random forest regression with the deflection basin parameters obtained from falling weight deflection testing. The regression coefficient R 2 of testing datasets are above 0.94 in the process of predicting the elastic moduli of structural layers and mechanical responses, which indicates that the prediction results have great consistency with finite element simulation results. This paper provides a novel method for fast and accurate prediction of pavement mechanical responses under instantaneous large impact load using partial structural parameters of pavements, and has application potential in non-destructive evaluation of pavement structure.

Accuracy analysis of modulus results considering the whole process of modulus back-calculation—based on GPR and FWD

• The numerical hypothesis model was corrected by combining GPR and FWD. • The applicability of different regression models for deflection basins was clarified. • The sensitivity of modulus back-calculation results was analyzed. • The accuracy of the modulus back-calculation result has been significantly improved. In this study, based on the consideration of the whole process of modulus back-calculation, the measured deflection basins of asphalt pavements under dynamic loading were obtained by using the falling weight deflectometer (FWD), and the parameters such as thickness, initial modulus range, and Poisson's ratio of each structural layer in the numerical hypothesis model were corrected based on the detection results of the thickness and damage status of each structural layer by the ground-penetrating radar (GPR). At the same time, mathematical regression models such as the Exponential regression model, Parabolic regression model, and Sigmoid regression model were used to fit the theoretical deflection basin, and the accuracy of the relationship model between the deflection basin parameters and the pavement structural parameters constructed after fitting the theoretical deflection basin by different regression models were compared. It is observed that the change in the numerical hypothesis model and the regression model of the theoretical deflection basin can have a significant impact on the modulus back-calculation results. The research results show that when the numerical hypothesis model and the regression model are not corrected and optimized, the absolute value of the relative error between the back-calculation modulus and the dynamic modulus of the asphalt layer obtained in the laboratory test is 64 %. After correcting the numerical hypothesis model and fitting the deflection basin with the Sigmoid regression model, the relative error is within ±4 %. In summary, it is an important method to improve the accuracy of modulus back-calculation by correcting the numerical hypothesis model and optimizing the regression model of the deflection basin.

Assessment of asphalt pavement overall performance condition using functional indexes and FWD deflection basin parameters

Highway organizations need an accurate evaluation of the overall condition of the pavement to make appropriate maintenance decisions. However, existing specifications only consider functional performance and rarely involve structural performance, especially the contribution of the base and subgrade parts to the overall service condition of the pavement surface. Therefore, by introducing principal component analysis and technique for order preference by similarity to ideal solution, this paper proposes an overall pavement evaluation framework based on functional and structural performance indexes and applies it to the Hubei section of the Beijing-Hong Kong-Macao Expressway. Results show that the method can accurately evaluate the overall performance of alternative sections, and the degree of influence of various indicators on the overall service status of the pavement is also determined and discussed. Among them, D0 contributes the most, while D4 contributes the least. The proposed method can provide some basis for the determination of pavement maintenance time and mode.

Asserting the Applicability of Copper Slag and Fly Ash as Cemented Base Materials in Flexible Pavement from a Full-Scale Field Study

This research made innovative use of copper slag and fly ash in the construction of a cemented base course of flexible pavement. A full-scale field study evaluated the structural and functional performance of flexible pavement test sections constructed using various combinations of copper slag and fly ash (Class F or Class C) with and without lime. Various performance parameters, namely deflection basin parameters, dissipated energy, back-calculated elastic modulus, service life ratio, and roughness index, were evaluated for flexible pavement test sections constructed with 250-mm-thick conventional granular base [wet-mix macadam (WMM)], 150-mm- and 250-mm-thick copper slag–Class F fly ash–lime (CFL) (70% copper slag +23% Class F fly ash +7% lime) and copper slag–Class C fly ash (CCF) (40% copper slag +60% Class C fly ash) base layers. Falling weight deflectometer tests and bump integrator tests were performed in situ; laboratory tests, namely unconfined compression and resilient modulus tests, were performed on core samples. The average elastic moduli, back-calculated from six FWD tests conducted over 15 months after construction, for CCF and CFL base were 430 and 602 MPa, which are more than 3 times that of WMM. Significant waste utilization up to 1,348 tons of copper slag and 945 tons of fly ash per kilometer length of road can be achieved by using CCF and CFL mixes in base layers of flexible pavement with a service life ratio as high as 1.78 and cost efficiency of 17.4%.

Field investigation and numerical analysis of an inverted pavement system in Tennessee, USA

Inverted pavement system has been introduced for many years with field investigations, laboratory studies and numerical simulation works. Field investigations of inverted pavement structures have not been widely conducted and are very limited in the USA. This study presents a comprehensive field study on a full-scale inverted pavement as well as a conventional control pavement section constructed in Tennessee, USA. A combination of multiple non-destructive testing (NDT) methods, including ground penetration radar (GPR), Benkelman beam test, 3D road profiling test by laser crack measurement system (LCMS), and falling weight deflectometer (FWD) tests were utilized to assess the actual thickness, structural capacity and surface conditions of the pavement structures. The road surface profiling test results showed that the inverted pavement outperformed the conventional section in roughness, cracking and rutting conditions. Deflection Basin Parameters (DBPs) such as surface curvature index (SCI), base damage index (BDI), base curvature index (BCI) and W7 (7th sensor’s value of FWD) values were compared to study the layers’ condition of the inverted and conventional pavement sections. In addition, a preliminary simulation analysis by a Finite Element Method (FEM) model was conducted to compare the performance of inverted and conventional pavement sections under FWD load. The simulation results showed that the inverted pavement structure could reduce the potential of crack initiation and propagation due to smaller tensile stress at the bottom of the asphalt concrete layer (AC). Also, the smaller deflection was measured at the top of subgrade soil (SG), which reduced the total deflection of the inverted pavement structure. Furthermore, the cement-treated base (CTB)-constrained unbound aggregate base (UAB) acted as a cushion to relieve the tension from CTB and support the AC layer. The stress-dependent property of UAB in the inverted pavement contributed to the performance and ductility of inverted pavement but had little influence on the conventional pavement.

Evaluation of inverted pavement by structural condition indicators from falling weight deflectometer

Inverted pavement has been a potential alternative to the conventional flexible pavement structure due to its cost-efficient usage of asphalt, comparable performance and durability. For increasing utilization of the inverted pavements, appropriate structural evaluation is necessary. The Falling Weight Deflectometer (FWD) test has been widely accepted for evaluating the structural condition of conventional pavements through pavement deflection basin parameters (DBPs). As a special type of pavement, inverted pavement relies on the stress-dependence of the unbound stone interlayer to withstand the heavy traffic loads, which typically affects a relatively larger pavement area. So far, there have been few systematic studies on the effectiveness of utilizing FWD to evaluate the structural conditions of inverted pavements. This study used a DBPs-based inverted pavement structure assessment system to assess an inverted pavement constructed in Georgia, USA. A nonlinear stress-dependent finite element model of the inverted pavement coupled with the impulse loading mode was built to simulate the realistic FWD loading process and investigate the effect of layer stiffness on the DBPs evaluation system. Furthermore, a full-scale inverted pavement section in Knoxville, TN, USA, was tested by the FWD method to obtain the corresponding deflection basin parameters. The DBPs data were used to evaluate this practical inverted pavement project based on the aforementioned DBPs-based assessment system. The analysis results show that the DBPs-based pavement evaluation method can provide a quick and comprehensive assessment for each layer in the inverted pavement structure without knowing the detailed properties of the layers. The evaluation results were consistent with the data from the testing vehicle equipped with the laser crack measurement system. Thus, the DBPs-based evaluation system is a promising method to assess the condition of the inverted pavement structures, contributing to the Inverted Pavement Management System (IPMS).

Prediction of critical responses in full-depth asphalt pavements using the falling weight deflectometer deflection basin parameters

Even though critical strain is the most reliable parameter for evaluating pavement structural conditions, it is difficult to regularly measure for in-service pavements. This study conducted finite element analyses to develop critical strain prediction models for full-depth asphalt pavements using the falling weight deflectometer deflection basin parameters. The parameters “area under pavement profile” and “base damage index” are shown to correlate well with critical strains and are used as input parameters. The developed models accurately predict critical strains, which can be incorporated into pavement management system to estimate the current pavement structural conditions, in terms of cracking and rutting.

Predicting equations for determining layer elastic moduli by using Deflection Basin Parameters (DBPs) from Falling Weight Deflectometer

ABSTRACT This paper presents models that correlate deflection basin parameters (DBP) with seed moduli, which are the input of the backcalculation processes. The models were obtained by means of statistical analyses of a set of DBPs for different pavement structures. The proposed equations showed potential and increased accuracy in the estimation of seed moduli, since these are derived from DBP-based models that consider the deflection basin geometry. To evaluate the effectiveness of the models, they were applied to pavements located in five regions of Brazil, and a good approximation between the values of the seed and backcalculated moduli was observed. Therefore, there was less computational effort in the backcalculation process, since the closeness between the values of the moduli reduced the amount of iterations required. In pavements with different structures and boundary conditions, the methodology can be used to achieve more refined results.

Investigations on development of early distresses on bituminous pavement in India and remedies

In the present study, reasons for early distresses noticed on the bituminous pavement of a four-lane divided highway between the Pardi and Agrasen sections of National Highway 6 from km 498.000 to km 544.000, in India, were investigated. The total length of the road project is 46 km. A detailed pavement condition mapping was carried out, and various distresses were noticed on the surface. To assess the reasons for the distresses, combined cores of the bitumen surface course and the base course were taken from 57 locations, 29 on the left-hand side and 28 on the right-hand side of the carriageway, and mix properties were evaluated in the laboratory. The investigation on the mixes revealed that bituminous cores collected from both the surface course and binder course have no resemblance to the job mix formula. Non-homogeneity of layer thicknesses, variation in mix properties, variation in aggregate gradation and high filler–binder ratios were observed. Aside from the laboratory investigation, the physical condition of bitumen cores was studied and the conditions of the pavement layers were assessed based on the deflection basin parameters. This paper presents a systematic procedure adopted for identifying the causes of early distresses, and appropriate treatments are suggested for rectification.

Structural Performance of Sections Treated with Thin Overlays for Pavement Preservation

Over the last decades, increased efforts have been made to identify cost-effective alternatives to achieve a longer pavement life by applying preservation treatments. The application of thin overlays to restore the surface condition of the pavement is widely practiced across the United States. Benefits include a long service life, a better riding surface, reduced noise, grade and slope geometry preservation, recyclability, and fewer maintenance regimes. Although thin overlays can provide significant improvements in both the immediate and long-term functional performance of the pavement, there is little information on how these treatments affect the structural performance of pavements. Although not expected to significantly improve structural capacity, thin overlays may be able to maintain a structurally sound pavement in good condition for longer. The objective of this study was to evaluate the structural performance of pavements treated with thin overlays as a preservation technique. To accomplish this objective, falling weight deflectometer and field performance data from six full-scale thin overlay test sections and a control section with high cracking were collected and analyzed over a period of nearly 8 years. The results indicated that, based on deflection basin parameters (DBPs), the treated sections had better performance and were projected to reach the “warning” zone much later than the untreated sections. The observed surface condition correlated well with these parameters as, in general, sections with higher DBPs also exhibited more cracking and rutting. The test sections continue to be monitored to fully quantify the extent of the structural benefit obtained from the treatments.

Prediction of asphalt pavement condition using FWD deflection basin parameters and artificial neural networks

Applications of non-destructive testing devices such as Falling Weight Deflectometer (FWD) provide crucial estimates of pavement health that assist in the optimisation of pavement management systems. However, regularly conducting these tests at a network level and post-processing of the collected data is cumbersome, which requires technical expertise, significant time, funds, and other resources. Due to this structural aspect of pavements during the selection of maintenance or repair, decisions are often ignored. This study attempts to develop reliable correlations for estimates of two different deflection basin parameters using a number of structural, functional, environmental, and subgrade soil attributes as input. The data has been obtained through field tests over a 124 km long pavement network. Different artificial neural network-based models are trained by varying the number of hidden layers and neurons in these layers, for the above-mentioned purpose. The coefficient of determination and mean square error is decisive for the selection of best network architecture. These outcomes are also compared to the results of the classical multiple linear regression method, and the superiority of neural networks over non-intelligent approaches for non-linear problems of pavement engineering is appreciated. In addition to this, the results justify the fact that the properties of the asphalt layer predominantly impact the entire pavement condition. The proposed approach is an alternative way to facilitate quick pavement condition assessment by reducing the frequency of deflection testing without compromising with the accuracy of its estimates. It would encourage the increased application of structural condition data in pavement maintenance and rehabilitation necessities with ease. However, the study does not intend to completely avoid conducting deflection testing and serve as a base for future studies.

Mechanistic Analyses and Modeling of Pavement Sections Utilizing Sustainable Aggregate Quarry By-Product Applications

This paper presents a modeling study based on finite element (FE) analysis to mechanistically evaluate flexible pavements constructed with quarry by-products (QB). Twelve pavement test sections, a control section, and 11 others incorporating QB as unbound subgrade replacement and chemically stabilized base/subbase applications were evaluated for field performance using accelerated pavement testing (APT). First, falling weight deflectometer (FWD) deflection basin parameters were calculated and compared with critical pavement responses to evaluate the structural adequacies of the QB pavement sections. The moduli of the constructed pavement layers were then backcalculated from the FWD deflections using the GT-PAVE FE analysis program with nonlinear and cross-anisotropic layer characterizations. For stabilized QB applications, the layer properties calculated from this analysis for the base/subbase layers were used to calculate critical pavement responses. The sections were compared using a response benefit parameter, defined as the ratio of maximum resilient surface deflection in a conventional pavement, as the control section, to that obtained for each section having a certain QB application in consideration. According to the results obtained from the APT sections and the mechanistic FE analyses, the measured and calculated FWD deflection basins were successfully matched with individual sensor errors not exceeding 5% for all 12 test sections. The calculated response benefits indicated significant advantages for using cement-stabilized QB applications over fly ash-stabilized QB applications and conventional flexible pavement sections. Considering the pavement structural response benefits and good performance trends observed, major cost benefits can be realized by routine use of these sustainable QB applications.

Using FWD deflection basin parameters for network-level assessment of flexible pavements

ABSTRACT Decisions regarding the selection and implementation of appropriate pavement rehabilitation methods is usually based on pavement functional and structural condition data. Visual distress surveys and Falling Weight Deflectometer (FWD) testing are often carried out by agencies as parts of their pavement preservation programmes. Although backcalculation of individual layer moduli from FWD data is a common approach to assess a pavement’s structural condition, the accuracy of this approach is largely dependent on exact estimates of individual layer thicknesses. Coring operations to determine pavement layer thicknesses require significant time and resource commitments, and hence cannot always be accommodated within an agencies’ operational constraints. Accordingly, alternative analysis methods to assess the pavement’s structural condition from FWD data are often desired. An ongoing research study at Boise State University is focusing on combined usage of pavement structural and functional evaluation data for making pavement rehabilitation decisions. Considering the lack of pavement layer thickness information for all locations, this study is using Deflection Basin Parameters (DBPs) calculated from FWD test data to make inferences regarding the structural condition of individual pavement layers. This manuscript presents findings from this study, and establishes DBPs as reasonable alternatives to be used in network-level pavement condition evaluation practices. The adequacy of DBPs to assess the structural condition of individual pavement layers was first assessed through Finite-Element Modelling. A series of analyses were performed by assigning typical modulus values to individual pavement layers, and the corresponding DBPs were calculated. The calculated DBP values mostly fell within typical ranges specified in the literature for different layer conditions. Once the DBPs were established as adequate alternatives for making network-level pavement assessment decisions, four selected pavement sections in the state of Idaho were analyzed based on this method, and the results were compared against those obtained from visual distress assessment routines.