By producing precast concrete in a controlled environment (typically referred to as a precast plant), the precast concrete is afforded the opportunity to properly cure and be closely monitored by plant employees. Utilizing a Precast Concrete system offers many potential advantages over site casting of concrete. The production process for Precast Concrete is performed on ground level, which helps with safety throughout a project. There is a greater control of the quality of materials and workmanship in a precast plant rather than on a construction site. Financially, the forms used in a precast plant may be reused hundreds to thousands of times before they have to be replaced, which allows cost of formwork per unit to be lower than for site-cast production.
Many states across the United States require a precast plant to be certified by either the Architectural Precast Association (APA), National Precast Concrete Association (NPCA) or Precast Prestressed Concrete Institute (PCI) for a precast producer to supply their product to a construction site sponsored by State and Federal DOTs.
There are many different types of precast concrete, forming systems for architectural applications, differing in size, function, and cost. Precast architectural panels are also used to
cladCladding is the application of one material over another to provide a skin or layer intended to control the infiltration of weather elements, or for aesthetic purposes....
all or part of a building
facadeA facade or façade is generally one exterior side of a building, usually, but not always, the front. The word comes from the French language, literally meaning "frontage" or "face"....
free-standing walls used for landscaping,
soundproofingSoundproofing is any means of reducing the sound pressure with respect to a specified sound source and receptor. There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using...
, and security walls, and some can be
Prestressed concretePrestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...
structural elements. Stormwater drainage, water and sewage pipes, and tunnels make use of precast concrete units. The
New South Wales Government RailwaysThe New South Wales Government Railways was the government department that operated the New South Wales Government's railways until the establishment of the Public Transport Commission in 1972. Although later known officially as the Department of Railways, New South Wales, it was still generally...
made extensive use of precast concrete construction for its stations and similar buildings. Between 1917 and 1932, they erected 145 such buildings.
Brief history
Ancient Roman builders made use of concrete and soon poured the material into moulds to build their complex network of
aqueductAn aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose....
s,
culvertA culvert is a device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common...
s, and tunnels. Modern uses for pre-cast technology include a variety of architectural and structural applications featuring parts of or an entire building system.
In the modern world, pre-cast panelled buildings were pioneered in
LiverpoolLiverpool is a city and metropolitan borough of Merseyside, England, along the eastern side of the Mersey Estuary. It was founded as a borough in 1207 and was granted city status in 1880...
,
EnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
in 1905. A process was invented by city engineer
John Alexander BrodieJohn Alexander Brodie was a British civil engineer.Brodie began his professional career in 1875 working in the Mersey Docks and Harbour Board engineering department under Chief Engineer George Fosbery Lyster, following this he set up a private consultancy and spent some time working in Spain...
, whose inventive genius also had him inventing the football goal net. The tram stables at Walton in
LiverpoolLiverpool is a city and metropolitan borough of Merseyside, England, along the eastern side of the Mersey Estuary. It was founded as a borough in 1207 and was granted city status in 1880...
followed in 1906. The idea was not taken up extensively in Britain. However, it was adopted all over the world, particularly in Eastern Europe.
Precast Concrete Products
The following is a sampling of the numerous products that utilize precast/prestressed concrete. While this is not a complete list, the majority of precast/prestressed products can fall under one or more of the following categories:
Agricultural Products
Precast concrete products can withstand the most extreme weather conditions and will hold up for many decades of constant usage. Products include bunker silos, cattle feed bunks,
cattle gridA cattle grid or cattle guard – also known as a vehicle pass, Texas gate, stock gap A cattle grid (or stock grid)(British English) or cattle guard (American English) – also known as a vehicle pass, Texas gate, stock gap A cattle grid (or stock grid)(British English) or cattle guard (American...
, agricultural fencing, H-bunks, J-bunks, livestock slats, livestock watering trough, feed troughs, concrete panels, slurry channels, and more.
Prestressed concretePrestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...
panels are widely used in the UK for a variety of applications including agricultural buildings, grain stores, silage clamps, slurry stores, livestock walling, and general retaining walls. Panels can either be used horizontally and placed either inside the webbings of RSJs (
I-beam-beams, also known as H-beams, W-beams , rolled steel joist , or double-T are beams with an - or H-shaped cross-section. The horizontal elements of the "" are flanges, while the vertical element is the web...
) or in front of them. Alternatively panels can be cast into a concrete foundation and used as a cantilever retaining wall.
Building and Site Amenities
Precast concrete building components and site amenities are used architecturally as fireplace mantels, cladding, trim products, accessories, and curtain walls. Structural applications of precast concrete include foundations, beams, floors, walls, and other structural components. It is essential that each structural component be designed and tested to withstand both the tensile and compressive loads that the member will be subjected to over its lifespan.
Building construction using precast concrete walls and floors
Retaining Walls
Precast concrete provides the manufacturers with the ability to produce a wide range of engineered earth retaining systems. Products include: commercial
retaining wallRetaining walls are built in order to hold back earth which would otherwise move downwards. Their purpose is to stabilize slopes and provide useful areas at different elevations, e.g...
, residential retaining walls, sea walls,
mechanically stabilized earthMechanically stabilized earth or MSE is soil constructed with artificial reinforcing. It can be used for retaining walls, bridge abutments, dams, seawalls, and dikes. Although the basic principles of MSE has been used throughout history, MSE was developed in its current form in the 1960s...
(MSE) panels, modular block systems, segmental retaining walls, etc. Retaining walls have 5 different types which include: gravity retaining wall, semigravity retaining wall, cantilever retaining wall, counterfort retaining wall, and buttress retaining wall.
Sanitary and Stormwater
Sanitary and Stormwater management products are structures designed for underground installation that have been specifically engineered for the treatment and removal of pollutants from sanitary and stormwater run-off. These precast concrete products include
stormwater detention vaultA stormwater detention vault is an underground structure designed to manage excess stormwater runoff on a developed site, often in an urban setting...
s, catch basins, and
manholeA manhole is an opening used to gain access to sewers or other underground structures, usually for maintenance.Manhole may also refer to:* Manhole , a metal band from Los Angeles* The Manhole, a computer game...
s.
Transportation and Traffic Related Products
Precast concrete transportation products are used in the construction, safety and site protection of road, airport and railroad transportation systems. Products include: box culverts, 3-sided culverts, bridge systems, railroad crossings, railroad ties, sound walls/barriers,
Jersey barrierA Jersey barrier or Jersey wall is a modular concrete barrier employed to separate lanes of traffic. It is designed to both minimize vehicle damage in cases of incidental contact while still preventing crossover in the case of head-on accidents....
s, tunnel segments, precast concrete barriers, TVCBs, central reservation barriers and other transportation products. Used to make underpasses, surface-passes and pedestrian subways, so that traffic in cities is disturbed for less amount of time.
Utility Structures
For communications, electrical, gas or steam systems, precast concrete utility structures protect the vital connections and controls for utility distribution. Precast concrete is nontoxic and environmentally safe. Products include: hand holes, hollowcore products, light pole bases, meter boxes, panel vaults, pull boxes, telecommunications structures, transformer pads, transformer vaults, trenches, utility buildings,
utility vaultA utility vault is an underground room providing access to subterranean public utility equipment, such as valves for water or natural gas pipes, or switchgear for electrical or telecommunications equipment....
s, utility poles, controlled environment vaults (CEVs,) and other utility structures.
Water and Wastewater Products
Precast water and wastewater products hold or contain water, oil or other liquids for the purpose of further processing into non-contaminating liquids and soil products. Products include: aeration systems, distribution boxes, dosing tanks,
dry wellA dry well is an underground structure that disposes of unwanted water, most commonly stormwater runoff, by dissipating it into the ground, where it merges with the local groundwater. Often called a soakaway in the UK....
s,
grease interceptorGrease traps are plumbing devices designed to intercept most greases and solids before they enter a wastewater disposal system. Common wastewater contains small amounts of oils which enter into septic tanks and treatment facilities to form a floating scum layer...
s, leaching pits, sand-oil/oil-water interceptors,
septic tankA septic tank is a key component of the septic system, a small-scale sewage treatment system common in areas with no connection to main sewage pipes provided by local governments or private corporations...
s, water/sewage storage tanks, wetwells, fire cisterns and other water & wastewater products.
Cemetery Products
Underground vaults or mausoleums - calls for quality watertight structures that withstand the tests of time and the forces of nature.
Hazardous Materials Containment
Storage of hazardous material, whether short-term or long-term, is an increasingly important environmental issue, calling for containers that not only seal in the materials, but are strong enough to stand up to natural disasters or terrorist attacks.
Marine Products
Floating docks, underwater infrastructure, decking, railings and a host of amenities are among the uses of precast along the waterfront. When designed with heavy weight in mind, precast products counteract the buoyant forces of water significantly better than most materials.
Modular PavingAn interlocking concrete paver is a pre-cast piece of concrete or brick commonly used in exterior hardscaping applications. Pavers were developed in Europe and introduced into the United States in the early 1970s....
Available in a rainbow of colors, shapes, sizes and textures, these versatile precast concrete pieces can be designed to mimic brick, stone or wood.
Prestressed/Structural Products
Prestressing is a technique of introducing stresses of a predetermined magnitude into a structural member to improve its behavior. This technique is usually found in concrete beams, spandrels, columns, single and double tees, wall panels, segmental bridge units, bulb-tee girders, I-beam girders, and others. "Prestressed member are crack-free under working loads and, as a result, look better and more watertight, providing better corrosion protection for the steel." Many projects find that prestressed concrete provides the lowest overall cost, considering production and lifetime maintenance.
Reinforced Concrete Box
A
reinforced concrete box, referred to as a box culvert in the UK, is a square or rectangular "pipe" made of
concreteConcrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
with
rebarA rebar , also known as reinforcing steel, reinforcement steel, rerod, or a deformed bar, is a common steel bar, and is commonly used as a tensioning device in reinforced concrete and reinforced masonry structures holding the concrete in compression...
or wire mesh fabric strewn throughout for the addition of extra strength. Multiple such boxes are arranged sideways to make a pipe or tunnel like structure.
It is often used for
sanitary sewerA sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...
trunks,
storm drainA storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...
spillways, pedestrian subways, utility tunnels, catch basins, and other similar underground passage ways. Due to the enormous strength of
reinforced concreteReinforced concrete is concrete in which reinforcement bars , reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. It was invented by French gardener Joseph Monier in 1849 and patented in 1867. The term Ferro Concrete refers only to concrete that is...
, it is often used in sewers or tunnels that have little cover above them which means they will be subjected to the stress of the
roadA road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
atop them. In India, pre-cast concrete boxes known as "Magic Boxes"" are used for the construction of
flyoverAn overpass is a bridge, road, railway or similar structure that crosses over another road or railway...
s and
underpassA tunnel is an underground passageway, completely enclosed except for openings for egress, commonly at each end.A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. Some tunnels are aqueducts to supply water for consumption or for hydroelectric stations or are sewers...
es.
Double Wall Precast — Concrete Sandwich Panels
The double wall process has been in use in Europe for many years. The walls consist of two
wytheA wythe is a continuous vertical section of masonry one unit in thickness. A wythe may be independent of, or interlocked with, the adjoining wythe...
s of concrete separated by an insulated void. The most commonly specified thickness of the wall panels is 8 inches. The walls can also be built to 10 and 12 inches thick if desired. A typical 8-inch wall panel consists of two wythes (layers) of reinforced concrete (each wythe is 2-3/8 inches thick) sandwiched around 3-1/4 inches of high
R-valueThe R-value is a measure of thermal resistance used in the building and construction industry. Under uniform conditions it is the ratio of the temperature difference across an insulator and the heat flux through it or R = \Delta T/\dot Q_A.The R-value being discussed is the unit thermal resistance...
insulating foam. The two wythes of the interior and exterior concrete layers are held together with steel trusses. Concrete sandwich panels held together with steel trusses are inferior to those held together with composite fibreglass connectors. This is because the steel creates a thermal bridge in the wall, significantly reducing the insulative performance and reducing the ability of the building to utilise its thermal mass for energy efficiency. There is also the risk that because steel does not have the same expansion coefficient as that of concrete, as the wall heats and cools, the steel will expand and contract at a different rate to the concrete, which can cause cracking and spalling (concrete "cancer"). Fibreglass connectors that are specially developed to be compatible with concrete significantly reduce this problem. The insulation is continuous throughout the wall section. The composite sandwich wall section has an R-value exceeding R-22. The wall panels can be made to any height desired, up to a limit of 12 feet. Many owners prefer a 9-foot clear height for the quality of look and feel it affords a building.
The walls can be produced with smooth surfaces on both sides because of the unique manufacturing process, which form finishes both sides. The walls are simply painted or stained on the exterior surface to achieve the desired color or textured surface. When desired, the exterior surface can be manufactured to have a wide variety of brick, stone, wood, or other formed and patterned appearances through the use of reusable, removable formliners. Interior surfaces of the double-wall panels are drywall quality in appearance right out of the plant, requiring only the same prime and paint procedure as is common when completing conventional interior walls made of drywall and studs.
Window and door openings are cast into the walls at the manufacturing plant as part of the fabrication process. Electrical and telecommunications conduit and boxes are flush-mounted and cast directly in the panels in the specified locations. The carpenters, electricians, and plumbers do need to make some slight adjustments when first becoming familiar with some of the unique aspects of the wall panels. However, they still perform most of their job duties in the manner to which they are accustomed.
Double-wall precast concrete sandwich panels can be used on most every type of building including but not limited to: multi-family, townhouses, condominiums, apartments, hotels and motels, dormitories and schools, and single-family homes. Depending upon building function and layout, the double-wall panels can be easily designed to handle both the structural requirements for strength and safety, as well as the aesthetic and sound attenuation qualities the owner desires. Speed of construction, durability of finished structure, and energy-efficiency are all hallmarks of a building that utilizes the double-wall system.
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