The Construction Industry witnessing construction of very interesting projects in all sectors of Infrastructure. High rise structures, under construction, include residential/commercial blocks up to a height of 320 m and Reinforced Concrete chimneys for thermal power stations extending upwards up to 275m. Majority of the structures are in structural concrete. The functional demands of such high rise structures include the use of durable materials. High Strength Concrete, Self–compacting Concrete are gaining widespread acceptance. Apart from the basic structural materials, modern projects require a variety of secondary materials for a variety of purposes such as construction chemicals, waterproofing materials, durability aids etc.
High Performance Concrete
In response to widespread cracking of concrete bridge decks, the construction process moved towards the use of High Performance Concrete (HPC) mixes. Four types of HPC were developed1:
- Very High Early Strength Concrete – 17.5 mPa in 6 hours
- High Early Strength Concrete – 42.5 mPa in 24 hours
- A Very High Strength – 86 mPa in 28 days
- High Early Strength with Fiber Reinforcement
- High Performance Concrete was introduced in India initially for the reconstruction of the pre-stressed concrete dome of the Kaiga Atomic Power Project, followed for parts of the Reactors at Tarapur and Rajasthan. Subsequently, a number of bridges and flyovers have introduced HPC up to M75 grade in different parts of India.
Self–compacting Concrete(SCC) was developed by the Japanese initially as a Quality Assurance measure, but now is being widely used for concrete structures worldwide. In India, one of the earliest uses of SCC was for some components of structures at Kaiga Atomic Power Project. Many components of the structures were very heavily reinforced and the field engineers found it difficult to place and compact normal concrete without honeycombs and weaker concrete. SCC was successfully used.
SCC leaving the batching plant is in a semi-fluid state and is placed into the formwork without the use of vibrators. Due to its fluidity, SCC is able to find its way into the formwork and in between the reinforcement and gets self-compacted in the process. SCC is particularly useful for components of structures which are heavily reinforced. The fluidity is realized by modifying the normal mix components. In addition to cement, coarse and fine aggregates, water, special new generation polymer based admixtures are used to increase the fluidity of the concrete without increasing the water content.
Due to its high fluidity, the traditional method of measuring workability by slump does not work. The fluidity is such that any concrete fed to the slump cone falls flat on raising the slump cone; the diameter of the spread of concrete is measured as an indication of workability of SCC. This is called Slump Flow and is in the range of 600 – 800 mm.
Apart from the use of superior grade chemical admixtures, the physical composition of the concrete for SCC has undergone changes. The concrete is required to have more of fine aggregates and compulsorily any of the mineral admixtures – fly ash, ground granulated blast furnace slag (GGBFS), silica fume, metakaolin, rice husk ash etc. Fly ash is abundantly available as a waste product at all the thermal power stations and the Government has encouraged use of fly ash by offering them practically free at the thermal power stations. GGBFS is again a by-product of the steel mills. During the production of steel, a molten steel is poured from blast furnaces and travels in special channels, leaving the impurities on top of the stream. The waste material, being lighter moves on top and easily diverted away from the usable steel.
The diverted slag is quenched and forms small nodules. These nodules are crushed and granulated into very fine product, with particle size smaller than that of cement. The product is marketed in 50 kg bags and available economically in the regions around steel mills with blast furnaces. In other regions, additional transport cost of this bulk material is involved but its use is justified because of contribution to durability of concrete. For the concrete components of the structure for Bandra and Worli sewage outfalls in Mumbai, the German prime contractor insisted on compulsory use of GGBFS for the M40 concrete in order to improve the durability of concrete. GGBFS had to be transported from Vizag in the eastern part of India, in spite of heavy transportation cost. Since then GGBFS is finding widespread use in different parts of India for ensuring durable concrete.
Recent Advances in SCC:
Nano-SiO2, a cement-based material, is used as nano-filler in the cement matrix where the total porosity is reduced at nano-scale which make it multi-functional nano-technological material and the concrete with nano-silica performs as a designed self-compacting concrete . One of the considerations with reference to the elastic performance of SCC is its inferior stiffness propensity in comparison to conventional concretes (CC) but it is designed in a way to perform much better results as a high performance concrete. Only a few researches carried out experimental studies for determining the fresh properties, hard properties and micro-structural properties with nano-silica. Different theories are evolved from their experimental data. A number of researchers reported dissimilar and inconsistent optimal amounts of nano-silica with some noteworthy effects that need a lot of concentration in the further research/studies.
Among the all nano-material's, Nano-SiO2 is the most abundantly used nano-material in the cement replacement and concrete to increase the performance. In this modernized world of advance infrastructure, it is essential to establish a high strength, stable, strong, sustainable and environment-friendly cementitious composites. Concretes incorporated with nano-silica results in the formation of denser and compact micro-structure with fewer amount of calcium hydroxide crystals. It also results in higher compressive strength, intensification in tensile strength and bending strength and acceleration of hydration as presented by various researchers in their work.
SCC, a concrete of high workability, has the quality of self-healing without segregation and bleeding. For the earthquake resistant structures, bridges, skyscrapers and industrial foundation high strength concrete is needed, this kind of concrete perform as a Ultra High Performance for multi-purpose to make high performance reinforced concrete structure (RCC). In the current scenario of modern construction SCC contributes a vital role to fulfill the demand of modern architectural and complex indeterminate structural construction having intricate geometrical configuration. One can easily say that it is a kind of 'Future Concrete'.
Comparison Between Conventional and SCC
The comparison between the SCC and CC with respect to various technical aspects is presented below.
|Comparison of Conventional Concrete with High-Performance Self-Compacting Concrete
||High Performance Self-Compacting Concrete (HPSCC)
||Conventional Concrete (CC)
|Cost and Time-Effectiveness
||High (due to Vibration
|Resistance to Segregation
|Voids/ Honey- Combing
||Low Strength in comparison to SCC
||Low Durable in comparison
Advantages of SCC:
It sets automatically i.e. eliminating the need of vibration.
The advantages of SCC have been summarized below:
- It has a designed rheological workability.
- It having the quality of segregation resistance.
- It has a well-defined quality of high flowability, passing ability and filing ability (improving the filling capacity of immensely congested structural members).
- It is a high performance concrete with high durability.
- It has a low yield stress and high deformability.
- It is a cost-effective & time–effective concrete as per field applications.
- Reduction in noise pollution and is eco-friendly (e.g. suitable for urban application where noise is a community concern).
- It doesn't require skilled labours and reduces the number of labour at the site.
- SCC has dense micro-structure which raises the strength and durability of structures built using SCC.
- It has negligible pores and voids ratio.
- It provides high serviceability and ultra-strength to structure.
- It is designed in such a way that it resists seismic load, wind forces, blast loads, debris impact loads, hydrostatic and hydrodynamic in even harsh conditions.
- It facilitates constructability and ensuring good structural performance.
- It even reduces the equipment wear.
- It produces superior surface finishes.
Future of SCC:
In the field of advance concrete research, SCC contributes a revolutionary part for the development. SCC is impending out of its infancy. In pre-cast concrete industry, SCC has a large impact due to its high performance. SCC offers much compensation and can be effortlessly produced and controlled. A lot of research all over the world is being carried out to explore all the possible applications and properties of SCC. Self-compacting concrete finds wide scope in the construction of various structures which play a vital role in country's development as well as future aspects of advanced technology.
- Hybrid RCC Structures such as Shear Walls, Concrete Bracings, in-fill Tubes, etc.
- Building Infrastructure such as schools, government buildings, hospitals, shopping complex, etc.
- Bridges and their various components like anchorages, arch, beams, girders, tower, pier, joint between pier & girder and others.
- Transportation Infrastructures and Box Culverts.
- Concrete filled steel tubes.
- Tunnel Linings and immersed tunnels.
- Dams (Concrete).
- High Performance Structures which resist seismic load, wind forces, blast loads, debris impact loads, hydrostatic and hydrodynamic in harsh conditions.
- Hydraulic Structures like Water Tank, Waste Water Plant, Canal and River Regulatory Structures.
The importance and its usage of SCC have been found out from various literatures. In the current scenario of modern construction, SCC plays an important role to fulfill the demand of modern architectural and complex indeterminate structural construction having complex geometrical configurations. Now, in the existing days of heavy and large modern reinforced concrete construction having complex formwork and reinforcement demanding to handle the field's multi-faceted constraints, with better concreting conditions.
Development of SCC in India:
- The advancements of SCC are measured as the greatest development in construction industry due to its several unequal benefits as it performs as a multi-purposed high performance concrete. In India, this advance technology is yet to realize its full potential and use.
- Many institutions, researchers, and companies have been working on SCC Technology. Example: Central Road Research Institute (CRRI) 2005, New Delhi, has been working since the year 2000 and carried out momentous research work on several aspects of SCC.
- SCC technology was a known since the time Nuclear Power Corporation of India Limited (NPCIL) was planning for vast enlargement of power generation within a squat period of time. This idea will save time, cost, enhance quality, durability and above all, a greener concept.
- SCC has been used in the construction of Kaiga nuclear power plant as well as Delhi Metro in India.
- Due to various advantages of SCC, many companies in India are utilizing SCC for speedy completion of the construction work.
SCC represents the recent advancement in concrete technology. The application of SCC is mainly a contribution towards an enhancement of the concrete technologically, economically and ecological/social forms at the manufacturing of the concrete. SCC came as an answer to the raised conditions of RCC buildings durability and high-quality stable and polished surface of architectural concrete. Presently, it is very ardently and widely used material in construction sites as well as manufacturing of precast members. Practical applications extend from large infrastructure project such as bridges, tanks, retaining walls, tunnels, etc. onto architectural buildings. Thus, SCC is considered as a future concrete and will allow the engineers/designers to design and build structures that last a century and beyond.