Review of Lightweight Deflectometer for Routine in Situ Assessment of Pavement Material Stiffness (original) (raw)
Related papers
Lightweight deflectometers for quality assurance in road construction
Proceedings of the 8th International Conference (BCR2A'09), June 29 - July 2 2009, Unversity of Illinois at Urbana - Champaign, Champaign, Illinois, USA, 2009
The use of Lightweight Deflectometers (termed LWDs in Europe, and occasionally PFWDs in the USA) for construction quality control or material investigation for road construction has increased worldwide. In the UK the change in pavement foundation design to a 'performance based approach' has brought about the use of Lightweight Deflectometers for field assessment of stiffness modulus. This paper reviews the LWD as a field evaluation tool. It discusses in some detail the test variables that can influence and affect the field data quality, and presents brief summaries of recent fieldwork where an LWD has been used as a quality control tool. The paper concludes both on the LWD usefulness and also its limitations for a variety of earthwork and road assessment scenarios, and describes a field test protocol for its use on a variety of materials. The findings demonstrate the flexibility of the LWD but also show that its determination of 'stiffness modulus' may differ from that of the conventional Falling Weight Deflectometer (FWD) to a varying extent. The paper provides a useful reference document for LWD users, consultants, material specifiers, contractors and clients.
Young’s Modulus and Deflection Assessment on Pavement Using a Lightweight Deflectometer
International Journal of GEOMATE, 2021
This research implemented direct assessment in the field on road structures using the Light Weight Deflectometer (LWD) method. This method is similar to the Falling Weight Deflectometer (FWD) method. The LWD method uses a lower loads compared to the FWD method. LWD method was chosen because the equipment is quite portable and straightforward allowing it to be used directly in the field, making inspection easier. The LWD method is more suitable for assessing the pavement conditions in which the volume of road use is not too high. This study aims to determine the value of the road structure conditions based on material properties. The location of the survey was Kupang City, East Nusa Tenggara, and Indonesia. The number of test points is 77 main points, with each point consisting of several tests. The test results obtained in this study are the value of deflection and modulus of elasticity at each test point. In addition, a radius of curvature analysis was carried out to determine the base of the pavement structure conditions. LWD testing by giving a load on the surface of the pavement was found to predict the base conditions of the road structure. This study also analyzes the EFWD conversion value from the ELWD test results and the correlation between these methods is presented.
Road Materials and Pavement Design
The traditional methods of evaluating the compaction quality of pavement subbase and subgrade construction require considerable time and resources. Therefore, there is a need for a safe, reliable, rapid, and cost-effective field measurement technique for compaction testing of unbound pavement layers. The Light Weight Deflectometer (LWD) is one such mechanism that offers field measurement of deflections and stiffness of unbound pavement layers under a given load. The LWD is gaining increased attention for quality control and quality assurance (QC/QA) during pavement construction. The Indiana Department of Transportation (INDOT) is planning on implementing the LWD in field QA/QC for unbound layers of pavements. As such, this research investigates the feasibility of developing statistical limits for the compaction of specified combinations of subbase and subgrade materials in terms of their maximum allowable LWD deflections. Statistical limits were developed for six of the most common subgrade, subbase, or subgrade-subbase combinations that are used for highway pavement construction in Indiana: lime modified, cement modified, natural subgrade and No. 53 crushed stone (53CS) subbase overlaying these subgrades. For the subbase layers, these statistical limits are applicable only to six inches of subbase over subgrade and may not be applicable to a different layer configuration in terms of the number of lifts or thickness of lifts. The ultimate goal is for the developed statistical limits to replace the need for site-specific LWD limits derived from the onsite test sections, ultimately saving time and money. Due to variability in the data and data limitations, caution must be exercised when generalizing the findings published in this report. Compared to the data from the acceptance test sections, the data collected from test sections saw less variability between projects, for any given material type. The test section data yielded maximum allowable deflections that did not vary significantly between projects for cement-and lime-modified subgrade, non-modified subgrade, and six inches of #53 crushed stone over lime-modified subgrade. Generally, within any specific contract location (project site), the data indicates adequate confidence that the test pads generate control measurements that can be used reliably to check the adequacy of compaction at that contract location. However, across different contact locations, even for the same material type, so much variability was observed that it is not possible to guarantee that the control measurements generated from a limited number of test sections (pads) can be confidently transferred to another site of the same material type.
REVIEW OF FALLING WEIGHT DEFLECTOMETER FOR ASSESSMENT OF FLEXIBLE PAVEMENT
ELK ASIA PACIFIC JOURNAL OF CIVIL ENGINEERING AND STRUCTURAL DEVELOPMENT , 2018
Fast development of road networks has become a trend in India and everywhere in the world. From the past couple of decades, it has been observed that numerous highways are in a phase of deteriorations. Identifying the reasons for deteriorations requires a pavement evaluation study. Many performances study have been made out by exploring flexible pavements, by the users of widely accepted falling weight deflectometer (FWD) as a non-destructive test (NDT) and considered it as a standard for structure assessment. The primary objective of this study is to a review of an FWD instrument and the also study of the empirically derived methods and a back calculation process for computing layer moduli and factors influencing it. The essential need of correction factors to get reliable layer moduli is an also discussed, in addition to the investigation of advancement of low-cost indigenous FWD models flexible pavements, by the users of widely accepted falling weight deflectometer (FWD) as a non-destructive test (NDT) and considered it as a standard for structure assessment. The primary objective of this study is to a review of an FWD instrument and the also study of the empirically derived methods and a back calculation process for computing layer moduli and factors influencing it. The essential need of correction factors to get reliable layer moduli is an also discussed, in addition to the investigation of advancement of low-cost indigenous FWD models
Analytical-Empirical Pavement Evaluation Using the Falling Weight Deflectometer
Transportation Research Record, 1985
Because of the rapid development of hardware and software during the past 10 years, it is now possible to use an analytical-empirical (or mechanistic) method of structural pavement evaluation on a routine basis. The Dynatest 8000 falling weight deflectometer that, when used with the ELMOn program, determines the modulus of each structural layer in a pavement system is described. The moduli are determined nondestructively and in situ under conditions that closely resemble those under the influence of heavy traffic. Some practical examples illustrating the use of the method are presented, and its empirical components are discussed. These empirical components are also programmed into the ELMOD program so an overlay design may be carried out concurrently with the analytical determination of layered elastic moduli. The method may be used for both flexible and rigid pavements, where joint evaluation is not needed. The evaluation of joint or corner conditions in jointed portland cement con...
Comparison of in situ devices for the assessment of pavement subgrade stiffness
The subgrade is the top surface of a roadbed upon which the pavement structure is constructed. The purpose is to provide a platform for construction of the pavement and to support the pavement without unwanted deflection that would reduce its performance. For those reasons subgrade bearing capacity have to be investigate during the construction process as a quality control, based on the design results. The dynamic in situ Falling Weight Deflectometer (FWD) tests are nowadays widely used and considered the most reliable and suitable approach to determine bearing capacity of road pavements and elastic moduli. In addition, the use of the Light Weight Deflectometer (LWD) takes the advantage of the dynamic application of load, and the flexibility of the handling of the equipment on construction area and unbound layer. In the present paper, a wide literature review is presented on the topic of correlation between different subgrade bearing capacity in situ tests. In order to assess the transferability of LWD measures, these results were compared with FWD test and Dynamic Cone Penetrometer (DCP) test. Soil samples, taken from the site, have also been investigate in laboratory to relate geotechnical and in situ test results.
A field investigation was conducted with two testing devices, the min-iaturized pressuremeter test (MPMT) and a lightweight deflectometer (LWD), to evaluate the elastic characteristics of granular pavement layers. The stress–strain data from the MPMT tests were used to determine the stiffness of pavement materials under the influence of static loading conditions in initial elastic modulus (E i) and reload elastic modu-lus (E r). The time–deflection data from the LWD tests were used to determine the stiffness parameters of pavement materials under the influence of dynamic loading conditions in dynamic deformation modulus (E d) and LWD plate deflection. The results of the MPMT tests were compared with the results of the LWD tests in two phases. First, a direct approach was conducted with statistical analysis. MPMT elastic moduli were compared with LWD dynamic moduli. The results indicate that E i and E r could be used to estimate E d. The initial-modulus model had the best prediction for granular pavement dynamic moduli, followed by the reload moduli model. Second, an inverse approach was achieved by implementing finite element analysis. Three MPMT modulus models were utilized as inputs in the two-dimensional finite element simulation to predict pavement layer deflections. The predicted deflections were compared with deflections measured from LWD tests. The results revealed that a strain-level model in numerical simulation of base course moduli provided satisfactory values of predicted deflection and that the reload modulus model yielded the best prediction deflections for subgrade soils. Modern pavement design methodologies depend on mechanistic-based models that incorporate the nonlinear behavior of unbound pavement materials in dynamic modulus to simulate the response of pavement structure to expected wheel loadings. The predicted pavement responses (i.e., stresses, strains, and deformations) are then utilized to compute incremental pavement distresses over time. The importance of nonlinear soil characteristics in recent pavement design procedures has moved highway agencies toward nondestructive field measurements that can emulate the effect of heavy traffic loads. The lightweight deflectometer (LWD) was developed to operate as a quality control tool for evaluating the structural performance of pavement layers. The LWD is a nondestructive testing device that is used to measure the in situ stiffness properties of unbound pavement materials under the influence of dynamic impact loads. This device provides a single dynamic stiffness backcalculated on the basis of acceleration of the impulse load propagated inside a pavement layer. The depth of the evaluated pavement layer varies from 1.5 to 2.0 times the diameter of the LWD loading plate (1–3). This paper presents an exhaustive review of publications on employing the LWD in pavement assessment as well as the general theoretical relations between LWD dynamic stiffness and measurements of other laboratory and field tests. Experimental work was conducted by Hossain and Apeagyei (4) to study the possibility of employing the LWD as a field-testing method to evaluate unbound granular materials for Virginia's roads instead of conventional density and moisture content tests. It was observed that the soil modulus obtained from the LWD increases with increasing density. In addition, the study found a significant effect of moisture content on decreasing LWD stiffness. This behavior may be attributed to high pore water pressure that develops when a soil is subjected to a high dynamic impact load during the LWD testing procedure. Louay et al. (5) performed a comparative study between a field LWD test and a laboratory triaxial test to predict the laboratory resilient moduli of subgrades for in situ soil moduli. The results of the analysis were presented in two models. The first model relates sub-grade resilient modulus (M r) with LWD soil modulus (E LWD). The statistical coefficients obtained from the model, including the coefficient of determination (R 2) and root mean square error (RMSE) were .54 and 9.66 MPa, respectively. The resulting equation is = × M E r 27.75 (1) LWD 0.18 Because of the weak correlation, several physical properties of the soils that were tested were included in multivariable statistical analysis. This process resulted in a regression model with a better correlation (R 2 = .7 MPa; RMSE = 7 MPa). This model predicts the resilient modulus of subgrades in dynamic LWD soil modulus and moisture content (w): M E w r () = + + 11.23 12.64 242.32 1 (2) LWD 0.2 A comparative investigation between the LWD and the falling weight deflectometer (FWD) was carried out by Fleming et al. (6). The authors reported that no significant correlation exists between FWD
Procedia Engineering, 2017
Within the the National Sustainability Programme I, project of Transport R&D Centre (LO1610), the determination of measured jointed plain concrete pavements deflections to load was monitored. Impacts of climate and other effects upon resulting concrete pavement deflections were studied in the first place. The main issue for FWD measurements is the selection of suitable climatic conditions. In addition, loading transfer efficiency (LTE) at slab joints, which is a specific feature of concrete road pavements, was studied.
Pavement foundation stiffness testing – a new regime
Proceedings of the ICE - Transport, 2010
Traditionally the construction of the foundations of paved infrastructure followed a recipe approach where specified materials are laid using specified plant in an approved away following a method specification. This approach is prescriptive and limits material use to those that meet the recipe assuming a given level of performance after completion. To encourage sustainability the UK Highways Agency launched new pavement and foundation design guidance that is moving away from this prescriptive approach (IAN 73/06 revised in 2009, and HA 26/06). The guidance aims to allow a more flexible design and assessment of the required foundation performance parameters of strength and resistance to permanent deformation. This also introduced stiffness assessment of the constructed foundation to confirm compliance with design. In contrast to the previous regime, the actual performance of the foundation can influence (and provide savings to) the design of the structural pavement layers above. The new guidance permits the use of Light Weight Deflectometers (LWDs) to assess stiffness compliance. LWDs are becoming increasingly common tools in the checking of foundations of paved infrastructure. This paper presents the background to the use of LWDs within the new guidance, and elements of a recently completed 'Good Practice' guide for their use.
ASSESSING PERFORMANCE THROUGH THE UTILIZATION OF LIGHT WEIGHT DEFLECTOMETER
Journal of Civil Engineering and Technology (JCIET), 2023
Rapid infrastructure development, particularly in India, has emerged as a prominent global trend. Over the past few decades, it has become apparent that many road projects necessitate early-stage maintenance. To identify the underlying causes, a comprehensive structural evaluation study is imperative to assess the existing material properties of pavements. While Light Weight Deflectometer (LWD) is gaining widespread acceptance and popularity as an in-situ spot-testing device worldwide, in India, only a few researchers have delved into its applications. This study aims to estimate the in-situ layer moduli of flexible pavements using LWD and further utilize these layer moduli for performance analysis. A series of tests were conducted at NH-15 on 52 distressed locations, and samples were systematically collected for subsequent laboratory testing. LWDmod software was employed to calculate the back-calculated modulus for each layer. The results revealed that the Coefficient of Variation (CV) of the back-calculated average modulus on both the Left-Hand Side (LHS) and Right-Hand Side (RHS) ranged from 24% to 30% for the bituminous surface, 33% to 45% for the WMM, 35% to 45% for the GSB, and 40% to 52% for the Sub-grade. It was observed that the CV value was higher for softer materials and subsequently decreased for granular layers. The performance analysis indicated that the existing pavement is structurally distressed.