Project 1: Porous asphalt parking lot
Location: Debert Industrial Park
Background: Installation of the porous asphalt parking lot was completed in December 2013. Design was based on a modified version of a specification developed at the University of New Hampshire's Stormwater Center.
The parking bays were installed as Porous Asphalt and, for durability purposes, the travel ways of the parking lot were installed with traditional pavement. The traditional pavement was sloped to feed stormwater into the porous section. This also gave us opportunity to compare the performance of both types of pavement.
This project was made possible with funding assistance through the Gulf of Maine Association, as a 2013 Leadership Grant recipient under the RBC Blue Water Project.
Porous Asphalt (Canadian Toonie used for Comparison)
Traditional Pavement (Canadian Toonie used for Comparison)
Composition: Composition of porous pavement differs in design. Traditional asphalt is designed to repel water and is constructed with a tightly compacted sub materials intended to support the asphalt layer. The sub grade materials have lots of fine material which help it to compact into a tight layer. Water is the enemy of traditional pavement. It works its way into cracks and crevices and through the freeze - thaw cycle opens a small imperfection into a pot hole.
Porous pavement on the other hand is design to receive water and pass it onto the sub -surface layers. The sub layers are thicker for porous pavement for two reasons. Because the sub layers are loosely compacted, more material is required to support the paved surface. Secondly, the space in the sub materials receive the rainwater that pass through the porous pavement. The rain water is filtered through a sand filter layer to help clean the water and a larger gravel base acts as a reservoir, holding post storm water until it can be absorbed by the surrounding soils.
Purpose of the Pilot Project:
The concept of porous asphalt is intriguing but is raises a series of questions to explore such as:
1. How does the surface perform under winter conditions?
2. Are the base materials sufficient to hold stormwater without it pooling on the surface?
3. Are special maintenance procedures required compared to a traditional paved surface?
4. Finally, how will the surface stand up over time will be an ongoing maintenance question?
An overflow pipe was installed and the top level of the underground reservoir. The pipe provides relief during large rain events that exceed the storage capacity of the gravel reservoir and ability of surrounding soils to absorb the water. It is also a way to monitor when the storage capacity of the gavel base is at its maximum.
Year 1: Performance Under Winter Conditions
Because of the late installation of the pavement, the first test for the pavement was snow removal and ice melt. Winter maintenance (snow removal, salting) was conducted in the same fashion for the porous as well as the traditional surface with no difference in the results. No special maintenance was required for the porous surface.
Due to the cold, sunny conditions, it was observed that ice melt on the traditional pavement would result in the re-freeze to form black ice. Water from ice melt on the porous pavement immediately disappeared into the pavement and avoided any unsafe walking conditions.
Post snow salt application with same results
Black ice forming on traditional pavement