HPC- Construction Workhorse
HPC – Construction Workhorse
High-performance concrete (HPC) is the preferred choice amongst the engineers in the construction industry. Ritesh Nayak, Chief Manager, Business, KJS Concrete spoke to Realty Plus on the reasons behind the need of high-performance concrete, it’s advantages & disadvantages and it’s growth potential in India.
Concrete is one of the most widely used construction materials in the world. With continuous evolution in the industry, there is now a shift from conventional Portland cement concrete to high-performance concrete (HPC). This new engineered concrete possessing the most desirable properties during fresh as well as hardened concrete stages is far superior to conventional cement concrete as the ingredients of HPC contribute most optimally and efficiently to its various properties.
Unlike in the past where construction used to take months even years to complete, modern-time development requires certain qualities to cope with aggressive environmental conditions and high energy absorption capacity among so many other requirements. In sync with today’s construction practices, the concrete needs to offer speed of construction, workability characteristics, early strength gain, excellent durability, resistance to aggressive media and a long service life.
High-Performance Concrete (HPC) is formulated to meet such defined strength, durability and curing specifications. From a structural point of view, high strength, high ductility and high durability are the key attributes of HPC and therefore it is natural that HPC is likely to be the construction industry workhorse in the coming days.
HPC is used in a project requiring sustainability and durability. Ii can be used in an environment where the impact of weather affects the use of conventional concrete leading to faster depreciation. It also finds application in projects where other environmental factors such that require the concrete to cure faster than in conventional concrete. Major applications of high-performance concrete in the field of civil engineering constructions have been in the areas of long-span bridges, high- rise structures, highway pavements, airport pavements, tunnels, underground structures, etc.
Additives & Substitutes used
High performance concrete comprises the same materials as that of the conventional cement concrete. HPC will require lower water-cement ratio, the presence of Pozzolans, chemical admixtures and other additives to make it meet intended purpose. The term ‘high performance’ is somewhat pretentious because the essential feature of this concrete is that it’s ingredients and proportions are specifically chosen so as to have particularly appropriate properties for the expected use of the structure such as high strength, durability, workability and low permeability.
The main ingredients of High Performance Concrete are Cement, Fine Aggregates, Coarse Aggregates, Chemical Admixtures (Plasticizers/ Super Plasticizers/Retarders/Air Entraining Agents), Mineral Admixtures (Fly Ash/ Silica Fumes/ Carbon Black Powder/ Anhydrous Gypsum Based Mineral Additives) and Water.
The production of portland cement, an essential constituent of concrete, leads to the release of significant amount of Carbon Dioxide (CO2), a greenhouse gas. The cement and concrete industries are making substantial contributions to sustainable developments by creating and adopting technologies that reduces the emissions of greenhouse gases.
The cement manufacturers have started production of blended cements which involves the inter-grinding of clinker with one or more additives; e.g., fly ash, granulated blast furnace slag, silica fume, volcanic ash, in various proportions. The use of blended cements is a particularly attractive efficiency option since the inter-grinding of clinker with other additives not only allows for a reduction in the energy used (reduced GHG emissions) in clinker production, but also directly corresponds to a reduction in carbon dioxide emissions in calcinations as well.
In addition concrete manufacturers are using recycled aggregate materials and preparations that reduce the rate of calcium release, in spite of a greater porosity of the concrete microstructure. The use of recycled materials has gained credibility and momentum in the concrete industry and aggregate is now mined from various solid wastes including fiberglass waste materials, discarded glass, granulated plastics, wood products, old tyres and more.
Other alternatives, such as foamcrete, ceramicrete, glass fiber reinforced concrete (GFRC) and grasscrete are also been introduced which reduce the overall amount of concrete in use, resulting in decreased emissions and energy expenditures. The emergence of new cement substitutes and concrete alternatives has convinced many green builders that concrete really can be an eco-friendly product.
Challenges in the Manufacturing & Application
The production of high performance concrete usually calls for some changes in the conventional processing technology. The selection of the materials is a problem because cements and aggregates are suitable with widely varying composition and properties. Physical and chemical characteristics of cement play a vital role in developing strength and controlling rheology of fresh concrete. Fineness affects water requirements for consistency.
When looking for cement to be used in High Performance Concrete one should choose cements containing as little Tricalcium Aluminate (C3A) as possible because the lower amount of C3A, the easier to control the rheology and lesser the problems of cement-super plasticizer compatibility.
Finally from strength point of view, this cement should be finally ground and contain a fair amount of Tricalcium Silicate (C3S). The properties of aggregates such as void ratio, gradation, specific surface and bulk density should be assessed in order to design dense high performance concrete mix with optimum cement content and reduced mixing water.
A number of chemicals and minerals admixtures must be used simultaneously, and there are no simple rules by which a judicious choice can be made. It is difficult to predict the effect and the result of using admixtures because many a time the change in the brand of cement, aggregate grading, mix proportions and richness of mix sometimes usually alter the properties of concrete. Carefulness is the watch word in the selection of admixture, and in also predicting the concrete. High Performance Concrete has to be manufactured and placed much more carefully than normal concrete. An extended quality control is required.
In HPC applications such as high-rise buildings, column sizes are large enough to be classed as mass concrete. Normally, excessive heat generation in mass concrete is controlled by using low cement content. When high-cement-content HPC mixes are used under these conditions, other methods of controlling maximum concrete temperature must be employed. Also, High Performance Concrete has a poor resistance to fire because the very low permeability of High Performance Concrete does not allow the egress of steam formed from water in the hydrated cement paste.
Current Market Scenario
The construction practices in India are continuously evolving to keep pace with the international developments and to meet customer’s special requirements. They are also expected to be consistent with environmental and sustainability guidelines. Typically, concrete manufacturers prefer standard strength concrete with high flow ability, segregation resistance and workability retention. Use of green materials such as fly ash, slag, silica fume, manufactured sand in concrete is also gaining acceptance. With increasing performance expectations, concrete technology has been continually advancing by innovatively using cementitious materials.
For imparting better durability to structures in aggressive environments, low permeability concrete is increasingly being made. Special concretes such as Reactive Powder Concrete (RPC), Self Compacting Concrete (SCC) and cement based grouts that need ultra fine materials for effective performance are also being made in more quantities than ever before. These developments present opportunities for developing new concrete materials.
The Growth Potential
Considering the speed at which infrastructure projects are being launched in India long-term performance (durability) of structures shall be a major concern to the economy of the country. Experience has shown that concrete is vulnerable to deterioration by nature due to alternate periods of rapid wetting and prolonged drying with frequently alternating temperatures. High Performance Concrete can take care of any specific requirements under most of different exposure conditions. HPC has got low permeability due to which it is mainly used to increase the durability of structures not just under extreme conditions of exposure but under normal circumstances also, because carbon dioxide is always present in the air that results in carbonation of concrete which destroys the reinforcement and leads to corrosion. HPC prevents deterioration of concrete and ensures long life of a structure exposed to such conditions. In this context, it is natural that High Performance Concrete (HPC) will soon gain a mainstream appeal, especially in fast developing nations like India.