HPC consumption in RMC Sector yet to pick up
When it comes to a quality construction, the usage of conventional concrete has now been replaced with the high-performance concrete. Talking to Realty Plus, Sanjay R. Chitnis, Head Technical Services Cell, JK Lakshmi Cement Ltd briefed on the various aspects of concrete usage.
What are the reasons for the need of high-performance concrete (HPC) in construction today?
The primary reasons for selecting High-performance concrete (HPC) are to produce a more economical product, provide a feasible technical solution, or a combination of both. Cost of one cubic meter of HPC generally costs more than a cubic meter of conventional concrete. HPC requires additional quantities of materials such as cement, fly ash, silica fume, admixtures to ensure that the concrete meets the specified performance. However, concrete is only one component in construction, and the total cost of the finished product is more important than the cost of an individual material.
To summarize, the reasons the HPC is used are directly related to its characteristics which are: high early strength (and high strength too), high modulus of elasticity, high abrasion resistance, high durability and long life in severe environments, low permeability and diffusion and resistance to chemical attack.
What are the materials/ additives & substitutes that go in the making of a HPC?
Few materials used in High-Performance Concrete & their contributions are:
- Cement/blended cement=> Cementing material, Durability, High strength
- Secondary cementitious materials (SCM) like fly ash, slag, silica fume, Calcined clay, Metakaolin => Cementing material, Durability, High strength
- Admixtures like PC based, super plastisizers, high range water reducers etc=> workability of concrete by controlling slump /flow ability
- Fibres=> control shrinkage cracks
- Graded aggregates=> strength & durability
What are the various applications for a high performance concrete?
High-rise Buildings: The reasons for using the high strength concrete in the area of high-rise buildings are to reduce the dead load, the deflection, the vibration and the noise, and the maintenance cost. The high strength concrete provides the most economical way to carry a vertical load to the building foundation. The three major components contributing to the cost of a column are concrete, steel reinforcement and formwork. By utilizing high-strength concrete, the column size is reduced. Consequently, less concrete and less formwork is needed. At the same time, the amount of vertical reinforcement can be reduced to the minimum amount allowed by the code. The net result is that the least expensive column is achieved with the smallest size column, the least amount of reinforcement and the highest readily available concrete strength.
Bridges: Bridges are national importance structures where performance & durability plays a vital role. With the help of HPC, we can design longer span girders & can reduce depth of beam. On multi-span bridges, the use of longer girders results in fewer spans and fewer substructures. The use of high performance concrete would result in smaller loss in pre-stress and consequently larger permissible stress and smaller cross-section being achieved. In addition, enhanced durability allows extended service life of the structure. In case of precast girders due to reduced weight the transportation and handling will be economical. Concrete structures are preferable for railway bridges to eliminate noise and vibration problems and minimize the maintenance cost.
Pavements: High Performance concrete is being increasingly used for highway pavements due to the potential economic benefits that can be derived from the early strength gain of high performance concrete, its reduced permeability, increased wear or abrasion resistance to steel studded tires and improved freeze-thaw durability. While the conventional normal strength concrete continue to be used in most cases of pavement construction, different types of high performance concretes are being considered for pavement repairs for early opening to traffic, bridge deck overlays, and special applications in rehabilitation of structures and other developments.
What are some of the advanced concrete products and their advantages?
Pervious Concrete: Pervious concrete pavement has a 15-25% void structure, allowing 12 to 30 litres of water per minute to pass through each square foot. When it rains, pervious drains, putting water back in the ground where it belongs.
Self Compacting concrete: Self compacting concrete is a high flow able and non segregating concrete that can spread into place, fill the formwork without honeycombing without any mechanical vibrator. This concrete is able to consolidate with his own weight and flows to virtually uniform level under the influence of gravity like water. It is available from concrete grades M 20 & above. About 40 to 50% of cement content can be replaced by supplementary cementing material like flyash; cost of the concrete is greatly reduced. The number of skilled supervisors, engineers, vibrator operators and pipe fitters can drastically be reduced. Formwork can be used for more number of times. Cost of repairing the structure is reduced as the numbers of defects are reduced to a great extent. Cast-in-place concrete construction in tight space and congested reinforcement, such as, drilled shafts, columns and earth retaining systems, can be accelerated by using SCC. Its applications are in Residential & Industrial buildings, High rise buildings, Bridges & Tunnels and in Pre-cast & pre-stressed industry,
Fibre Reinforced Concrete: Main role of fibers is to bridge the cracks that develop in concrete and increase the ductility of concrete elements. There is considerable improvement in the post-cracking behavior of concrete containing fibers due to both plastic shrinkage and drying shrinkage. They also reduce the permeability of concrete and thus reduce bleeding of water. Some types of fibers produce greater abrasion and shatter resistance in concrete imparts more resistance to Impact load. Its application areas are are Roller compacted concrete, Highway, Airfield Pavements, Industrial flooring, Manholes & Covers, Pipes, Sleepers, Hydraulic Structures, Shot Crete & Tunnel linings,
Pre-cast concrete: The large projects comprising of Townships, Mass Housings, IT/ITES parks and SEZs’ are of common occurrence these days and will only grow exponentially in the near future. Majority of such projects are still being constructed using the conventional methods. Precast Concrete Technology, the so called unconventional method in an Indian Space can facilitate both speed and quality of the construction and at the same time exploits the advantages that these large scale projects offer in terms of volume turnover and the repetitions. Footings, columns, beams, slabs, walls etc are manufactured at factory & erected at required site.
Geo-Polymer concrete: Geopolymer cement concretes’ (GPCC) are inorganic polymer composites. GPCC have high strength, with good resistance to chloride penetration, acid attack. These are commonly formed by alkali activation of industrial alumina-silicate waste materials such as FA and GGBS, and have a very small Greenhouse footprint when compared to traditional concretes.
The best ways of making concrete more sustainable is to follow the mantra of recycle and reduce. The aggregate is now mixed with various alternative material like fiber glass waste materials, discarded glass, granulated plastics, wood products etc. Fibre Reinforced Concrete & glass reinforced concrete are a way to move towards environment friendly practices.
What are the advantages of Ready Mix Concrete, its limitations and growing popularity in construction industry?
While the cement consumption in RMC Sector in the developed countries is much more (nearly 80%), it is yet to pick up in India or other developing countries in big way. A very low percentage of cement goes in organised RMC sector. Cyclical downturns in construction activity, slowdown in economy, deferral of infrastructure projects, policy hurdles and high interest rates all combined resulted in subdued RMC demand in last few years. However, the RMC segment is expected to grow at a healthy rate in the next few years with markets expecting to see a turn-around shortly and an increased emphasis on quality, safety and speed within the Indian construction industry.
One limitation of Ready Mixed Concrete could be timing .Generally RMC is delivered within a radius of 25 KM from the plant. It can be delivered up to 70 KM distance if proper precautions taken care while designing & delivering the concrete .Worsened traffic conditions make the RMC reach late at the site. Addition of retarders and admixture can be used to address the issue of setting of concrete in case of delay in transit time. However, it is used very judiciously so any loss of strength does not occur. Because of large quantity of concrete available in short span, advance planning is required which some people are not good at. Educating people on this aspect is what we do in such cases.
How is the current market for these new products in India?
The construction practices in India are continuously evolving to remain in sync with best of international practices and also to meet the satisfaction of customers with special requirements. These special requirements of customers are on gradual increase and their preference for specific products like high strength concrete with high flow ability, better workability, green concrete. With increasing performance expectations, concrete technology has been continually advancing by innovatively using cementitious materials and I think, India will witness a rapid change in the way we serve our customers in all sectors including RMC.