This paper details the efforts regarding the construction and analysis of three stabilized full-depth reclamation (SFDR) sections (cells 2, 3, and 4) constructed at the Minnesota Road Research Facility (MnROAD) on I-94 in 2008. Three test sections with varying pulverized asphalt concrete/granular base ratios were constructed in order to study the performance of full-depth reclaimed (FDR) pavements stabilized with engineered emulsion. Emulsion content and base structure varied between test sections. Each test section was designed for 3.5 million ESALs over a period of five years. The sections have been subjected to approximately 2.2 million ESALs as of 30 June 2012.
Strain gages were embedded at the bottom of the hot-mix asphalt (HMA) and SFDR layers in each test section to measure responses. The strain gages indicate that both the bottom of the HMA and SFDR layers are subject to horizontal tensile strain from falling weight deflectometer (FWD) and heavy vehicle loading. Pavement performance in terms of rutting, cracking, and international roughness index (IRI) has been measured periodically. The results indicate that all three cells are performing well. The only crack in the three cells exists in cell 3, IRI values are well within the acceptable range, and rutting, while progressing, is still acceptable.
Finally, the paper concludes with modeled responses and performance predictions from DARWinME and BISAR. Model predictions indicate that a SFDR layer will provide greater structural benefits and increased performance than similar structures with unstabilized FDR or granular base layers.
Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 2368, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/2368-11.
Laboratory remolded subgrade soil samples have been widely used to study subgrade resilient modulus. But physical conditions, such as moisture content and density, of such specimens may not represent in-situ conditions very well. Therefore, AASHTO and the Long-Term Pavement Performance program (LTPP) have recommended that undisturbed thin-walled tube samples should be used to study subgrade resilient behavior. The Minnesota Department of Transportation (Mn/DOT) is developing mechanistic-empirical pavement design approaches through the Minnesota Road Research project and has realized the importance of resilient modulus in the design approaches. Currently, the Mn/DOT is making an effort to study resilient modulus of unbound pavement materials through laboratory experiments. Under a research project at the Mn/DOT, several thin-walled tube samples of subgrade soil were obtained from six different pavement sections at the Minnesota Road Research project. Repeated loading triaxial tests were conducted on the soil specimens to determine resilient modulus at the Mn/DOT laboratory. Also, some soil properties, such as resistance R-value and plasticity index were obtained. R-value is an indicative value of performance when soil is placed in the subgrade of a road subjected to traffic. Two constitutive models (Uzan-Witczak universal model and the deviator stress model) were applied to describe the resilient modulus. The objective of the research was to compare these two well-known constitutive models in describing subgrade soil resilient behavior and to study effects of material properties on the resilient modulus.
From the specimens tested, the experimental results showed that the universal model described the subgrade resilient modulus slightly better than the deviator stress model and the coefficients in these two constitutive models were found to have correlation to material properties. Also, no well-defined relationships between R-value and the coefficients in the constitutive models were observed from the results of the tested specimens.
Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1786, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1786-03.
There has been a sustained effort in applying fracture mechanics concepts to crack formation and propagation in bituminous pavement materials. Adequate fracture resistance is an essential requirement for asphalt pavements built in the northern part of the US and Canada for which the prevailing failure mode is cracking due to low-temperature shrinkage stresses. The current Superpave specifications address this issue mainly through the use of strength tests on unnotched (smooth boundary) specimens. However, recent studies have shown the limitations of this approach and have suggested that fracture mechanics concepts, based on tests performed on notched samples, should be employed instead.
Research in progress at University of Minnesota investigates the use of fracture mechanics principles to determine the low-temperature fracture properties of asphalt mixtures. This paper presents a testing protocol that allows obtaining multiple measurements of fracture toughness as a function of crack propagation based on the compliance method to measure crack length. An increase in fracture toughness with crack length is observed, which is consistent with the behavior displayed by other brittle materials. The plateau of the curves may be representative of the asphalt concrete resistance to fracture because the initial values can be significantly influenced by the presence of the inelastic zone at the crack tip.
Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1789, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1789-21.
An earth pressure cell (EPC) is a device designed to provide an estimate of normal stress in soil. The practice of designing and manufacturing stress measurement devices revolves around the study of the interaction between the measuring device – the earth pressure cell – and the host material. However, distribution of normal stress is not necessarily uniform across a given surface. Consequently, output from an EPC may be different under soil loading conditions than under fluid pressure. In addition, depending upon the design, as the cell deflects, an arching-type phenomenon may develop.
The objectives of this study were to devise a scheme for calibration of earth pressure cells and to recommend a procedure for field installation. A new testing device was designed to permit the application of uniaxial soil pressure to the earth pressure cell using various types of soil and load configurations. Sensitivities computed from soil calibrations varied from those determined from fluid calibrations by as much as 30%.
A field installation procedure was developed from model tests. In the laboratory, a thin-walled steel cylinder with a geotextile bottom was filled with uniform silica sand in a medium dense state and the earth pressure cell was placed within the sand. The entire apparatus (earth pressure cell, cylinder, and sand) was carried into the field and installed in the desired locations. Once in place, the steel cylinder was pulled up out of the ground, leaving the cell, sand, and geotextile behind. Preliminary field data indicate that the soil calibration and placement procedure provide reasonably accurate measurements of the change in vertical stress.
Content Note: This is the author’s version of a work that was accepted for publication in the Transportation Research Record: Journal of the Transportation Research Board, Issue Number: 1772, Publisher: Transportation Research Board ISSN: 0361-1981. The final version can be found at https://doi.org/10.3141/1772-02.
MnDOT is currently implementing in-place recycling techniques as a maintenance and rehabilitation strategy for bituminous pavement structures. The techniques being employed include: Full Depth Reclamation (FDR), Bituminous Stabilized Full Depth Reclamation (SFDR), and Cold In-Place (Partial Depth) Recycling (CIR). In-place recycling of bituminous pavements has been used in Minnesota for more than ten years at the local level, longer in other parts of the country and the world. MnDOT has constructed 10 state projects since 2010 using a variety of processes and stabilizing additives.
Full Depth Reclamation (FDR) is the process of pulverizing a roadway’s flexible pavement section and a portion of its underlying base, and crushing and blending the recovered material to create a uniform base material.
Three test sections were constructed in 2008 on Interstate 94 at the MnROAD test facility to study pavement performance with stabilized full depth reclamation base using engineered emulsion. Each section used a different emulsion content due to the inherent differences in the sections.
Pavement testing, including rut and crack measurements, was performed, along with falling weight deflectometer tests. The three sections had slight
increases in rutting from April 2009 to July 2009 but leveled off by September 2009. This was likely due to material consolidation, which is commonly observed for most asphalt pavements immediately after opening to traffic. The amount of rutting is still low, with most of rutting less than 0.15 inches. No cracking has been observed. FWD testing showed the least average deflection occurred in cell 3, but cell 4 was the stiffest material, based on the Area index.
Laboratory testing characterized the mechanical properties of the three mixtures. The testing results showed that the mixture used in cell3 has the highest dynamic modulus, slightly greater than cell 4 at most frequencies. Cell 3 also has the best fatigue life, which indicates that this mixture type is probably an optimal design in terms of material strength and performance. Ultimate performance, however, will be determined from field results, dependent on materials and design of all layers and construction quality. The sections were designed for 3.5 million ESALs in five years, and it must be pointed out that the sections are still in early stage of the study and performing well.
Prepared for presentation and publication at the 90th Annual Meeting of Transportation Research Board, January, 2011, Washington, D.C.
This is a project update on the work that became Report 2012-08, "Effects of Implements of Husbandry (Farm Equipment) on Pavement Performance." It gives the status of the project after the testing had been completed, but before the final report was written.
Over the past few decades, farms have consolidated and farm size has increased significantly. The farm equipment industry has responded by producing larger and heavier equipment. For example, it is not unusual to see liquid manure application equipment that hauls 9,000 gallons or more. Innovations such as steerable axles, flotation tires (spreading the load over a much larger area), and new tire designs have been implemented on the equipment in recent years. The length, width, and axle loads of the large equipment could potentially accelerate damage on roads. However, there is insufficient data to show the effects of the equipment on pavement response and performance.
To demonstrate and test the concept of stabilized full depth reclamation as pavement base material, Full Depth Reclamation (FDR) with asphalt emulsion re-uses the existing asphalt mixture and adds stabilized additive to further increase material stiffness. This method was applied on three (3) cells located on the MnROAD mainline (Cells 2, 3 and 4).
