Though Concrete is one of the most widely used construction materials, there are lot of disadvantages associated with it. Some of these disadvantages of concrete are modified by adding admixtures or modifying the concrete structure and ingredients. Still there are lot of limitations associated with concrete. Major limitations of concrete are listed below.
1. Concrete is Quasi-brittle Material
Three major modes of failure of materials are brittle, quasi-brittle failure, and ductile failure. Typical failure of brittle and ductile failures are Glass and mild steel respectively. Brittle materials fail on onset of tension or once tensile strength is reached. Unlike these materials, concrete exhibits a strain-softening behavior these materials are called quasi-brittle materials.
Brittle and quasi brittle materials like concrete undergo very little deformations before failure. Less the deformation, lesser will be the warnings. Apart from this concrete has low fracture toughness. This is a major disadvantage of plain concrete. For these reasons, concrete is used along with steel to take tension and concrete takes compression loads effectively. Thus reinforced concrete is second generation concrete. Concrete adds stability to the structure.
2. Low Tensile Strength
Compression and tensile strength of concrete are not same. In fact the tensile strength of concrete is 1/10th of its compressive strength. Fibers and other polymers are introduced to concrete to increase its tensile capacity.
3. Concrete has Low Toughness
Ability of a material to consume impact energy is called toughness. It is the area under the load displacement curve. Another limitation of concrete is that compared to steel, the concrete has significantly low toughness. Toughness of concrete is only 1-2% of steel. Fibre reinforced concrete provide better toughness to concrete.
4. Concrete has Low specific strength
The ratio of strength to density is called specific strength. Specific strength of normal grade concrete is half that of steel, ie 20. Specific strength is controlled by decreasing density and increasing strength. Lightweight concrete & high-strength concrete mitigates these limitations of concrete.
5. Formwork is Required
Fresh concrete is liquid. Formwork is required to mould it in a shape and to support its self-weight. Shuttering can be of plastic, steel or wood. The formwork is expensive to install and procure. Installation requires intensive labor and time. Precast and Prefabrication techniques are adopted to overcome these limitations of concrete.
6. Long curing time
Concrete attains specified compressive strength in 28-days after casting and curing. Full strength development requires proper ambient temperature controlled over a month time. This is another disadvantage of concrete. Curing period is reduced by steam curing or microwave curing or by using admixtures.
7. Working with cracks
Tension face of concrete has a cover to protect the reinforcing steel bars. If tensile stress at extreme fibre exceeds the tensile capacity of concrete, it cracks and leads to corrosion of reinforcements. Normal reinforced concrete is assumed to be cracked in service loads for design. To overcome this limitation of concrete, third generation concrete, prestressed concrete is introduced.
8. Demands Strict Quality Control
Concrete demands strict quality control and skilled labor during mixing, placing and curing of concrete. This is important for superior quality of concrete. If not, concrete is viable to poor strength, durability and performance issues.