Bridges are important structures that help to span physical obstacles like water masses, roads, and valleys. And since the sole purpose of a bridge is to provide passage over an obstacle, it must be strong enough to withstand both static and dynamic loads. So what are the best materials for building bridges?
The best materials for building bridges depend on the type of bridge under construction. However, the most commonly used materials include concrete, steel, stone, and composite material. Concrete and steel are usually used in the construction of the superstructure members of a bridge.
This article will discuss the best materials for building bridges while also shedding more light on each material’s specific roles. Ready? Then let’s jump right into it.
Concrete is arguably among the most important materials used in bridge construction. Concrete gives bridges a high level of versatility and flexibility, making it perfect for weight absorption and distribution. The use of concrete allows construction engineers and architects to develop a wide range of practical structural forms.
Despite being great for use in large construction projects, concrete has a relatively low tensile strength. However, to address these issues, civil engineers opt to use reinforced concrete to construct bridges.
The use of reinforced cement concrete (RCC) increases concrete ductility, enabling the material to withstand heavy loads without bending or responding to other tensile actions.
Reinforced concrete has a similar coefficient of thermal expansion to that of steel, which helps eliminate internal stresses resulting from contraction or thermal expansion. Concrete also helps to absorb structural stress, allowing the load to be transmitted efficiently across different materials. This usually occurs when the cement paste inside the concrete hardens and conforms to the surface details and shape of steel.
A popular alternative to reinforced concrete is using prestressed concrete. Prestressed concrete is usually lighter compared to reinforced concrete that’s often bulky and heavy. Therefore, when constructing bridges and structures meant to absorb shock and impact, prestressed concrete is the most preferred option.
Unlike RCC that usually neglects the pressure below the neutral axis, prestressed concrete is highly effective in load resistance. Civil engineers also prefer prestressed concrete for heavily loaded structures since the reduced weight and cross-section translates to more savings in terms of materials used.
Benefits of Using Concrete in Bridge Construction
Concrete is a popular construction material that helps maintain the structural integrity of buildings and large construction projects. Below are some of the benefits of using concrete in constructing bridges.
- Concrete is highly durable and has a high compressive strength: Concrete is known to hold great loads, which makes it ideal for use in bridges.
- Concrete is versatile: You can choose to use either prestressed concrete or RCC, depending on the type of project you’re working on.
- Concrete is inexpensive: Concrete is among the most accessible concrete materials, which in turn lowers the overall cost of construction.
Drawbacks of Using Concrete in Bridge Construction
- Concrete is fairly brittle: Concrete is brittle unless reinforced or prestressed, which increases the risk of breaking or cracking without much warning.
- Concrete takes time to strengthen: Hydration usually takes a lot of time, which means the concrete members won’t gain their full strength until after a while.
It’s difficult to discuss bridge construction without mentioning steel. The strength, ductility, and versatility of steel make it a fantastic option for constructing bridges. You’ll find steel in railway bridges, long-span bridges, and even short and medium span bridges.
Normal construction steel usually has a compressive and tensile strength of an impressive 370 N/sq mm, which is considerably higher than concrete’s compressive and tensile strength. One of steel’s most remarkable features is its ductility. The ductility allows the steel to deform considerably before breaking when exposed to stress beyond its structural capabilities.
The Main Categories of Steel Bridges Used in Construction
Steel is a super material when it comes to large-scale or small-scale constructions. Besides responding well to both static and dynamic loads, steel is strong enough to distribute weight and hold other members in place, especially in massive constructions.
Below are the main categories of steel used in bridge construction.
- Carbon steel: One of the most affordable steel available and is ideal where stiffness is preferred over strength. Carbon steel is easy to weld but won’t work well for large bridge constructions.
- High strength steel: High strength steels obtain their strength from the addition of alloys. However, an experienced welder is required to weld this type of steel into shape.
- Weathering steels: This type of steel is known for its increased resistance to corrosion. Weathering steels usually boast a tough outer covering that helps to prevent gradual corrosion. This type of steel is extremely useful in salty environments where bridges are likely to rust and experience significant corrosion over time.
- Heat-treated carbon steels: This type of steel is strong and widely used in large projects. Once welded, this steel steal can withstand enormous loads, thus making it highly reliable and durable. There are several types of heat treatments, which include:
- Spheroidizing (when carbon steel is heated to around 700°C or 1212°F for more than 30 hours)
- Full annealing
- Process annealing
- Isothermal annealing
- Stainless steel: Initially, stainless steel was used in safety components such as handrails and guardrails due to its anti-corrosion properties. However, stainless steel has grown in prominence, often featuring in almost all structural components, whether the deck, suspension systems or tie-rods. Steel is also ideal for fabricating bearings and other bridge parts that need high corrosion resistance.
Advantages of Using Steel in Bridge Construction
High Strength to Weight Ratio
Steel’s high strength to weight ratio helps minimize overall construction costs by eliminating the need for substructures. Moreover, steel comes in handy when used in long-span bridges due to its lightweight nature. Steel also minimizes mechanical plants’ overall costs since it reduces the required counter-weight size, especially in swing and lift bridges.
High-Quality Construction Material
Steel is readily available (in various certified grades, sizes, and shapes). Steel can be prefabricated, and the trial assembly can be quickly done at the fabrication centers to eliminate the risk of fit-up problems on the construction site. The ease of prefabrication and fitting makes steel ideal for use in both large and small construction projects.
The prefabrication of steel means that construction will be fast, especially in hostile environments. And since steel bridges can be installed fast, roads and railway lines won’t be closed for too long before the public can use them again. Steel’s lightweight nature allows the smooth erection of large members, which consequently reduces the overall duration of the project.
There’s usually no limitation to how steel is installed in bridges. Depending on the project’s size, steel can be installed by slide-in techniques, launching, cranes, and even transporters. The erection contractor will have the much-required flexibility when installing the steel.
Repair, Modification, and Demolition
Steel is highly preferred in bridge construction due to its adaptability and ease of repair. Engineers can widen (and strengthen) the steel bridges to accommodate additional traffic lanes. Even better, steel girders can be cut into manageable pieces and recycled when the bridge is no longer in use.
The ease of repairing steel also makes it ideal for use in high-risk areas. All that needs to be done is cutting out the affected areas before welding in the new steel. Girders are also repairable by heat straightening.
Compared to concrete that can easily crack without any signs, steel is predictable due to its easily visible and accessible structural elements. The ease of visibility ensures that civil engineers won’t need to conduct extensive research to determine affected areas. And in case corrosion occurs over time, repainting the problematic areas will be enough to solve the problem.
Steel is among the best materials to use in bridge construction due to its ease of modification. You can modify the steel to look heavy or light, while the possibility of sculpturing further gives engineers and welders the freedom to come up with different shapes and trims.
Steel is also used in the construction of trusses, which, besides distributing loads across the bridge, also contributes to the construction’s overall beauty. Therefore, the flexibility that comes with steel allows engineers and welders to implement their creative designs.
Stone has been used in the construction of bridges for several centuries. Although not as popular as before, bridges built from stone are arguably among the strongest and most durable types of bridge.
However, in modern bridges, stones are usually used on the surfaces. This explains why you’ll likely find stones used as facing for piers, abutments, or arches. When choosing a stone for bridge construction, it’s crucial to ensure it’s weather-resistant to neutralize the negative effects of rain, salty winds, and even snow.
Best Stones to Use in Bridge Construction
Due to their role of absorbing and distributing both static and dynamic loads, bridges require heavy stones with high specific gravity. Below are some of the best stones to use in bridges.
- Basalt: Basalt stone is usually used in heavy construction due to its compactness, durability, and overall strength. Besides its impressive strength, basalt is also resistant to weather and, even more importantly, impervious to moisture. Basalt’s features make it an excellent option for use in bridge piers, river walls, and as an aggregate in the production of concrete.
- Granite: Granite is widely used in constructing bridges due to its frost resistance properties, low absorption value, and high compression strength. Granite takes polish incredibly well, which explains its use as a wall cladding. In bridges, granite can be used to construct bridge piers, curbs, and stone columns. It can also be used as an aggregate (coarse) in concrete.
- Sandstone: Some construction workers opt to use sandstone in the construction of bridge piers and river walls. For sandstone to work as a pier, it’s crucial to use siliceous sandstone as it’s highly durable and resistant to most agents of corrosion.
Benefits of Using Stone in Bridge Construction
- Strong and long-lasting: Stone is ideal for different types of construction, including building bridges. And although stones aren’t used as frequently as before, they make great materials for building bridge piers and abutments.
- Promotes environmental sustainability: Stones usually come naturally and don’t require preheating or massive modifications to be used in construction. Moreover, stone can be reused in case the bridge becomes defunct.
- Easily accessible: Some construction material is usually hard to acquire before construction. However, with stones, you’ll only need to transport the stones to the site before commencing construction.
Drawbacks of Using Stones in Bridge Construction
- Time-consuming: Stone structures cannot be pre-fitted without being in the physical location. Modifying steel is usually faster than setting up stones in bridges. And due to the little room for error when constructing bridges, stones usually lead to increased labor costs, which in turn increases the project’s overall budget.
- Difficult to correct errors made: Unlike steel that can be easily replaced and repaired, errors in placing stones might spell doom for the entire project. As a result, it is crucial to be extra careful when constructing bridges using stones as primary materials.
4. Composite Material
Composite material helps in the construction of new bridges and also comes in handy when making repairs. Fiber-reinforced plastic, for instance, is usually reinforced with either carbon or glass fibers. The resulting material is usually durable, lightweight, strong, and ductile.
Reactive powder concrete (RPC) is also becoming popular in the construction of slim columns in long-span bridges. You can also use composite material to repair or reconstruct columns and other supportive elements in a bridge. Epoxy impregnated fiberglass also helps to cover non-ductile columns, thus making them more resistant to external forces.
Basic Parts of a Bridge
Typical bridges are usually made up of the foundation, decking, and additional components like girders, bearings, trusses, and abutments. Please note that supplemental components usually vary depending on the type of bridge being constructed.
Below is a brief discussion of the main parts of a bridge and the ideal materials to use.
Also referred to as a pile, the foundation serves as the main support or legs of the bridge under construction. Foundations preserve the structural integrity of buildings and bridges by absorbing and distributing the total loads on the bridge.
Modern civil engineers prefer to use on-site piling where holes are deeply bored into the earth. Reinforced steel is then installed before concrete is poured on the perforations. Bridge foundations are usually the first to be constructed as their installation often determines the structure’s overall stability and strength.Concrete and steel are the most frequently used materials on foundations due to their strength and ability to handle varying types of loads.
The decking is usually the most used (and viewed) section of a bridge since it serves as the usable surface for vehicles and people to travel on. In reinforced concrete bridges, the decking is usually made from concrete that’s poured over a sturdy metal framework to strengthen the entire structure.
The girder normally acts as the arms of the bridge, ensuring the entire deck is fully supported. Girders are usually installed over caps to receive and distribute the weight to the foundation. A girder can be made from either steel or concrete, depending on the immediate environment.
Bearings help to absorb the pressure and stress resulting from vehicles and environmental factors. By absorbing pressure before it spreads to other parts, bearings are able to maintain the bridges’ structural integrity.
Some architects prefer using elastomeric bearings in bridges. These bearings are usually composed of quality steel plates fused with rubber or elastomer material. The increased elasticity allows the bridge to resist movements that could damage the steel-concrete structures.
Abutments connect a bridge to the land, thus providing support for the entire unit by absorbing the pressure caused by both static and mobile loads. Abutments should be stable and robust enough to receive loads from a bridge’s superstructure while also neutralizing the pressure emanating from earth movements.
Concrete is commonly used in the construction of abutments due to its ability to withstand heavy loads.
Trusses help to distribute loads across the entire bridge structure. Besides their important role in load distribution, trusses also help to make bridges more attractive. The beams and bars used in the construction of truss networks are often made from steel due to its weather and corrosion-resistant properties.
There are several materials that can be used in constructing bridges. The best materials, however, should suit the type of bridge that’s being constructed.
Over the years, concrete has emerged as an essential material for constructing short, medium, and long bridges. Another important material is steel, which is vital in helping a bridge maintain its structural integrity.
Stones also play a pivotal role in bridge construction, more so in the surfaces of piers, arches, or abutments. And since bridges need to be strong and sturdy enough to resist loads, using high-quality construction material is highly advised.
- Wikipedia: Reinforced Concrete
- E-education: Malleability and Ductility
- Wikipedia: Thermal Expansion
- Azom: Spheroidizing
- Wikipedia: Annealing
- Bodycote: Heat Treatment
- Gearsolutions: Understanding Different Types Of Heat Treatment
- About Civil: Materials Used In Bridges
- Civil Today: Advantages And Disadvantages Of Concrete
- Harford County MD: Bridge Construction Materials
- U.S. Bridge: Best Material Bridges
- The Constructor: Stones Used in Constructions