Evaluation of Joint and Crack Load Transfer Final Report

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The load transfer efficiency (LTE) of cracks and joints profoundly affects the performance of concrete pavements. Poor LTE may lead to longitudinal cracking and excessive faulting of jointed concrete pavements (JCP) and could accelerate punchout development in continuously reinforced concrete pavements (CRCP). These distresses could lead to roughness and poor ride quality. Conversely, joints and tightly closed transverse cracks with high LTE do not typically cause any pavement serviceability problems.

As part of the ongoing Long-Term Pavement Performance (LTPP) program, deflection measurements are being taken with the falling weight deflectometer (FWD) on all general pavement studies (GPS) and specific pavement studies (SPS) test sections. This deflection testing program is being conducted periodically to obtain the load-response characteristics of the pavement structures at critical points in time, depending on the experiment. These data are intended to provide pavement structural characteristic data that are needed to achieve the goals of LTPP program. Many State highway agencies also are collecting deflection data on their pavement systems for management, project rehabilitation, and forensic studies, and they consider deflection data to be as important as pavement condition and distress data.

Deflections, temperature, and joint opening size are all measured at joints/cracks. The data collected include the following:

• FWD deflection measurements in the outer wheel path at a joint/crack approach slab (tests J4 and C4 for JCP and CRCP, respectively).
• FWD deflection measurements in the outer wheel path at a joint/crack leave slab (tests J5 and C5 for JCP and CRCP, respectively).
• Width of opening through the pavement at the joints across which load transfer deflection tests were performed.
• Subsurface portland cement concrete (PCC) temperature at different depths.

Research Objectives

The primary objectives of this study are to compute:

• LTE for joints and cracks from deflection measurements over time and traffic.
• Joint/crack stiffness characteristics over time and traffic.
• Change in joint opening for the LTPP sections over time and traffic.

The computed parameters will then become a part of the LTPP database for use in future studies.

Secondary objectives of this proposed study are as follows:

• Evaluate available procedures for calculating the LTE and suggest modifications or alternatives if necessary.
• Evaluate available procedures for backcalculation of the joint stiffness.
• Develop guidelines for calculating the LTE using LTPP data.
• Assess variability in measured LTEs within each LTPP section.
• Using LTPP Seasonal Monitoring Program (SMP) data, evaluate daily and seasonal variability in measured joint opening and LTE.
• Evaluate the effect of different factors (presence of dowels, joint opening, base type, subgrade stiffness, PCC thickness) on LTE.
• Evaluate the relationship between the LTE level and amount of faulting and other distresses observed.

Scope of Work

The scope of this LTE analysis study for LTPP rigid pavement sections includes the following:

• Selecting a procedure to compute joint/crack LTE, joint stiffness, and change in joint opening.
• Developing representative indices and statistics for joint/crack LTE, joint stiffness, and joint opening parameters.
• Performing LTE and joint stiffness analysis for GPS, SPS, and SMP sections.
• Performing joint opening analysis for SMP test sections.
• Developing drafts of data tables for possible upload of analysis results to the LTPP database.
• Performing trend analysis for joint/crack opening, joint/crack LTE, and joint stiffness parameters and conducting any other analyses of interest.

Report Organization

This report documents the research effort and findings of the LTPP rigid pavement joint parameters such as LTE, stiffness, and variation in opening. This chapter presents background information. Chapter 2 provides details on the selection of the methodology for calculation of LTE and stiffness of joints and cracks. Chapter 3 presents the results of the assessment of FWD deflection data used in joint LTE calculation and describes the procedure used to determine representative LTE parameters. Chapter 4 presents results of the analysis for GPS and SPS test sections. Chapter 5 presents results of the LTE analysis for SMP test sections. Chapter 6 presents the methodology and results of the analysis of joint stiffnesses. Chapter 7 presents the methodology and results of the analysis of changes in joint opening. A summary and list of recommendations are presented in chapter 8.

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