Precast concrete is a composite building material used in architectural applications for floor and roof slabs, retaining walls, hollow-core floors and stair components.
Precast concrete works by placing a mould, or form, in the desired shapes of the finished product. This mould is often composed of wood, reinforcement of materials such as steel or plastic. A liquid concrete mixture (also known as "slurry") is poured into the mould and allowed to harden. When completed, this results in a single solid element that only has to be transported to its desired location; no further assembly work is required.
Concrete mixtures can include cement, sand, coarse aggregate, water and admixtures such as: superplasticisers, concrete lifting inserts air-entraining agents and retarders. Pre-cast concrete allows builders to achieve rapid construction and site-cast concrete workability in the construction industry by quickly and efficiently creating and retaining walls, beams, architectural panels, reinforced concrete panels, double tees, reinforced concrete surface, floor slabs and other elements in any shape or size required. On-site forming is not necessary.There are many reasons to use prefabricated concrete formwork over the traditional building method of onsite cement pouring, like the below.
Prefab concrete reduces construction time by up to 50%. This allows builders to complete projects such as office buildings, apartment buildings, tunnel segments, railroad ties, burial vaults, precast bridges and other entire buildings in half the time with less mess, dust and disruption to residents. The risk of accidents and injuries at a construction site is also reduced for an entire building as there is no need for a large workforce onsite all day long.
Onsite forming uses more materials because it needs supports such as posts and bridge beams, which usually end up as scrap once the construction is completed. Precast concrete can be easily cut to size and reused elsewhere if need be. In addition, it has superior fire resistance so let's not forget the fire insurance rates, energy efficiency, helps prevent corrosion even in open spaces and requires less labour.
Onsite forming not only wastes valuable resources such as wood and metal, it also uses an enormous amount of energy due to long hours spent pouring cement at high temperatures. Prefab concrete creates cost effectiveness, cost savings, less waste and has a smaller carbon footprint.
Concrete itself is recyclable and there are many precast concrete products that use recycled aggregate or industrial byproducts such as fly ash or blast furnace slag in their composition. This allows builders to create green buildings with minimal environmental impact.
Regular cast tends to have sand being one of its main components while precast concrete has cement as its major constituent Another difference is that in precast concrete construction and precast products, the design perimeters are more flexible with choices for shape geometry up to about 45 degrees when compared to regular cast where accuracy in dimensions must be respected down to fractions of an inch or even thousandths of an inch. A further distinction between regular cast and precast concrete structures is that the latter has a much more variety in terms of shapes and finishes enabling it to be adapted easily to architectural structures and designs such as parking structures.
When building with concrete, builders have two options: they can either pour wet concrete onto the site when it's needed or construct components in a factory using dry materials before shipping them to site where they are assembled into position using mortar. There are pros and cons for both methods depending on budget, space availability and time constraints. Precast concrete tends to cost slightly more than regular cast due to the additional processes involved in its manufacturing, but this is offset by the fact that it is both quick and safe to build with. On-site concrete tends to be cheaper, but this advantage is negated by the slow speed of construction despite doing it in a controlled environment. Precast concrete also offers more design options than onsite poured concrete as there is no need for a large number of skilled workers or equipment onsite, which means builders can create structures in shapes and sizes impossible with traditional building methods.
Granite, marble or even recycled materials can be introduced into the precast concrete structures and precast products in order to create attractive finishes on buildings. The precast concrete industry has expanded and precast concrete products are available in a huge variety of shapes and sizes. Because casting doesn't need to be onsite, components can be produced as small as 1m x 1m x 1m or as large as 10m x 20m x 30m.
Precast concrete has become popular in the industry due to a number of positives.
refabricated buildings can be erected far faster than traditional methods because there's no requirement for skilled labour onsite all day long. The wall panels used in constructing buildings using precast concrete don't require mortar either - instead, they interlock together forming a solid structure that is capable of supporting itself. Moreover, the fast installation process saves time and money. This means precast concrete offers more advantages for obvious reasons, especially structural advantages.
Precast components are incredibly strong and durable due to their thick concrete walls. A typical precast plant wall might be 6 inches (150mm) deep with an additional 7 inch (180mm) airspace inside, creating a wall that is almost 2 feet (600mm) in total thickness.
The fact that each component can be manufactured to suit specific dimensions means builders don't need to worry about designing bespoke details for projects of all shapes and sizes. Each individual element can have different finishes or even be designed so they interlock together without the use of mortar.
Precast concrete products are usually more expensive than regular cast buildings due to the additional processes involved in the precast concrete industry.
Regular cast buildings have a smooth, even finish that's easy to clean without damaging. However, mass production or manufacturing of precast concrete products tend to be bumpy which can provide an ideal surface for dirt and grime which is difficult to remove.