Corrosion of concrete happens due to various factors but it is necessary to repair the damage caused by such corrosion. In Part-1 of the two-part series, Upen Patel, Business Director, BASF India, dwells at length on the causes of deterioration and the remedy thereofOnce concrete repairs and strengthening was considered as an activity of rejuvenating the old structures and making them capable of loadings and environmental stresses in the future life. Today we are constructing more advanced and ever more-demanding structures with complex detailing and concrete repairs and strengthening starts during the construction stage itself. The complex and fast pace construction methods with reduced emphasis on adequate quality assurance results in to construction errors and creates needs for repairs and strengthening during construction. With the complex performance demands of the new structures and ever longer life expectancies makes concrete repairs, strengthening and protection procedures more and more demanding. This article is an attempt to present the fundamentals of concrete repairs and strengthening in a step-by-step process and focuses on the advantages and disadvantages of current practices and provides an insight in the futuristic but more simple to adopt techniques.Basic DefinitionsRepairs: To replace or correct deteriorated, damaged or faulty materials, components or elements of a concrete structure.Strengthening: The process of restoring the capacity of weakened components or elements to their original design capacity or increasing the strength of components or elements of a concrete structure.Protection: Making the structure capable to resist the likely deterioration due to the surrounding/ environment.Why concrete needs repairs?There are many factors which lead to the need of repairs such as:??Corrosion of reinforcement due to carbonation, chlorides??Sulphates??Alkali silica reaction??Environmental pollution??Deicing salts??Acid rains??Marine environment??Oils??Freeze thaw cycles??Abrasion or erosion from wind or water borne agents??Plants or microorganisms??Overloading??Physical settlement??Impact??Earthquake??Fire??Chemical attack by aggressive chemicals, sewerage or even soft waterAlso the deterioration gets aggravated due to errors/mistakes/poor workmanship during construction such as:??Higher w/c ratio??Honeycombs and compaction voids??Bleeding and segregation??Plastic shrinkages and hardening stage shrinkage cracks??Inadequate or no curing??In sufficient concrete cover??Cast-in chlorides from contaminated water/aggregates??Inadequate or excessive vibration during the concerting??Shutterwork or reinforcement movement during placement of concreteGenerally concrete structure requires repairs in the two events- New construction and during the service life. Repairs in the new construction require different approach then the repairs during service life and we shall deal one by one to better understand. The repairs during service life have more steps and we shall deal with it first. The repairs during service life arise due to certain deterioration taken place and understanding of the same is very vital in the design of the repair solution.Why concrete deteriorates?The reinforced concrete was designed with a basic understanding that its a marriage of two carrying spouses – concrete and steel. Concrete protects steel from getting corroded and steel protects concrete from getting cracked due to bending. The marriage was designed to last forever but the environment facilitates entry of many agents who leads the marriage to divorce…Major agents and their activities are described as under:-Carbonation: The high pH of concrete passivates steel reinforcement from getting corroded. The carbon dioxide / sulphur dioxide present in the atmosphere gets dissolved in the water and forms weak carbonic /sulphuric acid and enters the concrete reducing the pH, resulting in the loss of passivation layer around reinforcement. The reinforcement states getting corroded resulting in to the rust. The rust formed has 4- times the original volume of the metal creating bursting pressure in the concrete mass. The build up of the pressure eventually cracks the concrete and makes the access for ingress of corrosive water and other water dissolved agents easily. The quicker access aggravates the corrosion and structure starts deteriorating rapidly. Spalling of the concrete cover and formation of brown colored rust is a visual indication of the carbonation attack. The carbonation attack can be checked by phenolphthalein liquid. The reaction is at its best at 50-75 % relative humidity.Chloride attack: The main source of chlorides is the contaminated water or aggregates during construction and marine environment – direct contact with sea water or through wind borne chlorides in the splash zone. Chlorides ions are the passivating ferrous oxide layer on the steel reinforcement. Once reinforcement loses its passivation layer, it is highly susceptible to electro-chemical corrosion further induced by chlorides ions. The water dissolved chlorides ions form electro-chemical corrosion cell and establishes anodic and cathodic sites on the re-bar.The electro-chemical corrosion results in to pitting corrosion-reduction in the cross section of the re-bar at specific sites without noticeable deterioration of the concrete cover. The hidden reduction in the cross-section of the reinforcement can results in to sudden failure of the structure member-making this as one of the most dangerous deterioration in the concrete structure. There is no ‘net use’ of chloride ions during the corrosion process. Therefore, once enough chloride ions reach the steel to break the passivation layer only water, oxygen and a conductive medium is needed to maintain the corrosion reaction. Also note that since corrosion is a chemical reaction, temperature plays a role in the process. The higher the temperature the faster the corrosion reaction occurs. The general rule for the rate of chemical reactions is that for every 25 degree F increases, the reaction rate doubles.Sulphate attack: The main source of sulphates is the ground water. The sulphates attack on concrete, by reacting with the C3A in the concrete. The reactive product is larger in the volume resulting in to the expansive cracking in the concrete mass. The spalling and cracking of concrete takes place without any deterioration of the reinforcement to start with. With the time other forms of corrosion such as carbonation, chlorides becomes aggravated due to quicker access to the reinforcement. The sulphate attack can be reduced by using sulphate resistant cement which has low C3A content; but this reduces the resistance of chloride attack and hence no more a preferred option in the marine situation.Alkali-silica reaction (ASR): In the case of ASR the alkali-reactive aggregates forms expansive gels in the concrete structure resulting in to cracking and spalling.Step-by-step process to successful repairs:-Following steps are essential for successful repairs:-??Evaluation??Relating observations to causes??Selecting methods and material for repairs??Preparation of drawings and specifications??Selection of contractor??Execution of the work??Quality control??Preserve records for futureEvaluationEvaluate the current condition of the concrete structure. Structural analysis of the structure in its deteriorated condition, review of records of any previous repair work accomplished, review of maintenance records, visual examination, destructive and noon-destructive testing and lab analysis of concrete samples. Some of the popular tests used during the evaluation are summarised as under:-??Visual inspection and recording??Hammer sounding / Rebound hammer test??Phenolphthalein test for carbonation??Silver-nitrate test for chloride attack??Half-cell potential measurement??Core-cutting??Chemical analysis of concrete at different depthsRepair philosophyIt is most important to consider the full load envelope, which has been acting on the structure during the complete service life and in the future. The repair materials must have compatibility with the existing structure. The compatibility may be defined as a balance (equilibrium) of physical, chemical, electrochemical and dimensional properties between the repair material and the existing substrate in structural exposure conditions for a determined period of time.1st Compatibility: Physical/Permeability??Allow substrate to breath??Prevent entry of water and waterborne salts – Sulphate, Chlorides, SO2, CO2 2nd Compatibility: Chemical??No negative chemical interaction with the substrate??Absence of potentially dangerous substances such as chlorides, alkalies??No expansive ettringite formation of sulphate3rd Compatibility: Electro-chemical??Higher resistance to corrosion current??Must have conductivity and should not isolate substrate??Effective passivation of re-bars4th Compatibility: Dimensional stabilityCoefficient of Thermal Expansion: Different Coefficients of Thermal Expansion causes differential movement and hence shall be avoided.Modules of Elasticity: Under compression materials of different module will cause stress at the interface and hence shall be avoided.Drying shrinkage: Drying shrinkage of fresh mortar causes stresses at interface; hence needs to be controlled to minimum.(Extract from the paper presented by the author at the Construction Chemicals International Conference 2012 held in Mumbai)(Extract from the paper presented by the author at the Construction Chemicals International Conference 2012 held in Mumbai)
Delhi to hold FCC’s India Roads Conference on 12th Oct
To be hosted at Hotel Shangri-La Eros, New Delhi, the conference will witness more than 25 experts, policymakers, and industry leaders discussing innovative technologies, sustainable practices, and funding opportunities that promise to revolutionise the road construction landscape in India.
FIRST Construction Council (FCC) – an infrastructure think tank – will be hosting the 13th India Roads Conference (IRC) on October 12, 2023 at Hotel Shangri-La Eros, New Delhi, to explore new opportunities in the road construction business. To be hosted as a part of India Construction Festival 2023 (ICF 2023) along with Construction World Global Awards 2023 (CWGA 2023) and Equipment India Awards 2023 (EI Awards 2023), IRC 2023 will focus on transforming India’s road infrastructure by presenting an unique platform for networking, knowledge-sharing, and collaboration.
India’s road development sector is poised for unprecedented growth, housing one of the largest road networks in the world, spanning over 6.3 million km. The National Infrastructure Pipeline (NIP) forecasts a substantial investment of Rs 111 trillion in infrastructure projects during fiscals 2020-25, with a a significant portion allocated to the road sector. Against this backdrop, the 13th India Roads Conference intends to discover the abundant market opportunities, the latest trends, and how the industry can capitalise on this thriving sector.
Renowned experts, policymakers, and industry leaders will converge to discuss innovative technologies, sustainable practices, and funding opportunities that promise to revolutionise the road construction landscape in India. Some of the confirmed speakers for IRC 2023 are Lt. General Harpal Singh, Former Engineer-In-Chief, Indian Army; Dr Manoranjan Parida, Director, CSIR-CRRI; Ajay Kumar Mishra, President, Dilip Buildcon; RK Pandey, Former Member Projects, NHAI & Former ADG, MoRTH; SK Nirmal, Secretary General, India Roads Congress; Premjit Singh, CEO – Transportation, Welspun Enterprises; TR Rao, Director (Infra), PNC Infratech; Hardik Agrawal, Director at Dineshchandra R Agrawal Infracon Pvt Ltd, Thumu Karthik, CEO, LivSYT (DevIndia Technologies); Pawan Kant, CEO, LTIDPL IndVIT Services Ltd (IM to IndInfraVIT Trust); and Palash Srivastava, CEO, IIFCL Projects among others.
The roadmap of the future
India currently has one of the largest road networks in the world, spanning over 6.3 million km. Of this, around 2 per cent are National Highways, 3 per cent are State Highways and the rest are part of the district and rural road network. Over 64.5 per cent of all goods and 90 per cent of passenger traffic move by road.
India has seen significant growth in its road network over the last five years, as the government has given priority to this sector. For the financial year 2022-23, the Central budget allocated more than Rs 2.70 trillion to the Ministry of Road Transport and Highways (MoRTH). The importance attached to the sector is also evinced by the fact that it accounts for approximately 18 per cent of the National Infrastructure Pipeline (NIP). Various state governments are also developing critical road corridors as a catalyst of economic development. Lately the focus has been on road safety, green initiatives, digital transformation and augmentation of funding sources.
Explaining the significance of IRC 2023, Pratap Padode, President, FIRST Construction Council, said, “India, not China, has the second-largest road network in the world after the US, spanning about 63.32 lakh km. NHAI awarded total projects of 6,003 km with a value of Rs 1.26 trillion during FY23. A provisional target of constructing about 13,800 km has been set for 2023-24. This presents excellent opportunity for all the stakeholders in the sector. India Roads Conference 2023 will explore ways on how to build a robust, safe road network by using latest technologies while meeting environment norms.”
In line with the market trends, experts during the India Roads Conference 2023 will deliberate on following relevant topics:
- Shaping regulations for safe and sustainable roads
- Revolutionising road construction with technology
- Accelerating road infrastructure with better financing opportunities
- Safer roads: Innovative designs for enhanced safety
Attendees can gain valuable insights from dynamic panel discussions, insightful keynotes, and cutting-edge innovation showcases. Thus, by participating in India Roads Conference 2023, delegates can stay ahead of industry trends, forge valuable partnerships, and contribute to building safer, greener, and more efficient road networks.
IRC 2023 is supported by Tiki Tar and Shell India (Silver Partner), Tata Hitachi (Equipment Partner), PNC Infratech Ltd (Associate Partner), and LivSYT (Technology Partner).
About India Construction Festival 2023
Organised by the FIRST Construction Council in collaboration with Construction World and Equipment India magazines, the 9th India Construction Festival (ICF) stands as a cornerstone in the construction and infrastructure industry. India Construction Festival serves as the single largest platform for celebrating India’s remarkable infrastructure journey, bringing together all stakeholders in the industry under one roof. This comprehensive approach fosters collaboration, facilitates knowledge sharing, and creates networking opportunities that are pivotal for the growth and development of India’s infrastructure sector. ICF 2023 will comprise three major events: 13th India Roads Conference, 11th Equipment India Awards and 21st Construction World Global Awards.
About FIRST Construction Council:
FIRST Construction Council (FCC), an infrastructure think tank established in 2003, focuses on providing the latest updates on the construction industry in India, and is dedicated to promoting its causes and needs. FCC provides a platform to promote the adoption of best practices and be the torchbearer for all policy initiatives that are needed to enhance the importance and welfare of the construction industry and the industry’s unified voice. FCC also hosts conferences/events like India Construction Festival, Metro Rail Conference, Infrastructure Today Conclave 2023, etc.
Responsible Energy Management
Adani Cement is playing an instrumental role in responsible energy management in the Indian industrial sector. Here’s looking at their comprehensive efforts at sourcing alternative fuel and energy and optimising energy consumption in the cement manufacturing process.
Cement production stands as a prime example of an energy-intensive industry, where the role of energy is paramount in shaping both production costs and sustainability efforts.
One essential application of energy is in the transformation of raw materials, including limestone and additives, into clinker. This heat-intensive process is fundamental to cement production. Electricity plays a critical role in various phases of manufacturing. From grinding raw materials to achieving the final cement product, electricity consumption ranges between 56 to 73 kWh per metric tonne. Notably, the stages of raw material grinding, kiln operation and cement grinding contribute a significant 75-80 per cent to the overall electrical energy consumption.
Our dependence on energy is underscored by the consumption of fuels. For our 3 million tonnes per annum (MTPA) kilns, the daily consumption of fuels fluctuates between 1200 to 1600 tonnes. This sizeable amount of fuel is a prerequisite for sustaining our production operations. The electricity requirements are equally substantial. It surpasses 70 units of electricity per tonne of cement produced, encompassing the entire manufacturing cycle.
However, we are committed to enhancing our energy efficiency. Our efforts include ongoing initiatives to optimise existing installations and systems. Notable investments have been directed toward activities like cooler replacement, burner upgrades, and the incorporation of advanced thin liners in the cement mill. Several of these initiatives have already been implemented, underscoring our dedication to improved energy management.
Diverse Energy Sources
Our organisation employs a diverse array of energy sources to meet its manufacturing requirements, aligning with our commitment to sustainability and responsible energy management. At the heart of our production process, primary heat comes from fossil fuels, which are pivotal in the clinkering stage of cement manufacturing. We are progressively integrating alternative fuels, and we have set a robust roadmap to escalate this figure from present 7 per cent to 25 per cent. In terms of electrical energy, we draw power from both our captive/thermal power plant and the state grid to ensure a reliable supply.
Our emphasis on green energy is a cornerstone of our energy strategy. Solar energy plays a significant role as we harness its power through solar panels to contribute substantially to our electricity requirements. Additionally, wind energy further enriches our energy mix, tapping into wind turbines’ potential. Leveraging waste heat recovery systems (WHRS), we are innovatively converting waste heat from our processes into usable
energy, thereby reducing waste and optimising energy utilisation.
Sourcing Energy Sustainably
Our energy sourcing strategy is a comprehensive blend of primary and secondary sources, underscoring our dedication to both sustainability and efficiency. In the pivotal clinkering phase of cement production, our primary heat source encompasses a mixture of fossil and alternative fuels.
We engage in co-processing alternative fuels in our cement kilns. This includes a diverse spectrum of waste materials, like hazardous and non-hazardous waste from industrial processes, segregated municipal waste sourced from both fresh and legacy sites, as well as biomass like rice husk, soya husk and tuar husk. This innovative stride not only optimises energy use but also significantly contributes to conservation of natural resources and reduction of CO2 emissions.
Currently, around 7 per cent of our total heat requirement is met through alternative fuels, and our roadmap outlines a determined path to elevate this ratio to 25 per cent, aligning seamlessly with our mission to curtail environmental impact and foster sustainable practices. Our energy strategy embraces the robust use of green energy, comprising of solar, wind and WHRS. We are steadfastly working towards elevating both solar and WHRS contributions to at least 40 per cent of our total electricity demand.
All these initiatives serve as a testament to our unwavering commitment to responsible energy management and the stewardship of our environment.
Impact on Cost
The introduction of greener sources of electricity has had a negligible impact on our operations, whereas the influence is more nuanced in the context of our primary energy source, specifically heat generation. For instance, incorporating even a minor proportion of 1 per cent alternative fuel in clinker manufacturing could marginally increase thermal energy by approximately 1-1.5 kcal per kg clinker. It is important to note that this effect might not hold true for alternative fuels like dry biomass due to their distinct characteristics. However, our kiln system is equipped with inherent capabilities designed to mitigate such impacts, ensuring a balanced approach.
Considering the inherent volatility of fuel prices, the increased integration of green energy into our processes yields a significant advantage in terms of reducing the overall cost of cement production. By relying more on these sustainable sources, we can potentially mitigate the financial fluctuations associated with traditional fuel sources, leading to more stable and predictable production costs.
Optimising the Use of Energy
Automation and technology play an instrumental role in optimising energy utilisation within cement plants. These advancements contribute to enhanced productivity and heightened system reliability, creating a stable manufacturing environment. The harmonious synergy between automation and technology facilitates the most efficient allocation of energy resources, minimising wastage and enhancing overall energy efficiency. In line with this, we have implemented High-Level Control (HLC) systems for each kiln and cement mill circuit. These technologies not only streamline operations but also empower us to respond proactively to energy consumption patterns, driving us closer to our efficiency and sustainability goals.
Hurdles along the Way
The availability of fuels, particularly coal and petcoke, presents a significant challenge due to factors such as supply constraints and the volatility of their prices. This unpredictability in fuel availability and costs can impact the stability of our operations and cost structures. Additionally, the limited quantity of linkage coal further exacerbates this challenge, necessitating careful resource management and exploring alternative options.
Another notable challenge arises from the non-uniform regulatory procedures governing the utilisation of renewable power sources, namely solar and wind energy. The intricacies of these regulations vary geographically. This disparity introduces complexities in adopting renewable energy solutions consistently across regions, potentially impeding a streamlined transition to cleaner energy sources. Overcoming these regulatory hurdles demands strategic coordination and harmonisation of policies to ensure a more cohesive and efficient integration of renewable energy into our operations.
Compliance and Regulations
Effective energy management is a fundamental aspect of our operations, supported by well-established systems and dedicated professionals. Certified energy managers are stationed at each of our locations, underscoring our commitment to optimal energy utilisation and sustainability. Regular energy audits are a crucial part of our practices, with each site undergoing thorough assessments. The insights derived from
these audits inform actionable plans that are diligently tracked and implemented to enhance energy efficiency.
Furthermore, our commitment to responsible energy management is evident through our collaboration with the Bureau of Energy Efficiency (BEE). We actively share data on both electrical and thermal energy consumption with the BEE, aligning with the regulations and objectives of the Perform Achieve and Trade (PAT) programme. This proactive approach reinforces our dedication to not only internal efficiency but also broader national energy goals.
Adhering to the ‘golden rule’ of energy efficiency improvement, we place stringent monitoring and controls in place. This ensures that our energy management strategies remain dynamic and responsive, adapting to changes and consistently
driving efficiency enhancements. Our comprehensive approach to energy management is a testament to our commitment to sustainable practices, cost optimisation and environmental responsibility.
We employ an internal digital dashboard to meticulously track daily energy consumption encompassing both heat and electricity. However, the benchmarking of thermal and electrical
energy utilisation occurs monthly, both within our organisation and within the broader external context. This practice culminates in the acknowledgment of exceptional accomplishments by the most improved plant team through internal commendations and accolades.
Furthermore, our commitment to optimal energy utilisation is evidenced by annual external energy audits. These audits serve as a comprehensive evaluation of our energy practices, ensuring alignment with stringent standards. The resulting action plan, aimed at continuous enhancement, undergoes a rigorous assessment every three months. This iterative approach underscores our unwavering dedication to refining energy efficiency and reinforcing our sustainable commitments.
In the context of the cement industry, driving advancements in energy consumption is imperative. Regarding heat, it is essential to harness technological progress to curtail energy usage. Shifting the focus to electricity consumption, the installation of green energy sources like solar, wind and WRHS stand out as a promising approach.
Further, by enhancing overall efficiency of individual components, striving to minimise the impact of fluctuations in process parameters collectively hold the potential to revolutionise
energy consumption within the cement industry, driving it towards a more sustainable and
(Communication by the management of the company)
Concrete is the cornerstone of modern construction as it offers both utility and creativity. In the evolving landscape of urbanisation and infrastructure, precast concrete is playing an increasingly important role. From awe-inspiring skyscrapers to intricate facades and artistic installations, the potential of concrete and precast concrete knows no bounds. In this feature, ICR explores how the future of construction is shaping up.
Precast concrete shapes are custom-made concrete components that are produced in a controlled factory environment and then transported to the construction site for installation. These specialised concrete shapes are designed to meet specific dimensions and project requirements, offering several advantages such as enhanced quality control, reduced construction time and improved durability.
In the Indian cement and construction industry, precast concrete shapes play a vital role in expediting construction processes and ensuring quality outcomes. Various types of precast concrete shapes are widely employed to meet the diverse needs of construction projects in the country.
These include precast concrete panels, which are used extensively for building facades and walls, offering both durability and aesthetic appeal. Precast beams and columns are commonly used in structural elements, providing robust support and speeding up construction timelines.
Speaking about quality control, Rais Khan, CEO, Dynamic Precast, said, “We have a Quality Manual Plan in our system. Presently, a testing laboratory is active in our manufacturing premise. Regular tests for raw materials and concrete and quality checks are done here using tools, equipment and calibrated testing machines.”
“Quality checks in our factory starts from system update, raw materials, measurements and weighing process, compaction and ultimately in finished goods,” he added.
Additionally, precast modular units, such as interlocking blocks and paving stones, are utilised for landscaping, pavements and retaining walls, offering convenience in installation and durability. In the Indian context, precast concrete shapes are particularly valuable for addressing the growing demand for rapid and cost-effective construction solutions while maintaining high-quality standards. They also contribute to the versatility and sustainability of construction practices in a rapidly developing nation like India.
Narayan Saboo, Chairman, Bigbloc Construction, said, “AAC blocks are eco-friendly and sustainable, these are green building materials, light weight, and less transport cost. This material warms the room during the winter and cools it during the summer, reducing air-conditioning system usage by at least 25 per cent.”
“Non-toxic and pest repellent, they prevent soil erosion and consume less water. When red bricks are used, it results in an upper layer of soil erosion, which makes the land barren or infertile in the long run,” he added.
Speaking about the challenges faced by precast manufacturers, Vijay Shah, Managing Partner, India Precast, “A major challenge in the precast industry is the requirement of high volumes, repeatedly. The initial investment for the same is high. It becomes more suitable for the B and C types of city transports and handling at sites.”
He further elaborated, “One of the most significant challenges in precast detailing is the design and engineering complexities of creating precast components. Precast components must be designed and engineered to meet specific load and structural requirements, which can be complicated and time-consuming. Additionally, precast elements must be prepared to fit together seamlessly during installation, which requires precise measurements and accurate detailing.”
GLOBAL PRECAST PERSPECTIVE
According to a research report by Market and Market, the global precast concrete market size is projected to grow from US$144.6 billion in 2022 to US$198.9 billion by 2027, at a CAGR of 6.6 per cent from 2022 to 2027. The precast concrete market is expected to witness significant growth in the future as concrete is a natural building material which is 100 per cent recyclable and in combination with steel, it is a safe, sustainable and earthquake-resistant material with little wear and tear.
Most of the precast concrete market worldwide in 2022 was being used for commercial buildings. According to Extrapolate’s global precast concrete market research report, that material was valued at US$42 billion in its use for housing construction, and at US$29 billion for industrial buildings.
The market size in the Asia Pacific region stood at US$46.43 billion in 2020. It is anticipated to be the fastest growing region during the forecast period. Rising investments by countries such as China, India, and Japan to develop infrastructure will increase the demand for the product. Additionally, the growing residential sector in these countries will increase demand for precast concrete due to its cost efficiency, thereby adding impetus to the market.
MANUFACTURING OF PRECAST
The manufacturing of precast concrete shapes involves several techniques and processes to ensure precise dimensions, structural integrity and durability. The specific techniques used can vary depending on the type of precast product being produced, but some common methods include:
Formwork: Formwork is used to create moulds into which concrete is poured and allowed to set. These moulds can be made of various materials, including steel, wood or reusable plastic. The choice of formwork depends on factors such as the complexity of the shape and the number of repetitions required.
Reinforcement: Many precast concrete products, especially structural elements like beams, columns, and slabs, incorporate steel reinforcement (rebar) to enhance their strength and load-bearing capacity. Proper placement of rebar within the formwork is critical.
Concrete mixing: Precise control over the concrete mix is essential to ensure consistency and strength. The concrete mix design may vary depending on the specific requirements of the precast product. Advanced techniques like self-consolidating concrete (SCC) are sometimes used to eliminate the need for vibration during casting.
Casting and pouring: Once the formwork is prepared and reinforcement is in place, the concrete is poured into the molds. Special care is taken to eliminate air voids and ensure uniform distribution of concrete within the formwork.
Curing: Proper curing is crucial to achieving the desired strength and durability of precast concrete. Various curing methods are employed, including steam curing, water curing, and the use of curing compounds. Curing time and temperature are carefully controlled.
Demoulding: After the concrete has sufficiently cured, the precast shape is removed from the mould. This step requires care to avoid damaging the newly cast concrete product.
Surface finishing: Depending on the product’s intended use and appearance, additional finishing techniques may be applied. These can include sandblasting, acid etching or the application of coatings or paints.
Quality control and testing: Stringent quality control measures are implemented throughout the manufacturing process. This includes regular testing of the concrete mix, inspection of formwork and quality checks on the finished precast shapes to ensure they meet design specifications and structural standards.
Transportation and installation: Precast shapes are transported to the construction site and installed according to project requirements. Care is taken to ensure safe handling and transportation to prevent damage.
Joining and sealing: In cases where multiple precast elements need to be assembled on-site, techniques like welding, grouting, or adhesive bonding may be used to join them together securely. Proper seals are applied to prevent water infiltration and ensure structural integrity.
Post-installation finishing: Some precast elements, especially architectural features, may undergo additional finishing or detailing after installation to achieve the desired aesthetic appearance.
These techniques, when executed with precision and attention to detail, result in high-quality precast concrete shapes that offer numerous advantages in construction, including time savings, consistency, and structural reliability. Additionally, advancements in technology and automation have further improved the efficiency and quality of precast concrete manufacturing processes.
COMPOSITION AND QUALITY OF PRECAST SHAPES
The composition of materials employed in the creation of precast shapes is a pivotal factor, tailored to meet specific construction needs and applications. Fundamental to this composition is Portland cement, serving as the binding agent that brings the components together. Aggregates, encompassing both fine materials like sand and coarser substances like crushed stone or gravel, provide bulk and strength to the concrete mixture. The precise selection of aggregates can influence the texture and overall properties of the precast product. Water, meanwhile, plays a crucial role in the hydration process of cement, facilitating the concrete’s setting. Its quality, cleanliness and chemical characteristics can significantly impact the final product’s durability and strength.
Chemical admixtures, including plasticisers, accelerators, retarders, air-entraining agents and superplasticisers, introduce versatility to concrete properties, enhancing workability, curing speed, and resistance to external factors like freeze-thaw cycles. For structural integrity, precast elements like beams and columns often incorporate steel reinforcement, in the form of rebar or mesh, to bolster tensile strength. For aesthetic considerations, pigments or colorants can be integrated into the mix, allowing for the achievement of specific colours or decorative effects in architectural precast elements. Additionally, specialised applications may necessitate the incorporation of fibres or chemical adhesives and sealants to enhance strength, control cracking or bond joints effectively. Form release agents are used to prevent adherence to moulds during curing, ensuring easy removal of the precast shape, while for specialised environments, custom concrete mixes and additives are employed to tailor the product’s properties to withstand specific challenges, such as high temperatures, acid exposure, or aggressive chemicals. Precise mix designs are meticulously crafted by engineers and concrete specialists to align with project requirements, assuring the quality, strength and durability of the resulting precast shapes.
Precast concrete has cement as the key raw material. The kind of cement used to make the concrete is what defines its properties and quality. Cement should comply with the requirements of IS 456;2000, for gaining satisfactory performance in a structure. The Ordinary Portland Cements (OPC) 43 grade (IS:8112) and 53 (IS:12269) are normally used in precast concrete construction for general purpose. Portland Pozzolana Cement (IS 1481) and Portland Slag Cement (IS 455) are preferred in making precast concrete for structures in polluted environments. High silica cement is advised to be avoided as it suffers reversion and loses a large portion of its strength in warm and humid conditions.
Supplementary cementitious materials (SCM) like fly ash, ground granulated blast- furnace slag, metakaolin and silica fume enhance the results of ordinary portland cement (OPC) hydration reactions in concrete and are either incorporated into concrete mixes as a partial replacement for portland cement or blended into the cement during manufacturing. They should comply with the requirements of the appropriate parts of IS;3812 for fly ash, IS;12089 for GGBS and IS;15388 for silica fumes. The benefits of supplementary cementitious materials include reduced cost, improved workability, lower heat of hydration, improved durability and chemical resistance.
TYPES OF PRECAST
In the Indian construction industry, a wide variety of precast concrete products are manufactured to meet the demands of diverse projects. These precast elements include panels, beams, and columns, which serve as essential structural components, providing both strength and speed in construction.
Precast slabs are commonly used for flooring and roofing applications, offering efficient solutions for horizontal surfaces. Precast staircases and boundary walls are also widely produced, ensuring durability and quick installation. Furthermore, precast drainage elements, such as manholes and stormwater drains, help manage water and sewage systems effectively.
Interlocking pavers, blocks, and decorative elements enhance landscaping and pavement options, while precast septic tanks cater to sewage treatment needs. Additionally, precast boundary markers, kerbstones, retaining walls and modular housing units address various infrastructure and housing requirements. These precast solutions not only save time but also contribute to sustainable construction practices in India’s rapidly developing urban and rural areas.
Precast concrete shapes play a multifaceted role in the construction industry, serving a diverse array of purposes. These shapes are deployed in various applications, including building facades and cladding, where precast panels and architectural elements not only enhance aesthetics but also provide weather-resistant exteriors. Precast concrete beams, columns and slabs serve as robust structural components, expediting construction and delivering dependable support for commercial buildings, bridges, and parking structures. Moreover, precast slabs find their niche in flooring and roofing applications, offering superior load-bearing capabilities and thermal insulation.
Aayush Patel, Director, Atul Projects India, explained, “The use of precast shapes for multi-story elevations provides precise and diverse solutions for a variety of design objectives. However, it comes with obstacles such as extensive design and technical needs, communication barriers among multiple teams, assuring quality control, managing complex scheduling and sequencing, and dealing with limited on-site space and transportation restrictions. Overcoming these issues is critical for fully utilising the benefits of recast detailing in multi-story projects.”
Architectural details like precast concrete staircases, balustrades, and handrails ensure both safety and visual appeal in access points within buildings and public spaces. Boundary walls constructed from precast concrete provide security and privacy while seamlessly blending with the surroundings. In infrastructure projects, precast concrete comes to the fore with elements such as manholes, stormwater drains, and culverts, adeptly managing water and sewage systems.
For landscaping and pavements, interlocking precast concrete pavers and blocks offer an easy-to-install, aesthetically pleasing solution for walkways, driveways, and outdoor spaces. Additionally, precast concrete septic tanks meet sanitation standards in residential and rural settings. Precast concrete’s versatility extends to decorative architectural features like pillars, statues, and ornamental facades, elevating the visual appeal of structures and public areas.
In civil engineering, precast concrete retaining walls stabilise slopes, prevent erosion and create terraced landscapes efficiently. Moreover, precast modular housing units are emerging as a rapid, cost-effective response to housing shortages, manufactured with embedded infrastructure systems for swift on-site assembly. These versatile precast concrete components are also widely used in infrastructure projects, encompassing utility vaults, sound barriers, bridge components and highway barriers. The myriad applications of precast concrete shapes contribute significantly to construction efficiency, quality and architectural diversity, making them an asset in the construction industry.
PRECAST AND SUSTAINABILITY
Precast concrete shapes are integral to promoting sustainability in the construction industry. These components contribute to resource efficiency by minimising material waste and often incorporating locally sourced or recycled content. Energy-efficient manufacturing processes and facilities reduce energy consumption during production, while the reduced need for on-site construction and transportation lowers greenhouse gas emissions. The durability of precast concrete structures translates to fewer replacements and repairs, reducing the environmental footprint over their lifecycle. Moreover, the precast industry supports local economies through job creation and fosters design flexibility, allowing for energy-efficient building designs.
The low-maintenance nature of precast products, coupled with their recyclability, further underscores their sustainability. Precast concrete shapes align with green building certification systems, such as LEED, and enhance site management by creating cleaner and more organised construction sites. All these factors make precast concrete a sustainable choice that contributes to environmentally responsible and efficient construction practices.
In the ever-evolving world of construction, precast concrete shapes have emerged as champions of sustainability and efficiency. These versatile components optimise resource usage, reduce energy consumption and boast remarkable durability, aligning seamlessly with the principles of green building and environmental responsibility.
By fostering resource efficiency, precast shapes minimise waste generation and make efficient use of locally sourced or recycled materials. The energy-efficient manufacturing processes employed in precast facilities help lower energy consumption, while the reduced reliance on on-site construction cuts down greenhouse gas emissions. This longevity, combined with the low maintenance requirements and recyclability of precast products, emphasises their sustainability.
As the construction industry continues to embrace environmentally conscious practices, the precast concrete sector is poised for growth, promising innovations that will further revolutionise sustainable building solutions. The future undoubtedly holds exciting prospects for an industry that is shaping the green, efficient and resilient construction landscape of tomorrow.