Now a days conventional type of construction is fading up as compared to Precast construction. Precast concrete is a smart way to build any type of building, safely, affordably. It ensures fast construction time, high profitability and excellent quality . Precast concrete is an industrialized way to build. It means transfer of work from sites to factories. This improves productivity and quality and shoertens construction time of a building. Inshort, precast concrete lowers total construction costs considerably. This paper deals with the study of Precast technology and its advantages over Conventional construction.
Precast concrete is a construction product produced by casting concrete in a reusable mold or “form” which is then cured in a controlled environment, transported to the construction site and lifted into place (“tilt up”). In contrast, standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast concrete using a fine aggregate in the mixture, so the final product approaches the appearance of naturally occurring rock or stone. More recently expanded polystyrene is being used as the cores to precast wall panels. This is lightweight and has better thermal insulation.
Precast is used within exterior and interior walls. 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. Using a precast concrete system offers many potential advantages over onsite casting. Precast concrete production can performed on ground level, which helps with safety throughout a project. There is greater control over material quality and workmanship in a precast plant compared to a construction site. The forms used in a precast plant can be reused hundreds to thousands of times before they have to be replaced, often making it cheaper than onsite casting when looking at the cost per unit of formwork.
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 clad all or part of a building facades or free-standing walls used for landscaping, soundproofing, and security walls, and some can be prestressed concrete structural elements. Stormwater drainage, water and sewage pipes, and tunnels make use of precast concrete unit.
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. Also in building homes, they used EPS now in building precast concrete as this is much better in terms of the materials and the insulation.
Multi-storey car parks are commonly constructed using precast concrete. The constructions involve putting together precast parking parts which are multi-storey structural wall panels, interior and exterior columns, structural floors, girders, wall panels, stairs, and slabs. These parts can be large; for example, double-tee structural floor modules need to be lifted into place with the help of precast concrete lifting anchor systems.
Precast concrete provides manufacturers with the ability to produce a wide range of engineered earth retaining systems. Products include: commercial retaining walls, residential walls, sea walls, mechanically stabilized earth (MSE) panels, modular block systems, segmental retaining walls, etc. Retaining walls have five different types which include: gravity retaining wall, semigravity retaining wall, cantilever retaining wall, counterfort retaining wall, and buttress retaining wall.
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 wells, grease interceptors, leaching pits, sand-oil/oil-water interceptors, septic tanks, water/sewage storage tanks, wetwells, fire cisterns, and other water and wastewater products.
Advantages of precast construction
Precasting is great for producing large numbers of identical components. Let’s say we are building an affordable housing project with 3,000 identical apartments. We could then use precasting to produce wall slabs and floor slabs for all the apartments, and then lift them into place and connect them.
Since it is done in a purpose-built precasting yard or factory, it makes construction easier for the following reasons:
- The construction is done on the ground rather than at a height
- It can be done inside a climate-controlled structure, eliminating problems of rain, dust, cold, or heat
- Specialised formwork (moulds) can be built for doing many repetitions of the same component
- Specialised equipment can be used to make, move, and pour the liquid concrete
- Curing of the concrete can be done in a controlled environment
This means that the quality of precast components can be very high.
Since the components can be made beforehand, construction can be very quick. In cast-in-situ construction, engineers have to build each set of components after the previous set has finished, which does take time, as concrete generally takes 28 days to reach its full strength.
Precast concrete sandwich wall panels have been used on virtually every type of building, including schools, office buildings, apartment buildings, townhouses, condominiums, hotels, motels, dormitories, and single-family homes. Although typically considered part of a building’s enclosure or “envelope,” they can be designed to also serve as part of the building’s structural system, eliminating the need for beams and columns on the building perimeter. Besides their energy efficiency and aesthetic versatility, they also provide excellent noise attenuation, outstanding durability (resistant to rot, mold, etc.), and rapid construction.
In addition to the good insulation properties, sandwich panels require fewer work phases to complete. Compared to double-walls, for example, which have to be insulated and filled with concrete on site, sandwich panels require much less labor and scaffolding.
The efficiency, durability, ease, cost effectiveness, and sustainable property precast products have brought a revolutionary shift in the time consumed in construction of any structure. Construction industry is a huge energy consuming industry, and precast concrete products are and will continue to be more energy efficient than its counterparts. The wide range of designs, colours, and structural options that these products provide is also making it a favourable choice for its consumers.
Precast concrete is used in the following ways:
- to make beams, columns, floor slabs, foundations, and other structural members for buildings
- to make wall or cladding panels for buildings
- to make precast pre-stressed elements for buildings
- to make components for infrastructure projects: elements such as bridge spans, or metro line viaducts are often precast in a casting yard
- to make products for sale: precast water tanks, septic tanks, drainage chambers, railway sleepers, floor beams, boundary walls, water pipes are all available
Since it can be moulded into any shape, it can also be used to create one-off unusual forms such as boats, sculptures and suchlike
Different types of Precast System
Depending on the load bearing structure precast systems can be divided into the following categories: (a) Large panel systems (b) Frame systems (c) Slab column systems with wall (d) Mixed system.
(a) Large Panel System : This system refers to multi storey structures composed of large walls and floor concrete panels connected in the vertical and horizontal directions so that the wall panels enclose appropriate spaces for the rooms with a building . These panels form abond like structure. Both horizontal and vertical panels resists gravity loads.
(b) Frame Structure: Precast frames can be constructed using either linear elements or spatial beam-column sub assemblages. Precast beam-column sub-assemblages have the advantages that the connecting faces between the sub-assemblages can be placed away from the critical frame regions; however linear elements are generally preferred because of the difficulties associated with forming, handling and erecting spatial elements.
(c) Slab-Column system with Shear wall: These systems rely on shear walls to sustain lateral load effects, where as the slab-column structure resists mainly gravity loads. There are two main systems in this category: (i) Lift slab system with walls : In this system, the load bearing structure consists of precast reinforcement concrete columns and slabs. Precast columns are usually two stories high. All precast structural elements are assembled by means of special joints. (ii) Pre stressed slab-column system: Inpresstressed slab-column system uses horizontal prestressing in two orthogonal directions to achieve continuity. The precast column elements are 1 to 3 stories high. The reinforcement concrete floor slabs fit the clear span between columns.
Precast- The Smarter Way
Precast is a modular building system based on ready-made, factory-manufactured components and intelligent connections. It provides a way to design and construct a sufficient number of suitable homes to meet the needs of city dwellers in a reasonable time-frame and at a reasonable cost. Compared to traditional cast-in-situ, precast uses less cement, water, steel, and labor. Most of the work is transferred from the site to a safe and controlled, automated factory environment. This results in improved productivity and minimal logistics: precast products can be transported to a site ready-to-install.Precast buildings are well-suited to hot climates. Both the thermal and sound insulation properties of precast are very advanced. Precast concrete buildings absorb and store surplus heat and slowly release it back into the air.
Precast can also be used for buildings in seismic areas, when the specific local requirements are taken into account in analysis and design. Demands for precast connection types vary among different precast products, local building conditions, occupancy requirements, and loads. A building can be fully or partially precast, depending on the local construction conditions and requirements. Design and engineering play a key role in the successful implementation of precast technology. A professional structural engineer can find the most practical and cost-efficient solutions for any type of precast building. This is not the case with traditional cast-in-situ construction because the projects are often deficient in preliminary planning and proper calculations.
Precast concrete is an industrialized way to build. It means transfer of work from sites to factories. This improves productivity and quality and shortens construction time of a building. In short, precast concrete lowers total construction costs considerably. Precast also has lower lifetime costs than any other building solution. It is possible due to consistent high quality of industrially produced products. Precast minimizes e.g. structural and facade maintenance needs during years. With precast, logistics needs are minimal. Precast floors, walls, frames and foundations are transported to a construction site ready-to-install. Logistics to building site is arranged with just one delivery vehicle instead of several raw material transfers back and forth.
Precast concrete suits well for any type of building: residential, commercial, industrial, public to name a few. There is a suitable solution for both indoor and outdoor precast production. The smart match can be found for different kinds of building projects in terms of elements produced, factory capacity and labor needs. Precast can be made into any shape or color and finished with several techniques. This together with longer spans gives architects and other designers more freedom than ever. Precast can be used as the only building material, but it can as well be combined with steel or be utilized as a composite structure only. Use of precast in a building depends largely on local building traditions and restrictions.
Compared to cast-in-situ, precast uses less of everything less cement, less water, less steel, and less labor. It produces less waste on the site and in the factory. This makes CO2 footprint of precast much smaller than in cast-in-situ construction. Precast offers a safer and healthier working environment. Material handling is easier and less scaffolding is needed. Precast technology works in virtually all environments cold, hot, moist or dry. Concrete hardens on site basically throughout the year, in temperatures from -15 to +40°C. To avoid too fast or slow hardening in more hot, moist or dry climates, several curing and concrete mixing solutions can be applied. As an industrially produced building material, precast is always of the highest quality. In production of precast, selected raw materials are used following carefully designed production process. The controlled environment enables real time monitoring and easy adjustments. The outcome is totally cured, finished and equipped. While precast comes only harder during years, it doesn’t burn, melt, or rot. High quality precast does not breed any harmful microbes, either.
The on-site installation of precast components can be a high-risk activity involving the use of heavy plant, cranes and personnel working at height. Consideration should be given therefore to safeguarding against risks when receiving delivery, moving, and placing units.
Consideration should be given to:
- The method and sequence of assembly and erection.
- The method of providing temporary supports.
- Structural connections and joint details.
- Handling and rigging requirements.
- Site accessibility for delivery and storage.
- Crane capacity and working clearance for hoisting.
- Sample measurement to confirm the accuracy of critical dimensions.
- Visual inspection of concrete finishes for defects.
- Locations and conditions of lifting inserts for hoisting.
- Site VS. Factory precasting
Precasting can be done at a casting yard, in or near the site, or in a factory. A key aspect of determining whether to use site or factory precasting are the transport costs. Factory work offers superior quality for obvious reasons, so if there is a factory close to the site, it makes sense to use it.
If a precasting yard is to be created, space must be laid out for the following activities:
storing the raw materials, such as cement, aggregate, sand, admixtures, water, reinforcement bars, and steel or plywood sheets for formwork
- a formwork making and maintenance yard
- a concrete mixing plant
- a steel reinforcement yard to make rebar cages to be placed inside the concrete
- a casting area
- a curing area
- a stacking area for finished components?
For infrastructure projects, a casting yard is created on a piece of open land in the city. It is important that this be located near a major highway, as the precast elements can be very large or heavy, and cannot be taken through narrow roads.
Precast chemical and panels
In regard to construction chemical, the future of construction industry in India is in the hands of Precast industries. Its contribution to fast and cost-effective construction /infrastructure development in the past decade is very commendable. Mapei is doing commendable work in this regard. Mapei Admixtures like Dynamon SX626, Dynamon SX628 and Dynamon SX550 are hyperplastisicing admixture based on new generation of Polycarboxylate Ether for high performance concrete mixes with very low water cement ratio, high early compressive strength specially designed to improve the rheology of precast concrete.
Precast panels are reinforced for crack control and typically made of high-quality concrete with low water-to-cement ratios and very low water absorption. It is for these reasons that they can act as a reliable barrier to water penetration. Millions of square feet of precast panels installed over the last five decades have provided the real-life proof of this. High-density, large format precast concrete panels are, by themselves, resistant to air and water penetration. Provided that panel joints are well-designed and properly maintained, the system, as a whole, offers excellent protection from climatic conditions. In buildings where the panels are used as the interior finish, a precast concrete wall panel offers a smooth, dense surface that may be easily cleaned thereby minimizing the collection of dirt and contaminants. Precast concrete also does not impact the occupants’ indoor air quality as it does not off-gas. Nevertheless, given the environmental exposure that all buildings must endure, all enclosure systems require some maintenance activity over time. Let us discuss products from Mapei that can be used during making and maintenance of precast concrete.
Precast connections ensure safety and durability of a precast building. They carry the predefined loads in different building structures and resist fire and water. Industrially produced precast connections are fast and easy to install no matter what the precast product. Precast is a modular building system based on components and connections. Some type of a precast connection is needed between each produced precast unit. Demands for precast connection types vary among different precast products, local building conditions and restrictions, and loads on the structure. Generally every country has its own system for precast connections. There are several pre-tested connection types for precast floor products, and seismic and support connection.Typically precast connections can be done with an industrially produced connection part, wet connection, bolt, or weld connection. In precast connection design the key variables are strength, volume changes, ductility, durability including fire and corrosion, simplicity in production, installation and maintenance, temporary loading conditions, economy and appearance.
Precast buildings suit well for hot, cold and also seismic areas, when the specific local requirements are taken into account in connection design. If planning a building for a seismic area, it is recommended to involve seismic connection design experts into the process.
The Demand of Precast Construction
The report “Precast Concrete Market by Element (Columns & Beams, Floors & Roofs, Girders, Walls & Barriers, Utility Vaults), Construction Type (Elemental, Permanent Modular, Relocatable), End-use Sector (Residential, Non-residential) – Global Forecast to 2022”, The precast concrete market size is projected to grow from USD 104.03 Billion in 2017 to USD 138.96 Billion by 2022, at an estimated CAGR of 5.96%. The precast concrete market is projected to witness significant growth in the next few years with the increasing demand for new constructions all over the world due to rapid urbanization and industrialization with large-scale investments in the industrial and infrastructural sectors. Rising
construction activities in emerging
economies and increasing inclination toward sustainable construction methods are increasing the reliance on modern construction techniques, subsequently creating growth opportunities for the precast concrete market.
The non-residential segment dominated the market in 2016 and is projected to be the fastest-growing end-use sector over the next five years. As a result of the rising urbanization and industrialization, along with the growing demand for better quality bridges, airports, metros, and buildings among others. This market is mostly driven by the upward surge in demand for new constructions all over the world. Rising public and private investment in the infrastructure sector in the emerging economies of Asia Pacific, the Middle East, and South America are drivers for the growth of this market. Asia Pacific contributes a major market share in the global precast concrete market. Increasing industrialization as well as growing population in China, Indonesia, and India are experiencing high demand for residential and non-residential constructions. The rapid urbanization in these countries demands faster and cheaper construction of buildings and facilities without compromising on quality. Additionally, increased government investments in infrastructure constructions provide potential for growth of the precast concrete market in these countries.
According to marketsandmarkets.com report, The overall precast concrete market is expected to grow from USD 99.13 billion in 2016 to USD 138.96 billion by 2022, at a CAGR of 5.96% from 2017 to 2022. It has been growing in accordance with the advancing degree of urbanization, industrialization, and infrastructural developments. The gradual shift of building contractors and consumers toward cost-efficient, eco-friendly, and modern building techniques is creating growth opportunities for the precast concrete market. The increasing disposable income of people in the developing countries and the changing preferences of construction methods are increasing the reliance on modern construction techniques, which drive the precast concrete market growth. The precast concrete elements are used in residential and non-residential sectors. The base year considered for the study is 2016, and the forecast has been provided for the period between 2017 and 2022.
According to alliedmarketresearch.com Growth in urbanization and industrialization are among some of the key factors that drive the precast construction market. The rapid growth and development of urban housing demand causes for shorter construction timelines and reduced cost. Due to this, construction companies are adoptive for cost effective, proven technologies of precast to ensure the highest standards and uniform quality, which can be met by precast technology. The impact of this factor is presently moderate and it is expected to increase during the forecast period mainly due to increase in awareness of this technology with the rise in urbanization. The global precast construction market is segmented based on product type, construction type, end users, and geography. Geographically, the market is analyzed across four regions, namely, North America, Europe, Asia-Pacific, and LAMEA along with their prominent countries. Based on product type, the precast construction market is segmented into columns & beams, floors & roofs, walls, staircases, girders, paving slabs, and others. Columns & beams are the most dominant product type constituting for around 24.5% of the overall precast construction market share in 2015. Precast columns & beams provide flexible solution to the structural component of the project. These products can be used for number of applications ranging from parking structures to the structural framework of commercial buildings. The columns & beams segment is projected to grow at the CAGR of 6.6% during the forecasted period, owing to the factors such as easier material handling and minimized need for framework.
Based on construction type, the precast construction market is bifurcated into modular construction and manufactured homes. Modular construction segment dominates the market in 2015 and is expected to maintain its dominance during the forecast period growing at a CAGR of 6.8%. The demand for modular construction market is on an increase globally mainly due to customer demand for speed of construction, improved quality, and for early return on investment. The precast construction market based on end-users is classified into residential and non-residential segments. The latter includes infrastructure projects such as tunnels, bridges, flyovers, railway sleepers, metro projects and others. It also includes stadiums, museums, supermarkets, hospitals and others. In precast non-residential constructions around 50-90% of construction of structures is completed at an off-site facility in a controlled environment and then transported to the final site. Builders can enhance the overall performance of the project using precast and pre-assembled components.
By geography, Asia-Pacific generated the maximum revenue, and is estimated to grow at a CAGR of 7.2%, followed by Europe. Asia-Pacific region is estimated to grow at the fastest CAGR mainly due to increase in urbanization and infrastructure development in the emerging countries of India, China, Indonesia, and others.
Growth in urban population is a major megatrend, which is transforming the construction industry in most countries. In addition, demand for affordable housing is increasing, along with soaring demand for transport and utility infrastructure. This, in turn, is anticipated to propel the market over the coming years.
Short construction time and low cost are the major advantages offered by precast concrete. This renders it popular among builders and contractors. Temperature, stripping time, and mix designs, which is a very important factor for manufacturing of strong concrete products, can be monitored and checked in a factory setting. Hence buildings made of precast concrete are stronger in comparison to those made with conventional concrete.
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