Agenda - Council - 02/11/2020 - Laserfiche WebLink

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Chapter 2. Laboratory Testing and Evaluation Introduction There is no one test that is universally accepted as an indicator of stripping potential, some tests worked well on some materials and not on others. One of the goals of this project is to provide a test(s) that can be performed relatively inexpensively and provide results quickly and accurately. With this in mind, excessive conditioning, such as multiple freeze -thaw cycles in the Lottman test, is not being considered. Preference was given to accepted tests and methodologies which could be implemented/performed with little investment. In addition, an experimental plan was formulated based upon recent data findings from forensic investigations of local streets. These forensic investigations revealed that pavements with stripping problems also seemed to have high in -place air voids. All of them had in -place voids greater than 10%, up to as high as 14%, other samples were unable to be tested due to disintegration of the core during the coring operation. This led the researchers to hypothesize that reduced density would lead to an increased susceptibility of the pavement to experience moisture induced damage. The hypothesis was tested by utilizing the current standard employed by Mn/DOT (Lottman test with Mn/DOT modified conditioning), experimenting with the Asphalt Pavement Analyzer (APA), or rutting test conducted on saturated and dry specimens as well as a new method proposed by the researchers that involves immersing a sample into boiling water for a pre -determined period of time (referred to as the modified boiling test)". Laboratory Procedure and Test Results Laboratory Permeameter (Karol -Warner flexible wall Permeameter) The laboratory testing was conducted on a level 3 SuperPave mixture, derived from a relatively common Minnesota job mix formula. This mixture has not been observed to be susceptible to striping problems. The samples were sampled from the field and prepared in the laboratory by trained Mn/DOT personnel using a SuperPave gyratory compactor. The mixture had 30% RAP content, with 4.8% new asphalt binder and it conformed to Mn/DOT's gradation requirements. Permeability testing was accomplished using the laboratory Permeameter (Figure 2.1), also known as the Karol -Warner flexible wall permeameter. The coefficient of water permeability, k was found using the relationship described in Figure 2.1. The coefficient of permeability provides an indication of the ease with which water can pass through the specimen, higher values indicate that it's easier for water to flow through the specimen and lower values indicate that it's more difficult for water to flow through the specimen. According to the Mn/DOT pavement design manual, permeability for class 5 aggregate base is approximately 4.8 inches per day (in/day) and drainable bases have permeability values between 3,600 to 12,000 in/day. B-9