MTE Services was contacted by MN DOT to investigate the low temperature fracture - properties and fatigue properties of three research bituminous mixes which had been constructed at the MNROAD test facility near Rogers, MN in 1999. In addition the SHRP PG test properties of the three binders used on each respective test section were to be determined. The bituminous mixes to be investigated utilized the same aggregate structure and differed only in the binder grade used for each test section. The grades were PG 58-28 (unmodified), PG 58-34 (polymer modified) and PG 58-40 (polymer modified)
This paper’s purpose is to provide an update on the pavement condition of MnROAD’s three low volume road (LVR) Superpave test cells constructed in 1999 with different asphalt binders, see table below. These cells were built to field validate the current low temperature performance grading (PG) system currently being used at Mn/DOT and many other agencies around the world. The paper will document the mix designs, laboratory testing, forensics, environmental conditions, and the resulting distresses observed include rutting, transverse cracking, fatigue cracking and how they are affecting pavement performance and ride.
The effects of vehicle loads on pavement performance are usually estimated using a system based on the American Association of State Highway Officials (AASHO) Road Test data that was collected in the late 1950s. Analyses of this data led to the development of empirically derived expressions representing the relationships between vehicle loads, pavement performance, and pavement design variables. These expressions were then used to develop so-called “load equivalency factors” which were used to quantify the effects of different axle configurations and loads in terms of an equivalent number of passes of a particular axle configuration and load.
Falling Weight Deflectometer (FWD) data and the corresponding pavement stiffness moduli and deflection basin areas vary as functions of both time and space. This paper focuses primarily on extracting information from the spatial variability of FWD deflection data. Spatial variability occurs both horizontally and vertically within a pavement system; it is inherent in the system due to the heterogeneity of the material composing the subgrade. and is further influenced by the construction process and the resulting variations in density, moisture content, and thickness of the subbase, base, and surface layers.
To assess spatial variability of just the subgrade and then the overall pavement structure, FWD tests were conducted on 71 test points on top of each of the layers composing a pavement system. and a statistical analysis was conducted on the data. Test pavements included two mainline (five-year design) and two low-volume test cells at the Minnesota Road Research Project (MN/ROAD).
By comparing differences between pairs of measured deflections at increasing test point separation distances. one can incorporate distance weighting techniques into a statistical form frequently used in the fields of geology and mining. The geostatistical semi-variogram can be applied to pavements and used to model the degree of correlation between data at any two test points. As the distance between test points increases, corresponding data become decreasingly dependent upon each other until, at some appreciable distance. they are independent of each other. From the semi-variogram. one can readily determine the separation distance at which values are independent of each other. Conventional statistical analyses are also used to supplement geostatistical techniques.
Valuable and cost-saving information can be acquired by analyzing baseline FWD data with this technique. The efficiency of future FWD testing can be maximized, and optimum FWD test point spacing can be determined for pavement evaluation and overlay design. Furthermore, the geostatistical techniques discussed are applicable to any problem involving the distribution of a variable in one. two, or three dimensions.
This report presents ways pavement and materials engineers can use dynamic cone penetrometers (DCPs). The Dynamic Cone Penetrometer (DCP) is a test device used for measuring the strength and variability of unbound layers of soil and granular material. The DCP is not a new test device but transportation organizations in Canada and the United States, including the Strategic Highway Research Program (SHRP), have shown a renewed interest in its unique capability of measuring a profile of in situ foundation characteristics. A desire to more fully characterize subsurface conditions on the Minnesota Road Research Project (MnROAD) led to the initial use of DCP's by Mn/DOT. From an operational perspective it is very attractive because the DCP is both portable and simple to use. The objective of this research was to explore ways that DCP's could effectively be used by Minnesota pavement and materials engineers and to perform the testing, analysis, and learning necessary far establishing relationships between DCP test results and other commonly used foundation parameters. This report describes the design and operation of the DCP as well as an overview of the theoretical basis for use of the device. In addition, correlation results, data profiles, case histories and related information are presented.
Objectives of the Study:
1) Establish the basis for Mn/DOT'S current quality specifications/tests for concrete aggregate.
2) Through a literature search and personal contacts, evaluate a wide variety of existing tests and report the author's opinion on the ability of each to
predict aggregate freeze-thaw durability in PCC pavements.
3) State Author's opinions of best test(s) for the laboratory determination of aggregate freeze-thawdurability for use in Minnesota.
Deflection tests have been used in the past by some districts to provide information on the spring thaw period although there has not been a uniform procedure established for statewide use. The committee decided to have additional deflection data collected and analyzed to determine how these tests could be used to establish criteria for the setting or removal of spring load limits.
The type of questions that had to be answered were:
1. Can deflection tests be used to determine when the posting period should start?
2. Can deflection be used to determine when the posting will end?
3. Are deflection tests necessary on all posted highways during the spring thaw period?
4. Should testing be done daily, weekly or bi-monthly?
5. What analysis can be done with deflection data that may lead to the establishment of spring posting period criterion?
6. How many test sections would be needed and where should they be located?
Premature deterioration of continuously reinforced concrete pavement (CRCP) has become a serious problem in Minnesota. Spalling and delaminations, similar to those found on deteriorating bridge decks, have appeared on sections of CRCP, many after less than 10 years of service. Tension failures, or rupturing of the longitudinal reinforcing steel caused by loss of section due to corrosion, have also been a problem. Other sections of CRCP remain in good condition, but the potential for early deterioration exists for them, as well. Two methods were tried to halt the ongoing corrosion: a cathodic protection system and a low slump dense concrete (LSDC) overlay. Robert G. Tracy, Research Project Engineer, (now in private business), designed and supervised the cathodic protection system project. Installation was done through the cooperation of District 9 Maintenance and Physical Research personnel. Construction of the LSDC overlay was done by Progressive Contractors, Inc., under the control of Paul Juckel, Project Supervisor, Oakdale. The projects were done in conjunction with the FHWA's Highway Planning and Research Program.
The Minnesota Department of Transportation (Mn/DOT) investigated a polymer concrete (PC) patching material in cooperation with the Brookhaven National Laboratories (BNL) and the Federal Highway Administration (FHWA). This material has been previously tested by other states throughout the country. The material is claimed to be a rapid curing, durable material for patching potholes and deteriorated cracks in Portland cement concrete pavements and bridge decks.
Previous field tests of PC materials have been small in scope and size. The problems associated with the material were the tendency of the monomer to drain from the system, the development of shrinkage cracks in the polymerized material, and the need for a knowledge of chemistry to mix the monomer system. The BNL material is supposed to correct these drawbacks.
Mn/DOT made a laboratory study of the PC material by producing a control mix of portland cement, low-slump concrete to evaluate how PC material compares to the low-slump concrete with respect to:
- freeze thaw durability,
- compressive strength,
- tensile splitting strength; and
- chloride permeability.
Shear bond strength tests of the PC material are being conducted by the BNL. Field evaluation of the PC material has proven to be inconclusive. Patches failed in both the concrete pavement and the bridge deck. The bridge deck patches had to be removed completely. These failures are not due to the PC material itself.
