Pervious Concrete

I am always sucker for a good YouTube video, especially if it is transit oriented.  I am mesmerized by the below video demonstrating the effectiveness of pervious concrete.  It is simply stunning how the concrete disperses all the water and seemingly not a single drop makes it to the side of the road.

I’ll let the National Ready Mixed Concrete Association explain how it works.

In pervious concrete, carefully controlled amounts of

water and cementitious materials are used to create a paste that forms a thick coating around aggregate particles. A pervious concrete mixture contains little or no sand, creating a substantial void content. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly. Typically, between 15% and 25% voids are achieved in the hardened concrete, and flow rates for water through pervious concrete are typically around 480 in./hr (0.34 cm/s, which is 5 gal/ft min or 200 L/m, although they can be much higher. Both the low mortar content and high porosity also reduce strength compared to conventional concrete mixtures, but sufficient strength for many applications is readily achieved.

While pervious concrete can be used for a surprising number of applications, its primary use is in pavement. This site focuses on the pavement applications of the material, which also has been referred to as porous concrete, permeable concrete, no-fines concrete, gap-graded concrete, and enhanced-porosity concrete.There is more info on the linked website to explain the science of pervious concrete, how it is made, how it is poured, how it is maintained, and its many benefits.

The Daily Reporter wrote about a recent construction project in Shoreview, MN where the construction was paved with pervious concrete.  The material is admittedly not cheap, but by using a system that prevents run off it also saves costs in various other infrastructure like storm drains.

The pavement isn’t cheap; its upfront cost is about 50 percent more than traditional concrete, Lee said. But he added that it’s cost-effective considering that “you are getting a storm water management system” instead of just a driving surface.

Maloney concurs.

“When you net out what you don’t have to build — mainly ponds and piping and catch basins and manholes — when you consider the cost of those things, it is almost a break-even,” Maloney said. “We would not be doing the project if that weren’t the case.”

As more contractors become familiar with the product, and learn how to apply it with the proper tools and techniques, the price is likely to fall.

There are obvious questions about how the pavement will keep when the weather freezes, so the technology may be better suited for Florida than North Dakota.  Regardless, I am excited about any product that can reduce the amount of infrastructure needed and save space while accomplishing the same functions as older systems.

 

Building Communities to Lower CO2 Emissions

Courtesy of Smart Growth America comes a review of a new Transportation Research Board (TRB) report on the role of planning and transportation on carbon emissions.  The report is titled TRB Special Report 298: Driving and the Built Environment: Effects of Compact Development on Motorized Travel, Energy Use, and CO2 Emissions. While this blog focuses on transportation there is no doubt that transportation policy and land development, especially housing models, are deeply interconnected.  The history of American sprawl, suburban development and exurban expansion are deeply based on the fact that American policy for an entire century was based on building roads and making individual home ownership a priority.

Geoff Anderson of Smart Growth America summarized the conclusion succinctly:

Because the transportation sector accounts for nearly a third of greenhouse gas emissions and 70 percent of our oil use, we have to find a way to reduce the amount each of us has to drive each day, especially as population grows toward 400 million.

Market research shows that a majority of future housing demand lies in smaller homes and lots, townhouses, and condominiums in neighborhoods with nearby access to jobs, activities and public transportation. The researchers note that demographic changes, shrinking households, rising gas prices, lengthening commutes and cultural shifts all play a role in that demand.

While demand for such smart-growth development is growing, the authors note that government regulations, government spending, and transportation policies still favor sprawling, automobile-dependent development. Changing those policies should play a role in addressing climate and energy issues, the report concludes.

Developing or redeveloping community to feature new more dense housing and mixed use communities has a positive effect on transit.  It is hard and impracticable to develop public transportation in areas that are not dense.  Moreover, the report also points out that such development has also positive effects on land use in terms of environmental effects, construction of infrastructure like sewers and telecommunications, and prevention of sprawl.  In addition, denser communities could potentially have positive social effects as Jane Jacobs would observe.

There are hurdles to such construction, as the report points out, because American and state policies are not geared toward the development of such neighborhoods.  However, developing new mixed-use communities with multi-modal transit are two parts of the same solution.  Building dense communities is useless and building transit without a community is equally so.  America is waking up the insanity of its transportation and housing policies in light of climate change and the housing foreclosure crisis.  We cannot expect Phoenixes and Las Vegases to spring up again, it is time to build new communities that are focused on walkability, public transit, and places where people can still own their own houses, but do not necessarily have a huge back yard with it.

 

Infrastructure Investment Does Not End With Construction

The New York Times published an article on the decaying infrastucture in Russia, in particular The Sayano-Shushenskaya hydroelectric dam in Siberia.  While the United States does not have infrastructure falling apart in the same way, the I-35 W bridge tragedy in Minneapolis last year awoke the American conscience to the necessity of infrastructure upkeep and its costs.  As we go forward with infrastructure investment in the 21st century and debate what means transportation are best and most economically efficient it is important to keep in mind the cost of maintenance going forward.  The cost of transportation infrastructure is not truly depicted in the cost of construction, maintenance costs occur every year.

America has the twofold problem of historically not calculating the cost of maintenance when building transportation infrastructure and frequently choosing to build the cheapest option, which of course also usually deteriorates fastest.  While Stephen B. Goddard’s references in his 1994 book, Getting There,  are slightly dated, he also describes an awful lot of the infrastructure in this country:

In a nutshell, the Europeans build their freeways thicker and with a deeper base than in America.  Washington also gives states an incentive to neglect maintenance by paying 90 percent of the the cost for new roads , yet nothing for their repair.

In America the lowest bidder usually wins a highway contract, which removes incentive for innovation.  And neither are contractors held responsible.  When in 1991 Congress considered a bill requiring contractors to build to performance standards, the measure had the support of Washington’s highway establishment, state officials, and advocacy groups; but the Transportation Builders Association lobbied successfully for Congress to kill it.

I am not suggesting that the U.S. is in danger of approaching Russia’s level of difficulty.  Rather, all I am suggesting is that as infrastructure debates go forward we examine the total cost of a system; the cost of maintenance, operation and construction.  When we examine the cost of infrastructure on construction estimates alone we are practicing negligent economics.  A road that must be rebuilt every 20 years is not actually as cheap as it first looks.  We should invest more money up front to make our investments in infrastructure last.  In addition, a change in federal procedure would benefit all, if allocations for transportation funding included commitment to upkeep of new infrastructure, for at least a period of time.