Hot-mix asphalt (HMA) is extensively used throughout Italy and the world as a reliable and cost-effective pavement surfacing for roads, parking lots, and airfields, however its performance can be greatly affected by many materials and construction (M&C) factors, as well as traffic and environmental variables. In the past, design and construction procedures of HMA, tended to be more empirical and heuristic than scientific, in that they relied primarily upon the experience and engineering judgment of the mix designers and road agencies. During the last two decades, important advances in HMA technology have occurred in the areas of materials (particularly binders) and mix design (e.g. studies on mix design in the Strategic Highway Research Program - SHRP), whereas less attention was devoted to construction quality specifications (CS). At the same time It is generally acknowledged that quality of the construction process is a major factor in determining how well a pavement will perform under traffic loading and when subjected to environmental influences. To improve the construction process, quality control/quality assurance (QC/QA) procedures and pay incentives, taking pavement performance into consideration, have to be instituted. Contractor pay incentives serve at least two objectives: they encourage the contractor to construct pavements with significantly improved performance in comparison to those meeting minimum specification requirements; and they provide a rational alternative for dealing with marginally inadequate/adequate construction. We can distinguish between four different levels of construction quality control procedures/specification, that take pavement performance into consideration [CHAMBERLAIN, 1995]: • Acceptance Quality Characteristics (AQCs); • Direct Measures of Performance (DMP); • Performance Based Specification (PBS); • Performance Related Specification (PRS). In AQCs procedure, that is largely applied, the materials and construction factors, used to control quality (e.g. binder content or relative compaction), is primarily tied to performance through intuition, engineering judgment, or both: These conventional QA acceptance procedures use engineering judgment also to establish individual AQC pay adjustments (and weighting factors for each) for determining the overall price adjustment for the lot. On the other side, are DMP in which specifications describe how the finished product should perform over time (e.g. IRI < 3 after 20 years, area cracked < 10 % after 20 years , rut depth < 10 mm after 15 years). These type of specification have not been used in Italy so far, because quality and pay factor could be established after a great time to construction; therefore they could take the form of warranty or guarantee in which contractor agrees to build and maintain the pavement for a specified period of time, rather than construction specification. In the performance-based specification (PBS) quality characteristics are directly tied to performance through empirical, or mechanistic, prediction model that accounts for the effect of deviations of the as-constructed QC level from the as-designed QC level. The difference in predicted performance between the as-designed and as-constructed pavement is then used as a basis for a contractor pay adjustment (PA). Performance related specification (PRS), as PBS, require prediction model to evaluate the effect of deviations of quality characteristics level from its target, but the quality characteristics are less directly tied to performance. As matter of fact in PRS the effect of an overall specification, containing multiple quality characteristics, is evaluated, and the prediction models are used to develop a secondary prediction relationship, that establish the link between multiple quality characteristics (vector of QCs) and performance. PRS have two major advantages over conventional and PB specifications: they are able to identify desirable levels of AQC that provide a desired pavement performance and they provide a rational basis on which pay adjustments can be determined (basing on Life Cycle Cost Analysis). The objective of this paper is to demonstrate a rational and feasible method for define PSR and quantitatively establishing penalties/bonuses for asphalt concrete construction with the initial emphasis placed on new asphalt concrete pavement construction. The approach taken herein for the development of pay factors take into consideration HMA quality control adopted in Italy so far, in an attempt to bridge the gap between currently used specifications and fully implementable PRS. Furthermore attention is focuses primarily on the economic impacts to the highway agency while user costs are not included.

A Rational Approach for the Evaluation of Pavement Pay Factors”

PERNETTI, Mariano
2005

Abstract

Hot-mix asphalt (HMA) is extensively used throughout Italy and the world as a reliable and cost-effective pavement surfacing for roads, parking lots, and airfields, however its performance can be greatly affected by many materials and construction (M&C) factors, as well as traffic and environmental variables. In the past, design and construction procedures of HMA, tended to be more empirical and heuristic than scientific, in that they relied primarily upon the experience and engineering judgment of the mix designers and road agencies. During the last two decades, important advances in HMA technology have occurred in the areas of materials (particularly binders) and mix design (e.g. studies on mix design in the Strategic Highway Research Program - SHRP), whereas less attention was devoted to construction quality specifications (CS). At the same time It is generally acknowledged that quality of the construction process is a major factor in determining how well a pavement will perform under traffic loading and when subjected to environmental influences. To improve the construction process, quality control/quality assurance (QC/QA) procedures and pay incentives, taking pavement performance into consideration, have to be instituted. Contractor pay incentives serve at least two objectives: they encourage the contractor to construct pavements with significantly improved performance in comparison to those meeting minimum specification requirements; and they provide a rational alternative for dealing with marginally inadequate/adequate construction. We can distinguish between four different levels of construction quality control procedures/specification, that take pavement performance into consideration [CHAMBERLAIN, 1995]: • Acceptance Quality Characteristics (AQCs); • Direct Measures of Performance (DMP); • Performance Based Specification (PBS); • Performance Related Specification (PRS). In AQCs procedure, that is largely applied, the materials and construction factors, used to control quality (e.g. binder content or relative compaction), is primarily tied to performance through intuition, engineering judgment, or both: These conventional QA acceptance procedures use engineering judgment also to establish individual AQC pay adjustments (and weighting factors for each) for determining the overall price adjustment for the lot. On the other side, are DMP in which specifications describe how the finished product should perform over time (e.g. IRI < 3 after 20 years, area cracked < 10 % after 20 years , rut depth < 10 mm after 15 years). These type of specification have not been used in Italy so far, because quality and pay factor could be established after a great time to construction; therefore they could take the form of warranty or guarantee in which contractor agrees to build and maintain the pavement for a specified period of time, rather than construction specification. In the performance-based specification (PBS) quality characteristics are directly tied to performance through empirical, or mechanistic, prediction model that accounts for the effect of deviations of the as-constructed QC level from the as-designed QC level. The difference in predicted performance between the as-designed and as-constructed pavement is then used as a basis for a contractor pay adjustment (PA). Performance related specification (PRS), as PBS, require prediction model to evaluate the effect of deviations of quality characteristics level from its target, but the quality characteristics are less directly tied to performance. As matter of fact in PRS the effect of an overall specification, containing multiple quality characteristics, is evaluated, and the prediction models are used to develop a secondary prediction relationship, that establish the link between multiple quality characteristics (vector of QCs) and performance. PRS have two major advantages over conventional and PB specifications: they are able to identify desirable levels of AQC that provide a desired pavement performance and they provide a rational basis on which pay adjustments can be determined (basing on Life Cycle Cost Analysis). The objective of this paper is to demonstrate a rational and feasible method for define PSR and quantitatively establishing penalties/bonuses for asphalt concrete construction with the initial emphasis placed on new asphalt concrete pavement construction. The approach taken herein for the development of pay factors take into consideration HMA quality control adopted in Italy so far, in an attempt to bridge the gap between currently used specifications and fully implementable PRS. Furthermore attention is focuses primarily on the economic impacts to the highway agency while user costs are not included.
978-88-902409-9-7
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11591/206279
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact