One of the most common terms used to describe pavement treatments for preservation or rehabilitation is seal (e.g., cape seal, chip seal, crack seal, scrub seal, slurry seal). Pavement treatments, for good reason, aim to associate themselves with the ability to keep water out of pavements because excessive amounts of water entering into and remaining in a pavement is detrimental to longevity. There are a few ways to measure permeability or infiltration into pavements as shown in Figure 1. This note focuses on the Mississippi Permeameter (MSP) as it has been shown to be a fairly universal method to measure the ability of different seal treatments to prevent water entry into pavements.
From an agency viewpoint, there is value in specifying a given amount of water infiltration that can be measured in the field by one device so all measurements can be directly related to each other. For example, a reading of 10 tested on seal treatment type A is allowing twice as much water to enter the pavement as a reading of 5 on seal treatment type B. This fundamental principle was elusive for pavements for many years, and it is still being improved upon in present day.
The MSP is performed by loading the standpipe to assist with sealing to the pavement surface, filling the standpipe with water, and recording the time required for water to fall 12.7 cm down the standpipe (or in the case of fairly impermeable surfaces, the distance water has fallen in 5 minutes is recorded). A review of literature shows a range of challenges with techniques that follow Darcy’s Law to assess pavement permeability, and as such the MSP uses infiltration rate (Inf) as a reasonable index of permeability and is calculated as shown in Equation 1.
Where,
Inf = infiltration rate (cm/min)
a = inside cross-sectional area of permeameter standpipe (cm2)
A = cross-sectional contact area (cm2)
t = elapsed time between h1 and h2 (min)
h1 and h2 = initial and final head, respectively, across the test specimen (cm)
Additional preparations are required for test locations over rough surfaces such as chip and scrub seals. Specific steps to prepare rough surfaces are omitted, but note that successful measurements have been taken over cracks that have had chip seals applied where surface preparation was performed in only a few minutes. Work is continuing in the area of proper and efficient sealing to rough surfaces such as alternative gasket materials, larger bases and machined metal bases.
To date, the MSP has been successfully used for several field applications ranging from open graded friction course (OGFC) to dense graded asphalt (DGA) with ranging nominal maximum aggregate sizes (NMAS) to chip seals. Table 1 shows surfaces that have been tested and representative values that were obtained to show the versatility of these measurements and how they can be applied to a range of surfaces. MSP data in addition to Table 1 shows reduced permeability for asphalt mat measurements compared with longitudinal joints, reduced permeability after fog seal treatments and reduced permeability, on average, when joint adhesives were placed in longitudinal joints.
Table 1. Typical Pavement Surface Infiltration as Measured by the MSP
| Material | Project(s) | Typical Infiltration (cm/min) |
|---|---|---|
| DGA | Thin lift joints – cracked | 100 to 125 |
| OGFC | South Mississippi interstate over time | 80 to 100 |
| Chip Seal | Cracks that were chip sealed | 13 |
| Scrub Seal | Cracks that were scrub sealed | 3 |
| DGA | 12.5 mm NMAS and + 2.5 inch thick mat | 0.1 to 20 |
| DGA | + 6 mm NMAS and + 0.75 inch thick mat | 0 to 0.3 |
| DGA | Thin lift joints – not cracked | 0 to 1 |
| Rejuvenating Seal | Airport runway pre and post rejuvenating seal | 0 to 1 |
| Crack Seal | Cracks in an impermeable mat that were sealed | 0 to 0.2 |
It is the view of the authors that continuing to improve the ability to measure any pavement surface’s ability to prevent water from entering pavements is a tool that stands to improve pavement preservation’s ability to provide the right treatment to the right pavement at the right time.
Acknowledgements
The Mississippi Department of Transportation supported some of these efforts. Ben C. Cox (previously) and Jessica V. Lewis (currently) hold the Ergon Asphalt & Emulsions Distinguished Doctoral Fellowship in Construction Materials. Permission to publish was granted by the Director, Geotechnical and Structures Laboratory, US Army Engineer Research and Development Center.
Isaac L. Howard received bachelor’s, master’s, and doctoral degrees from Arkansas State University, West Virginia University, and the University of Arkansas between 2001 and 2006. Construction materials, asphalt pavements, and infrastructure are primary interests, where characterization, rehabilitation, recycling, and interfacing materials/design with construction are focus areas.
Ben C. Cox received bachelor’s, master’s, and doctoral degrees from Mississippi State University between 2011 and 2015. Airfield pavements, cold-in-place recycling, improved test methods for bituminous paving materials, and military engineering are focus areas.
Jessica V. Lewis received bachelor’s and master’s degrees from Mississippi State University in 2021 and 2023, respectively, and is currently working on a doctoral degree. Construction materials, asphalt paving, infrastructure, and workforce development are focus areas.
Written by Isaac L. Howard, Ben C. Cox and Jessica V. Lewis
Aug 21, 2023
