Chapter 4: Pavement Evaluation

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Section 1: Overview

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1.1 Introduction

Pavement evaluations are conducted to determine functional and structural conditions of a highway section either for purposes of routine monitoring or planned corrective action. Functional condition is primarily concerned with the ride quality or safety aspects of a highway section (surface texture, cross slope, splash and spray, etc.). Structural condition is concerned with the structural capacity of the pavement as measured by deflection, layer thickness, and material properties.

At the network level, routine evaluations can be used to develop performance models and prioritize maintenance or rehabilitation efforts and funding. At the project level, evaluations are more focused on establishing the root causes of existing distress and the in situ material properties in order to determine the best rehabilitation strategies.

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1.2 Visual Condition Surveys

Visual condition surveys document aspects of both functional and structural pavement conditions, but generally serve as a qualitative indicator of overall condition. Specialized equipment is used to quantify both functional and structural properties of the pavement structure. Ideally, for any given section of highway, two or more evaluators would arrive at the same assessment of the section’s current condition. However, there are still many aspects of pavement evaluation that are highly subjective. For example, in visual condition surveys, the percent of surface area affected by alligator cracking is highly dependent upon the visual acuity of the evaluator. Progress continues in automating the mapping of common surface distress to eventually eliminate this subjectivity.

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1.3 Non-destructive Testing (NDT)

NDT is the collective term for evaluations conducted on an existing pavement structure that do not require subsequent maintenance work to return the pavement to its pretesting state. This is generally desirable to minimize disruption to traffic, and is essential as a screening tool to determine locations where selective material sampling should be conducted to evaluate other material properties in the laboratory. As such, its focus is to assess in situ properties that can be used to evaluate the need for further “destructive” testing (i.e., coring, boring, trenching), location of that destructive testing, and the current structural capacity of the highway as related to layer stiffness and strength. Non-destructive testing methods can assess either functional or structural condition. For NDT, data collected in the field is generally objective in nature, but engineer’s data analysis and interpretation are subjective.

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1.4 Destructive Testing

Destructive testing opens the door to characterization of the pavement’s constituent materials not possible to obtain through non-destructive testing alone. Material characterization includes:

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  • evaluation of mechanical, physical, and chemical properties (samples are obtained through coring, Shelby tubes, augering, and trenching), and
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  • visual inspection of pavement layers through coring, augering and trenching.

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