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A laboratory-based linear loading pavement test stand, the Minnesota Accelerated Loading Facility (Minne-ALF) simulates the passage of heavy traffic loads moving at speeds up to 65 kph (40 mph) over small, full-scale pavement test slabs. Hydraulic actuators control a rocker beam, which simulates loads. Researchers simulated the passage of 40-kN (9-kip) single-wheel loads at a rate of 172,000 per day, although wheel loads up to 100 kN (22 kip) can be simulated at varying speeds. Full-axle simulations are possible with frame modifications. Concrete slabs were cast and dowels were installed in slots across cracks/joints. Test variables included joint face texture, repair backfill material, and dowel material and length. Test outputs included measurements of load transfer efficiency and differential deflection across the joint/crack. The effect of joint/crack face texture was great when the joint/crack remained tight. Load carrying performance was improved using Speed Crete 2028 in place of 3U18 concrete backfill with similar joint and dowel bars. Load transfer was unaffected by the use of stainless steel-clad dowel bars in lieu of epoxy-coated dowel bars. Researchers recommend additional testing to examine the effects of dowel length and dowel materials.

This innovation update relates to Report 2009-12, "Using the Dynamic Cone Penetrometer and Light Weight Deflectometer for Construction Quality Assurance," published in February of 2009.

Low-volume roads constructed in regions susceptible to freezing and thawing periods are often at risk of load-related damage during the spring-thaw period. The reduced support capacity during the thawing period is a result of excess melt water that becomes trapped above the underlying frozen layers. Many agencies place spring load restrictions (SLR) during the thaw period to reduce unnecessary damage to the roadways. The period of SLR set forth by the Minnesota Department of Transportation is effective for all flexible pavements; however, experience suggests that many aggregate-surfaced roads require additional time relative to flexible pavements to recover strength sufficient to carry unrestricted loads. An investigation was performed to improve local agencies' ability to evaluate the duration of SLR on aggregate-surfaced roadways. This was accomplished through seasonal measurements of in situ shear strengths, measured using the dynamic cone penetrometer (DCP), on various Minnesota county routes. In situ strength tests were conducted on selected county gravel roads over the course of three years. Strength levels recorded during the spring-thaw weakened period were compared to fully recovered periods that typically occur in late spring/summer. The results indicate that aggregate-surfaced roads generally require 1 to 3 additional weeks, over that of flexible pavements, to reach recovered bearing capacity. Additionally, a strong correlation was found between duration required to attain given strength recovery values and climatic and grading inputs.

Mineralogical analyses were performed on the Mesabi Select aggregate taken from a stockpile (-1 inch size) at MnROAD comprised of crushed material obtained from the top 25 feet of the 'Lower Cherty' member, or LC-8 bed (LC-6 bed in NRRI study), of the United Taconite mine near Eveleth. The material was utilized in asphalt (cell 32) and concrete pavement (cell 54) constructed at MnROAD's low volume loop.