PROPERTIES OF FRESH AND HARDENED CONCRETE

PROPERTIES OF FRESH AND HARDENED CONCRETE

Properties of concrete can be divided into two parts- Fresh and Hardened properties. Here we have covered concrete properties in detail. Properties of concrete depend upon many factors like water-cement ration, aggregate, cement, grade etc.

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Concrete is made up with cement, coarse aggregates, admixtures, fine aggregates and is one of the most used buildings material worldwide.

 Water cement and aggregates are the basic ingredients of concrete/reinforced concrete.
Mix proportions and ratio of cement, sand, water, aggregate, grade of concrete, etc influence the properties of concrete.

We need to have a look about different types of properties to achieve desired concrete strength, workability, setting time, etc.

To learn more about the Uses of concrete click here. [OPENS IN NEW TAB].

Learn more about GREEN CONCRETE [OPENS IN NEW TAB].

Okay, let's back to the topic...

Properties of concrete are wide area to cover, therefore we have divided the properties of concrete into Two segments.

1. FRESH PROPERTIES
2. HARDENED PROPERTIES

∎ FRESH PROPERTIES OF CONCRETE

First, let me help you to revise your basic knowledge about concrete.

Fresh concrete is the period of concrete in which concrete can be moulded and remains in the plastic state.

Whereas, hardened concrete is the period of concrete which comes after plastic state in which concrete is able to withstand structural and service load and durable enough to protect the structure from environmental exposure.

Now, let's start discussing the Fresh properties of concrete. 

1. Setting time

  Initial and final setting time should be in permissible limit. Most of the time Setting time of cement is influenced by the type of cement.

The initial setting time of concrete is the time elapsed b/w the moment the water is added to the cement to the time that starts losing its plasticity.

The final setting time of concrete is the time elapsed b/w the moment water is added to the concrete and the time when the paste has completely lost his plasticity.

Different types of cement provide a different setting time of concrete.

But always keep in mind that final setting time of concrete should not be more than exceed 10 hours.

Normally initial setting time and final setting times lie between 30-60 minutes and 5-6 hours respectively.

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2. Workability

Workability of concrete defines the degree of fluidity or mobility.
The factors affecting workability of concrete are:

• WATER CONTENT- The higher the water content per cubic meter of concrete, the higher will be the workability of concrete.
• MIX PROPORTIONS- Higher aggregate-cement ratio means lesser workability. Similarly, the lower aggregate-cement ratio will provide us with higher workability.
• SIZE OF AGGREGATE- Size of aggregate ∝ Workability of concrete.
• SHAPE OF AGGREGATE- Rounded aggregates provides poor workability and smooth aggregate causes higher workability.
• GRADING OF AGGREGATE- The better the grading higher the workability.

3.Segregation and bleeding

Segregation of concrete is a type of concrete error which can be defined as the separation of constituent materials of concrete.

Segregation can be of three types-

1. Separation of coarse aggregates from the rest of the mixture.
2. Cement paste gets separated from the coarse aggregate.
3. Separation of water from the total material.

Similarly, bleeding is a form of segregation

In the case of bleeding water from concrete comes out to the concrete surface.

Poor mix proportions may cause bleeding.

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4. Alkali-Aggregate reaction

It comes within the chemical properties of concrete.

It is a reaction between the alkalis present in cement and the active silica or carbonates of aggregates.

Factors which promotes alkali-aggregate reaction are-

1. high alkali content in cement
2. Optimum temp. condition
3. reactive type of aggregate
4. High moisture content

∎ HARDENED PROPERTIES OF CONCRETE

1. Strength

In civil engineering, we always deal with achieving the desired amount of strength. That strength can be compressive, tensile, splitting strength etc.

Let's discuss each of them one by one.

⟾ The compressive strength of concrete :

  Well, it's a universal truth that concrete is good in taking compression than tension. That's why reinforced concrete is used to withstand the adequate amount of tensile force.

The strength of concrete can be affected by the concrete mix, water-cement ratio etc.

Lower the water-cement ratio higher will be Compressive strength.

⟾ The tensile strength of concrete and Splitting tensile strength: 

  Direct tensile strength and flexural strength are the different forms of tensile strength.

 The formula to determine flexural strength and splitting tensile strength are given below-

Other properties of concrete

• Shrinkage- It is defined as the change in volume from fresh concrete to hardening state of concrete.
• Creep- Increment of strain in concrete due to sustained load.
• Modulus of elasticity

The factors which affect the quality of good concrete

1. The quantity of C2S (dicalcium silicate), C3S (tricalcium silicate) and C3A (tricalcium aluminate).    C2S gives long term stability in concrete and generates minimum heat during the hydration process. C3S gives short term strength. C3A helps to rapid hardening of concrete.
2. Plasticizer
3. Retenders
4. Accelerators
5. the quantity of gypsum.

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