Our office was invited to tour the Tennessee Concrete Association’s (TCA) new headquarters in Nashville. The focus of the tour was to learn more about their experience with pervious concrete. They had a few examples of pervious concrete pours on site, and I thought the one in the photograph above was particularly interesting. TCA is experimenting with mixes to increase the Solar Reflectance Index (SRI) value of pervious concrete. Mix A in the left side of the photograph is a pervious concrete mix that replaces 20% of the required cementitious content with fly ash. Mix B to the right has replaced 50% of the required cementitious content with slag. Both substitutes are by-products of industrial process. Fly ash is from the process of burning coal for energy and slag is from the production of both iron and steel.

As you can see there is a noticeable difference in the color between the two samples. The slag sample is much lighter in color. We were told it was difficult to determine the SRI of pervious concrete due to the voids. As a result, TCA could not definitively tell us the SRI value. They are interested in finding someone to perform more testing.

In regard to cost, TCA stated the slag is readily available in Tennessee but not all producers carry it. Fly Ash is the less expensive option compared with cement and slag, but slag is typically less expensive than cement (especially white cement)

It does appear the slag mix  provides a great option to improve solar reflectance. I hope more data will be available in the near future that supports this.

-Brian Phelps

]]> http://hpigreen.com/2010/02/10/pervious-concrete-and-solar-reflectance/feed/ 2 hpigreen porous concrete http://hpigreen.com/2009/11/11/epa-to-test-porous-pavement-and-raingarden-benefits/ http://hpigreen.com/2009/11/11/epa-to-test-porous-pavement-and-raingarden-benefits/#comments Wed, 11 Nov 2009 15:49:11 +0000 hpigreen http://hpigreen.com/?p=264 ]]>
1700 Charlotte in Nashville
Combines Porous Concrete & Bioswales

Traditional asphalt parking lots may seem to be the most cost efficient, but underlying costs such as increased pollution and water load on our sewer systems need to be considered as well. In an attempt to measure those underlying costs the EPA has replaced nearly 43,000 SF of their traditional asphalt parking with 3 different types of permeable pavement systems and several raingardens with different planted vegetation. At their Edison, NJ facility they will conduct a decade long study to evaluate and document the performances of these permeable systems on the basis of removing pollutants and filtering capabilities. Having these systems all in the same location will likely result in more balanced testing of each material.

This study comes at an ideal time as many cities are beginning to re-evaluate old paving methods in order to reduce the load on existing sewer systems or just to reduce the amount of toxin runoff from paved surfaces to our nearby rivers and lakes. Traditional asphalt parking lots collect oil, grease and other debris over time, after a heavy rain or snowstorm these toxins are washed from the parking surface to the nearest storm drain or permeable surface. Replacing this impervious surface with a permeable pavement or raingarden will allow plants and soils to naturally filter the pollutants, while re-charging the ground water table.

Porous Concrete

-Will Marth

The recent transformation of Deaderick Street recalls the historic importance of the street and enhance the corridor’s prominence as an important civic axis. Prior to the renovations, the street had become most widely known as the central transfer point for the Metro bus system. In the Fall of 2008 the bus system’s hub was relocated one block over to the ambitious Music City Central, presenting an opportunity to re-envision the street itself

The renovations to the street primarily focused on addressing stormwater issues and urban trees. The existing streetscape was home to an assortment of unhealthy trees ranging in sizes from 2” caliper up to 24”+. Each and every one of them were shoehorned into a 4’x4’ planting zone and struggling to adapt to urban conditions. The renovations included removing those trees and providing larger and deeper planting areas that would not only give a larger volume of soil for the tree roots, but also provide many areas in which the stormwater could travel to, thus reducing the loads into the storm system. Bioretention zones were implemented in pedestrian bulbs at the intersections and in relation to the existing catch basins. These planting areas were also excavated to a depth that would accept enough engineered soils to allow infiltration and planted with plants that can adapt to the extremes of wet and dry conditions. Pervious area within the corridor was increased by over 700%.

Many other elements of sustainability were included, such as:

• Crushed and recycled concrete used for the pavement subbase,
• Fly ash utilized in the concrete mix,
• Porous concrete,
• LED light fixtures,
• Native and drought tolerant plant materials,
• Solar powered parking meters,
• Water efficient irrigation system,
• Many local vendors and fabricators,
• The addition of bike racks to help encourage a healthier way to travel, and
• The addition of recycling receptacles along the street.

We’re hoping that in the near future, permanent retail kiosks that were proposed in the master plan will be added to the street, further enlivening the corridor. Those kiosks are proposed to have an extensive greenroof on each. In addition, the master plan identified areas for future free standing retail buildings and liner buildings that could be added on the blank facades.

- Laura Schroeder