Prestressed concrete is a revolution in the field of industrial floor construction. It introduces a whole new concept of quality and a professional approach to concrete construction. With prestressed concrete planning and execution, problems and subsequent dilatation problems are thing of the past.
Concrete floors are used as the base slab for most commercial and industrial floor finishes. They are characterized by high quality, durability and versatility relative to cost. Since concrete flooring is able to withstand pressure from heavy equipment, such as trucks or forklifts, it’s frequently used in warehouses, factories and production facilities.
Concrete floors meet the highest flooring requirements:
- Support operational and stationary loads
- Minimize the number of exposed joints
- Utilize maintenance isolation joints that do not impede vehicle operating speed
- Provide a durable abrasion-resistant and dust-free surface
- Appropriate levelness and flatness tolerances to support material handling systems
- Balance surface texture traction with cleanability
- Provide a safe and pleasant working environment
- Are flexible to accommodate possible future changes in operations
In many industrial environments, the concrete floor is subjected to aggressive (mechanical) or corrosive (chemical) processes or materials that damage the floor. This damage costs the owner large sums in maintenance or replacement, and reduced productivity. For the owner, a far worse expense is the cost in repair-downtime of the floor, with attendant loss of production and worse, loss of customers!
The most commonly used type of floor construction for medium and heavy loaded industrial plants are heavy floating concrete floors. This type can be further distinct as: Plain concrete floors, Weak reinforced concrete floors, Fibre concrete floors, Reinforced concrete floors and Prestressed concrete floors.
Plain concrete floors are the simplest concrete floors made of nothing but concrete. There is no reinforcing steel in a plain concrete slab floor. These floors are typically inappropriate for industrial purposes because they have low tensile strength. This means that when a heavy load compresses the concrete, the concrete directly underneath the load can handle the pressure, but the concrete to the side gets pulled down and cracks. A step up from plain concrete floors is those reinforced with one or more layers of steel mesh, which creates a network of squares throughout the concrete. In terms of strength, concrete floors reinforced with steel mesh are still unlikely to hold up to the demands of a typical industrial facility. To improve the overall durability of concrete, including resistance to surface abrasions, fibres made of steel, glass or polypropylene can be mixed in with the concrete. Reinforcing concrete floors with fibre is useful when the concrete may be exposed to high heat, as this method improves concrete’s resistance to thermal shock. But as for tensile and compressive strength, it is not the most robust option on this list. Steel rebar reinforced concrete is generally a better construction material than all the above ordinary stuff. Using steel bars of various thicknesses is one of the most popular ways to add tensile strength to concrete. The bars are distributed evenly throughout the concrete mould before it is poured, and rebar may even be combined with steel mesh for added stability.
In ordinary reinforced cement concrete, compressive stresses are taken up by concrete and tensile stresses by steel alone. The concrete below the neutral axis is ignored since it is weak in tension. Although steel takes up the tensile stresses, the concrete in the tensile zone develops minute cracks. The load-carrying capacity of such concrete sections can be increased if steel and concrete both are stressed before the applications of external loads. This is the concept of prestressed concrete. Prestressed concrete is that concrete in which internal stresses of suitable magnitude are introduced so that the stresses resulting from the external loadings can be counteracted to a desired degree. In R.C.C. members, prestress induced is of compressive nature so that it balances the tensile stresses produced due to external load. It makes the whole section effective (the concrete area in the tension zone also) in resisting loads.
Prestressing removes a number of design limitations that conventional concrete places on span and load and permits the building of industrial floors with longer unsupported spans. This allows architects and engineers to design and build lighter and shallower concrete floors without sacrificing strength. Prestressing is active against loads caused by the use, environmental influences, shrinkage and interaction with the subsoil. Prestressing is designed for the worst load situation to avoid the tensile failure in concrete and introduction the pressure load incorrect time before the creation of shrinkage cracks. This completely prevents failure in concrete unlike other ways of crack control, which are based on increasing passive reinforcement for limiting crack width according to certain requirements.
With prestressing technology, it is possible to design a very large area without expansion joints. Expansion joints are often the epicentre of the failure of the floor structures. Their elimination leads to financial savings on maintenance costs. Apart from the cost savings, it also achieves material savings because, with prestressed technology, it is possible to design floors with a thickness up to 30% smaller than with commonly used solution.
Main advantages of prestressed concrete floors
- Material savings – steel and concrete in comparison with reinforcement.
- Smaller deflections than with steel and reinforced concrete
- Good crack behaviour and therefore permanent protection of the steel against corrosion.
- Almost unchanged serviceability even after considerable overload, since temporary cracks close again after the overload has disappeared.
- High fatigue strength, since the amplitude of the stress changes in the prestressing steel under alternating loads are quite small.
To sum up, the use of prestressed floor construction is very advantageous for large scale and heavily loaded floor structures. The initial cost of technology is higher in comparison with the commonly used design solution. But on the other hand, prestressed floor technology has high quality, longer life and cost savings on maintenance.
