The method entails utilizing knowledge obtained from Falling Weight Deflectometer (FWD) testing to estimate a numerical index representing the general load-carrying capability of a pavement construction. The FWD applies a managed impulse load to the pavement floor, and sensors measure the ensuing deflections at varied distances from the load. These deflection measurements are then utilized in backcalculation procedures to estimate the elastic moduli of the pavement layers. The structural quantity is in the end derived from these moduli and layer thicknesses.
This analysis technique is essential for pavement administration and rehabilitation planning. Correct evaluation of structural capability permits engineers to establish pavement sections which might be structurally poor and prioritize upkeep or rehabilitation efforts. This strategy gives a non-destructive various to damaging testing strategies, decreasing disruption to site visitors move. Traditionally, this analysis course of has enabled knowledgeable selections concerning useful resource allocation, extending pavement service life, and optimizing funding in infrastructure.
The next sections of this doc will delve into the specifics of FWD testing procedures, backcalculation methodologies, and the derivation of the structural quantity. Components influencing the accuracy of the analysis, equivalent to temperature results and layer situation, can even be addressed. Lastly, the sensible functions of this structural index in pavement design and efficiency prediction will likely be examined.
1. Deflection Knowledge Acquisition
Deflection knowledge acquisition types the foundational stage in evaluating pavement structural capability utilizing FWD testing. The accuracy and reliability of this knowledge instantly influence the validity of subsequent backcalculation processes and the ultimate dedication of the pavement structural quantity. Consequently, cautious consideration to element throughout knowledge acquisition is paramount.
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FWD Gear Calibration and Operation
The FWD should be correctly calibrated to make sure the utilized load and measured deflections are correct and constant. Calibration entails verifying the load cell readings and deflection sensor outputs towards recognized requirements. Correct operation consists of deciding on acceptable load ranges for the pavement kind and situation and guaranteeing the FWD is positioned appropriately at every take a look at location. Defective tools or improper operation can introduce important errors within the deflection knowledge, resulting in an inaccurate evaluation of the pavement’s structural capability.
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Sensor Placement and Spacing
The position and spacing of deflection sensors considerably affect the characterization of the pavement’s deflection basin. Typical sensor configurations contain putting sensors on the heart of the utilized load and at growing distances away from the load. The spacing between sensors should be rigorously thought of primarily based on the anticipated pavement response. Insufficient sensor spacing might fail to seize the complete extent of the deflection basin, resulting in an underestimation of the pavement’s stiffness and in the end affecting the derived structural quantity.
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Environmental Concerns (Temperature)
Pavement temperature considerably impacts the fabric properties of asphalt concrete, instantly impacting deflection measurements. Larger pavement temperatures end in decrease asphalt moduli and elevated deflections. Due to this fact, correct pavement temperature measurements should be recorded concurrently with deflection knowledge. These temperature readings are important for making use of temperature correction components to the deflection knowledge earlier than backcalculation, mitigating the affect of temperature variations on the estimated layer moduli and the derived structural quantity.
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Knowledge High quality Management and Validation
Rigorous high quality management procedures are important to establish and take away misguided or suspect knowledge factors. This entails visually inspecting the deflection basins for irregularities, checking for sensor malfunctions, and verifying the consistency of the info. Any questionable knowledge factors needs to be investigated and, if essential, faraway from the dataset. Failure to implement correct high quality management measures can introduce bias into the backcalculation course of, resulting in an inaccurate evaluation of pavement structural capability and an unreliable structural quantity.
In abstract, the method of buying correct and dependable deflection knowledge is an indispensable prerequisite for the significant analysis of pavement construction utilizing FWD testing. Correct tools calibration, sensor configuration, environmental consideration, and rigorous high quality management collectively make sure that the ensuing structural quantity gives a consultant indication of the pavement’s true load-carrying capability.
2. Backcalculation Algorithms
Backcalculation algorithms are a central part in ascertaining pavement structural capability by FWD testing. The deflection knowledge acquired throughout FWD testing serves because the enter for these algorithms. These algorithms carry out an inverse evaluation, utilizing the measured floor deflections to estimate the elastic moduli of the person pavement layers. The accuracy of the estimated layer moduli instantly impacts the reliability of the derived structural quantity. With out using backcalculation strategies, FWD knowledge gives solely uncooked deflection values, missing the required interpretation to quantify the load-bearing capabilities of the pavement construction. For example, a bit of pavement exhibiting excessive deflections below a given load might seem structurally weak. Nevertheless, after backcalculation, if the underlying layers are discovered to own excessive moduli, the pavement may nonetheless possess a passable structural quantity, indicating a localized floor subject reasonably than a systemic structural deficiency. The suitable choice and utility of a backcalculation algorithm are due to this fact essential for a significant analysis.
Sensible functions of backcalculation are evident in pavement rehabilitation design. When confronted with a structurally poor pavement part, engineers make the most of backcalculated layer moduli to find out the optimum overlay thickness required to revive the pavement’s load-carrying capability to a suitable stage. Completely different backcalculation strategies exist, every with its personal underlying assumptions and computational strategies. Iterative strategies, for instance, refine the estimated layer moduli by successive approximations till the calculated deflections carefully match the measured deflections. Closed-form options present a direct calculation of the layer moduli primarily based on simplified assumptions concerning the pavement construction. The selection of algorithm depends upon components such because the complexity of the pavement construction, the accuracy of the deflection knowledge, and the obtainable computational sources.
In conclusion, the correct utility of backcalculation algorithms is indispensable within the total technique of utilizing FWD testing to guage pavement structural capability. Whereas challenges exist in deciding on essentially the most acceptable algorithm and precisely accounting for components equivalent to temperature and materials variability, the insights gained from backcalculation are important for knowledgeable pavement administration selections. By precisely translating deflection knowledge into estimates of layer moduli, these algorithms present the inspiration for deriving a dependable structural quantity, in the end enabling efficient methods for pavement upkeep and rehabilitation.
3. Layer Modulus Estimation
Layer modulus estimation represents a essential step within the technique of utilizing Falling Weight Deflectometer (FWD) testing to find out a pavement’s structural quantity. The modulus of every layer, a measure of its stiffness or resistance to deformation, is a basic enter for calculating the general structural capability of the pavement. Inaccurate modulus estimates will invariably result in an incorrect structural quantity, impacting subsequent selections concerning pavement upkeep and rehabilitation.
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Influence of Materials Properties
The inherent materials properties of every pavement layer, equivalent to asphalt concrete, granular base, and subgrade, instantly affect their respective moduli. Components like mixture kind, binder content material, and compaction density in asphalt layers, and the gradation and moisture content material in unbound layers, all contribute to the layer’s stiffness. For instance, an asphalt layer with a better binder content material might exhibit a decrease modulus than a layer with a decrease binder content material below the identical loading situations. Correct characterization of those materials properties, both by laboratory testing or reliance on established materials correlations, is essential for correct modulus estimation.
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Affect of Environmental Components
Temperature and moisture variations exert a big affect on the moduli of pavement layers. Asphalt concrete is especially delicate to temperature modifications, exhibiting a decrease modulus at larger temperatures and a better modulus at decrease temperatures. Equally, the modulus of unbound granular layers is affected by moisture content material, with elevated moisture typically resulting in a lower in stiffness. Correct temperature and moisture measurements throughout FWD testing, coupled with acceptable correction components or fashions, are essential to account for these environmental results and acquire life like modulus estimates.
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Position of Backcalculation Software program
Specialised backcalculation software program packages are employed to estimate layer moduli from the deflection knowledge obtained throughout FWD testing. These applications use iterative algorithms to regulate the assumed layer moduli till the calculated deflection basin carefully matches the measured deflection basin. Completely different software program packages might make the most of various algorithms and assumptions, probably resulting in totally different modulus estimates for a similar pavement part. The number of an acceptable backcalculation software program package deal, together with cautious consideration of its underlying assumptions and limitations, is crucial for dependable modulus estimation.
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Impact on Structural Quantity Calculation
The estimated layer moduli, together with layer thicknesses, are utilized in a structural capability equation (sometimes primarily based on AASHTO design procedures) to calculate the pavement’s structural quantity. The structural quantity represents the general load-carrying capability of the pavement and is used to find out the necessity for rehabilitation or overlay. An overestimation of layer moduli will end in an inflated structural quantity, probably resulting in a choice to defer essential upkeep or rehabilitation. Conversely, an underestimation of layer moduli will end in a deflated structural quantity, probably resulting in untimely or pointless intervention. Due to this fact, correct layer modulus estimation is paramount for acquiring a dependable structural quantity and making sound pavement administration selections.
The estimation of layer moduli, due to this fact, stands as a cornerstone within the total technique of figuring out a structural quantity from FWD knowledge. Its accuracy is instantly linked to the reliability of the structural evaluation and the effectiveness of subsequent pavement administration methods. Cautious consideration of fabric properties, environmental components, and the appliance of acceptable backcalculation strategies are all essential to acquiring significant and dependable modulus estimates.
4. Temperature Correction
Pavement temperature considerably influences the stiffness of asphalt concrete, a major part of many pavement buildings. Throughout Falling Weight Deflectometer (FWD) testing, variations in pavement temperature instantly have an effect on deflection measurements. Larger temperatures typically end in elevated deflections because of the lowered stiffness of the asphalt layer, whereas decrease temperatures result in decreased deflections. Because the structural quantity is derived from these deflections, uncorrected temperature variations can result in substantial errors within the estimated structural capability of the pavement. A pavement examined at a excessive temperature may seem structurally weaker than it really is, leading to an underestimation of the structural quantity. Conversely, a pavement examined at a low temperature may seem stronger, resulting in an overestimation. Temperature correction, due to this fact, is a vital step in guaranteeing that the decided structural quantity precisely displays the true load-carrying capability of the pavement at a typical reference temperature.
The temperature correction course of sometimes entails measuring the pavement temperature on the time of FWD testing and making use of correction components to the measured deflections. These correction components are sometimes primarily based on established relationships between asphalt concrete stiffness and temperature, derived from laboratory testing or empirical knowledge. Varied temperature correction fashions exist, every with its personal underlying assumptions and applicability. The number of an acceptable temperature correction mannequin depends upon components equivalent to the kind of asphalt binder used within the pavement, the pavement’s age and situation, and the weather conditions of the area. For example, a pavement constructed with a polymer-modified asphalt binder might require a unique temperature correction mannequin than a pavement constructed with a traditional asphalt binder. Furthermore, inaccurate temperature measurements or using an inappropriate temperature correction mannequin can introduce important errors into the structural quantity calculation, undermining the reliability of the FWD testing outcomes.
In abstract, temperature correction is an indispensable facet of utilizing FWD testing to find out pavement structural numbers. The affect of temperature on asphalt concrete stiffness necessitates correct temperature measurements and the appliance of acceptable correction components to make sure that the derived structural quantity precisely displays the pavement’s true load-carrying capability. Neglecting temperature correction or utilizing insufficient correction strategies can result in misguided structural assessments and probably flawed pavement administration selections. The accuracy of the derived structural quantity depends, partly, on the meticulous implementation of temperature correction procedures through the FWD testing and knowledge evaluation course of.
5. Layer Thickness Accuracy
The precision of layer thickness knowledge is paramount within the dedication of a pavement’s structural quantity derived from Falling Weight Deflectometer (FWD) testing. FWD testing gives deflection knowledge, which is then utilized in backcalculation procedures to estimate the elastic moduli of pavement layers. These moduli, along with layer thicknesses, are major inputs into the structural quantity calculation. An inaccurate layer thickness worth instantly impacts the backcalculated moduli; a thinner assumed layer will sometimes end in a better backcalculated modulus to match the measured deflections, and vice versa. This distorted modulus then propagates into the structural quantity equation, resulting in an misguided evaluation of the pavement’s load-carrying capability. Contemplate a situation the place the asphalt layer thickness is underestimated by 20%. The backcalculation algorithm might compensate by assigning an artificially excessive modulus to that layer. Consequently, the calculated structural quantity will likely be larger than the precise worth, probably resulting in a choice to defer essential upkeep or rehabilitation.
The acquisition of correct layer thickness knowledge might be achieved by varied strategies, together with coring, ground-penetrating radar (GPR), and building data. Coring gives a direct measurement of layer thicknesses at discrete areas. GPR provides a non-destructive technique of assessing layer thicknesses alongside a steady profile, though its accuracy might be affected by materials properties and moisture content material. Development data, if obtainable and dependable, can present useful data on as-built layer thicknesses. Nevertheless, it’s essential to account for any potential variations on account of building practices or subsequent pavement deterioration. The number of essentially the most acceptable technique depends upon components such because the mission scope, finances, and required accuracy. Moreover, the quantity and site of thickness measurements needs to be rigorously thought of to adequately characterize the variability of layer thicknesses alongside the pavement part.
In conclusion, the accuracy of layer thickness knowledge is an indispensable aspect within the technique of figuring out pavement structural numbers from FWD testing. Inaccurate layer thickness values introduce bias into the backcalculation course of, resulting in an misguided estimation of layer moduli and, consequently, an unreliable structural quantity. The potential penalties of inaccurate structural numbers embrace deferred upkeep, untimely rehabilitation, and inefficient allocation of sources. Due to this fact, diligent efforts to acquire correct layer thickness knowledge, coupled with an intensive understanding of its influence on the structural quantity calculation, are important for efficient pavement administration.
6. Materials Property Assumptions
Correct dedication of pavement structural quantity from FWD testing depends closely on the assumptions made concerning the fabric properties of every pavement layer. These assumptions function essential inputs for backcalculation algorithms, which estimate layer moduli primarily based on measured floor deflections. The validity of those assumptions instantly influences the reliability of the estimated moduli and, consequently, the accuracy of the structural quantity.
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Poisson’s Ratio
Poisson’s ratio, representing the ratio of transverse pressure to axial pressure below stress, is a fabric property that should be assumed for every layer within the backcalculation course of. Whereas Poisson’s ratio sometimes has a smaller influence on the backcalculated moduli in comparison with different parameters, an inappropriate assumption can nonetheless introduce errors. For instance, assuming an excessively excessive Poisson’s ratio for a granular base layer might result in an underestimation of its modulus. Typical values vary from 0.15 to 0.35 for asphalt concrete and 0.2 to 0.4 for unbound supplies. Choice needs to be primarily based on typical values for related supplies or, ideally, laboratory testing.
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Linear Elasticity
Backcalculation algorithms generally assume that pavement supplies behave in a linear elastic method below the utilized FWD load. This assumption implies that the fabric’s stress-strain relationship is linear and that the fabric returns to its authentic form upon removing of the load. Whereas this assumption simplifies the evaluation, it might not precisely signify the habits of all pavement supplies, notably asphalt concrete at larger temperatures or below repeated loading. Deviations from linear elasticity can introduce errors within the backcalculated moduli, particularly for asphalt layers. Extra superior viscoelastic or nonlinear materials fashions can enhance accuracy however enhance the complexity of the backcalculation course of.
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Layer Homogeneity and Isotropy
Backcalculation typically presumes that every pavement layer is homogeneous (uniform properties all through) and isotropic (properties are the identical in all instructions). In actuality, pavement layers can exhibit spatial variability of their materials properties on account of variations in building practices, materials segregation, or environmental results. Assuming homogeneity and isotropy when these situations are usually not met can result in inaccuracies within the estimated layer moduli. The extent of this error depends upon the diploma of heterogeneity and anisotropy inside every layer.
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Subgrade Habits
The subgrade, the soil layer underlying the pavement construction, is usually modeled as a semi-infinite elastic half-space. This assumption simplifies the evaluation however might not precisely signify the habits of all subgrade soils, notably these with shallow bedrock or groundwater tables. The assumed subgrade modulus considerably influences the backcalculated moduli of the overlying pavement layers. If the subgrade modulus is underestimated, the moduli of the opposite layers could also be overestimated to compensate, resulting in an inaccurate structural quantity.
The number of acceptable materials property assumptions requires an intensive understanding of pavement materials habits and the constraints of the backcalculation algorithms utilized in figuring out a pavement’s structural quantity from FWD testing. Whereas simplifying assumptions are sometimes essential to facilitate the evaluation, it’s important to acknowledge their potential influence on the accuracy of the outcomes and to contemplate various modeling approaches when warranted.
7. Structural Quantity Calculation
Structural quantity calculation represents the culminating step within the technique of figuring out pavement structural capability utilizing Falling Weight Deflectometer (FWD) testing. The FWD take a look at gives deflection knowledge, which is subsequently analyzed utilizing backcalculation strategies to estimate the elastic moduli of particular person pavement layers. These layer moduli, together with the thicknesses of every layer, function major inputs right into a predetermined structural quantity equation. This equation, sometimes derived from AASHTO design methodologies, aggregates the person layer contributions right into a single numerical index representing the general structural capability of the pavement. Due to this fact, the structural quantity calculation is the direct consequence and ultimate quantification of the complete “figuring out pavement structural quantity from fwd testing” process. The method of deflection measurement, backcalculation, and modulus estimation are all precursors essential for the ultimate structural quantity calculation.
The computed structural quantity instantly informs pavement administration selections. For example, if the calculated structural variety of an current pavement falls under a predetermined threshold for its supposed site visitors loading, it alerts the necessity for structural rehabilitation or overlay. Conversely, a structural quantity considerably exceeding the required threshold may point out that the pavement is over-designed or that upkeep interventions might be optimized. State Departments of Transportation (DOTs) routinely use FWD testing and subsequent structural quantity calculations to prioritize pavement sections for rehabilitation initiatives. Furthermore, the structural quantity serves as a key parameter in mechanistic-empirical pavement design, the place it’s used to foretell pavement efficiency and assess the effectiveness of various rehabilitation methods. The accuracy of the structural quantity calculation is due to this fact paramount, because it instantly impacts the cost-effectiveness and longevity of pavement infrastructure.
In essence, the structural quantity calculation serves because the definitive translation of FWD testing knowledge into actionable data for pavement engineers and managers. It bridges the hole between uncooked deflection measurements and knowledgeable selections concerning pavement upkeep, rehabilitation, and design. Whereas challenges stay in guaranteeing the accuracy of enter parameters and accounting for materials variability, the structural quantity stays a basic and extensively utilized metric for characterizing pavement structural capability. Its derivation is the final word goal of “figuring out pavement structural quantity from FWD testing”, guaranteeing the knowledge obtained instantly helps knowledgeable pavement asset administration methods.
Ceaselessly Requested Questions
This part addresses frequent questions concerning the dedication of pavement structural quantity utilizing knowledge acquired by Falling Weight Deflectometer (FWD) testing. These FAQs present concise explanations of essential ideas and potential challenges.
Query 1: Why is it essential to find out a pavement’s structural quantity?
The structural quantity quantifies the general load-carrying capability of a pavement. It gives a numerical index for assessing pavement situation, figuring out structurally poor sections, and prioritizing upkeep or rehabilitation efforts.
Query 2: What’s the major knowledge supply for figuring out the structural quantity?
The first knowledge supply is deflection knowledge obtained from FWD testing. The FWD applies a managed load to the pavement floor, and sensors measure the ensuing deflections at varied distances from the load. These deflections are then utilized in backcalculation procedures.
Query 3: What’s backcalculation, and why is it important?
Backcalculation is an iterative course of that makes use of measured floor deflections to estimate the elastic moduli of particular person pavement layers. It’s important as a result of it interprets uncooked deflection knowledge into significant estimates of layer stiffness, enabling the derivation of the structural quantity.
Query 4: How does temperature have an effect on the accuracy of structural quantity dedication?
Pavement temperature considerably influences the stiffness of asphalt concrete. Larger temperatures result in decrease stiffness and elevated deflections. Correct temperature measurements and correction components are essential to mitigate these results and acquire a dependable structural quantity.
Query 5: What position do layer thicknesses play within the structural quantity calculation?
Layer thicknesses, together with layer moduli, are key inputs into the structural quantity equation. Inaccurate layer thickness values can introduce bias into the backcalculation course of and result in an misguided estimation of layer moduli and the structural quantity.
Query 6: What are some frequent challenges encountered when figuring out structural quantity from FWD testing?
Frequent challenges embrace inaccurate FWD calibration, environmental results (temperature and moisture), uncertainties in layer thickness, materials variability, and the number of acceptable backcalculation algorithms and materials property assumptions.
These FAQs spotlight the significance of cautious knowledge acquisition, correct backcalculation, and consideration of varied influencing components when figuring out pavement structural quantity. An intensive understanding of those ideas is essential for efficient pavement administration and decision-making.
The next part will discover the sensible functions of the structural quantity in pavement design and efficiency prediction.
Key Concerns for Figuring out Pavement Structural Quantity from FWD Testing
The method of “figuring out pavement structural quantity from fwd testing” requires adherence to rigorous methodologies and an intensive understanding of influencing components. The next ideas are essential for guaranteeing accuracy and reliability within the analysis course of.
Tip 1: Prioritize Correct FWD Calibration: Constant calibration of the Falling Weight Deflectometer (FWD) is paramount. Deviations in utilized load or sensor readings can considerably skew deflection knowledge, resulting in misguided structural quantity estimations. Common calibration checks towards established requirements are necessary.
Tip 2: Implement Rigorous Temperature Correction Procedures: Pavement temperature profoundly impacts asphalt concrete stiffness. Correct pavement temperature measurements, coupled with acceptable temperature correction fashions, are important. Failure to implement strong temperature correction will introduce substantial errors into the structural quantity calculation.
Tip 3: Get hold of Correct Layer Thickness Knowledge: Exact dedication of layer thicknesses is essential. Make the most of a mix of coring, ground-penetrating radar (GPR), and building data to determine correct thickness profiles. Reliance solely on assumed thicknesses can compromise the integrity of the structural quantity calculation.
Tip 4: Make use of Validated Backcalculation Algorithms: The choice of an acceptable backcalculation algorithm is essential. Consider totally different algorithms primarily based on their underlying assumptions, computational effectivity, and sensitivity to enter parameters. Go for validated algorithms with demonstrated accuracy for the precise pavement kind and situation.
Tip 5: Rigorously Contemplate Materials Property Assumptions: Assumptions concerning materials properties, equivalent to Poisson’s ratio and layer homogeneity, can affect the backcalculated layer moduli. Base these assumptions on obtainable materials testing knowledge, historic data, and established materials correlations. Train warning when deviating from typical values.
Tip 6: Validate Outcomes with Native Expertise: Examine the calculated structural numbers with historic knowledge and native pavement efficiency data. Important discrepancies warrant additional investigation and will point out potential errors within the testing process, backcalculation course of, or materials property assumptions.
Tip 7: Doc All Procedures and Assumptions: Preserve thorough documentation of all testing procedures, backcalculation parameters, and materials property assumptions. This documentation is crucial for high quality management, knowledge traceability, and future reference.
Adherence to those ideas will improve the accuracy and reliability of the structural quantity dedication, resulting in extra knowledgeable pavement administration selections. By prioritizing accuracy at every stage of the method, transportation businesses can optimize useful resource allocation and make sure the long-term efficiency of pavement infrastructure.
The concluding part will summarize the advantages of correct structural quantity dedication and its position in efficient pavement administration.
Conclusion
The previous dialogue has totally examined the method of figuring out pavement structural quantity from FWD testing. This analysis technique facilitates the evaluation of a pavement’s load-carrying capability by using knowledge from deflection measurements. The accuracy of this evaluation depends on meticulous FWD operation, acceptable knowledge processing, correct backcalculation methodologies, and knowledgeable assumptions concerning pavement materials properties. The ensuing structural quantity serves as a essential parameter in evaluating the structural adequacy of a pavement part.
The “figuring out pavement structural quantity from fwd testing” effort is, due to this fact, important for efficient pavement administration. Transportation businesses should prioritize adherence to established protocols and put money into the coaching of certified personnel. Constant and dependable implementation of this process will allow knowledgeable selections concerning pavement upkeep, rehabilitation, and reconstruction, in the end contributing to the security, effectivity, and longevity of pavement infrastructure.
