Precast and Infrastructure

The United States' intricate network of vital infrastructure sectors aims to ensure that our country runs smoothly and its residents are safe. The assets, systems, and networks are governed by Presidential Policy Directive 21 (PPD-21) and protect the national public health and safety and the national economic security. Significant national resources are devoted to advancing and improving these sectors on an ongoing basis.

What is Classified as Key Infrastructure?

PPD-21 encompasses 16 key infrastructure sectors that have been identified. These industries are so vital that the destruction or incapacitating of even a small portion of them would have a crippling impact on overall national security. Here are the sixteen sectors:

• The chemical industry is in charge of turning raw materials into more than 70,000 goods that are necessary for survival.

• The commercial facilities sector is in charge of many locations that gather big crowds of people, including office buildings, malls, and accommodations.

• The communications sector is in charge of delivering interconnected services like wireless and satellite, as well as the providers who collaborate to guarantee interoperability.

• The critical manufacturing sector is responsible for the components vital to economic growth and national security.

• The dam sector is in charge of hydroelectric power generation, flood control, industrial waste management, and many other vital water retention and control services.

• To meet the needs of the US military, the Defense Industrial Base Sector is in charge of the research, development, production, delivery, and maintenance of military weapons systems, subsystems, and components.

• The emergency services sector is responsible for the highly skilled individuals who respond to incidents nationwide.

• The energy sector is accountable for performing an "enabling role" to provide a reliable energy supply to all other vital infrastructure.

• The financial services sector is in charge of hundreds of depositories, investment product suppliers, and companies that provide credit and financing.

• The manufacturing, processing, and storage of food supplies are done primarily by privately owned businesses in the food and agricultural sector.

• The government facilities sector is in charge of various structures that the federal government either owns or leases for public and private functions.

• The healthcare and public health sectors safeguard the economy against terrorism, pandemics, and natural disasters.

• The information technology sector ensures the security of technologically related systems and services used by enterprises, governments, academic institutions, and citizens.

• The nuclear reactors, materials & waste sector oversees 20,000 licensed users of radioactive sources, research/test reactors, fuel cycle facilities, and operating and retired reactors.

• The Transportation Systems Sector ensures that goods and people are transported safely, quickly, and securely across the country's transportation networks.

• The Water & Wastewater Systems Sector provides clean drinking water and treats sewage for the entire country.

Why Highway and Bridge Infrastructure Works with Precast

Due to the country's vast number of bridges, roads, and highways, many of which will need to be updated or repaired, roads and bridges will continue to be the primary use for precast concrete in infrastructure construction.

Our country's infrastructure has traditionally relied heavily on precast concrete. DOTs have utilized it for various purposes, including walls, bridges, barriers, and more, due to its robustness, dependability, quality, and ease of installation.

Other precast parts stand out because of inherent colors, unusual shapes, insets, and finishes that give them a second role. Some precast elements do their purpose diligently but go mostly unnoticed as they blend into roadside environments.

These elements provide much more than solid infrastructure. Highway sound walls have embedded regional animals or distinctive patterns, giving them life. Other states have made architectural choices like natural stone, wood grain, or brick that complement the neighborhood's aesthetics. Precast is ready to take on the challenge of being not only a superior structural construction material but also an aesthetically versatile one.

Precast concrete offers the appropriate appearance, quick installation, and long service life. Precast concrete may frequently be installed more quickly than competing materials. Retaining walls and MSE in a variety of forms are also offered by precast manufacturers around the nation.

Despite their higher cost, precast concrete components will increasingly be used in new and repair road and bridge construction. For instance: 

• Because of their lightweight and capacity to endure stresses brought on by the weight of other bridge components and strong traffic loads, prestressed bridge components, tees, and slabs are utilized on bridges.

• Because they are strong and have extended lifespans, precast concrete sound and traffic barriers are frequently employed.

Precast concrete may span anything from gullies to gorges and can reflect the architectural character of a community while also protecting the environment. Precast can offer an aesthetically pleasing, long-lasting design, whether the product is a short-span bridge or a full solution that can cross a significant river.

Benefits of Precast for Infrastructure Projects

The US has an open society, making it susceptible to events that endanger safety and security. Aside from unpredictable and uncontrollable natural disasters like floods, tornadoes, earthquakes, and hurricanes, the US also faces several covert adversaries who aim to harm our way of life through physical attacks on buildings and transportation systems and cyberattacks on the financial and technology sectors. Precast concrete building products address a demand in the ongoing endeavor to safeguard these national treasures.

Blast Resistance

Precast concrete is incredibly resilient to the concussive effects of blasts and can be built to withstand gradual collapse. Precast is a great option for data centers, military and governmental buildings, and other locations holding critical equipment and information because of this property.

Fire resistance

Precast concrete buildings do not burn and contain fires, giving first responders a chance to evacuate residents and stop the spread of the fire. Concrete is fireproof, which helps to control fires and reduces total damage to the structure in the event of a fire.

Storm resistance

Precast concrete's intrinsic strength is unaffected by strong winds, rising water, or vibrating ground. Precast concrete "weathers the storm" better than any other building material and is used in FEMA-approved projects due to its durability.

Sustainability

Precast concrete has replaced other building materials as one that supports the "one and done" attitude as we have come to appreciate the necessity to construct durable structures with ecologically friendly features. Precast construction will last for decades, as opposed to other building materials that need continual maintenance and replacement.

Reduced maintenance

Because precast concrete is stronger and more durable than conventional building materials, it needs less "service after the sale." Both interior and exterior precast applications are top performers in all climates and geographical regions due to their exceptional mold/mildew resistance and great longevity.

Resource-Efficient

90% of concrete's composition comprises its primary element, water, coupled with sand, stone, or gravel. Surprisingly, each ingredient's sourcing and assembly use very little energy. Cement, which makes up 10% of concrete, is also the component that releases all of the CO2 into the atmosphere.

Makes for Energy-Efficient Buildings

Concrete makes it possible to restore our infrastructure efficiently, thanks to LEED certification for construction. Insulation and little air infiltration are frequently incorporated into concrete construction techniques to increase energy efficiency.

Additionally, recycled materials can be used in concrete, reducing both the carbon footprint and the number of materials that would otherwise wind up in a landfill. Industry preferences for more environmentally friendly concrete are fly ash and slag.

Has a Long Service Life and Quick Build Time

Concrete is incredibly resilient to the elements and long-lasting, making it the ideal material for rebuilding our infrastructure. Additionally, new and improved concretes are lighter and stronger than traditional precast. Compared to other building materials like steel, wood, and asphalt, concrete is also the undisputed champ in terms of sustainability and cost-effectiveness.

The selected concrete reinforcement, however, requires more consideration. Choosing the appropriate rebar can make all the difference in corrosion. Concrete structures that use stainless-clad steel reinforcing bars have demonstrated lifespans of more than 100 years.

Precast concrete projects can be constructed quickly in emergencies, and precast concrete factories have completely changed the game for places that need to be extensively rebuilt quickly.

Precast FEMA Storm Shelters

As extreme weather events become increasingly common, storm shelters are becoming more crucial across the US. In particular, hailstorms, tornadoes, and dramatic temperature swings have increased in the southern part of the US over the past few years. The upcoming decades are expected to have a similar perspective. Communities are looking into long-term, affordable options like precast concrete building to protect inhabitants.

A safe room is a fortified building created especially to meet FEMA requirements and offer nearly complete protection from extreme wind occurrences, such as tornadoes and hurricanes.

The occupants of a safe room constructed in accordance with FEMA guidelines will have a very high possibility of being protected from harm or death, according to our present understanding of tornadoes and hurricanes. This level of safety is referred to as "near-absolute protection."

Precast concrete satisfies every requirement for safe rooms in FEMA P-361. For storm shelters, it can be applied at the most fundamental design level. FEMA has stricter regulations than other building codes and mandates near-absolute protection for occupants during extreme weather events from wind and debris. The FEMA-selected wind speeds emphasize safety and call for the capacity to resist winds exceeding 250 mph. These exacting requirements are met by precast concrete.

Precast concrete gives value to a building in addition to protecting its residents. Precast provides structures a number of additional advantages, including:

• strengthened structural integrity

• protection from strong winds

• shorter construction periods

• advantages of thermal mass

Precast buildings sometimes function as multipurpose constructions and are built with gyms or auditoriums in mind. When individuals are compelled to utilize the shelter due to an extreme weather occurrence, these additional design features offer comfort and ease. The environment for inhabitants is improved by thick, insulated precast walls that absorb sound and FEMA-rated windows that let in natural light.

Advantages of Precast Storm Shelters

Structural Integrity

In order for a structure to be considered structurally sound, it must be stronger than the highest possible service stress or storm loading. A precast concrete safe room's structural integrity enables it to withstand service loads independently, without relying on surrounding support materials or soils. The building is deemed suitable to carry out its function if the planned strength of a precast concrete safe room exceeds the anticipated maximum applied stresses by an acceptable factor of safety and it complies with the extra FEMA 320 and FEMA 361 requirements.

Wind Protection

Tornadoes, hurricanes, and other such catastrophes rarely produce constant high winds. The pressure and stresses on the various components of a structure increase due to the constant varying and changing of wind speeds and directions. Wind forces operating on both sides (inside and outside) of a safe room structure will also have an impact.

Access and Entry

When choosing a secure room, access points are a crucial aspect to take into account. Easy accessibility, resistance to missile-type forces, and adequate attachment to a structural backing material are all characteristics that can be easily addressed in a precast concrete design for an access point (a door or window). Doors that comply with ICC-500, Section 306.3.1; windows that comply with ICC-500, Section 306.3.2; and all other openings that comply with ICC-500, Section 306.4 are valid entry and exit points for authorized precast concrete safe rooms that can survive tornado events.

Transportation and Installtion

Safe rooms made of precast concrete can be produced well in advance of installation on site. There is no need to wait for cast-in-place concrete buildings to set or cure because they are fully cured before being delivered to the site. Precast concrete safe rooms are readily available, competitively priced, and ready for use as soon as they are delivered. When compared to other materials, these precast advantages can save a project valuable days, weeks, or even months.

Thermal Mass

In the construction business, the term "thermal mass" refers to a material's natural capacity to absorb heat energy. The daily temperature changes in the building's internal spaces can be reduced by using a wall material with a high thermal mass. Because precast concrete has a high thermal mass, it requires a significant amount of heat energy to adjust its temperature. Because safe rooms are intended to house numerous people for an extended period of time, and because the ventilation and temperature within are crucial to ensuring occupant health and safety, the capacity of precast to moderate temperature changes is significant.

Ventilation

The 2006 IBC and IRC codes1 are applicable if the local jurisdiction has not issued a building code; ventilation in approved precast concrete safe rooms complies with the building codes or regulations adopted by the local jurisdiction. Precast concrete safe rooms have ventilation through either the ceiling or the floor. Any ventilation apertures must be shielded with a shield or cowl that passes missile impact testing. When specifying a precast concrete safe room, it is conveniently satisfied the requirement for mechanical ventilation if the safe room is intended for occupancy of more than 50 persons. During the precast manufacturing process, ventilation apertures are simply created and placed to precise requirements.

FAQs about Precast and FEMA Storm Shelters

What is the best material for a storm shelter?

One of the most typical materials found in shelters is concrete. It is quite heavy and loses some of its mobility in strong winds. There aren't many anchorages, extra fixtures, or installation needed. It is more affordable than other materials like steel, works well for many different storm shelter designs, and has a track record of withstanding severe weather.

How thick should a concrete storm shelter be?

According to FEMA, foundations must be at least 3.5 inches thick and in many cases winds will create loads that need greater thicknesses. More information and technical details from FEMA can be found here.

What types of materials are storm shelters made from?

Storm shelters can be made from a variety of materials including wood, steel, and concrete.  Some shelters make use of more than one of these materials that work together to provide protection to the occupants inside.

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Robert J Curry Public Safety Center

The Robert J Curry Public Safety Center is built to FEMA 361 design and construction guidance for community shelters and can withstand the stringent 200 mph wind requirements. It is also used as a first responder shelter to house more than 275 personnel for pre and post-disaster functions.  The project consisted of 563 pieces of over 68,000 SF of exterior cladding most of which are 8” thick architectural precast concrete walls.

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Precast Resiliency Resources

PCI recently highlighted precast and its ability to perform well in storms in their Ascent magazine.  Read some of the articles below.

Precast Enclosure Systems

Precast, as an enclosure system, provides a distinct advantage over other building materials.  Precast walls act as both the structural support for a structure and the component that provides the building’s insulation. By choosing precast, designers and clients are choosing a product that lasts a life-time and provides the support and protection needed to keep residents safe.

Types of Precast Walls

The versatility of precast walls ranges from providing architectural cladding for the exterior of a structure to a total precast system that provides insulation and structural support for the overall building. The following graphic depicts different types of precast walls.

Solid Walls

Solid walls are manufactured completely of concrete with insulation added to the interior finishing wall system. These types of walls can have any type of finish added to the back.

Sandwich Walls

Sandwich walls encompass the normal characteristics of a standard precast concrete wall with the added benefit of insulation which provides energy performance and moisture protection. More information about sandwich walls can be found in the State of the Art Sandwich Wall Panel technical document.

Thin-Shell and GFRC

Thin-shell wall panels are made from a thin outer-wythe of concrete and are connected to the backup structural system which usually consists of steel or concrete. Glass fiber-reinforced concrete (GFRC) is a type of thin-shell system which includes concrete that contains alkali-resistant glass fibers.

Lite Walls

Lite walls are used on precast structures and involve shear walls with a void that provides openness and a feeling of security. 

Depending on the needs of a client, one or more of these types of walls can be used to create the enclosure of the structure.

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PCI’s Designer’s Notebook: Envelope Tolerances for Architectural Precast discusses the tolerances and clearances required for joining different building materials.

PCI also offers a collection of technical documents regarding Building Enclosure Design here for professionals looking for more guidance in designing building enclosures with precast.

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Benefits

Like other precast components, precast walls provide valuable benefits for a building’s enclosure. Some of the benefits include: 

• Moisture Resistance: Precast wall systems are a barrier or face-sealed systems. They are superior to rainscreen systems because they do not require a space where water can collect and cause further issues. There are several supporting technical documents on the Building Enclosure Design web page under Air and Moisture Management.

• Thermal Mass: Precast concrete buildings save energy in various types of climates due to their ability to absorb and store heat and react very slowly to changes in outside temperature. This is further discussed in PCI’s Thermal Mass technical document.

• Quick Erection: Precast building enclosures can be erected in a few days or weeks which greatly reduces the overall project construction schedule.

• Eliminates Threats: The speed of installation eliminates the need for fireproofing, termite treatments, and additional insulation.

• Versatility: Precast walls can be designed to match a specific color or texture and help buildings blend into their surroundings in urban environments or match existing nearby structures.

When used as a building enclosure,  precast/prestressed concrete provides substantial benefits to both the owners and occupants of the structure. The versatility of concrete allows for designs of all sizes, shapes, and colors which meets the unique characteristics of each project. 

Precast and Carbon Emissions

At current rates, global carbon emissions are 36 billion tons annually and rising.  With a new focus on reducing carbon emissions to help counteract climate change, the precast industry has begun focusing on improving their processes and educating design professionals on the sustainability that concrete can bring in the long-term.

How much carbon does precast contribute to global emissions? 

Cement accounts for 3% of global emissions because of its use of clinker and limestone which emits carbon during production. This percentage also includes the actual energy inputs needed to produce the cement itself.

What is the comparison to timber?

Precast is often compared to timber when designers are considering sustainable materials to use in their structures.  Deforestation is responsible for 2.2% of global emissions (which is the difference between carbon from deforestation and the positive offset of replanting), with 8-10% of timber in the construction industry coming from deforestation.  Most timber comes from forest degradation which means trees are selected to be cut down leaving other trees intact.  

The actual carbon emissions of the timber industry is not fully analyzed because there are no international standards for tracking it.  Wood harvested from one country can be shipped to another with the carbon emissions impacted only being counted in one country or not counted at all. 

For example, each year 80,000 hectares of trees in North Carolina are cut down to produce wood pellets that are then burnt in power plants in the UK, as well as for paper and timber. The state does not count the resulting emissions. This makes it nearly impossible to determine the actual global emissions from the timber industry and compare it to precast.

Although it is true that if managed correctly for long-term carbon storage timber is an amazing carbon storage device, currently timber is harvested well before trees can fully store their potential for carbon making it less efficient in comparison to precast.

What ways can precast help with its emissions?

New technologies to capture or reduce carbon 

Since there are no other construction materials like concrete, professionals have been trying to implement new technologies to help reduce its carbon footprint.  There are a variety of methods being tested including direct-air capture (DAR) which is a machine that acts as an artificial tree collecting CO2 particles out of the air passed through it.  There are also ideas such as capturing CO2 from smokestacks and putting that carbon into cement products to replace certain high carbon materials in concrete like limestone with other less carbon producing compounds.

New greener concrete formulas

Concrete professionals are currently working on other types of cement to help counteract the carbon emissions of current products.  One of these newer innovations is called PLC or Portland-Limestone Cement.  This concrete provides the same durability and resilience, but has a reduced carbon footprint of 10%. It can be used for basically any structure with no modifications to mix design or placing procedures.

Reduces waste over the long term 

At its core, precast is inherently resistant to storms and provides protection from wind, surge, and flying debris.  This storm resistance has been confirmed through numerous impact tests.  But aside from its resistance, precast structures are able to recover quickly after storms. Because the precast is mold/mildew resistant, it is able to not only withstand flooding, but recover without long lasting damage. This resiliency translates into structures that last longer and withstand much more than timber structure which have to be replace more frequently and end up causing more materials to be sent to the landfill.

The Takeaway

Improvements in both the timber and precast industries could mean larger impacts on reducing global carbon emissions for the construction industry as a whole.  Working together they could significantly cut their emissions together and provide designers solutions that meet their clients long-term carbon and sustainability needs.