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What is this week's blog about?
In this week’s blog, Hilan Shah MRICS, discusses the differences between steel and concrete construction, across six main areas.
This is essential reading for any RICS APC or AssocRICS candidates with Construction Technology & Environmental Services as a technical competency.
The six areas we will cover are costs, strength, fire resistance, sustainability, versatility and corrosion.
1. Costs
Structural steel: A large majority of all steel manufactured today comes from recycled materials. This recycling usage makes the material much cheaper when compared to other materials. Although the price of steel can fluctuate, it typically remains a cheaper option compared to reinforced concrete.
Steel, while having a high lead time, is known for its fast erection on site. This can allow the building to be occupied sooner. In addition, reduced labour costs are possible through dryness of form in comparison with concrete.
However, something that can add to the cost is that steel needs fire protection whereas within concrete this is inherent, i.e., it is already present. Prefabrication of steel also allows thin film intumescent coatings to be applied offsite.
The construction of a steel framework is comparatively lightweight, as much as 60% lighter than a comparable reinforced concrete frame solution, which might allow for a less expensive foundation system. In addition, modification to the building can sometimes be facilitated by simple removal of a structural steel member.
Concrete: A large cost benefit is the fact that the price of concrete remains relatively consistent. On the other hand, concrete also requires ongoing maintenance and repairs, meaning added costs throughout its lifetime.
Even though concrete can be poured and worked directly onsite, the process to completion can be lengthy and can accrue higher labour costs. However, the use of precast concrete construction can also help to significantly reduce build time.
2. Strength
Structural steel: Structural steel is extremely strong, stiff, tough, and ductile. This makes it one of the leading materials used in commercial and industrial building construction.
Concrete: Concrete is a composite material consisting of cement, sand, gravel and water. It has a relatively high compressive strength, but lacks tensile strength. Concrete must be reinforced with steel rebar to increase a structure’s tensile capacity, ductility and elasticity.
3. Fire Resistance
Structural steel: Steel is inherently a non-combustible material. However, when heated to extreme temperatures, its strength can be significantly compromised. Therefore, steel must be covered in additional fire resistant materials to improve fire safety properties. Prefabrication of steel can allow a thin film of intumescent coating to be applied offsite.
Concrete: The composition of concrete makes it naturally fire resistant and thus in line with most building codes and regulations. When concrete is used for building construction, many of the other components used in construction are not fire resistant. Surveyors should adhere to all safety codes and Building Regulations during the construction process to prevent complications within the overall structure.
4. Sustainability
Both concrete and steel framed structures have environmental issues associated with their use, including high embodied energy in their manufacture.
Structural steel: Structural steel is nearly 100% recyclable. In fact, 90% of all structural steel used today is created from recycled steel. Due to its long lifespan, steel can be used and adapted multiple times with little to no compromise to its structural integrity. When manufactured, fabricated and treated properly, structural steel should have a minimal impact on the environment.
Concrete: The elements within concrete are naturally occurring. Concrete may also be crushed and used in future mixtures. This type of recycling can reduce the presence of concrete in landfill. In terms of the mixes, this is often waste materials such as Ground Granulated Blast-Furnace Slag (GGBS) and Pulverised Fuel Ash (PFA) that can be included within the mix.
However, there are some issues with recycled concrete such as moisture content and material variability, which could dictate that it is economically unviable.
5. Versatility
Structural steel: Steel is a flexible material that can be fabricated into a wide array of designs for various applications. The strength-to-weight ratio of steel is much higher when compared to other affordable building materials. Steel also offers many different aesthetic options that different materials, such as concrete, cannot compete with.
Concrete: Although concrete can be moulded into many different shapes, it does face some limitations when it comes to floor-to-floor construction heights and long, open spans.
6. Corrosion
Structural steel: Steel may corrode when it comes into contact with water. If left without proper care, this can affect the safety and security of a structure. Professionals should care for steel with processes such as water-resistant seals and paint care. Fire-resistant features can be included when water-resisting seals are applied.
Concrete: With proper construction and care, reinforced concrete is water resistant and should not corrode. However, it is important to note that steel reinforcement inside concrete structures should never be exposed. If exposed, the steel becomes compromised and can easily corrode, compromising the strength of the structure.
Comparisons in Practice
When you stack up the two materials side by side, you can see that steel tends to be the clear winner.
To make this clearer, let us take a look at a scenario: choosing between a concrete or steel framing solution for a commercial office building.
This is what we would look at and review:
1. Programme requirements, which may be a key consideration on a commercial building as typically steel is quicker to erect on site than concrete
2. Requirement for column free spaces within the office
3. Complexity of design, with steel providing greater flexibility
4. Aesthetics and client aspirations
5. Fire protecting requirements
6. Repetitiveness of design. This will have a large impact on the cost of temporary works, such as formwork
7. Market conditions and supply costs - with this, you should undertake a cost comparison
8. Height of the building
9. The mechanical and electrical services strategy
10. Technical performance requirements of the building, including office floor loads and fire protection
11. Site logistics, e.g. delivery of materials to site, on/ off site storage and plant restrictions
12. Foundation design, as this could vary the cost considerably
Conclusion
We hope you enjoyed reading about the many differences between steel and concrete.
There are many decisions that need to be made on any construction project. Making the wrong choice could prove to be detrimental in the end and so it is important to have a grasp of the differences between the two materials and how they can affect construction projects.
Understanding this at level 1 is essential to justifying the actions you have taken at level 2, and the advice you have given at level 3.
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N.b. Nothing in this article constitutes legal, professional or financial advice.