Flexible or Bendable Concrete – Composition and Uses

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A flexible or bendable concrete is an engineered cementitious composite (ECC) that exhibits the property of ductile material unlike the brittle nature of conventional concrete. The material composition of conventional concrete is altered in order to impart flexible nature in concrete. The flexible or bendable concrete was developed by Prof. Victor Li at the University of Michigan.

The composition, features, and applications of flexible or bendable concrete are briefly explained in the article.

Composition of Flexible Concrete

In a flexible concrete mix, the coarse aggregate is eliminated and more of fibers are incorporated.

Flexible concrete is composed of:

1. Cement
2. Fibers
3. Sand
4. Water
5. Superplasticizer

Some of the important constituents of flexible concrete are briefly explained below:

1. Fibers in Flexible Concrete

The most commonly used fibers are silica fibers, asbestos fibers, glass fibers, steel fibers, etc. The flexibility property in a bendable concrete is imparted by the fibres present in it. The fibres also act as reinforcement for the concrete.

The fibers are provided with an anti-friction coating called the slick coating. This coating helps the fibers to slip over the other. This won't create friction between the fibers that hence prevent the formation of cracks in the concrete. This also increases the flexibility of the concrete. Cement used here can be normal ordinary portland cement.

2. Fine Aggregates in Flexible Concrete

Normally, the fine sand used for water treatment activities is the best fine aggregate for flexible concrete. If this is unavailable, normal sand can be used. Some of the replacements like silica fume, blast furnace slag and fly ash can also be used for this concrete making.

3. Superplasticizers in Flexible Concrete

Flexible concrete requires higher workability which hence demands superplasticizers. Some of the superplasticizers used for flexible concrete are:

1. Lignin
2. Naphthalene
3. Melamine formaldehyde
4. Sulphonate
5. Polycarboxylate ether
6. Lignosulfonates

Also Read: Selection of Superplasticisers for High-Performance Concrete

Features of Flexible Concrete

The fibres act as the reinforcement material in the flexible concrete. In ECC, after a crack, the composite strain hardens, unlike fiber reinforced concrete. In a fiber reinforced concrete, the cracks start developing with the rupture of fibers. This reduces the stress-bearing capability of fibre reinforced concrete. But in the case of flexible concrete, they score good because they have high fracture toughness and high damage tolerance. Special features of bendable concrete include:

1. The tensile strength of flexible concrete ranges from 10 to 15 MPa
2. The compressive strength of flexible concrete can be achieved up to 70MPa.
3. Flexible concrete gains self-healing property which helps to fill the microcracks by a complex product that is formed by the reaction of cement with the rainwater.
4. The ultimate tensile strain of bendable concrete can go up to 3 to 5%.
5. The strain capacity of flexible concrete is three hundred times greater than the conventional concrete. This is the factor that provides flexibility to the concrete.

Advantages of Flexible Concrete

The basic advantages of flexible concrete are:

1. High durability
2. High ductility
3. High strength
4. Flexible concrete does not emit harmful gases unlike conventional concrete
5. Higher resistance to cracking
6. Flexible concrete is light in weight compared to conventional concrete by an amount of 20 to 40%.
7. Reduced use of steel reinforcement.
8. Gains self-healing property

Disadvantages of Flexible Concrete

The few disadvantages of flexible concrete are:

1. Flexible cost requires skilled labor
2. The initial cost of flexible concrete construction is high
3. The availability of special materials for flexible concrete is difficult to obtain.
4. The quality of flexible concrete is dependent on the quality of the materials and the atmospheric conditions it is made.
5. The compressive strength of flexible concrete is less compared to conventional concrete.

Applications of Flexible Concrete

The main applications of flexible concrete are:

1. Construction of Roads and Bridges

Construction of roads and bridges using flexible concrete eliminates the use of expansion and contraction joints. This is because the flexible concrete has the ability to change its shape within it.

2. Construction of Earthquake Resistant Buildings

Buildings made out of flexible concrete have the ability to take more tensile stresses. Hence, these can resist high vibration caused due to dynamic forces like an earthquake.

3. Construction of Concrete Canvas

The concrete canvas mostly constructed for military purposes is supposed to be highly strong and durable. This can be achieved efficiently by the use of flexible concrete.