Concrete

The construction material par excellence

Concrete is a composite material or mixture resulting from different components. In general, the main ingredients used are sand, gravel, cement and water.

Contents Hide

1 Concrete

1.1 What is concrete?

1.2 Concrete components

1.3 Different types of concrete

1.4 Decorative Concrete

1.5 High-performance concrete

1.6 Concreting: mixing the concrete

1.7 Concrete setting time

What is concrete?

It is a material that once installed, can last for decades and is still used today because of its strength. Among its principal uses: structures, concrete floors and it is even used for the manufacture of furniture or decorative sculptures.

The concrete surface can be industrial and cold, as well as traditional and warm. The truth is that we can safely say that concrete offers a multitude of possibilities.

Concrete is a material that adapts according to needs. Concrete types vary and have different characteristics and qualities, depending on the quantities and types of aggregate materials. The possibilities are many, which allows its use in each particular case.

Here we explain how the concrete curing process is.

Concrete components

The components, ingredients or constituents of concrete are as follows:

Cement
Water
Aggregates
Addtives

Cement

Cement is the hydraulic binder by excellence. It is usually composed of limestone and clay. It is one of the main components of concrete, which joins its components together and gives it certain essential characteristics, such as its strength.

The composition of cement can vary according to different types of needs, which divides it into several categories:

CEM I (Portland cement) is a cement suitable for reinforced or prestressed concrete design because it offers a high level of strength.

CEM II A or B (composite Portland cement) have the particularity of being very flexible. Therefore, they are used in works of common use, as for traditional floors or for simple coatings.

EMC III A, B or C (blast furnace cement) are suitable for harsh environments and are known to be durable.

EMC IV A or B (pozzolanic type cement) are also suitable for aggressive environments, ideal for hydraulic structures.

CEM VA or B (composite cement) have the same physical properties as CEM III but not the same constituents.

Water for mixing

Water is an essential element in the preparation of concrete. It hydrates the cement, which releases its binding capacity and also facilitates concrete application.

The water used must be clean! (Avoid using seawater) and be careful not to add it excessively as this can affect the performance of your concrete. In fact, it may decrease its strength and durability.

Concrete aggregates

Aggregates of natural or artificial origin are mineral grains of variable size. As main components of concrete, they transmit certain technical and aesthetic characteristics, in particular their resistance.

The choice of the type of granulate used should not be made in a light way, as it will influence the durability of your concrete. There are different types of aggregates: fillers, sands, gravel, shavings and ballasts.

The different types of aggregates are classified according to their dimensions, expressed by the formula d / D.

d = the smallest diameter of the aggregate.

D = larger diameter of aggregate.

Example: If a granulate has little mass and passes through a 6 mm sieve and a large amount of mass passes through a 10 mm sieve, it will be called “6/10 granulate”.

Concrete Additives

Additives are chemicals that are added during concrete mixing and dosed lightly during preparation (less than 5% of concrete mass).

These products offer the possibility of improving certain characteristics of the concrete, such as its curing time or its water-repellent properties.

Today, very widespread, there are different types of additives that will allow you to obtain the concrete of your dreams.

Different types of concrete

With the new technological advances, the concrete range is in constant evolution.

Concrete is a material whose composition is evolving. Its dosage and components can be adapted according to the desired performance.

All this is achieved by altering any of its basic components and adding different additives. This makes concrete a very versatile material.

Brief description of the different types of concrete

Fibre-reinforced concrete

Fibre-reinforced concrete is a material in which synthetic or metallic fibres of various sizes are integrated and distributed homogeneously in the mass of the concrete.

There are different types of fibres, with different impacts on the concrete. Their function is to improve certain characteristics of the concrete, such as resistance to flexion or limitation of cracking.

Dosage from 0.5 to 2% per m³ of concrete, these fibres have intrinsic characteristics: composition, size, shape.

There are different categories of fibres, which include:

Steel fibres
Organic fibres
Mineral fibres

Useful links on fibres for reinforcing concrete

(A couple of links to technical studies)

Self-compacting concrete

Self-compacting concrete, characterized by its fluidity, differs from traditional concrete by its properties in fresh state.

In fact, the SCC (Self Compacting Concrete), thanks to the diverse components that compose it, has the capacity to set itself where it is applied, without resorting to a vibration system to homogenize it.

Benefits of self-compacting concrete

Installation or implementation

It does not need a vibration system to adapt to the formwork.
Reduces concreting time.
Good for moulds or “difficult” formworks where other concrete does not flow.
This results in a smooth surface.

Decorative Concrete

In addition to satisfying many needs in the world of construction, concrete is a material that has also become trendy in terms of decoration.

Especially when used on floors. Whether indoors or outdoors, it appears in different forms, resulting in various methods of application.

Decorative concretes include the following:

Deactivated concrete or Washed concrete

To achieve this finish, an additive is used in the mixture, the “deactivant”, which makes the concrete take a long time to set.

When there is little left to dry, the surface layer is cleaned to remove all cement and leave aggregates exposed.

For this finish it is important to use aesthetic and quality aggregates, as these will be the visible part.

deactivated concrete — Photo of our colleagues www.deltapav.it in Italy.

This finish is widely used in parks, cities, sidewalks, etc.

Coloured concrete

Concrete can be colored in four different ways:

Tint
Integral Pigments
Color Densifiers
Acid

Each of these coloring methods produces different aspects and has its own set of advantages and disadvantages.

Waxed concrete

It is a decorative concrete on which a wax is applied after hardening. It can be applied to many substrates, is waterproof, durable and easy to maintain.

High-performance concrete

High Compression Concrete (HCC), or high performance concrete, appeared in the 1980s and is characterized by its mechanical strength (ranging from 50 to 100 MPa) compared to conventional concrete (25 to 35 MPa).

Beyond a resistance of 100 Mpa, we are talking about ultra high performance concrete.

Here we leave you a technical link of interest on ultra high compression concrete.

This mixture has the following characteristics:

Resistance:

High compressive strength, reducing the amount of concrete needed
Very low porosity

Durability:

The durability of this material allows its use in hostile environments and reduces maintenance costs in the structure.

Concreting: mixing the concrete

To build a foundation, slab or wall, you’ll probably have to use concrete. It’s good to know before you start that manual mixing of concrete is a relatively difficult operation that will require a little practice!

Therefore, if you have to produce a large quantity of concrete, the use of a concrete mixer will be of great help.

Mixing concrete manually

Step 1

To begin with, make sure that the floor on which you are going to pour the concrete is clean.
Dosage your materials in the proper proportions for the type of concrete you want and place them in the previously cleaned area.

Step 2

Using a shovel, mix your gravel and sand in small successive piles to obtain a homogeneous mixture.

Step 3

Then place the cement in the pile you made in the previous step and mix everything together to get a homogeneous pile again.

Step 4

With the shovel, form a small crater in the center of your stack to pour the water.
Bring the mixture to the centre of the crater successively using the back of your shovel until a homogeneous and firm mixture is obtained.
To find out if your mixture is ready for use, you can check with your shovel that it has a good consistency.

Making concrete with a concrete mixer

In addition to being easy, quick and less tiring than manual mixing, using the cement mixer will make your job easier and allow you to make larger quantities of concrete.

The type of concrete mixer can vary according to the desired volumes. For a high volume of concrete, consider a large one with a gasoline engine. For lower volumes, a small tank and an electric motor are sufficient.

Before starting mixing, take some precautions:

Make sure the concrete mixer is clean.
Check that the machine is installed and anchored correctly.

Step 1

Turn on the concrete mixer (this is obvious)
Gradually add water, leaving it to mix to avoid water flowing out.
Mix until a consistent paste is formed.

Step 2

Pour the cement
Let this one dissolve

Step 3

Taking into account the correct proportions, pour the sand and gravel.
Let it mix for a while.

Step 4

When the mixture is ready pour it into a wheelbarrow
Keep in mind that it is very important to clean the concrete mixer with plenty of water after you finish using, otherwise the concrete will solidify inside.

Concrete setting time

Here we leave you a post that talks about the setting of concrete.

How long does concrete take to set?

Drying the concrete or technically called as curing is the main concern after pouring the concrete. It is this step that will allow the concrete to achieve its capabilities.

These are strength and durability. Just as the proportions and manner of making concrete is important, so is how long it is allowed to dry and under what conditions.

Concrete drying time is characterized by two important dates when tests are performed to verify the quality of the concrete:

Test after 7 days
Test at 28 days

We will see that multiple factors influence the drying time of concrete, such as external conditions, type of concrete, quality of concrete: water content, quality of aggregates, type of additives. But the most important factor is its field of application.

Concrete compaction

The compactness of concrete is a value that is often indicated by a “c” to determine the void volume contained in a material. It is simply the relationship between the apparent volume of the object considered in its actual volume (without the voids).

How to dry concrete properly

The drying time of concrete, whatever it is, is regulated by the standards NF EN 206-1. The curing of the concrete (in other words, its hardening) is the last essential step in order not to neglect to obtain the desired characteristics.

This last step requires special attention and should be carried out as homogeneously as possible.

It is obvious that waiting for the deadlines indicated in the standards, for optimal drying, is rarely respected on construction sites.

However, minimum lead times are recommended before work is resumed to ensure future strength characteristics of the concrete and to prevent the newly poured slab from collapsing under its feet.

The concrete will have reached its class resistance in 28 days and, as there is no concrete drying system, you will have to be patient and simply wait for the recommended times.

Precautions when setting concrete

Warm environments

If the temperature increases, the concrete will set faster! And contrary to what you might think, it’s not always a good situation. Taking too fast can result in a long-term loss of strength.

Hydration solutions or even cooling of the structure can be implemented, so it will be necessary to regularly water the surface of your concrete or provide refrigerated slabs. Yes, even your concrete can catch a hot shot!

Cold environments

In the event of frost, the concrete curing process can be negatively affected and its adjustment slowed down. It is necessary to refer to the regulatory texts they contain and to indicate the procedure to be followed in the event of a sudden drop in temperature.

Namely, the impact of temperature around 5°C can extend the concrete setting up to a factor of 5! It is for this reason that the implementation of concrete at a temperature lower than 5°C is prohibited.

Risks of improperly set concrete

In addition to the loss of strength mentioned above, the worst consequences that can lead to a poor curing of a concrete is, of course, the long-term cracking of the structure.

And, unfortunately, this pathology of concrete is very common, but it should not always be put on the back of a poorly dried concrete. Many other factors come into play to explain the appearance of these cracks.