Nowadays, from foundations to floors, with footings in between, reinforced concrete is spread far and wide on construction sites. Provided it can withstand compression and tensile stress, it’s where it belongs. Rebar, or steel reinforcements, are the turning point. 

Reinforced Concrete: Composition and Properties

What Does Reinforced Concrete Mean and How Is It Made?

Reinforced concrete is a composite material made of the following: 

• Cement

• Water

• Sand

• Aggregates (maximum size of 20 mm, as per standard CSA A23.1) 

• Adjuvants (polycarboxylate, sulfonate, organic acid salts, etc.)

• Rebar

The “reinforcement” part of the material’s name comes from the steel reinforcements, also known as “rebar.” Rebar isn’t solely meant to reinforce the concrete, but also decide between longitudinal or shear reinforcement, the latter performing best under extensive loads. 

This standard recipe can include other materials aimed at improving the efficiency of reinforced concrete, courtesy of a better understanding of physical properties. 

All substances used to make reinforced concrete are standardized to assess the following: 

• Concrete’s mechanical properties (most notably ASTM C39, C42, C293, etc.) 

• Chloride penetration resistance (ASTM C1152, C1218, and C1202)

• Permeable voids (ASTM C642)

• Freeze-thaw cycle resistance (ASTM C457, C666, and C672)

• Cement-aggregate alkali reactivity (most notably ASTM C227, C1260, C1293)

• Cement length change (ASTM C157 and C3421)

• Aggregate quality (most notably ASTM C295, C127, C128, C403)

Consequently, its physical properties will be granted on account of the right combination of materials.   

Why It's Commonly Used: The Many Benefits and Advantages of Reinforced Concrete

Resistance

Compression force is the foremost property. Said property will determine whether reinforced concrete will or won’t be used on a construction site. However, beyond its ability to withstand heavy loads, other key factors must be considered, such as: 

• Tensile strength (10 times weaker than load resistance)

• Elastic modulus (Young’s modulus)

• Fatigue strength

• Damping coefficient 

Reinforced concrete was designed to withstand cyclic behaviour under tension and compression triggered by: 

• Seismic activity 

• Traffic (roadway, railway)

• Wind 

While it does have significant compression strength (10 to 100 MPa), its tensile strength is weak. Despite its inherent resilience, reinforced concrete is not impervious to all situations. 

Fire Resistance 

Concrete has a 35% higher residual resistance compared to steel reinforcements. Consequently, reinforced concrete’s weakness lies in its steel structures in case of a fire. 

At temperatures of 750°C, steel loses all resistance. Therefore, to shield it from heat, one must count on the concrete’s density, which will insulate the rebar. That way, it makes achieving a 3- to 6-hour fire resistance rating possible, based on the building in question.  

Seismic Resistance

We already mentioned the damping coefficient notion. Said value is used to determine the damping qualities of a reinforced concrete structure during seismic activity. In other words, the concrete’s purpose is to absorb the energy produced by an earthquake.

When it reaches its limit, reinforced concrete may crack. However, reinforced concrete has the advantage of being manufactured with rebar, which strengthens the substance against tensile stress, unlike unreinforced concrete. As such, it’s much more resilient against seismic activity, since it’s more elastic, provided that a very good concrete-rebar ratio is maintained.

Therefore, a reinforced concrete engineer’s role is to master seismic mechanics, allowing concrete to crack in pre-determined zones, meaning away from load-bearing walls and beams. Said load-bearing method limits the tension on indispensable parts of a building’s structural integrity, thereby preventing its collapse.

Durability 

Reinforced concrete boasts high durability, with a lifespan exceeding 100 years. However, the longevity of the structure heavily relies on the environmental conditions it encounters. It is crucial to consider these conditions when optimizing the concrete. The client will specify the desired service life for the structure based on the following factors: 

• Type of project

• Operating requirements 

• Environment 

A multitude of problems may arise once the building is erected, such as the following: 

• Freeze-thaw cycling cracking, warping, or bursting

• Rebar corrosion on account of the concrete’s elevated pH level 

• High temperatures (fire) coupled with a too-thin concrete layer

More accurately, reinforced concrete is subjected to two periods: 

• Incubation period: Corrosion-related chemical reactions are manifested

• Propagation period: Corrosion sets in and spreads throughout the structure

Here’s why industry professionals are striving to increase the incubation period in order to improve the lifespan of reinforced concrete structures. When said phase reaches maturation, the concrete structure in question has yet to lose its load-bearing capacity and the propagation period will still take years to settle in.

The methods implemented to stretch out said period are based on, for example, the choice of non-reactive aggregates, meaning materials incapable of triggering an alkali reaction. 

Versatility 

Reinforced concrete can be used for a plethora of structural elements used during the course of a building project requiring significant compression strength, as well as tensile strength: 

• Foundations

• Slabs

• Posts 

• Overhangs 

• Beams

Hence, reinforced concrete is particularly versatile.  

Low Maintenance

Said material can’t be “maintained” per se. Once both periods above-mentioned (incubation and propagation) are completed, concrete repair phases can be initiated. There are three:

• Traditional concrete repair by replacing degraded concrete 

• Corrosion inhibitor 

• Electrochemical treatments

Ultimately, the solution undertaken depends on the state of the structure, its porosity, its carbonation level, or even its moisture content.   

It Can Be recycled

Eighty percent of concrete stemming from building deconstruction is later recycled. The remaining 20% is stored in inert waste storage facilities. The reason concrete is entirely recycled is solely on account of the recycling chain, which has yet to be sufficiently developed. In fact, unrecycled concrete primarily stems from rural areas, from which waste management facilities are out of reach, rendering recycling too expensive. 

Another factor: note that concrete must be separated from the materials below to be recycled: 

• Rebar

• PVC; 

• Plaster

• Insulation materials 

• And others  

In Quebec, concrete recycling is deemed useful in agricultural fields, where sediments from cleaning concrete mixers are spread. Doing so ensures soils have a well-balanced pH level. 

From Retaining Walls to Floors: The Uses of Reinforced Concrete in Construction

Reinforced Concrete Foundations and Piles

Reinforced concrete pilings are used especially in unstable grounds, such as clay soils found along the St. Lawrence River. They can be used to attain grounds that are hard and solid enough, serving as a foundation’s base.

The above-mentioned piles are more beneficial compared to wood piles on account of their greater resilience, and they also happen to be longer-lasting. The sole drawback: their installation is rather noisy and requires significant equipment. 

A building’s foundation is typically made with reinforced concrete for the aforementioned reasons. The purpose of a foundation is straightforward: support the structure and transfer its load into the ground. Engineering firms will then determine its dimensions and the amount of rebar to be added, based on the size of the construction and the soil type.  

How to Build a Reinforced Concrete Wall or Slab

Concrete wall or slab formwork is done in five steps. 

Step 1: Establish plans

Prior to pouring concrete, the area where the reinforced concrete wall or slab will stand must be outlined precisely. You have to establish the following: 

• Ceiling height

• Final wall height

• Floor height 

Most importantly, bear in mind that your wall or slab must have the necessary fittings to ensure piping can be routed to your home. 

Step 2: Material preparation and steel bar installation

Now comes the time to reinforce the concrete. To do so, you will need a rebar bender, as well as steel reinforcements. In terms of steel, you have two choices: 

• Stainless steel 

• Carbon steel 

Some rebar is straight and smooth, while others are straight and ribbed, or ring-like. With diameters ranging from 5 mm to 50 mm, rebar can span 12 metres. 

Use a rebar bender to contort or cut the reinforcements to the exact measurement needed, then position them starting with the wall's midpoint, moving outward, 12 inches (30 cm) apart.

Step 3: Drainage

Drainage is installed at the bottom of the retaining wall. Put in 3-inch (7 cm) wide pipes perpendicular to the wall with an 8-foot gap (2.4 m) between each pipe. Having a network of pipes will prevent rainwater from pooling on your foundation. 

Step 4: Formwork Planks

Now that your rebar is in place and your drains are installed, it’s time to position your formwork planks. They can be positioned against the shims and wedges, mounted facing one another before being secured with anchoring connectors.

To ensure the formwork’s structure can withstand the pressure of concrete, add clamping rods, as well as a bracing system on either side of the formwork.

Step 5: Pour in the Concrete

Pour the concrete that was made on-site, or delivered by a cement truck, into the formwork. Vibrate the concrete as you pour it into the formwork, and then smooth the surface using a concrete float.

Fibre-Reinforced Concrete vs. Reinforced Concrete

Reinforced Concrete Feat Forestry

Environmental Consequences

Life cycle comparative analyses between concrete beams and glued-laminated timber beams highlight the fact that concrete emits fewer greenhouse gasses than wood. This is most notably due to the transportation of wood via roadways over considerable distances. 

However, raw material extraction factored into concrete’s composition, such as cement, still increases the industry’s CO2 emissions, accounting for 8% of global emissions. A rate that can be translated into a staggering 4 billion tons. 

To mitigate said numbers, the concrete industry is attempting to develop new concrete recipes, some of which can spare its foremost pollutant: cement. Enter fly ash, a sort of waste rejected by coal-fired power plants, which was first used in concrete to build the Hoover Dam in 1929. While it can’t replace cement entirely, it still curbs its use. 

Integrated Landscape Approach

This notion is based on a new concept known as a biophilic design. It entails coupling concrete buildings, or any other material, with its surrounding nature. 

To do so, architects are now introducing the idea of integrating nature on, or inside, buildings. This is especially seen by way of green walls that are just as prevalent indoors as they are outdoors. 

Sustaining Biodiversity 

Twenty-four cement suppliers—30% of the market—decided to create the Cement Sustainability Initiative (CSI). Said organization is active in over 100 countries, ensuring the survival of biodiversity during the entire life cycle of cement.  

To do so, the CSI put in place performance indicators, serving as guides for its members. One of the many environment-related claims highlighted by such organizations is that the exploitation of quarries does lead to the extinction of certain species, but also creates new streams, lakes, and artificial gravel pits, which are conducive to the development of new ecosystems. 

Want to learn more about concrete and concrete-related topics? Check out these articles:

• Concrete-Adjacent: Being a Reinforcing Ironworker

• Everything to Know About Hemp Concrete

• Cost of Asphalt, Paver Stones, and Concrete Paving

• How to Break Up a Concrete Slab: Practical Guide and Tips

• A Solid Base: Everything About Concrete Foundations