Performance Specifications without Percent within Limits (PWLs); a Counter Point of View

The paper briefly summarizes a procedure to quantitatively establish pay factors for asphalt concrete pavement construction using performance models for fatigue and rutting based on accelerated performance tests. The performance models make use of means and variances rather than PWLs for asphalt concrete construction parameters. For rutting, the influence of asphalt content, air-void content, and aggregate gradation are considered. For fatigue, air-void content, asphalt content, and asphalt concrete thickness are included. Using a pre-selected target (design) value and a reasonable standard deviation (excluding test variance) for a specific mix property or pavement parameter, the relative performance (RP) of the as-constructed mix can be determined based on its measured mean property and standard deviation. In this instance RP is defined as the ratio of off-target traffic (ESALs) to target or design traffic (ESALs). Costs are established using a cost model considering only agency cost consequences of delaying or accelerating the time to the next rehabilitation. The shortest RP for the combined RP’s for mix and pavement characteristics considered for a specific distress mode permits determination of the pay factor from the cost model. The argument is made that this approach, based on the use of target values and standard deviations, is a sounder approach to establishing pay factors than PWLs. This is accomplished by using established performance models for specific distress modes and mechanistic-empirical pavement analysis to estimate expected pavement performance (in terms of ESALs) and a cost model which considers agency cost consequences resulting from off-target construction. The approach emphasizes the importance of adhering to the target value for a specific pavement characteristic (mix property and layer thickness) and maintaining uniformity (low standard deviation) to achieve or exceed the desired performance level. In addition, pay factors are combined for a specific distress mode, making use of a multiplicative procedure, which Monte Carlo simulations have demonstrated is a simple yet reasonable method. The results from a process used by a State DOT for obtaining a combined pay factor, using weighting factors for selected mix parameters, are compared with the multiplicative procedure. The comparison suggests that weighting factors for specific mix parameters are dependent on the mode of distress; for example, the effect of asphalt content is different for fatigue and rutting.

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  • English

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  • Accession Number: 01041422
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jan 30 2007 1:29PM