Sustainable Concrete - An Inevitable Need for Present & Future

Ratan Kumar Jha, Zonal Head- Customer Technical services, JK Cement Limited, New Delhi

Concrete has become, by far, the most widely used construction material in the world. It is surpassed only by water as the most used material on earth. Concrete is perceived and identified as the provider of a nation’s infrastructure and indirectly of its economic progress and stability, and indeed, of the quality of life of the people. Concrete is easily and readily prepared and fabricated in all sorts of conceivable shapes and structural systems for application in infrastructure, habitation, transportation, work and play. Its simplicity lies in its constituents that are readily available anywhere in the world.

When a material becomes as integral to the structure as concrete, it is important to analyse its environmental impact to conclude if the material is as sustainable as it is prevalent. If the material does not satisfy the credential of sustainability, it should be a matter of concern, especially today when people and authorities are more conscious environmentally.

In 1987, the World Commission on Environment and development defined sustainable development as Development that meets the needs of the present without compromising the ability of future generations to meet their needs, and later on at the 1992 Earth Summit in Rio de Janeiro as economic activity that is in harmony with the earth’s ecosystem.

As a matter of fact, concrete related activities consume gigantic quantum of non-renewable resources both in direct and indirect manner. It is dis-heartening to hear that corrosion of steel in concrete shrinks the life span and serviceability of large number of structures. A huge sum of national wealth is spent for repairs and rehabilitation of concrete structures. Ever increasing problem of early aging & short life cycle of concrete structures has been adding to the huge volume of restoration, repair & rehabilitation works. Additionally, high volume of structural repair works consume huge quantum of non-renewable resources. Thus, to make concrete and built structures sustainable one has to make it more durable and more emphasis has to be given to the durability right from the designing stage of the structures.


Important goals of a concrete structure:

1. Safety
2. Economy
3. Durability
4. Sustainability

Safety, Economy and Sustainability are functions of Durability. Hence, achievement of Durability is most critical and important in concrete construction.

Durability: A durable concrete structure is one that performs satisfactorily in the working environment during its anticipated exposure conditions during service (IS 456-2000).

Durability depends on two main factors:

1. The concrete system &
2. The service environment

1. Concrete system is based on
   • Quality and quantity of materials used and
   • Processes involved in manufac- ture of concrete.
2. Service environment affects concrete by way of-
   • Physical actions and
   • Chemical action on concrete.

Quality of ingredients of concrete impact the strength and durability. Nowadays, blended cement or concrete with mineral admixtures are preferred for construction and by structural engineers. Blended cement not only has an edge over OPC as far as high performance or durablity is concerned, but has environmental benefits as well. It is a well-known fact that in manufacturing of 1 MT of cement nearly I MT of CO2 is emitted in the environment. By choosing PPC or PSC in construction, we are not only using our limestone (natural resource) but utilizing waste of thermal & steel plants (fly ash & slag) and converting it in to wealth.

Permeability of concrete plays an important role in durability because it controls the rate of entry of moisture that may contain aggressive chemicals and the movement of water during heating or freezing. Higher the permeability lesser will be the durability.

It can be seen in the figure below that one of the most common and serious causes of deterioration of concrete is corrosion of reinforcement and permeability is an important cause of it among others.


The way forward

• Blended cements like PPC and PSC have been well accepted in the country. However, we need to improve the percentage of fly ash and GGBS content in our cement and concrete.
• We may have Indian Standards for pozzolanic cement with up to 50% replacement of OPC by fly ash for high volume fly ash concrete roads and other applications.
• We need to have positive support from the authorities in this endeavour for sustainable construction.
• We have to encourage use of micro fine products like silica fume or micro silica, etc. for producing impermeable, high strength and super high strength concrete to assist in building more with less, with savings of about 50% of concrete volume.
• We need to increase use of classified fly ash by processing fly ash into different categories based on its fineness so that it can contribute effectively in producing very high strength as well as normal strength and durable concrete with lower cement utilization.
• Recycling of concrete from C&D wastes.
• More responsible and professional approach in designing and execution of work (effective workmanship).

Conclusion

Basic concept of sustainable construction is conserving the natural resources for future generation, by conserving virgin materials and protecting the environment by reducing, re-using and recycling the waste and reducing CO2 emission.

Indian Cement, Concrete and Construction industry has made substantial contribution in sustainable construction. However, there is a long way to go and we are able to build more with less (by increasing use of ultra-high strength concrete). The day we consume our entire industrial by-products like fly ash, blast furnace slag, etc., we can claim that we have really contributed to the nation and to the world at large.