Search Content

This Soil Factor Design Method was written for counties, townships, and municipalities for use in designing aggregate roads. Although many design methods for aggregate roads exist, most require thorough soil identification and soil strength testing. Since most local agencies do not have the means to perform elaborate testing of soils and because they are familiar with soil factors, this design method should be helpful. This procedure requires soil identification, traffic counts and rational judgement. At present Mn/DOT does not have a design method for aggregate roads. It is not the intention of this manual to change the present legal load limits for gravel roads. For those who would like a more thorough design method, or more background information on aggregate roads, the method includes information on the use of the U.S. Forest Service Aggregate Surface Design Guide. Also included is information regarding compaction, drainage, frost action, geosynthetic use, lime stabilization, and an appendix with sample problems based on the Soil Factor and Forest Service design methods.

Asphalt mixture variations that result from moisture fluctuations in aggregate stockpiles pose a serious problem at dryer-drum plants. The moisture content of a stockpile is infrequently measured, if at all. If the proportion of aggregate is not adjusted to account for its moisture content, an improper mix will result. This project looked at identifying a practical and accurate field method or probe for measuring the moisture content of aggregates, testing the probe in a hot-mix plant, and developing a control strategy for asphalt oil addition to the mix. Researchers identified a suitable commercial probe by reviewing past research and conducting laboratory studies. Testing in the plant showed that this probe could rapidly measure aggregate moisture in plant conditions at the same level of accuracy as gravimetric measurements. Researchers also developed a control strategy for the asphalt oil addition. Testing showed the effectiveness of this control, in conjunction with commercial probe moisture measurements in the feed bin. A problem with probe operations robustness was identified.

This report presents the results of an investigation into the use of the Superpave asphalt mix design methodology at the local government level in Minnesota. In the project, researchers combined low-cost natural sand with locally available aggregates from four sources: limestone, quartzite, and partially crushed river gravel, and granite. They evaluated coarse and fine aggregate gradations, along with the use of two asphalt grades. It was difficult to achieve the Superpave volumetric requirements of voids in mineral aggregate (VMA) and voids filled with asphalt (VFA) at 4% air voids, regardless of the gradation. A target air void content of 3% satisfied the VFA requirement, even though the VMA requirement could not be fulfilled. The fine aggregate gradations produced densities indicating that the mixtures might be tender during construction, but not necessarily be susceptible to rutting. The coarse-graded mixtures did not show the tenderness problem, but did show that they might be susceptible to rutting. Resilient modulus testing showed little or no difference in the mixtures, regardless of aggregate source or gradation. The difference in resilient modulus due to asphalt grade was apparent only at the intermediate temperatures, and not at the highest or lowest test temperatures. Moisture sensitivity testing showed that all the mixtures studied had adequate durability. Indirect tensile creep and APA rut testing indicated that resistance to low temperature cracking and rutting may be improved by decreasing the lower PG binder grade and increasing the upper PG binder grade.

The Washington Hydraulic Fracture test was developed under the Strategic Highway Research Program to address the need for a rapid, inexpensive test for concrete aggregate freeze-thaw durability. The original test and analysis procedures were not sufficiently reliable and accurate to merit widespread adoption and implementation. Several follow-up research efforts have been performed and each has resulted in improvements to the test. This report describes the results of recent research efforts to improve the test. The "hydraulic fracture index" has been replaced by a model that predicts freeze-thaw test dilation as a function of the distribution of particle mass retained on various sieves after testing. This model was developed using data obtained from freeze-thaw and hydraulic fracture testing of 18 quarried carbonate and gravel aggregate sources, and the resulting correlation is exceptional (r-squared = 0.98). In addition, a large test chamber was developed to allow testing of aggregate samples five times larger than the original small chamber, thereby allowing aggregate durability characterization with a single test run. It is believed that the hydraulic fracture test is now ready for more broad-based validation testing and eventual widespread acceptance and implementation as an accurate screening tool for concrete aggregate freeze-thaw durability.

This project focuses on the second construction phase of the Minnesota Road Research facility (Mn/ROAD) and evaluates three typical, locally available, surfacing aggregates along with a rollover section from the initial phase for performance. The project results indicate that the adsorption test did not predict the performance of the sections in this experiment. All of the aggregates were characterized as marginal in terms of moisture and frost susceptibility. The sections with the greatest percentage of fines typically performed better than sections with a low percentage of fines. The Minnesota Department of Transportation issued a technical memorandum to change the specification from 0-15% to 8-15% passing the No. 200 sieve for Class 1 surfacing aggregate. The project also compared freezing and thawing rates on the aggregate sections to nearby hot mix asphalt (HMA) sections. Soil at any particular depth froze four to five days before HMA sections. The aggregate sections also thawed at exponential slower rates as depth increased from 11 to 35 days, which means that an aggregate surfaced road will freeze sooner and thaw slower than an HMA surfaced road. This information impacts the management of spring load restrictions and winter load limits.

This report evaluates the technical and economic viability of using coarse taconite tailings for construction aggregate purposes by analyzing the results of tests run on their physical, geological, mineralogical, and chemical properties as well as doing a market analysis.

This Technical Summary pertains to the LRRB-produced Report 2009-32, “Hydraulic and Mechanical Properties of Recycled Materials,” published October 2009.

This report presents the results of laboratory testing to validate the use of Fine Aggregate Angularity (FAA) measurements with the Superpave method of Hot Mix Asphalt (HMA) design. A search of literature and Minnesota FAA data was conducted in preparation for FAA testing of aggregates and HMA design. Laboratory tests of aggregates included sieve analysis, specific gravity and FAA. Additional work was also performed by acquiring digital imaging data for the aggregates. Testing of asphalt mixtures included dynamic modulus tests and asphalt pavement analyzer tests. Testing was performed on four asphalt mixtures representing a range of Minnesota FAA values. Dynamic modulus testing was performed at three temperatures and five frequencies. Data from the dynamic modulus tests were processed using nonlinear regression. The resulting master curves of dynamic modulus vs. frequency were referenced to test temperature 54C. Asphalt pavement analyzer data at 54C was analyzed with respect to rutting curve. Laboratory test results for aggregates and mixtures were analyzed together using statistical methods to develop correlation coefficients and linear trends. It was found that dynamic modulus and rut resistance values are strongly related to aggregate blend FAA. Some additional parameters from digital imaging also predicted modulus and rut resistance very well and should be included in future reference.

Study goals included: 1) identify mechanisms causing premature failure in Minnesota concrete pavements; 2) evaluate the accuracy of existing tests of aggregate freeze-thaw durability using Minnesota aggregate sources and pavement performance records; 3) develop a new methodology for quickly and reliably assessing aggregate freeze-thaw durability; and 4) evaluate techniques for mitigating D-cracking. Research results indicate that the poor durability performance of some Minnesota PCC pavement sections can often be attributed to aggregate freeze-thaw damage. However, secondary mineralization, embedded shale deposits, poor mix design and alkali-aggregate reactions were also identified as problems. Petrographic examination can help to differentiate between these failure mechanisms. A reliable and universal method for quickly identifying D-cracking aggregate particles was not identified. A test protocol was developed for improved aggregate durability evaluation. It includes several tests which are selected for use based on aggregate geological origin and composition and the results of previous tests. Further validation of the proposed test protocol is recommended. Several techniques appear to be effective in improving the freeze-thaw durability of concrete prepared using marginally durable aggregate: mix design modifications, reductions in aggregate top size, and the blending of durable and nondurable aggregates. Some chemical treatments showed promise, but may not be economical.

The Minnesota Department of Transportation (Mn/DOT) has concluded a research study on the proper techniques involved in seal coating. A key part of the research project involved performing seal coat designs using the procedure developed by Norman McLeod. In addition, research personnel were present on many seal coat construction projects assisting the inspector and contractor. The primary purpose of this handbook, revised in 2006, is to provide a solid background in seal coat materials, equipment, design and construction for the field inspector. Divided into two main sections, this updated handbook provides direction for designers and field personnel. Thomas J. Wood handled this revision. The original work was prepared by David W. Janisch and Frank S. Gaillard. NOTE: A revised version of Minnesota Seal Coat Handbook was published in December 2022 (report 2022-22).