Steel and concrete are the building blocks of almost any construction, both residential and commercial. Yet, we hardly know much about the role that these two materials play in assuring the strength and durability of a building. What properties does each of these materials possess? Are concrete and steel constructions sustainable? Which of these materials is stronger than the other?
It’s essential that one understands the similarities and differences between steel and concrete as building materials to make better decisions on their suitability for a project. In this ideabook, we highlight the various properties as well as the pros and cons of steel and concrete, the various grades of these materials as well as the benefit of using them for constructing modern houses. It will present an insight into why architects use steel and concrete for construction.
In most houses and commercial constructions in India, the type of steel that is used is mild steel, which is known for its superior strength. The material is so strong that a circular bar of it when hung from the ceiling, can support up to 20 tons or 20,000 kilograms. That’s about 1/5th the weight of a blue whale, as much as five and a half hippopotamuses or 45 grand pianos!!
It’s this incredible strength of steel that makes it suitable for constructing buildings. Additionally, steel frames are highly flexible, allowing them to bend without cracking. This means that even under stress a building made of steel might flex but not snap. The third significant characteristic of steel is that it is ductile and easy to mould compared to other materials such as glass that easily crack. What this means is that a steel building might get slightly bent out of shape if it’s affected by powerful cyclonic winds or earthquakes, but it will not collapse.
The main disadvantage of steel is that it cannot handle temperatures above 500 degrees Celsius. Beyond this temperature the material becomes weak, and its strength reduces by half. A trick for protecting steel from being exposed to such high temperatures is to spray it with fire protection material or cover the frames with boards.
The concrete that is used for construction is called RCC or reinforced cement concrete. This type of concrete has steel reinforcement bars within its structure. The compression offered by concrete and the tensile strength of steel together create a very strong material for construction. Concrete can be either cast on site or made in a factory (pre-cast concrete) and shipped to the site.
The process of mixing concrete is an exact science, commonly referred to as concrete mix design. The expert mixer will work out the recipe for the mix after considering the desired properties that are expected from it. Within a construction, often two different types of mixes might be required. For example, in an area that isn’t easily accessible, the mix might need to be of a more flowing texture so that it can be poured into every corner of the framework. However, in general, the standard mixes of RCC are M20, M30 and M40. The number denotes the concrete strength in n/mm2 (Newton per millimetre square), which specifies the stress it can bear. For instance, M20 means that the compressive strength of the concrete mix is 20 n/mm2.
Aggregates are another component of the concrete mix. They refer to the maximum size of stone chips that can be included in the mix. For example, if an engineer asks for an M20/20 mix, it means that he wants M20 concrete with an aggregate size of 20mm.
While concrete is commonly used for constructing residential and commercial buildings, a little-known fact is that the material is available in several types. Here are the most common ones.
High strength concrete
This usually refers to concrete that has a compressive strength of 40Mpa (Megapascals). This type of concrete can resist loads, which normal concrete can’t. Typically, high-strength concrete has better elasticity, which contributes to the stability and reduced deflections of the material.
High performance concrete
This term refers to a concrete mix that offers better performance than standard concrete. It not only has a longer lifespan but also offers several other benefits such as ease of use, anti-corrosive properties, permeability and density, among other parameters.
This type of concrete gets its name from the fact that it uses lightweight aggregates like small thermocole balls in the mix. Often, foaming agents are introduced into the mix to reduce its weight. However, the lightness of the material makes its strength low, making this type of concrete suitable mostly for non-structural elements in the construction. The most commonly used type of lightweight concrete is AAC or aerated autoclaved concrete blocks, which are used for building walls. It’s also known as aerated concrete or cellular concrete.
Self-consolidating or self-compacting concrete refers to a mix that is of a flowable nature, allowing it to spread easily into the form work. Sometimes, the mix includes mineral fillers and admixtures that minimize segregation and bleeding. One of the advantages of concrete that is self-compacting is that it retains the durability and matches the performances of regular concrete.
This type of concrete, which is also known as shotcrete, can be sprayed on a surface as a coating. Unlike other concretes, which are poured into the formwork or mould, this one is sprayed as an uneven and thick coating on a surface. Its most common use is to repair cracks on old concreted surfaces.
Usually, concrete is permeable, allowing water to pass through its surface. However, water-resistant concrete is engineered by including fine particle cement replacements in the mix that prevent water from passing through. They are best suited to areas such as basements that are prone to waterlogging or for structures such as dams, water tanks and bridges, which need the ability to resist water.
Micro reinforced concrete
This new generation concrete includes tiny fibreglass, steel or plastic fibres in the mix, which alters the properties of the concrete. Among the advantages of reinforced concrete is that it improves its strength and performance.
It’s not easy to find the perfect mix of concrete or the right steel structure for a residential or commercial property. Based on the requirements, we recommend consulting a professional who has a team of experts, including site engineers with years of experience in developing the right concrete mix for the building. On homify, you can find a list of qualified professionals with years of experience in constructing homes and commercial complexes.