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

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Chapter 1. Introduction Objectives of Report and Research This report represents task 2 of the Minnesota Local Road Research Board (LRRB) project number (Investigation) 2010-042, entitled, "Stripping of Hot Mixed Asphalt Pavements (HMA) under Chip Seals". The overall goal of this research project is to determine why stripping distresses are observed in the underlying HMA pavements of some streets and not others. Identify which pavements are at greatest risk and implement risk mitigation strategies that include improved specifications and practices. The goal of this specific task report is to identify, or develop a methodology that can be used to asses potential at -risk streets before they are treated with a surface treatment. This methodology (in the form of a laboratory test) is designed to provide guidance on the susceptibility of the proposed pavement section to the stripping under chip seal distress, which would allow agencies to make informed decisions on the application of preventive maintenance (PM) treatments. Stripping Under Chip Seal Distress This problem has been observed for more than twenty years; however recently, Mn/DOT has received increased reports of stripping of the upper 1/2 to 1 inch of hot mixed asphalt (HMA) pavements under chip seal surface treatments. This stripping distress (Figure 1.1) usually starts out as a small blister and develops to small potholes, at which point the chip seal delaminates from the pavement. These stripping distresses can become an expensive maintenance problem. Figure 1.1. Early stage of HMA deterioration under a chip seal (251 Reid). The distress appears to be limited to local, low speed roads (30 - 40 miles/hour) with curb and gutter and Task 1 of this research project (1) surveyed local agencies and found that (60% of 66 respondents) have this problem. Due to the relative widespread nature of the phenomenon the study will not focus on material specific causes of the stripping, such as aggregate/asphalt incompatibility. The focus of the study will be on the stripping phenomenon as it relates to the pavement structure as a whole, specifically, it is theorized that pavements with poor drainage, low density and traffic action are at an increased risk of stripping when a chip seal is applied. The basis for this theory is that many observed cases have been local streets (with presumably higher density) and curb and gutter (no edge drains for water to escape). Review of Published Literature The vast majority of the literature found focused on a "microscopic" investigation of the problem, namely the properties/performance of the asphalt and aggregate, or the mixture as a whole. The following paragraph is an excerpt from Kiggundu and Roberts (2), "Hubbard states B-6