N Mike Jackson

Precision Statements for the Surface Resistivity of Water Cured Concrete Cylinders in the Laboratory

A rigorous round-robin testing program was conducted for surface resistivity (SR) measurements of water cured concrete cylinders in the laboratory. Fourteen different laboratories participated in this effort, testing twelve different Portland cement concrete mixtures containing a wide range of constituent materials. Also, test results from two different commercially available SR meters were compared for statistical equivalence of the data. The results of this effort have been used to formally document the repeatability (single-operator precision) and reproducibility (multilaboratory precision) of SR measurements in the laboratory.

Practical Approach to Measuring and Reporting Friction and Macrotexture at Variable Test Speeds

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)40R and the complementary MPD data together may be readily employed to characterize the frictional properties of the pavement. This approach builds on Floridas 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.

Harmonization of Texture and Friction Measurements on Florida’s Open-Graded and Dense-Graded Pavements

A study was initiated to harmonize the dynamic friction tester and a locked-wheel tester on Floridas 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 Floridas conditions.

Recommended Practice for Identifying Vibration-Sensitive Work Zones Based on Falling Weight Deflectometer Data

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.

Measuring Friction of Patterned and Textured Pavements: A Comparative Study

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 Floridas experience with patterned and textured pavements.

Assessment of Precision of Circular Track Meter and Dynamic Friction Tester

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.