By Kirk Stelsel
For the next 10 seconds, close your eyes and picture yourself leisurly lounging on a veranda in an isolated tropical paradise.
Are you there? Listen to the waves crash rhythmically onto shore. Hear birds in the distance as the wind moves slowly through the trees. Take a deep breath of the crisp air carrying the scent of rain. Hear the skies open up to release a steady shower that patters off the roof and leaves around you.
Moments like that help us shed the burdens of life and give in to nature. In that moment, water was all around you – the ocean waves, the rain, and in the birds and plants. Even you yourself are about 60% water (1).
Enjoying nature, our built environment and the basic amenities we often take for granted requires movement and management of water. To do so, we have a maze of networks, and precast concrete plays a vital role.
Out of sight, out of mind
In the tropical paradise we escaped to, we can’t forget that eventually we’ll come in off the porch and use running water. Evidence of humans harnessing water with concrete goes back to the Roman Empire. The Roman Aqueducts (2) and Cloaca Maxima (3) helped carry potable water to the city and take wastewater away. Today, concrete continues to play a vital role in our water infrastructure.
Manholes, pipe and other precast concrete products all disappear into our unseen infrastructure to meet our needs for decades to come. But precast is used even when a connection to city infrastructure is not feasible. Just southwest of Detroit in Milan, Michigan, Milan Vault provided on-site wastewater treatment tanks for a newly installed 4-H restroom and shower facility. To meet effluent regulations, a series of four 3,350 gallon precast tanks advance the treatment of the water until it’s ready for the final treatment area.
According to Jed Dingens of Dingens Architects in Corunna, Michigan, using precast provided a variety of benefits including strength, durability, flexibility of design and ease of installation in a timely manner. The tanks were manufactured for 6 ft of cover with custom risers to grade with cast iron covers, and are strong enough to withstand an accidental drive-over by heavy vehicles. Customizations were a part of the plan.
“We were able to place inlet and outlet penetrations at any location they had need for,” said Sam Wagner, vice president of Milan Vault. “We were also able to place access openings in any location they chose.”
Sometimes, though, getting rid of the water is not the need. On a commercial and residential level, rainwater detention and retention systems give overburdened stormwater systems a break and can hold back the water for beneficial reuse (for an example, see precast.org/superbowl). In Canada, RH20 was hired to take the residential rain barrel concept to the next level for a LEED-Platinum neighborhood in Newmarket, Ontario.
The company installed underground precast rainwater harvesting systems in the fronts of 34 homes to provide water for flushing toilets and lawn irrigation. The tanks met the town’s requirements to reduce household water draws by 25% and overall water discharge flows by 60%.
Listing all of the underground products that manage our water in some way would be nearly impossible due to custom products, but in almost any city you’ll find grease interceptors keeping our sewers safe from greases and fats, lift stations ensuring our water gets to where it needs to go and manholes providing human access to the network. The list of custom products is limited only by a need, some imagination and a little engineering knowhow.
“I think precast is very important in the underground infrastructure of our country,” Wagner said. “Concrete has a long-standing history of being a durable, economical and readily available product. It is easy to work with on site, requires little maintenance when installed correctly, and saves time and money for on-site contractors.”
Water under the bridge
To get to our tropical paradise, it’s very possible we crossed a bridge or two. Bridges are an integral part of our transportation network. According to the American Society of Civil Engineers (ASCE), the U.S. currently has 607,380 bridges that get us over everything from bubbling brooks to raging rivers. However, these bridges are aging. The latest ASCE report card gave U.S. bridges a C+, which is only slightly better than the paltry D+ for overall infrastructure (4).
Replacing bridges takes time and money and snarls traffic, but those headaches can be minimized. As MassDOT found out, precast concrete bridge components install fast (visit precast.org/fast14), and less time means less on-site labor and a happier public. Whether it’s precast beams and columns for larger bridges or precast culverts for short-span bridges, speed and durability make precast concrete the product of choice. This was the case in Arizona when wildfires ravaged critical wooden bridges (visit precast.org/prefast). Add in precast approach and deck slabs, headwalls, endwalls, wingwalls, parapets, retaining walls and railings and you have a complete bridge solution.
Increasing efficiency is exactly what North Carolina has set out to accomplish with the replacement of 14 aging bridges in multiple counties across the state. Due to staff reduction in recent years, the state sought the expertise of an outside engineering firm to plan and execute the bridge replacements in order to take advantage of federal funds. The bridges are express design builds that mainly consist of small stream crossings best served by precast concrete 3-sided culverts.
Cherry Precast, an NPCA member in Lewisville, North Carolina, bid the job and was awarded the contract for all 14 bridges. “Using precast, you have the option to cast all of the parts of the structure (culvert, wing wall, wing wall footers, etc.) before the contractor moves on site,” said Nelson Fulcher, vice president of Cherry Precast. “Then, once he’s there, he can reduce the duration of time by removing the existing structure, pouring the new foundation and placing the new structure all within a couple of weeks. By doing so, the contractor reduces his overhead, traffic controls, erosion controls, manpower on site, etc.”
Revisiting our paradise one last time, local engineers have probably managed natural water sources in some way to make habitation possible. Custom precast concrete products enable cities to harness natural water in all sorts of ways. In California, the El Dorado Irrigation District needed a custom product for Flume 41, a section of a larger system that carries water down a mountainside to a power station.
The existing wooden flume had long since met its expiration date, but to replace the 584-ft section, a number of requirements had to be met. The precast sections needed to be lightweight, and the mix required a 6% air content to combat the freeze-thaw nature of the area, which sits at 3,000 ft directly above Riverton, California. At the precast plant, Universal Precast in Redding, California, the design was perfected by starting with 3-D modeling. After that, it was just a matter of getting the pieces cast and set.
“We had never done anything like this before, and this is the largest repair job that the district itself has done – so it was the first time for a lot of people,” said Rick Rice, project manager with ProVen Management. “It’s in a remote location, so having Universal Precast perform the work cut costs and provided better controls on batching concrete, and the wood pieces we replaced are not nearly durable enough. The precast was brilliant – everyone is extremely pleased with how the project turned out.”
Now installed, the project engineer estimates Flume 41 to have a 100-year lifespan thanks to the precaster’s quality control measures.
“Precast sections allowed for better mix control and for a higher-quality product than possible with on-site cast-in-place,” said Dave Jermstad, principal-in-charge for the design, construction administration and quality control inspection plan for Carlton Engineering. “We have had great success with the construction and performance of the precast flume sections over the past 20 years. This includes extreme exposure and incidental rock-fall or tree-fall impacts.”
Just a few states to the east in Utah, Oldcastle Precast took on a waterway restoration project of its own: the reconstruction and improvement of approximately six miles of mostly open, unlined channels that feed critical water to farmers. Prompted by a deadly landslide in 2009, the precast channel provided a complete reconfiguration of the canal.
Oldcastle supplied approximately 10,000 ft of specially designed precast concrete box culvert and pipe that was used in the upper portions of the canal. To match the canal, designers beveled the majority of the segments to curve with the existing footprint until they emerge into a 66 in. concrete pipeline. During installation, the contractor was able to average more than 15 segments a day. Once installed, it was backfilled with 6 in. of road base to provide a maintenance access road and a recreational trail.
Considering that approximately 71% of the earth’s surface is covered by water and the average daily use of ground and surface water in the U.S. was around 410.6 billion gallons per day in 2005 (5), it’s no wonder we have such extensive networks to manage water. To contact a local precaster who can help you find a product suiting your water management needs, visit precast.org/find.
Kirk Stelsel is NPCA’s director of communication and marketing.