Deflectometer Research Articles

Moving Wheel versus Impact Deflections and Their Use in Pavement Evaluation

Traffic speed deflection devices (TSDDs) have been developed since around 2000 to allow for safe and efficient structural evaluation of highway networks. One barrier to TSDD implementation is the inherent differences in deflections produced by moving truck loads and by falling weight deflectometer (FWD), the current deflection testing standard. To better understand the differences in data produced by the two devices, FHWA sponsored research into one particular TSDD, the rolling wheel deflectometer (RWD). The study utilized the finite layer program ViscoWave to model both FWD and RWD loads to demonstrate the effect of their inherent differences on pavement deflections and other simulated parameters. In addition, ViscoWave was used to generate theoretical FWD and RWD deflections for a diverse set of pavement structures and subgrade conditions. The resulting deflections were used to develop correlations between the two devices, which were validated with side-by-side FWD and RWD field tests performed on 23 sites. The research determined that the differences between FWD and RWD deflections vary depending on pavement factors and loading characteristics. The two devices produced similar deflections on thicker, stiffer, lower-deflection pavements, while the FWD produced relatively higher deflections on thinner, weaker, higher-deflection pavements. Therefore, use of common FWD data analysis programs will produce different results, such as layer moduli, for TSDD devices. Advanced analysis routines capable of modeling the TSDD’s moving load and loading configurations are needed.

Influence of Geocomposite Properties on the Crack Propagation and Interlayer Bonding of Asphalt Pavements.

The application of geocomposites as reinforcement in asphalt pavements is a promising solution for the maintenance/rehabilitation of existing pavements and for the construction of new pavements, whose effectiveness strongly depends on the physical and mechanical properties of the geocomposite. This study aims at assessing the influence of four different geocomposites, obtained by combining a reinforcing geosynthetic with a bituminous membrane, on the crack propagation and interlayer bonding of asphalt pavements. First, a laboratory investigation was carried out on double-layered asphalt specimens. The crack propagation resistance under static and dynamic loads was investigated through three-point bending tests (carried out on specimens with and without notch) and reflective cracking tests respectively, whereas the interlayer shear strength was evaluated through Leutner tests. Then, a trial section was constructed along an Italian motorway and a Falling Weight Deflectometer (FWD) testing campaign was carried out. The laboratory investigation highlighted that—as compared to the unreinforced system—the geocomposites increased the crack propagation energy in the layer above the reinforcement from five to ten times, indicating that they can significantly extend the service life of the pavement by delaying bottom-up and reflective cracking. However, they also worsened the interlayer bonding between the asphalt layers (de-bonding effect). The field investigation indicated that all geocomposites decreased the stiffness of the asphalt layers with respect to the unreinforced pavement as a consequence of the de-bonding effect, thus corroborating the laboratory results. Based on the results obtained, it is desirable that the geocomposite possess a high energy dissipation capability and an upper coating ensuring good adhesion between the asphalt layers. The monitoring of the existing trial section in the future will provide useful data on the long-term field performance of reinforced pavements subjected to actual motorway traffic.

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.

In-vitro Functionality of Clozapine Biphasic Release Minitablet Using Advanced Statistical Tools

Background: The better control of the drug release with immediate effect is the major concern to achieve better therapeutic action and patient compliance. The failure of the solid dispersion complex during storage as well as in-vivo is another concern for the oral solid dosage form. Objective: The prime objective of the present study was to optimize the biphasic minitablet incorporating quality by design approach using the combination of waxy erodible and water-impermeable excipients. Exploration of Soluplus as a precipitation inhibitor and Dexolve as a solubility enhancer in oral solid dosage form was the secondary objective. Methods: The drug-Excipient compatibility study was assessed by FTIR. Clozapine was chosen as a model drug that has poor aqueous solubility. The complex was formulated using B-cyclodextrin or HP B-CD or Dexolve by kneading method. The screening of solubility enhancers and their amount were performed based on phase solubility study. The precipitation inhibitor was screened as per the parachute effect study. Immediate release minitablets were formulated using a direct compression method using different disintegrating agents. The IR minitablets were evaluated for different evaluation parameters. The sustained release minitablets were formulated by hot-melt granulation technique incorporating the Precirol ATO 5 as a waxy excipient and ethyl cellulose as water impermeable excipient. The SR minitablet was optimized using a central composite design. The amount of Precirol ATO 5 and ethyl cellulose were chosen as independent variables and % drug release at 1, 6, and 10 h was selected as responses. The designed batches were evaluated for different pre and post-compressional parameters. The IR and SR minitablets were filled in a capsule as per dose requirement and evaluated for in-vitro drug release. The in-vivo plasma concentration was predicted using the Back calculation of the Wagner - Nelson approach. Results: Drug - Excipient study revealed that no significant interaction was observed. Dexolve was screened as a solubility enhancer for the improvement of the solubility of clozapine. The Soluplus was chosen as a precipitation inhibitor from the parachute effect study. The immediate-release tablet was formulated using Prosolv EASYtab SP which yielded less disintegration time with better flowability. The sustained release mini-tablet was formulated using Precirol ATO 5 and ethyl cellulose. Two-dimensional and three-dimensional plots revealed significant effect of the amount of Precirol ATO 5 and ethyl cellulose. The overlay plot locates the optimized region. The in-vitro drug release study revealed the desired drug release of the final combined formulation. The in-vivo plasma concentration-time confirms the drug release up to 12h. Conclusion: The biphasic mini-tablets were formulated successfully for better control of drug release leads to high patient compliance. The use of soluplus as a precipitation inhibitor is explored in the oral solid dosage form for a poorly aqueous drug. Prosolv EASYtab SP was incorporated in the formulation as super disintegrant. The amount of Precirol ATO 5 and ethyl cellulose significantly affected drug release in sustained-release minitablet. The approach can be useful in the industry.

Influence of bonding condition between layers on overlay design of flexible pavements

The interface bonding conditions between the pavement layers is one of the main factors influencing the performance of the pavement structure. The present paper analyzes the effects of the interface conditions between the layers on the process of overlay design in flexible pavements. The data were collected by deflection testing using Falling Weight Deflectometer (FWD) and by drilling cores. Simulations were performed in the software BackMeDiNa, MeDiNa and AEMC for three different conditions of interface between the layers. The data of backcalculated moduli, overlay thicknesses, cracked area and fatigue damage were compared under different bonding conditions. In most of the simulations, backcalculated moduli in the de-bonding condition were higher than ones in the full-bonding between the layers. For the overlay design, the modular sets obtained from the different interface conditions led a slight difference in the thickness of the new asphalt layer (reinforcement), but with higher percentages of cracked area for the structures with full-bonding condition. In the analysis of the fatigue damage, the results showed that the damage obtained with the full-bonding layers was higher than that one obtained with de-bonding interfaces and the bonding between the surface and base layers.

Stiffness evaluation of compacted geo-materials using crosshole-type dynamic cone penetrometer (CDP), rPLT, and LFWD

Evaluation of the strength and stiffness of compacted geo-materials is required to ensure that it has sufficient bearing capacity and stiffness to the acting loads. In this study, a crosshole-type dynamic cone penetrometer (CDP) was applied to investigate the strength and stiffness characteristics of a compacted subgrade. The CDP characterizes the subgrade strength by the penetration index (CDPI) and evaluates the stiffness by the shear wave velocity (Vs) and maximum shear modulus (Gmax). CDP tests were conducted at three testing points. Repetitive plate loading tests (rPLTs) and light falling weight deflectometer (LFWD) tests were conducted as standard testing methods for the stiffness estimation of the subgrade. Experimental results show that while the rPLT and LFWD evaluate the equivalent elastic moduli (Ev1, Ev2, and Evd) within the influence zone, the CDP provides the CDPI, Vs, and Gmax along the depth. Linear relationships between the Gmax and the equivalent elastic moduli are constructed. The strain levels corresponding to Ev1, Ev2, and Evd are estimated. This study demonstrates that the CDP is an effective testing method for both strength and stiffness evaluations of the subgrade along the depth.

Parametric study to investigate the deflection and stress behaviour of Interlocking Concrete Block Pavement

Interlocking Concrete Block pavement (ICBP) is a prominent pavement type that is extensively used in low and high traffic areas. The objective of the present study is to analyse the influence of the block shape, block thickness and block laying pattern in the deflection behaviour of Interlocking Concrete Block Pavement (ICBP) using repetitive and nonrepetitive static plate load tests. Linear Variable Differential Transformer (LVDT) and pressure cells were utilised to study the deflection and vertical stress of the pavement section. Also, non-destructive portable devices, namely Light Weight Deflectometer (LWD) and geogauge were used to measure the deflection and modulus values of the prepared test sections. The optimisation of the most influential parameters was performed using design expert software. It was observed that the lowest deflection is experienced by the ICBP section of 120 mm block thickness, zigzag shape laid in herringbone laying pattern.

Influence of seasonal and diurnal FWD measurements on deflection-based parameters for rigid pavements

ABSTRACT Seasonal and diurnal variations can significantly impact Falling Weight Deflectometer (FWD) measurements and, thus, any deflection-based parameter such as slab elastic modulus (Epcc ), modulus of subgrade reaction (k), and load transfer efficiency (LTE). Also, general guidelines for the FWD measurements are needed to help agencies better interpret the derived parameters. Long-Term Pavement Performance (LTPP) Seasonal Monitoring Program (SMP) study data for Jointed Plain Concrete Pavements (JPCP) were analyzed. The results showed that seasonal and diurnal changes impact the derived parameters for the rigid pavements in different climatic regions. PCC slab’s upward curling and full contact with the underlying layer at lower temperatures resulted in higher Epcc and k-values and vice versa. Trends seen for k-values closely followed those for moduli values. Therefore, any guidelines concerning FWD testing should consider PCC layer temperature, which affects its shape at testing time. Also, LTE was found higher at elevated temperatures due to locked joints. Relating testing temperatures with observed trends of parameters helped determine general guidelines for FWD testing. The preferred temperature ranges for FWD testing are 55 to 70°F and 60 to 75ᵒF in freeze and non-freeze regions respectively; testing before noon is recommended in spring and fall seasons in all climates.

Assessment of pavement structure using multi-source data from a moving vehicle

In this paper we propose a novel method for assessing pavement structure based on multi-source data from a moving vehicle. The classification of pavement on subgrade (POS) and pavement on bridge deck (PBD) was used as examples. A mobile acquisition system was designed to collect multi-source data. Vehicle accelerations on PBD and POS were analyzed, and some features were selected to build 15 Support Vector Machine classifiers. Our results show that some features are helpful, including vehicle speed, maximum value, minimum value, standard deviation of acceleration in the time domain, and three peak frequencies in the frequency domain. The accuracy was 91.67%. Then, some sections were tested with a falling weight deflectometer to verify the structural differences between POS and PBD. Our results provide a novel method for analyzing pavement structure via vehicle vibration, and this work will be built on for more detailed analysis of pavement structure in the future.

Developing a distress-based traffic equivalency to efficiently evaluate the effect of traffic loads on pavement performance

ABSTRACT Traffic loading is considered one of the main factors contributing to pavement deterioration. Large illegal loads in the form of vehicles traveling with axle loads above the permissible legal limits and/or overall overweight magnify the traffic impact on the performance of pavements. These overloads contribute to the deterioration of pavement sections which leads to substantial maintenance and repair costs. This paper illustrates an example of an approach to determine the effect of both normal and overweight loads on the performance of rigid pavements using the Long-Term Pavement Performance (LTPP) traffic data. The traffic load was evaluated by estimating the legal and illegal ESALs related to both fatigue and erosion damage by visual observation and by field-assessment of the degree of bonding based using the Falling Weight Deflectometer (FWD). The illustrated example utilized LTPP data from nine Jointed Plain Concrete (JPC) pavement sites with different traffic mixes. This study reveals that the damage in JPC pavements could be either (i) visible by the formation of transverse cracking as would be related to fatigue related ESALs or/and (ii) invisible by the reduction of the effective thickness as would be related to erosion ESALs.

Field assessment of improvement in composite modulus of geosynthetic-reinforced pavements

A field study was carried out by constructing 15 test sections on Sahol-Kim state highway (city: Surat, India) using different geosynthetic materials and three control sections. The benefits of geosynthetic reinforcement were evaluated in terms of composite modulus obtained by Light Weight Deflectometer and field California Bearing Ratio tests of the granular layer. The effect of geosynthetic type, its properties, the location of the geosynthetic, infill material, and so on was investigated. The increase in the tensile strength of the geogrid had less effect on composite modulus improvement factor (CMIF) compared to the aperture size of the geogrid. The placement depth of the geogrid also had a strong influence on CMIF. Pavements with geocell-reinforced bases exhibited higher modulus improvement compared to geogrid-reinforced pavements. Geocell sections with wet mix macadam as an infill material exhibited better performance compared to those with fly ash as an infill material.

Soil stiffness as a function of dry density and the degree of saturation for compaction control

A data set of the coefficient of vertical subgrade reaction for a plate diameter of 30 cm, KP.FWD, measured by Portable Falling Weight Deflectometer tests in full-scale compaction tests on sandy soil using various types of compaction machines was analysed. Based on this analysis and the previous analysis of a CBR data set from another full-scale compaction test series, a set of conclusions could be drawn. The soil stiffness indexes (SSIs), CBR and KP.FWD, can be expressed by, respectively, an empirical equation multiplying a function of ρd and another of Sr, where CBR and KP.FWD decrease significantly as Sr increases. As such, ρd values cannot be estimated from SSI alone. By fixing the field ρd – w compaction curve by keeping the soil type and the field compaction energy level, CELf, to those in the field compaction tests in which the SSI – ρd – Sr correlation has been calibrated, field compacted ρd &w states can be estimated by measuring the SSI values. Then, by the upper-bound and lower-bound control of SSI, the field compacted states approach the specified target, where, typically, ρd = the maximum dry density for CELf and Sr = the optimum degree of saturation, (Sr)opt. A method to incorporate this indirect but fast SSI-based compaction control into the conventional ρd &w-based compaction control is proposed.

LEMaC-DE01/16: Methodology for determining effective structural contribution in unpaved roads using Light Weight Deflectometer (LWD) without geophones and back-calculation according to AASHTO93 Guide

LEMaC-DE01/16: Methodology for determining effective structural contribution in unpaved roads using Light Weight Deflectometer (LWD) without geophones and back-calculation according to AASHTO93 Guide

Determining the Rayleigh damping parameters of flexible pavements for finite element modeling

The dynamic analysis has been successfully used to predict the pavement response based on the finite element modeling, during which the stiffness and mass matrices have been established well, whereas the method to determine the damping matrix based on Rayleigh damping is still under development. This article presents a novel method to determine the two parameters of the Rayleigh damping for dynamic modeling in pavement engineering. Based on the idealized shear beam model, a more reasonable method to calculate natural frequencies of different layers is proposed, by which the global damping matrix of the road pavement can be assembled. The least squares method is simplified and used to calculate the frequency-independent damping. The best-fit Rayleigh damping is obtained by only determining the natural frequencies of the two modal. Finite element model and in-situ field test subjected by the same falling weight deflectometer pulse loads are performed to validate the accuracy of this method. Good agreements are noted between simulation and field in-situ results demonstrating that this method can provide a more accurate approach for future finite element modeling and back-calculation.

Impacts of Material Orthotropy on Mechanical Behaviors of Asphalt Pavements

Material anisotropy significantly impacts the mechanical behaviors of asphalt pavements. However, most current asphalt pavement design methods treat the material properties only as isotropic, which could significantly skew the mechanical behaviors. There is a need to evaluate the impact of material anisotropy on pavement mechanical behaviors. In this study, we first developed a new and efficient 3-dimensional finite element (FE) model of anisotropic material. Then, the feasibility of the proposed FE model was verified using field data collected with a falling weight deflectometer. Finally, using this model, the contributions of each layer anisotropy to the mechanical properties were determined. The results showed that the mechanical behaviors were more sensitive to the orthotropy than to the transverse isotropy of the material. The all-layer orthotropy was the most unfavorable combination. In addition, the subgrade orthotropy showed the most significant effect on increasing the surface deflection and compressive strain of the subgrade top (by about 10%). Based on the study results, we recommend that the homogeneity degree of the filling subgrade should be strictly controlled to ensure adequate pavement capacity and anti-rutting performance during construction.

Performance analysis of cement treated base layer by incorporating reclaimed asphalt pavement material and chemical stabilizer

Milling of an existing pavement after it's service life engenders massive production of reclaimed asphalt pavement material (RAPM), which may cause disposal issues. The current study highlights the sustainable valorization of RAPM in the cement-treated base (CTB) layer by incorporating chemical stabilizers by the full-depth reclamation (FDR) method. CTB mix was prepared in the laboratory by using 100% RAPM with varying cement and chemical admixture content. In order to identify the effect of different content of cement and chemical stabilizer on the laboratory measured different engineering properties of CTB mix were evaluated. Furthermore, to impart more insights on the laboratory-designed CTB mix under actual traffic conditions, the test track was also laid and being monitored by the durability properties of fields sample and falling weight deflectometer (FWD) analysis. Four cement contents of 3.5, 4.0, 4.5, and 5 percent and five chemical stabilizer contents of 0, 3.0, 3.5, 4.0, and 4.5 percent by weight of cement were added. From obtained data, it can be concluded that mix prepared with 4.5% cement and 4% chemical stabilizer provides the best result in terms of strength parameters and durability properties of studied samples. FWD data advocates that constructed pavement with a designed CTB layer imparts low fatigue behavior as compared with the performance criteria prescribed in Indian Roads Congress (IRC) guidelines. Our study accentuated that 100% recycling of RAPM in FDR technology can be a viable solution as the comprehensive cost analysis showed a 45% cost reduction for the proposed mix by incorporating studied materials.

Influence of high moisture content on road pavement structure: A Polish case study

Communication infrastructure is one of the most important criteria determining the comfort and quality of life in a given country, as well as an important indicator helping to determine the pace of its economical growth. The main objective accompanying the development of the road network is to ensure the required durability of the pavement structure. Undoubtedly, one of the factors that shorten the life of the road pavement and cause its premature damage is the increased moisture content in the pavement structure, in particular in unbound granular layers. The article presents a case study on the accelerated degradation of a section of state-importance road located in the southern part of Poland, where a problem of increased moisture content in the road pavement structure occured. The research part shows the results of measurements of the transverse evenness of the pavement, monitoring of the groundwater table level and measurements of pavement deflection using Falling Weight Deflectometer. The conducted research and observations showed that the pavement on the selected road section worked permanently in high moisture conditions, where the groundwater table stabilized at an average level of 30–60 cm below the pavement surface. During the observation period, an increase in the rut depth in the right wheel track was noticed, reaching a value of 3.2 mm. In addition a significant development of damage visible on the wearing course was observed. Based on the results of defelection measurements, a back-calculation analysis was performed, which allowed to obtain estimated resilient moduli values of subsequent pavement layers and the subsoil. Resilient moduli values of the unbound subbase and the bituminous layers were significantly lower than the expected values, which was related to the high moisture content in the road pavement structure.

Investigating the Performance of Geogrid Reinforced Unbound Layer Using Light Weight Deflectometer (LWD)

Investigating the Performance of Geogrid Reinforced Unbound Layer Using Light Weight Deflectometer (LWD)

Investigation of Mechanical and Hydrologic Characteristics of Porous Asphalt Pavement with a Geocell Composite.

Porous asphalt pavement is a part of the permeable pavement system, which can be used to mitigate the negative impacts of urbanisation on the water hydrological cycle and environment. This study aims to assess the mechanical and hydrologic characteristics of porous asphalt pavements, with and without geocell composites, using a plate load test, falling weight deflectometer test, and rainfall simulation test. The corresponding results indicate that the elastic modulus of the unreinforced pavement is lower than that of the reinforced pavement. The analysis demonstrates that the use of geocell composites effectively increases the load-bearing capacity of the pavement. When the base layer is reinforced with geocells, its load-bearing capacity increases. Observation of the rainfall simulation tests on the reinforced pavement indicates that the reinforced pavement effectively handles the surface runoff.

Comparison of the Bearing Capacity of Pavement Structures with Unbound and Cold Central-Plant Recycled Base Courses Based on FWD Data

Bearing capacity changes over the year, depending on the water content in a pavement structure: the higher the water content, the lower the bearing capacity. As expected, the highest water content in a pavement structure is observed in the early spring as the ice lenses melt. Thus, spring is a critical period for pavement performance, because a decrease in bearing capacity results in faster pavement deterioration. The bearing capacity of pavement structures with an unbound base course and the negative effect of spring thawing on pavement performance have been analyzed by a considerable number of researchers. However, very little is known about the bearing capacity of pavement structures with a cold-recycled base course despite the significantly increasing usage of cold-recycled mixtures. This paper focuses on the bearing capacity of both unbound and cold central-plant recycled base courses at different seasons and their stability. A cold central-plant recycled (CCPR) base course was constructed from a mixture of 38.8% reclaimed asphalt pavement (RAP), 3.1% foamed bitumen and 2.3% cement. A virgin aggregate was added to achieve desirable aggregate gradation. The bearing capacity of the unbound and CCPR base layers, as well as the whole pavement structure, was evaluated by back-calculated E moduli from falling weight deflectometer (FWD) data. In addition to this, the residual pavement life was calculated using mechanistic-empirical pavement design principles. The results showed that the durability of pavement structures with a CCPR base course is more than seven times lower compared to that of pavement structures with an unbound base course, irrespective of season. Nevertheless, the bearing capacity (surface modulus E0) of the pavement structure with a CCPR base course gradually increases due to the curing processes of bituminous and hydraulic binders (in this study, within four years of operation, it increased by 28–47%, depending on the side of the road).