Lightweight deflectometers for quality assurance in road construction (original) (raw)
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Review of Lightweight Deflectometer for Routine in Situ Assessment of Pavement Material Stiffness
Transportation Research Record: Journal of the Transportation Research Board, 2007
The use of a portable lightweight deflectometer (LWD) for construction quality control or material investigation for earthworks and road construction is increasing around the world. LWD is reviewed as a field evaluation tool, the test variables and data quality are discussed, and the usefulness and limitations for a variety of earthwork and road assessment scenarios are described. A state-of-the-art reference document is provided for LWD users, consultants, material specifiers, contractors, and clients. Data from road foundations (subgrades, granular capping, and subbase) and fully constructed in-service (thinly surfaced) roads were reviewed to demonstrate the flexibility of the LWD and to show that its determination of stiffness modulus may differ from that of the conventional falling weight deflectometer to a varying extent. A series of laboratory investigations was undertaken to demonstrate the sensitivity to uniformity of plate-surface contact and the limitations in the interpre...
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.
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.
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.
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.
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
FALLING WEIGHT DEFLECTOMETER BOWL PARAMETERS AS ANALYSIS TOOL FOR PAVEMENT STRUCTURAL EVALUATIONS
The falling weight deflectometer (FWD) is used world wide as a well established and valuable non-destructive road testing device for pavement structural analyses. The FWD is used mostly for rehabilitation design investigations and for pavement management system (PMS) monitoring on a network basis. On project level investigations, both design charts and mechanistic approaches using multi-layered linear elastic theory and back-calculation procedures are often used to provide structural evaluations and rehabilitation options. As an alternative to this a semi-mechanistic semi-empirical analysis technique has been developed in South Africa whereby new deflection bowl parameters measured with the FWD used to give guidance on individual layer strengths and pinpoint rehabilitation needs. This approach is fully suited to supplementary analysis of FWD data in the Australian design systems, and overcomes some of the limitations of the curvature parameter. This paper briefly describes the current practice and basis of this use of deflection bowl parameters, and illustrates the use with a current pavement rehabilitation project underway in South Africa.
A benchmark analysis method was developed using Falling Weight Deflectometer (FWD) data for comparative evaluation of the structural condition of flexible pavement structures. This is established as a preliminary design and analysis tool, and aspects of it are incorporated in TRH 12. Experiences with benchmark analyses on roads and airports are reviewed and adjusted criteria are recommended with a colour coded three tiered condition assessment method. Exploratory studies on additional deflection bowl parameters are conducted to gauge their potential for inclusion in benchmark analyses. Deflection bowl parameter benchmarking has found application at network level analysis in a number of road authorities world-wide. Modified Structural Number (SNP) and Pavement Number (PN) have recently also been illustrated as being able to accurately calculate from the full deflection bowl and can be used in such enhanced benchmark analyses of flexible pavement structures.
Academia Letters, 2021
The use of LWD in flexible pavement structural designs is increasing. The LWDs are offered under 2 typologies; with or without geophones to set the deflection bowl. LWDs with geophones allow to apply mechanistic analysis directly, but LWDs without geophones not. For this reason, the LEMaC Center for Road Research UTN FRLP - CIC PBA (Argentina) analyzes this problem through a research project; their results allow the use of LWD without geophones in pavement design using the AASHTO93 Guide. This “short report”, as allowed by the Letters Academy, presents a summary of the tasks performed and the work procedure developed. No section of conclusions and exhaustive antecedents and studies of the models presented are included, due to the limit imposed on the number of words for these “short reports”. This information can be consulted in the “Correlation model for the use of modulus back-calculation on LWD measurements” (Rivera & Alderete, 2012).
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...