Kurt D Smith

CURRENT PRACTICE OF PORTLAND CEMENT CONCRETE PAVEMENT TEXTURING

The importance of surface texture characteristics to roadway safety was first recognized during the late 1940s and early 1950s when increases in traffic volumes and vehicle speeds resulted in increases in wet-weather crashes and fatalities. As a result, agencies conducted extensive research, including experimental projects around the country, to better understand and improve the surface conditions of portland cement concrete pavement in wet-weather conditions. As new surface-texturing methods were tried and evaluated, pavement engineers recognized that a general trade-off existed between friction and noise; that is, surface textures with higher friction tended to produce greater tire-pavement noise. Although considerable information exists on the influence of surface friction characteristics on safety and tire-pavement noise, it is dispersed among numerous sources. An effort is made to identify and summarize key texture-related information and recommendations based on the current state of the practice. Specifically, pavement texture nomenclature is introduced, methods of measuring and quantifying texture are discussed, traditional and innovative texturing methods and techniques are described, respective conclusions pertaining to the influence of texture characteristics on surface friction and tire-pavement noise are summarized, and current state-of-the-art texture-related recommendations are provided.

EFFECT OF INITIAL PAVEMENT SMOOTHNESS ON FUTURE SMOOTHNESS AND PAVEMENT LIFE

Initial pavement smoothness has an effect on the future smoothness and life of asphalt concrete (AC) and portland cement concrete (PCC), as well as AC overlays of existing AC and PCC pavements. Initial pavement smoothness has a significant effect in 80 percent of new construction (both AC and PCC pavements) and in 70 percent of AC-overlay construction. Furthermore, using two different analysis techniques, added pavement life can be obtained by achieving higher levels of initial smoothness. Combined results of roughness-model and pavement-failure analyses indicate at least a 9 percent increase in life corresponding to a 25 percent increase in smoothness from target profile index (PI) values of 7 and 5 in./mi (0.11 and 0.08 m/km) for concrete and asphalt pavements, respectively.

APPLYING ECONOMIC CONCEPTS FROM LIFE-CYCLE COST ANALYSIS TO PAVEMENT MANAGEMENT ANALYSIS

In recent years, FHWA has made a concerted effort to develop guidelines for the use of life-cycle cost analysis by transportation agencies and to promote the use of multiyear prioritization in pavement management. These efforts resulted in the development of a Technical Bulletin and Demonstration Project course materials that have been presented to state highway agencies throughout the country. A key part of multiyear prioritization is emphasis on the use of life-cycle cost information in cost-effectiveness calculations. An agency implementing multiyear prioritization as part of its pavement management system would naturally attempt to utilize the FHWA’s guidelines in developing the cost component of its economic analysis. However, because of the types of analyses required in pavement management and the ways in which cost information is reported and used, the recommendations provided in FHWA’s Technical Bulletin cannot be applied directly. The types of economic analyses that are used in an incremental benefit-cost analysis and the types of economic considerations that must be taken into account are discussed. Several of these economic considerations differ from the recommendations made in FHWA’s Technical Bulletin, so the reasons for these variations are also described.

Evaluation of Rubblized Pavement Sections in Michigan

In 1987 the Michigan Department of Transportation (MDOT) began using rubblization of portland cement concrete (PCC) pavement followed by the application of a hot-mix asphalt (HMA) overlay as a rehabilitation method for deteriorated PCC pavements. Early projects constructed in Michigan used the resonant frequency breaker to rubblize the PCC pavement, but by 1997 MDOT began to use the multi-head breaker (MHB) also. In 1999, because some rubblization projects needed rehabilitation after fewer than 12 years of service, MDOT initiated a study to identify causes for underperforming rubblized concrete pavement projects. The current study, initiated in 2005, was conducted specifically to investigate the performance of rubblized projects constructed with the MHB with the use of data provided by MDOT. Analysis of projects constructed in Michigan that used the MHB between 1997 and 2002 revealed that 20 of the 21 pavement sections evaluated had a distress index (DI) condition rating of good, and all sections had ride quality index values in the excellent or good category. The international roughness index values also indicated that all pavements were in good condition, with values of less than 95 in./mi. The DI for most sections indicated that the distress was due to longitudinal cracking at the pavement construction joint and at the pavement edge. Most distresses present on the pavement sections seemed to be related to poor or insufficient drainage, overlay construction issues, or HMA mixture problems.

Estimating Remaining Life of Airfield Pavements

Currently, there is no universally accepted procedure or approach to performing remaining life analyses for airfield pavements. However, there are several methods that have been employed to estimate the remaining life of airfield pavements, each with advantages and limitations. Airport managers and engineers understand the importance and significance of this concept, and are increasingly interested in seeing reported some measure of remaining life as a part of pavement management and evaluation projects. This paper describes in detail several different approaches that are used to estimate the remaining life of airfield pavements (both bituminous- and concrete-surfaced). These include a design-based or traffic-based approach, a PCI approach, and a mechanistic-empirical analysis approach. The advantages and disadvantages of each approach are discussed. Although it is acknowledged that estimating remaining life is not an exact science, and that the chances of obtaining the same result from different approaches is slight, the information obtained from such analyses is extremely useful as part of an overall evaluation of an airports pavements, as well as in planning and programming pavement rehabilitation activities.

Development of Prototype Performance-Related Specification for Concrete Pavements

The development of a prototype performance-related specification (PRS) for concrete pavement construction is summarized. The prototype PRS requires that a pavement lot be divided into consistent sublots for the measurement of quality characteristics, which are then used to estimate future performance and life-cycle costs. The difference between the life-cycle costs of the target (as-designed) pavement and the actual (as-constructed) pavement lot is used to determine a rational pay adjustment. Both means and variations of all quality characteristics are directly considered in the pay factor determination. Extensive laboratory testing was conducted to determine material relationships needed in the prototype PRS. A Windows-based computer program, PaveSpec, was developed for use with the specification in simulation and in generating pay adjustments. However, additional work is required to make this a fully practical PRS.

Evaluation of Potential Long-Term Durability of Joints Cut With Early-Entry Saws on Rigid Pavements

Early-entry sawing is an attractive operation to expedite the construction of jointed concrete pavements; however, there are some concerns that early-entry sawing may compromise the pavements long-term performance. The Illinois Department of Transportation initiated this study as an initial effort to investigate the durability of joints sawed by using early-entry sawing. Joint performance as a function of saw-cut depth and timing was also considered. The study was integrated into an active construction project along Illinois Route 59 in Plainfield. During construction, paving and sawing operations were observed and documented; of particular interest were the sawing operations, during which signs of surface scarring, joint raveling, and slab edge breakouts were recorded and the extent of sawing-related damage was subjectively assessed. In addition to general observations, climatic conditions were monitored, as was pavement temperature from time of paving onward. Ambient climate conditions, portland cement concrete mixture, and slab temperature data were used to perform a HIPERPAV analysis to assess the potential for early-age cracking. Compressive strength cylinders were also cast and tested at 3, 7, and 28 days. In addition, cores were retrieved from joints throughout the test section and a battery of durability tests—including petrographic analysis, freeze–thaw testing, and resistance to salt scaling—was conducted. Overall observations from the field construction and findings from the laboratory testing indicate that the use of early-entry sawing is viable and that joint durability is not compromised.

Field Study of Air Content Stability in the Slipform Paving Process

This study evaluated the impacts of construction on the air content and air void system structure of portland cement concrete pavements. The primary intent was to quantify the air content of fresh concrete before and after it had gone through the slipform paver. The air void system parameters of hardened concrete were then assessed with cast cylinders and extracted core specimens. The results of the air content testing on fresh concrete and the concrete cylinder specimens cast in the field suggested that some loss of air (approximately 1%) occurred as the concrete passed through the paver. Laboratory testing performed on cores extracted from the pavement did not provide conclusive evidence that entrained air was lost during the slipform paving process. In fact, many extracted cores had measured air content values that were much higher than those measured in the fresh concrete and even higher than the specification requirement. If excessive, such values could result in increased permeability and low-strength-related issues. The results suggested that the air content testing on fresh concrete did not capture the true air content of the concrete as it was placed with a slipform paver. The fresh concrete air content in general was lower than was the air content measured in the cores.

Blast Furnace Slag as Sustainable Material in Concrete Pavements

Slag materials are byproducts of metallurgical processes that include metal production from ore and refinement of impure metals. Air-cooled blast furnace slag (ACBFS) has been used for different pavement-related applications. Appropriate use of ACBFS can significantly enhance sustainability, rather than disposing of it, by effectively contributing to all aspects of the “triple bottom line.” Proper use of ACBFS can also result in economic, environmental, and social benefits as long as the performance of the concrete structure is not compromised through such use because any short-term economic and environmental gain would be rapidly eclipsed by the economic, environmental, and social costs of poor pavement performance. Thus, it is essential that engineers and contractors who use ACBFS aggregates in concrete understand its unique properties to make sure that the expected performance of the pavement over its design life is achieved. The chemical composition of ACBFS may affect its performance and has to be considered when ACBFS is used as a coarse aggregate. Physical properties of ACBFS, such as texture, absorption, and specific gravity, also have to be considered when ACBFS is used in concrete. ACBFS also affects fresh and hardened properties of concrete. Specific design, construction, and quality control considerations have to be taken into account when ACBFS is used. In this paper, sustainability aspects of using ACBFS as a coarse aggregate in concrete pavements and considerations for its use in this application are presented. A best practices guideline recently published by FHWA presents the same discussions in more detail.

USING EPIFLUORESCENCE OPTICAL MICROSCOPY TO IDENTIFY CAUSES OF CONCRETE DISTRESS: CASE STUDY

Materials-related distress (MRD) has affected many portland cement concrete pavements. Identifying the specific cause of MRD is not always possible, but with the use of appropriate techniques and a diagnostic approach, the cause can be determined in many cases. In a case studied as part of an FHWA project titled Detection, Analysis, and Treatment of Materials-Related Distress in Concrete Pavements, apparent MRDs were identified. In one case study, determination of the effective water-to-cement ratio (w/c) by epifluorescence microscopy was the key to understanding the cause of distress. The effective w/c, which may not be exact for a given concrete on an absolute basis, was used to compare two concrete microstructures on a relative basis. Stereo-optical microscopy, petrographic optical microscopy, and scanning electron microscopy were also used to identify the MRD diagnostic features present in the distressed concrete. As a result of this analysis, evidence of paste freeze–thaw and deicer attack was identified, but the principal cause of the distress probably was a high w/c in the distressed concrete.