Rebar, or reinforcing bar to give it its full name, is used routinely within construction projects to give concrete components strength and integrity. Whilst concrete is phenomenally strong in terms of compression, it is relatively weak in terms of tensile strength. That means that it’s incredibly hard to break or fracture concrete by dropping something on it or pressing down on it with great weight, but it’s relatively easy to compromise it by exerting twisting forces on it. To provide that lateral, or tensile, strength, concrete is reinforced with steel rods, called rebar, or with mesh sheets made up of multiple rebar rods that are welded or tied together. In this article, we provide an overview of the most common types of rebar in use today, with some details of the various applications for each type.
Mild Steel Bar
This type of rebar has a smooth surface and is available in a variety of diameters, from 6mm up to around 50mm. It is commonly used as a dowel in expansion joints within poured concrete elements, in applications where the bar needs to be inserted into a sleeve (typically made from paper or metal), and for contraction joints in roads, pavements and runways.
Deformed Steel Bar
This type of rebar is perhaps the most common type seen in construction projects in this country. The word ‘deformed’ refers to the surface patterning on the bars, which may include ribs and indentations in different styles. These deformations add an important property to the rebar, in that they increase contact with the poured concrete and reduce slippage. Overall, this increases the tensile strength and lateral integrity of the concrete element. As with mild steel bars, deformed rebar is available in diameters ranging from 6mm up to 50mm. It’s important to note that the diameter is measured across the core of the rebar strut, without taking into account the ribs or other deformations.
Within this overall category of rebar, there are two principal types: TMT bars and high strength deformed bars. The difference between the two lies mainly in the manufacturing process. TMT stands for thermo mechanically treated, and these bars are hot treated, in order to produce a bar that has incredible strength, high resistance to corrosion, and excellent bonding properties. High strength deformed bars, in contrast, are cold processed, and they are more economical to produce. Given this, high strength deformed bars are the most commonly used type of rebar.
European rebar is a particular type of rebar that is made from a steel and manganese alloy. The alloy used makes European rebar relatively inexpensive, when compared with deformed steel bar and other rebar types, but it also reduces the strength of the rebar. For that reason, European rebar is not suitable for use in environments where extreme weather events are likely, such as hurricanes or earthquakes. It is also unsuitable for projects that demand significant structural strength from the rebar component.
Carbon Steel Rebar
This type of rebar has a high carbon content, and is often known as black bar because the carbon content produces a dark-coloured rod. This is a cost-effective rebar type and it has a high tensile strength – combined, these factors make it one of the most commonly used rebar types, for construction projects of all sizes. The only downside to carbon steel rebar is that it is prone to corrosion. As every construction professional knows, corrosion of the rebar used within a concrete element can lead to structural integrity problems and even failure of the entire element. It’s important therefore to ensure complete concrete coverage of the rebar, and to minimise the time that it is left exposed to the elements.
One solution to the problem of rebar corrosion is epoxy-coated rebar. This is simply carbon steel rebar that has had an epoxy coating applied to it. The tensile strength of this rebar is the same as its uncoated equivalent, but it is significantly more resistant to corrosion. Epoxy-coated rebar is preferable to standard carbon steel rebar in applications where the potential for corrosion is increased – for example, in bridges or other structures that may be submerged in water, in sea walls or other marine projects and in infrastructure projects where roads may be regularly gritted with de-icing chemicals.
Galvanising rebar is another way of protecting it from corrosion. It has a major advantage over epoxy-coated rebar in that the galvanised coating is very difficult to damage, whereas epoxy coatings are very delicate and susceptible to damage during transport or in the construction process. Unfortunately, whilst its durability is a significant advantage over epoxy-coated rebar, galvanised rebar doesn’t offer the same level of corrosion resistance as epoxy coatings provide, and it is significantly more expensive than epoxy-coated rebar. As always, there is a trade-off to be calculated between the relative benefits and the costs for each type.
Glass fibre reinforced polymer (GFRP), or fibreglass rebar, is a more modern type of rebar, for use in specialist applications. It is incredibly light, and does not corrode at all. It’s also much more expensive than epoxy-coated rebar, so it’s typically only used when other rebars are not suitable. The main disadvantage of GFRP rebar is that it cannot be bent to shape on site, so it has to be fabricated to order.
Stainless Steel Rebar
The most expensive rebar type of all is stainless steel rebar. Since stainless steel is incredibly resistant to corrosion, it does not rely on uniform concrete coverage or the high alkalinity of concrete, to provide protection. This type of highly corrosion-resistant rebar is not necessary for every construction project, but for projects that are exposed to seawater, for example, it could be the best all-round choice.
Grades and Standards
Each of the types of rebar mentioned above has to meet certain standards, and all rebar is graded in order to be easily compared by construction professionals. To learn more about the various grades used to identify rebar in the UK, check out this article on steel standards and production methods.
Whilst this article covers rebar specifically, it’s worth mentioning reinforcement mesh at the same time. Whilst some projects call for a reinforcement layer to be made up of a criss-cross of standard rebar rods, many projects can save time and money by using mesh sheets instead. These are available in the same rod diameters as for standard rebar, and with a mesh size that complies with building regulations and best practice. Additional reinforcement mesh products include flying end mesh, where the final strut on one side of the panel is missing, to allow overlapping of panels across the surface of a large slab.
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