Precast Concrete Manholes and Proper Manhole Management
Those who plan and implement infrastructure programs must be visionaries, whether for new urban development or for urban renewal and restoration. Urban planners must predict population density and potential infrastructure use and then build systems capable of supporting communities for decades into the future.
Bridges, dams and ports are more visible parts of a community’s infrastructure. Manholes and sewers are less visible yet equally as important. The EPA estimates there are more than 20 million manholes in the United States,1 with the majority installed prior to the 1960s and in many communities, more than 100 years ago.
Selecting the right materials and an experienced business partner like Mack Industries for precast concrete manholes and sewer systems can ensure a long life and proper service for generations to come. A good supplier can also streamline selection, sizing and ensure proper installation.
Manholes allow access to underground public utilities for inspection, maintenance and system upgrades. Public utilities such as wastewater, telephone, electricity, storm drains, heating and gas rely on manholes however they are most common in sewer systems. One source said, “Manhole rehab(ilitation) is one of the most underutilized methods in the industry,” when it comes to inflow and infiltration (I/I) reduction. In a focus on plant capacity (sewage plants), approximately 40-70 percent of the I/I was identified at the manhole.
Material Choices for Manholes
The three main materials used in today’s manhole construction are fiberglass, HDPE or concrete, either precast or poured onsite. Precast concrete manholes have an unmatched reputation for quality and lifespan—they can last for more than 100 years.
Mack Industries supplies Ohio, Pennsylvania, Michigan, North Carolina and Florida with precast sanitation and storm manholes as well as other precast concrete forms and materials. Mack Industries is DOT approved in several states and supplies superior service and high quality.
Advantages of precast concrete manholes include:
Protection – concrete is non-flammable and watertight
Superior Strength – concrete won’t be affected by backfill
Speed – precast manholes can be installed on demand and immediately backfilled
Ease of installation – precast concrete can be installed in one day
Buoyancy – precast concrete has a higher specific gravity compared to other materials
Uniformity – precast is made in a controlled environment ensuring the highest quality
Lifespan – concrete manholes can last more than a century
Specific gravity in relationship to buoyancy deserves a closer look. The higher the specific gravity, the more easily a manhole or tank can resist buoyant forces. Precast concrete has a specific gravity of 2.40, while fiberglass is 1.86 and HDPE is 0.97.2 Materials with lower specific gravity involve extra labor and additional steps during installation, requiring anchoring to counter this buoyancy.
Concrete, according to the Northeast Precast Concrete Association (NEPCA), is “nontoxic, environmentally safe and made from natural ingredients.” Companies interested in LEED certification often turn to concrete because they require minimal site disturbance to install, can properly handle stormwater runoff, and often are made from regionally available materials, friendlier to the environment than other choices. The vast majority of materials that go into the manufacture of concrete manholes are generally available within a 500-mile radius of the precast plant.
MACK offers a full line of manhole options from 48” to 96” diameter built to ASTM C-4778 standards. For other standard features or to ask about our availability, please call Mack Industries at 800-482-3111 or visit our web site at www.mackconcrete.com.