Reinforced Concrete for Construction
Over the past few weeks we’ve been taking a detailed look at concrete. Concrete has often been dubbed a boring building material and this is probably due in part to the Brutalist architecture movement that flourished here in the UK from the 1950’s through to the 1970’s. The term Brutalism originates from the French word for “raw” which was used by Le Corbusier to describe his preference of material “beton brut” (raw concrete). This style of architecture was popular with institutional and governmental clients in many countries of the world and was used in educational buildings, high rise housing and shopping centres across the UK. However, concrete is an innovative and interesting building material and offers so many possibilities that the mind boggles.
Today, we’re taking a look at Reinforced Concrete in which concrete’s relatively low tensile strength and ductility are counteracted by the inclusion of reinforcements that have a higher tensile strength and ductility. The Romans (who discovered concrete in the first place) were also the first to reinforce concrete, albeit in a rudimentary fashion by adding horse hair to concrete to stop it from cracking during the hardening process.
Nowadays concrete reinforcement is usually achieved by including steel reinforcing bars (rebar) which are passively embedded into the concrete before it sets. Modern reinforced concrete may contain a variety of reinforcing materials made of steel, polymers or alternate composite materials, sometimes in conjunction with rebar and sometimes without.
For concrete to have the necessary strength, ductility and durability, the reinforcement requires the following properties:
- High toleration of tensile strength
- High relative strength
- A good bond to the concrete irrespective of pH, moisture and other factors
- Durability in the concrete environment irrespective of corrosion or sustained stress
- Thermal compatibility, not causing stresses in response to changing temperatures
Reinforced concrete falls into two categories – precast or cast-in-place concrete. Reinforced concrete enables the construction of so many structures that include walls, beams, slabs, columns, foundations, frames, etc.
Modern concrete can also be prestressed which will radically increase its load-bearing strength. In order to achieve this, the reinforcing steel in the bottom part of a concrete beam (which will be subject to the most tensile forces when in service) is placed in tension before the concrete mix is poured around it. When the concrete hardens, the tension on the reinforcing steel is released and places a built-in compressive force on the concrete. This means that when loads are applied, the reinforcing steel will take up most of the stress while the compressive force in the concrete itself is reduced without becoming a tensile force.
Another way of prestressing concrete is to insert plastic tubes into the bottom of the beam and then insert rebar into these tubes. The concrete is then poured around the tubes and when it hardens, the rebar is tensioned and the formwork removed. Tension is usually applied via hydraulic jacks.
Another method of reinforcing concrete involves the use of fibres (usually made from steel, glass or plastic) and this type of concrete is widely used in a variety of applications. Other non-steel reinforcement methods include fibre-reinforced polymer (FRP) and glass-reinforced plastic (GRP).
Here at Safety Fabrications we’ve been finding out so many interesting facts about concrete that we’re becoming experts on the subject! Next week we’ll be taking a look at some of the futuristic types of concrete that are becoming available due to innovations in technology and materials.