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A study was initiated to harmonize the dynamic friction tester and a locked-wheel tester on Florida's typical open-graded and dense-graded surfaces under various speed conditions. In addition, two texture measuring devices, the circular track meter and a high-speed 64-kHz laser mounted to the locked-wheel tester, were evaluated. These devices were first harmonized at a standard test speed of 40 mph (65 km/h). Because of the increased level of macrotexture in the open-graded mixtures, the open- and dense-graded surfaces were assumed to show different frictional behavior under different speed conditions. As a consequence, the harmonization equations for the open- and dense-graded surfaces were developed separately. Harmonization of different test speeds was also performed for each given test method to allow for converting the friction measured at a range of speeds—30 mph (50 km/h) to 60 mph (95 km/h)—back to that of the standard speed. The flexibility provided by these harmonization efforts is of great practical use and provides an alternative to the international friction index for Florida's conditions.

As part of Florida DOT (FDOT)’s Partnering Program, a temporary roadway was designed and constructed using three different pavement sections. The program consisted of pavement construction monitoring and field/laboratory testing during construction, prior to opening to traffic and demolition. The study documents the findings of the ongoing efforts by FDOT to assess the applicability of untreated recycled asphalt pavement (UNRAP) as base course for pavement sections. Three different temporary pavement sections were constructed. Two sections were constructed with UNRAP, one with a stabilized subgrade and the other with a compacted subgrade. The third section was constructed with a limerock base and stabilized subgrade, and was used for comparison purposes. The UNRAP material used in the temporary pavement sections was milled off of the existing roadway. Laboratory and field testing, including Dynaflect and falling weight deflectometer (FWD), were performed and evaluated. The study suggested the UNRAP base p...

The Florida Department of Transportation initiated a field study to compare the suitability of two friction-testing devices for measuring the friction characteristics of patterned and textured crosswalks: (a) a site-specific dynamic friction tester (DFT) and (b) a semicontinuous locked wheel tester. The locked wheel testing was performed with both ribbed and smooth tires at 20, 30, and 40 mph (30, 50 and 65 km/h), respectively. Ten test sections were randomly selected to include the different types of patterned and textured processes currently approved for use in Florida. The results of this study indicated that the smooth tire measurements were, generally, in good agreement with the DFT, regardless of test speed. The correlation between the DFT and the ribbed tire test improved with the increasing speed of the locked wheel testing. In addition, for a given test method, harmonization of different test speeds was also performed to allow for the speed conversion of the friction coefficients. The flexibility provided by these harmonization efforts is of great practical use in evaluating the frictional characteristics of patterned and textured crosswalks, especially when dealing with constraints such as speed limits. The testing program, the data collection effort, and the subsequent analyses and findings are described, as well as the lessons learned from Florida's experience with patterned and textured pavements.

As part of the evaluation of the potential use of the international friction index as the standard for the reporting of friction measurements, the Florida Department of Transportation (FDOT) conducted an assessment of the precision of the dynamic friction tester (DFT) and circular track meter (CTM) test methods. The FDOT CTM equipment and DFT equipment were compared with similar portable equipment owned and operated by the National Center for Asphalt Technology (NCAT) in an attempt to quantify both the repeatability and the reproducibility of the test data obtained. The FDOT portable equipment was mobilized to Auburn, Alabama, for side-by-side testing with the NCAT equipment. This paper summarizes the results of an assessment of the precision of the DFT and CTM equipment on 10 different test surfaces at the NCAT Pavement Test Track. Tests with DFT and CTM were performed at five different locations within each of the 10 different test sections by using both NCAT and FDOT equipment. On the basis of the results of this comparison testing, proposed precision statements are presented for both the repeatability and the reproducibility of the data for the respective pieces of equipment. Correlation relationships are also presented for the portable equipment and the full-scale equipment currently used by FDOT and others.

Because of safety concerns associated with friction testing on both high-and low-speed facilities, testing at variable speeds has been investigated by the Florida Department of Transportation (DOT) and others. Previous research has demonstrated that reasonable correlations may be developed between friction test data obtained at the standard test speed of 40 mph (64.4 km/h) and other speeds. As part of an effort to harmonize its fleet of full-scale, locked-wheel friction testing equipment with portable reference test equipment (ASTM E 1960), the Florida DOT also evaluated the skid number speed gradient ( Gv) for use in transforming friction and macrotexture measurements obtained at variable highway speeds. This paper documents the results of this evaluation. On the basis of the results of this study, a practical method of measuring pavement friction and macrotexture at variable highway speeds with the Florida DOT locked-wheel test unit and the ribbed tire is presented. Since the results of the ribbed tire test are known to be significantly influenced by pavement microtexture and since the mean profile depth (MPD), as measured with the high-speed laser, is a direct measure of macrotexture, the friction number (FN)40 R and the complementary MPD data together may be readily employed to characterize the frictional properties of the pavement. This approach builds on Florida's historical database of locked-wheel, ribbed-tire test data, while adding a direct measure of macrotexture and the flexibility of testing at variable speeds. Practical implementation recommendations and examples are provided.

In recent years, larger vibratory rollers have been implemented because of their improved efficiency. An unfortunate consequence is that greater ground motion caused by these larger vibratory rollers might damage adjacent infrastructure, particularly in or near urban areas. Various federal, state, and foreign agencies have proposed vibration limit criteria; some are intended to mitigate damage to structures while others are based on limiting human annoyance. Two of these existing criteria (U.S. Office of Surface Mines blasting level criteria and German DIN 4150 standard level for human annoyance) were selected to form the basis of a recommended practice for limiting vibratory compaction in critical work zones. These criteria are used to differentiate three zones on a plot of peak particle velocity versus vibratory roller frequency. A square-root scaling law of ground motion is used to predict the ground motions from vibratory compaction equipment based on falling weight deflectometer (FWD) data. With this predictor, a potentially vibration-sensitive portion of a resurfacing project can be identified using displacement time histories from the FWD obtained during routine preconstruction testing. Detailed knowledge of the layering of the pavement structure or the geology of the surrounding site is not required. It is demonstrated that this predictor can successfully be used to restrict vibratory compaction near sensitive structures, including fragile buried infrastructure.

Thermal cracking of asphalt concrete pavements is responsible for millions of dollars in annual maintenance and rehabilitation costs in the United States and Canada. Thermal cracking typically is associated with low temperatures in northern climates and at high elevations. Another form of thermal cracking, known as thermal fatigue cracking, has been proposed by several researchers as a potential mode of distress in regions with relatively moderate climates. The objectives were to evaluate the possibility of the occurrence of the thermal fatigue cracking mode of distress and to identify a suitable laboratory test procedure to facilitate a mechanistic analysis of this mode of distress. The most promising test procedures evaluated included the direct tensile creep test and the thermal stress restrained specimen test. The results suggest that thermal fatigue distress in asphalt concrete mixtures is not a viable mode of distress in the absence of environmental aging. From the data presented and results documented by others, it is evident that distress often attributed to thermal fatigue cracking is more likely the result of low-temperature cracking of environmentally aged mixtures or subgrade-related distress. It is concluded that fatigue distress due to thermal loading of semirestrained pavements does not occur.

A lab investigation into the resistance to freezing and thawing of recycled aggregate concrete (RAC) as compared with that of natural aggregate concrete (NAC) is described. Three different cases were considered for RAC and NAC. Case I consisted of using a medium water-cement ratio (w/c) of 0.47 for both RAC and NAC. Case II was varied from Case I by lowering the w/c from 0.47 to 0.29 (high-performance concrete). Case III consisted of varying the base mixtures by entraining them with an air content of 5%. The durability performance of the RAC in Cases I and II was negatively affected by the recycled aggregates. These results contrast with those found for NAC in which full development of the freeze-thaw durability was reached. With use of entrained air (Case III), however, RAC was found to be as durable as NAC.

Early-age cracking can adversely affect strength, serviceability, and durability of concrete bridge decks. Early age is defined as the period after final setting, during which concrete properties change rapidly. Many factors can cause early-age bridge deck cracking including temperature change, hydration, plastic shrinkage, autogenous shrinkage, and drying shrinkage. The cracking may also increase the effect of freeze and thaw cycles and may lead to corrosion of reinforcement. This research paper presents an analysis of causes and factors affecting early-age cracking. It also provides a tool developed to predict the likelihood and initiation of early-age cracking of concrete bridge decks. Understanding the concrete properties is essential so that the developed tool can accurately model the mechanisms contributing to the cracking of concrete bridge decks. The user interface of the implemented computer Excel program enables the user to input the properties of the concrete being monitored. The research study and the developed spreadsheet were used to comprehensively investigate the issue of concrete deck cracking. The spreadsheet is designed to be a user-friendly calculation tool for concrete mixture proportioning, temperature prediction, thermal analysis, and tensile cracking prediction. The study also provides review and makes recommendations on the deck cracking based mainly on the Florida Department of Transportation specifications and Structures Design Guidelines, and Bridge Design Manuals of other states. The results were also compared with that of other commercially available software programs that predict early-age cracking in concrete slabs, concrete pavement, and reinforced concrete bridge decks. The outcome of this study can identify a set of recommendations to limit the deck cracking problem and maintain a longer service life of bridges.