Prolonging concrete pavement life

Research findings
One of the most important effects of joint sealant effectiveness on concrete pavement performance is related to its potential for subbase erosion. The focus of this study is to link joint seal effectiveness at an age beyond the initial performance period to the time faulting would initiate through the use of a prediction model, addressing the potential for erosion before faulting occurs.

One Excel application demonstrates several aspects of sealant effectiveness on pavement performance. This spreadsheet, developed by Zollinger, uses a mechanistic-empirical approach to consider three main elements of subbase erosion:

• the erosion resistance of the base/materials;
• the number of wet days; and
• the traffic loading.

Additional findings showed:

• if joint seals are properly installed, they can be very effective in preventing moisture infiltration (unsealed joints have significantly higher inflow rates compared to joints with damaged sealants);
• the water infiltration rates for ‘dirty joints,’ such as sealants installed in an unclean reservoir or dirt-filled unsealed joints, are as high as those for clean joints with 50 percent debonding; and
• the management of a sustainable concrete pavement system requires greater emphasis on performance monitoring rather than performance repair—
  a concept challenging traditional repair and rehabilitation philosophies.

Mechanistic-empirical fault prediction model
A mechanistic-empirical fault prediction model—previously developed under National Ready Mixed Concrete Association (NRMCA)—was improved upon as part of this research. The impact of joint seal effectiveness was directly examined within the fault prediction model. One important factor addressed in the model was a means of evaluating the number of wet days based on water existing underneath the slab at the slab/subbase interface. The figure is not only a function of annual rainfall, but also surface inflow, sealant effectiveness, and subbase drainability.

The erosion resistance of materials, number of wet days, and traffic load were defined and coupled in this model to effectively analyze the potential for faulting and erosion in jointed concrete pavements. The model uses faulting/erosion as a function of the number of load repetitions with respect to wet days and the erosion resistance of the subbase.

The erosion model follows the Gumbel cumulative probability function, which refers to structural damage due to aging and loading overtime or traffic. The model calculates erosion in percentage equal to the ratio between the current faulting and total amount of faulting. To convert the daily traffic to an erosion-based equivalency, a traffic model was incorporated into the analysis process. The determination is expressed in terms of an equivalent single axle-load, having included factors such as lane distribution, equivalent load, equivalent axle, equivalent wander, and an estimated number of trucks. The model can be calibrated for local conditions as a function of distinct characteristics of the subbase or subgrade—an important capability in life cycle analysis. The model has been successfully implemented into a spreadsheet format. Results show the model fits well with the field data and can be implemented for design and maintenance management purposes.

Conclusion
Results confirm if joint seals are properly installed, and can therefore be very effective in preventing moisture infiltration and performance issues related to erosion damage. Thorough use of the mechanistic-empirical fault prediction model, one can determine the effectiveness of sealant in pavement sustainability. Unsealed joints had significantly higher flow rates compared to joints with varying degrees of damaged sealants. The results of this study also demonstrated the positive effects of proper sealant installation on joint seal drainage performance. Using this model, DOTs and contractors can determine how to effectively seal joints so the pavement can last longer.

Scott Eilken is a co-chair of the Seal/No Seal Group and owner of Quality Saw & Seal. He also provides information and makes presentations on best practices for sealant installation. Eilken is active in the International Grooving & Grinding Association (IGGA). He can be reached via e-mail at seilken@qualitysawandseal.com.

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