Testing

A pavement testing facility, the Minnesota Road Research Project (Mn/ROAD) contains a two-lane Low Volume Road (LVR) loop with dedicated traffic supplied by a five-axle tractor semi-trailer truck that has maximum legal gross weight of356 kN (80,000 pounds) when it travels in the clockwise direction and an overloaded 456 kN (102,500 pounds) in the counterclockwise direction. The LVR contains four 152.4 m (166 yard) sections with a 305 mm (12 inch) aggregate s1mcture, two of which arc surfaced with a double chip seal. These four sections include three main experimental variables: vehicle loads, graduations of aggregate, and surface types. This study involved monitoring the performance of these four sections from June 1994 to May 1995. Study conclusions include the following: • Aggregate gradations are not reliable predictors of performance as an aggregate wear. • A simplified test is needed to evaluate aggregate wearing materials • The performance of chip seals with respect to ride and rutting was better than the aggregate surfaced sections constructed with the same aggregate.

This report evaluates the Minnesota Department of Transportation's (Mn/DOT) Salt Solutions program over the past two years. The evaluation documents the components of the program, describes the technology, and provides a detailed cost-benefit analysis. Recognizing the potential to reduce the level of salt and sand use, the maintenance division began a reduction initiative in District 1 during the 1996-97 snow and ice season. The Salt Solutions program sought to develop a set of tools and a system that allowed operators to make better application rate decisions, support those tools and systems with ongoing training, develop controls and measurements to track the effectiveness of the tools and training, and recognize improved performance. The program expanded statewide in the 1997-98 winter season. Results of this evaluation show that the program is cost-effective means of reducing the amount of salt and sand applied to Minnesota roadways while still maintaining a safe operating environment. In its first year, the program saved an estimated $177,000.

As part of a project at the University of Minnesota to investigate the application of high-strength concrete in prestressed girders, four shear tests were performed on high-strength concrete prestressed girders. Originally constructed in August 1993, the girders, Minnesota Department of Transportation (Mn/DOT) 45M sections were 45 inches deep. Each girder utilized 46 0.6-inch diameter prestressing strands on 2-inch centers. The girders were designed assuming a 28-day compressive strength of 10,500 psi. Later, a 4-foot-wide and 9-inch-thick composite concrete deck was added to each girder using unshored construction techniques. The shear test results were compared with predicted results from ACI 318-95 Simplified Method, ACI 318-95 Detailed Method (AASHTO 1989), Modified ACI 318-95 Procedure, Modified Compression Field Theory (AASHTO LRFD 1994), Modified Truss Theory, Truss Theory, Horizontal Shear Design (AASHTO 1989), and Shear Friction (AASHTO LRFD 1994). The calculated shear capacities were in all cases conservative compared to the actual shear capacity.

Researchers conducted an experimental program to investigate production techniques and mechanical properties of high-strength concrete and to provide recommendations for using these concretes in manufacturing precast/prestressed bridge girders. High-strength concretes with 28-day compressive strengths in the range of 8,000 to 18,600 psi (55.2 to 128 MPa) were produced. Test variables included total amount and composition of cementitious material, portland cement, fly ash, and silica fume; type and brand of cement; type of silica fume, dry densified and slurry; type and brand of high-range water-reducing admixture; type of aggregate; aggregate gradation; maximum aggregate size; and curing. Testing determined the effects of these variables on changes in compressive strength and modulus of elasticity over time, on splitting tensile strength, on modulus of rupture, on creep, on shrinkage, and on adsorption potential as an indirect indicator of permeability. The study also investigated the effects of test parameters such as mold size, mold material, and end condition. More than 6,300 specimens were cast from approximately 140 mixes over a period of three years.

This report describes the design, instrumentation, construction, and test set-up of two high-strength concrete prestressed bridge girders. The girder specimens were constructed to evaluate prestress transfer length, prestress losses, flexural fatigue, ultimate flexural strength, and ultimate shear strength. Each test girder was a 132.75-foot long, 46-inch deep, Minnesota Department of Transportation (Mn/DOT) 45M girder section reinforced with 46 0.6-inch diameter 270 ksi prestressing strands. The 28-day nominal compressive strength of the girders was 10,500 psi. Each girder was made composite with a 9-inch thick, 48-inch wide composite concrete deck cast on top with a nominal compressive strength of 4000 psi. Girder I used a concrete mix incorporating crushed limestone aggregate while Girder II utilized round glacial gravel aggregate in the mix with the addition of microsilica. In addition, the two test girders incorporated two different end patterns of prestressing--draping versus a combination of draping and debonding--and two different stirrup configurations--standard Mn/DOT U versus a modified U with leg extensions. More than 200 strain gages were imbedded in each girder during construction. Other reports present flexural and shear testing results.

This study evaluated the thermodynamics of stress-laminated bridges under laboratory conditions. After assembling three timber laminated bridge deck panels of 120" x 43" x 12", high tension rods were used to form "stress-laminated" panels. Researchers placed the panels in a laboratory freezer, with cold temperature settings of 10*, 0*, -10*, -20°, and -300 Fahrenheit and repeated the process three times, each with the wood at a different moisture content--a "green" moisture content greater than 30 percent, a 17 percent moisture content, and a 7 percent moisture content (mc). The results showed that the bar force reduction in the green moisture content sample was significantly greater than in either the 17 percent or 7 percent me tests. The study concluded that the moisture content levels and temperature fluctuations cause variations in rod stressing levels; that the tensioning losses occur within a few hours of the temperature drop; that the green moisture content levels have a severe adverse effect on the stressing levels; and that tensioning levels somewhat stabilize with moisture contents below 17 percent. Based on this study, it would appear that any existing stressed bridge decks should be closely monitored until the moisture content of the members is less than 19 percent. Further study may be needed to determine the behavior of bridge decks with a moisture content above 17 percent and below the fiber saturation point.

This report presents a series of testing protocols used at the Minnesota Road Research Project (Mn/ROAD), the Minnesota Department of Transportation's (Mn/DOT) pavement testing facility. This report helps establish a history of the tests conducted and testing procedures, and also serves as a reference for researchers outside of Mn/DOT to compare the values found in independent or cooperative studies to Mn/ROAD test results and procedures. The following protocols are included: -pavement condition testing plan and testing protocols -deflection test protocols -subsurface temperature testing protocols -frozen soil measurements testing protocols -traffic measurements testing protocols -material samples testing protocols -soil moisture measurements testing protocols -climate data testing protocols -bituminous testing protocols.

This effort involved calculating maximum frost penetration depths for each of the 40 test cells at MnROAD, the Minnesota Department of Transportation's pavement testing facility, for the 1993-94, 1994-95, arid 1995-96 winters. The report compares results with measured maximum frost penetration depths for the same three winters. Generally, calculated depths were within plus or minus 15 percent of measured depths, but differences were much greater for the four test cells underlain by the granular subgrade. Researchers conducted sensitivity tests to determine the influence of the n-factor, soil moisture content, material density, layer thickness, thermal conductivity, mean annual soil temperature, and volumetric latent heat of fusion. Conclusions included the following: -Small variation in layer thickness will have a very minor effect on computed frost. depths. -Reasonable variations in moisture content and density of the various base course, subbase course, and subgrade layers will have a minor effect on calculated frost penetration depths. -Large n-factors caused deeper calculated frost penetration depths, and the use of n-factors of .90 and .95, respectively, for flexible and rigid pavements provided the most reasonable estimates of frost depths. -Increasing the thermal conductivity of the materials by 25 percent resulted in closer calculated agreement with measured frost depths. -Using a mean annual soil temperature of 9.4√ C rather than 11.1√ C resulted in better agreement between calculated and measured data.

Technical Research Center of Finland (VTT) conducted wheel tracking and fatigue tests of Minnesota Road Research Project (Mn/ROAD) bituminous mixtures as a result of the cooperation between Finnish National Road Administration (FinnRA) and Minnesota Department of Transportation (Mn/DOT). FinnRA funded the tests. Mn/ROAD, Mn/DOTs pavement testing facility, sent raw materials (aggregates and binders) and ready- made mixtures. In spite of the differences between Mn/ROAD and Finnish mixtures, the rutting of Mn/ROAD mixture measured by wheel tracking device was similar if compared to a dense graded mixture with binder of similar penetration. The Mn/ROAD mixture with low stiffness binder deformed much more and tested outside the Finnish specifications. However, it may be successful in Minnesota because of smaller axle loads. The fatigue properties in strain control tested about the same as corresponding Finnish bituminous mixtures. However, the behavior in stress mode was different. The Mn/ROAD fatigue line tested flatter than any Finnish bituminous mixture with straight run bitumen, and only some with polymer modified bitumen were similar. The report recommends careful analysis of the fatigue properties of Mn/ROAD pavement performance

This report examines the diametral compression test, as described in ASTM D4123-82 (1987) and SHRP Protocol P07 (1993) procedures. The test helps determine the resilient modulus of asphalt concrete, and less frequently its Poisson's ratio, both mechanical parameters of an ideally elastic material. However, the actual behavior of asphalt concrete is not elastic, but viscoelastic. The viscoelastic behavior of asphalt concrete under traffic-induced loads can be described by the phase angle and the magnitude of the complex compliance or complex modulus. These can be determined from the diametral compression tests that subject the specimen to haversine load history, and from the viscoelastic data interpretation algorithms derived in the current research. To avoid inaccuracies in the data interpretation, the vertical deformation should be measured over a 1/4 diameter central sector of the cylinder by means, for example, of the in-house developed displacement gage. A series of tests on specimens with various asphalt binder viscosity verified the validity of the viscoelastic data interpretation. Specimens from Mn/ROAD materials showed the presence of viscoelastic properties even at temperatures well below freezing.