Question

What are the advantages and disadvantages of high strength concrete? (30%)

Answer 1

At first we have to understand the grading system of concrete.

We named concrete as M10,M15,M20 etc.

Here M refers for mix and 10 refers for Characteristics strength of concrete (f_ck)

for M10 - When a 150mm cubic block of concrete being tested in compression testing machine then we have obtained the cube strength 10 N/mm² after 28 days of casting.

Characteristics strength refers - Not more than 5 precent results are expected to be fail.

We generally classified the concrete as folllowing based on its strenght :

Ordinary concrete    M10-M20

Standard concrete M25-M55

High strength concrete    M60-M80

High strength concrete as the name signifies is concrete having compressive strength more than 40MPa. Nowadays due to high technological development it is possible to obtain concrete strengths of about 150MPa, thus only strengths above 60MPa are recognised as high strength concrete in recent days. Compressive strength is the most important characteristic which is considered to state whether the concrete is suitable for construction or not, though other properties like tensile and flexural strength are being tested for, compressive strength holds prime importance in the construction industry. Hence with higher compressive strengths the concrete becomes more desirable.

The history of high strength concrete is about 35 years old, in late 1960s the invention of water reducing admixtures lead to the high strength precast products and structural elements in beam were cast in situ using high strength concrete.

Here we have to explain the advantages and disadvantages of high strength concrete.

Advantages :-

1.High compressive strength.

2.Adequate tensile strength

3.Fire and weather resistance

4.High Durability

5.Reduced maintenance and repair.

6.Less deflection when used as a beam or slab in a structure.

7.Used as a precast structural components.

8.The size of structural members like beams and columns are reduced since smaller sections are enough to carry high loads.

9.Since the size of members are reduced the cost of formworks are less.

10.In bridge construction the use of high strength concrete becomes inevitable because longer spans with minimum supports can be constructed.

11.Construction of slabs and floors with thinner sections is made possible.

Disadvantages :-

1.Not economical as cement content increases cost increases.

2.Need skilled labours for casting, manufacturing and placing.

3.When we need to dismantle the structure then it bacome very difficult to break.

4.As cement is more in it then soluble salts in concrete cause efflorescence if moisture reacts with them.

5.Concrete made with ordinary Portland cement, gets integrated in the presence of alkalies, sulfates etc.

6.The weight of compared is high compared to its strength.

7.There is a very less elasticity in the high strength concrete due to this it creates a lots of hurdles just because of rigidity.

8.We can not use this in a temporary structures.

9.More workmanship and testing required to check its stength.