Technology

Fly ash | From Trash to Cash

Published

10 years ago

July 4, 2016

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Many civil engineers are attracted to fly ash today, mostly due to commercial considerations. However, if it is looked upon as a performance improver, fly ash can solve many problems.

Fly ash is a by-product obtained while generating electrical power using coal as a fuel. For the last few decades, the demand for electricity has been increasing continually due to growing population and new industries being launched across the world.

During the year 2014-15; the total generation of fly ash has been 184.14 Million Tonnes out of which 102.54 Million tonnes is used, i.e.about 55.69 per cent of generated fly ash. (Information sourced from Central Electricity Authority, Govt. of India) But since fly ash contains a lot of heavy metals, its production causes problems to the environment. Because of this reason, it has become necessary to invent some newer aspects for utilising fly ash, rather than stick to the conventional ways. Fly ash disposal is a serious environmental concern due to its hazardous properties, impact on agriculture and long-term risks to both ecosystems and human beings. Fly ash is a coal-combustion product, composed of the fine particles that are driven out of the boiler with the flue gases. Ash that falls in the bottom of the boiler is called bottom ash. In modern coal-fired power plants, fly ash is generally captured by electrostatic precipitators or other particle filtration equipment before the flue gases reach the chimneys. Together with bottom ash removed from the bottom of the boiler, it is known as coal ash.

Depending upon the source and makeup of the coal being burned, the chemical composition of fly ash will vary considerably; but in general, all fly ash includes substantial amounts of silicon dioxide (SiO2) – both amorphous and crystalline, aluminium oxide (Al2O3) and calcium oxide (CaO), the main mineral compounds in coal-bearing rock strata.

Past Processes
In the past, fly ash was generally released into the atmosphere, but air pollution control standards now require that it be captured prior to release by fitting pollution control equipment. In many countries, fly ash is either stored at coal power plants or placed in landfills. A substantial part of fly ash goes to the cement industry as a cement substituting material, to produce hydraulic cement or hydraulic plaster and a replacement or partial replacement for Portland cement in concrete production. Pozzolans ensure the setting of concrete and plaster and provide concrete with more protection from wet conditions and chemical attack.

Cenospheres are the most important ingredient of fly ash. These are unique free-flowing powders composed of hard-shelled, hollow, minute spheres. Cenospheres are made up of silica, iron and alumina. These have a size range from 1 to 500 microns with an average compressive strength of 3000+ psi. Colours range from white to dark grey.

Chemical composition
Fly ash particles are generally spherical in shape and range in size from 0.5?m to 300?m. The major consequence of the rapid cooling is that few minerals have time to crystallise, and that mainly amorphous, quenched glass remains. Nevertheless, some refractory phases in the pulverised coal do not melt entirely, and remain crystalline. In consequence, fly ash is a heterogeneous material. SiO2, Al2O3, Fe2O3 and occasionally CaO are the main chemical components present in fly ash. The mineralogy of fly ash is very diverse. The main phases encountered are a glass phase, together with quartz, mullite and the iron oxides hematite, magnetite and/or maghemite. Other phases often identified are cristobalite, anhydrite, free lime, periclase, calcite, sylvite, halite, portlandite, rutile and anatase. The Ca-bearing minerals anorthite, gehlenite, akermanite and various calcium silicates and calcium aluminates identical to those found in Portland cement can be identified in Ca-rich fly ash. The mercury content can reach 1 ppm, but is generally included in the range 0.01 – 1 ppm for bituminous coal. The concentrations of other trace elements vary as well according to the kind of coal combusted to form it.

The fineness or the particle size of fly ash is a very critical property. The commercial value of fly ash depends on the particles and percentage of unburned carbon. A total of 75 per cent of the ash must have a fineness of 45 -?m or less, and have carbon content, measured by the loss on ignition (LOI), of less than 4 per cent. The quality of fly ash also depends on the type of technology used in the boiler and the quality of coal. Indian coal generally has high percentage of ash compared to either Australian or South African coal.

The bottom ash, which is still a neglected portion of the same waste, can also find its way into concrete, replacing the stone aggregates. But a lot needs to be done on this material in our country.

Benificiation, the value addition
By using air separators, the fly ash can be divided into different grades depending on the particle size. The best example is that of Dirk India, a company which is only into selling of fly ash, and thriving. Dirk sources its fly ash from state electricity generating companies, and by using air classifiers, produces four different varieties of fly ash which have a good demand in the market.

Challenges in handling fly ash
In a typical fly ash handling system, the material that is generated as a result of combustion is captured by an electrostatic precipitator (ESP) or a bag house before the flue gases reach the stack. These ESPs and bag houses generally have multiple pyramidal hoppers at the bottom, in which the ash is collected by gravity and is then transferred to a storage silo. These storage silos generally have provisions for a truck load-out to carry the fly ash for disposal or reuse. As a result of the frictional nature and fine particle size distribution, fly ash handling systems often experience problems if they are designed without following a prudent engineering approach.

Flow rate limitation
The permeability of fly ash is typically very low, due to its fine particle size distribution. As a result, when de-aerated, fly ash provides considerable resistance to the flow of air or other gases. During discharge from a silo or hopper outlet, air counter-flow through the fly ash bed provides an opposing force to gravity. This air ingress occurs as a result of the natural expansion of the ash bed within the hopper as it flows, or simply due to leakage from the conveying system below. As a result, fly ash hoppers and silos are limited in terms of the maximum discharge rates that they can provide by gravity alone.

Flooding or uncontrolled flow
As a fine powder, fly ash can behave like a fluid when sufficient air is present. Flooding can result, particularly when the handling rate is too high to allow sufficient time for the entrained air to escape. In this case, the fly ash may become fluidised and flush through the outlet unless the feeder can contain it. Flooding not only creates a challenge in metering the discharge, it can also lead to serious environmental, health and safety concerns.

Wear
The presence of a significant portion of silicon dioxide makes fly ash very abrasive and frictional. As a result of material sliding and impacting within the handling equipment, wall surfaces undergo tremendous wear.

Dust generation
Dusting can particularly occur at transfer points where the air entrained in the powder is suddenly expelled, carrying these finer particles with it. Dust generation also occurs when local air currents have sufficient velocity to pick up particles from the surface of a pile. Dust by itself is a nuisance and, more importantly, it can result in safety concerns including the health effects of operator exposure and the potential for explosions.

Other problems
Agglomerated lumps of fly ash and foreign materials can create flow problems, especially when handling fly ash with air slides or aerated bin bottoms. Therefore handling of fly ash always requires proper engineering inputs. The progress made so far has been reasonable, but a lot still needs to be done considering the potential of the material. Let us look at some of the possibilities.

Fly ash as cement replacement and high-volume fly ash concrete
Indian codes permit use of fly ash up to 35 per cent as cement replacement in cement manufacturing. However, in the case of concrete, the percentage will depend on the mix design recipe. If we see the practise abroad, up to 65 per cent of fly ash can be used in concrete.

Two researchers, Dr PK Mehta and Dr VM Malhotra, have made a significant contribution to the engineering community. Dr Mehta is well known for his work on high-volume fly ash concrete. Here is an extract from one of his papers called ?Cement & Concrete Mixtures for Sustainability?:

"For a variety of reasons, the concrete construction industry is not sustainable. First, it consumes huge quantities of virgin materials. Second, the principal binder in concrete is Portland cement, the production of which is a major contributor to greenhouse gas emissions that are implicated in global warming and climate change. Third, many concrete structures suffer from lack of durability which has an adverse effect on the resource productivity of the industry. Because the high-volume fly ash concrete system addresses all three sustainability issues, its adoption will enable the concrete construction industry to become more sustainable."

In this paper, a brief review is presented of the theory and construction practice with concrete mixtures containing more than 50 per cent fly ash by mass of the cementitious material. Dr Mehta is a champion of using more than 50 per cent fly ash by mass of the cementitious material. Mechanisms are discussed by which the incorporation of high volume of fly ash in concrete reduces the water demand, improves the workability, minimises cracking due to thermal and drying shrinkage, and enhances durability to reinforcement corrosion, sulfate attack, and alkali-silica expansion. For countries like China and India, this technology can play an important role in meeting the huge demand for infrastructure in a sustainable manner, says Dr Mehta.

High-performance concrete (HVFA)
As per Dr Mehta, the characteristics defining a HVFA concrete mixture are, minimum of 50 per cent of fly ash by mass of the cementitious materials must be maintained, low water content, generally less than 130 kg/m3 is mandatory and for cement content, generally no more than 200kg/m3 is desirable. For concrete mixtures with specified 28-day compressive strength of 30 MPa or higher, slumps more than 150 mm, and water-to-cementitious materials ratio of the order of 0.30, the use of high-range water-reducing admixtures (super-plasticizers) is mandatory. For concrete exposed to freezing and thawing environments, the use of an air-entraining admixture resulting in adequate air-void spacing factor is mandatory. For concrete mixtures with slumps less than 150 mm and 28-day compressive strength of less than 30 MPa, HVFA concrete mixtures with a water-to-cementitious materials ratio of the order of 0.40 may be used without super-plasticizers. Dr Mehta further concludes in his paper, that throughout the world, waste-disposal costs have escalated greatly. At the same time, the concrete construction industry has realised that coal fly ash is a relatively inexpensive and widely available by-product that can be used for partial cement replacement to achieve excellent workability in fresh concrete mixtures.

Consequently, in the modern construction practice, 15 to 20 per cent of fly ash by mass of the cementitious material is now commonly used in North America. Higher amounts of fly ash in the order of 25-30 per cent are recommended when there is a concern over thermal cracking, alkali-silica expansion or sulfate attack. Such high proportions of fly ash are not readily accepted by the construction industry due to a slower rate of strength development at an early age.

The high-volume fly ash concrete system overcomes the problems of low early strength to a great extent through a drastic reduction in the water-cementitious materials ratio by using a combination of methods, such as taking advantage of the super-plasticizing effect of fly ash when used in a large volume, with the use of a chemical super-plasticizer, and a judicious aggregate grading.

Consequently, properly cured high-volume concrete products are very homogenous in microstructure, virtually crack-free, and highly durable. Because there is a direct link between durability and resource productivity, the increasing use of high-volume concrete will help to enhance the sustainability of the concrete industry.

In conclusion, high-volume fly ash concrete offers a holistic solution to the problem of meeting the increasing demands for concrete in the future in a sustainable manner and at a reduced or no additional cost. At the same time, it reduces the environmental impact of two industries that are vital to economic development – the cement industry and the coal-fired power industry. The technology of high-volume fly ash concrete is especially significant for countries like China and India, where, given the limited amount of financial and natural resources, the huge demand for concrete needed for infrastructure and housing can be easily met in a cost-effective and ecological manner.

Economy & Market

SEW-EURODRIVE India Opens Drive Technology Centre in Chennai

Published

4 hours ago

March 25, 2026

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The new facility strengthens SEW-EURODRIVE India’s manufacturing, assembly and service capabilities

SEW-EURODRIVE India has inaugurated a new Drive Technology Centre (DTC) in Chennai, marking a significant expansion of its manufacturing and service infrastructure in South India. The facility is positioned to enhance the company’s responsiveness and long-term support capabilities for customers across southern and eastern regions of the country.

Built across 12.27 acres, the facility includes a 21,350-square-metre assembly and service setup designed to support future industrial growth, evolving application requirements and capacity expansion. The centre reflects the company’s long-term strategy in India, combining global engineering practices with local manufacturing and service capabilities.

The new facility has been developed in line with green building standards and incorporates sustainable features such as natural daylight utilisation, solar power generation and rainwater harvesting systems. The company has also implemented energy-efficient construction and advanced climate control systems that help reduce shopfloor temperatures by up to 3°C, improving production stability, product quality and working conditions.

A key highlight of the centre is the 15,000-square-metre assembly shop, which features digitisation-ready assembly cells based on a single-piece flow manufacturing concept. The facility also houses SEW-EURODRIVE India’s first semi-automated painting booth, aimed at ensuring uniform surface finish and improving production throughput.

With the commissioning of the Chennai Drive Technology Centre, SEW-EURODRIVE India continues to strengthen its manufacturing footprint and reinforces its long-term commitment to supporting industrial growth and automation development in India.

Economy & Market

RAHSTA Roundtable Sets Agenda for Smarter, Safer Highways

Published

1 week ago

March 16, 2026

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Roundtable discussions focus on innovation for safer highways.

Held on 12 March 2026 at Courtyard by Marriott, Mumbai, alongside the Infrastructure Today Airport Conclave, the RAHSTA Roundtable brought together stakeholders from across the highways and infrastructure ecosystem to shape the agenda for the 16th RAHSTA 2026, scheduled for 8–9 July 2026 at the Jio Convention Centre, Mumbai. The session focused on key industry themes including road construction, technology, safety and long-term sustainability.

Opening the discussion, Pratap Padode, Founder, FIRST Construction Council, said the roundtable marked the beginning of a broader consultative process leading up to the July event. The aim, he noted, is to bring together industry stakeholders to refine the agenda for discussions on the future of roads, bridges, tunnels and allied infrastructure.

Padode noted that while central road project awards have slowed in recent years, states are increasingly driving the next phase of infrastructure growth. Maharashtra, with its long-term road development plans and agencies such as MSRDC and MSIDC, is expected to play a significant role in this expansion.

RAHSTA Expo 2026 as a specialised platform dedicated to road infrastructure, covering highways, tunnels, bridges and flyovers along with construction technologies, safety systems and maintenance solutions. He also highlighted the growing importance of rural connectivity and said the organisers are engaging with government bodies to highlight rural road development initiatives.

Tanveer Padode, CIO, ASAPP Info Group, presented insights from IMPACCT, the group’s infrastructure intelligence platform. He pointed to a strong project pipeline despite slower highway awards earlier in the year, noting that states such as Maharashtra, Odisha and Arunachal Pradesh are emerging as key drivers of new projects. The data also revealed that only a small group of contractors participates in large-value infrastructure bids.

Lt Gen Rajeev Chaudhary, former Director General, Border Roads Organisation and Chairman of the RAHSTA Expo Committee, emphasised the need for stronger collaboration across the ecosystem, including policymakers, contractors, technology providers and financiers. He also called for addressing systemic issues within the sector and encouraged greater participation of women in infrastructure leadership.

The discussion also explored the evolving economics of road development. Phani Prasad Mandalaparthy, Associate Director, CRISIL Intelligence, noted that the slowdown in project awards reflects a shift towards higher-value logistics corridors rather than simple road widening projects. However, private participation through BOT and TOT models remains limited.

From the contractors’ perspective, Sudhir Hoshing, Whole-Time Director, Ceigall, said companies are becoming more selective in bidding, favouring projects with clearer payment mechanisms and efficient processes. While NHAI continues to offer greater operational clarity, states such as Uttar Pradesh and Bihar were cited as relatively supportive environments for project execution.

Durability and sustainability also emerged as key themes. Himanshu Agarwal, COO – Road & Infrastructure, Zydex Group India, highlighted the need to prioritise lifecycle performance and resilient pavements, while participants discussed the potential of alternative materials such as plastic waste, steel slag and industrial by-products in road construction.

Dr LR Manjunatha, Vice President, JSW Cement, emphasised that India has abundant fly ash, slag and other industrial materials that can improve durability and sustainability if integrated into specifications and policy frameworks.

Technology and equipment challenges were also discussed. Dr Lakshmana Rao Mantri, Dy General Manager, Afcons Infrastructure, highlighted the shortage of tunnel boring machines (TBMs), which is delaying several underground infrastructure projects. Participants agreed that developing domestic TBM manufacturing capabilities will be critical for future infrastructure expansion.

The future of concrete pavements was another area of discussion. Dr V Ramachandra, President, Indian Concrete Institute, stressed that the debate should focus on lifecycle performance rather than material choice alone, noting that evolving design standards are improving the feasibility of concrete roads.

Prof Dharamveer Singh of IIT Bombay added that while India has made significant progress in infrastructure development, stronger capacity building and better execution practices are essential to ensure consistent road quality.

The discussion also touched upon technology adoption in the sector. Rushabh Mamania, Partner & CBO, Roadvision, highlighted the growing role of AI in road infrastructure, noting that AI-driven monitoring systems are already being deployed across large stretches of national highways.

Overall, the roundtable underscored that the future of highway infrastructure will depend not only on the pace of construction but also on durability, safety, technology integration and sustainable materials. The discussions offered valuable insights that will help shape the agenda for RAHSTA 2026 and guide future collaboration within the industry.

Economy & Market

CTS Roundtable Charts Tech-Led Roadmap for Construction

Published

1 week ago

March 16, 2026

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CTS Roundtable Maps Technology Roadmap for Construction

Ahead of the Construction Technology Show (Con Tech Show) 2026, industry leaders, technology innovators and academia came together in Mumbai to deliberate on how digitalisation, automation and industrialised construction can reshape the sector. The discussion made one thing clear: construction can no longer afford to treat technology as optional.

Held on 12 March 2026 at Courtyard by Marriott, Mumbai, alongside the Infrastructure Today Airport Conclave, the CTS Roundtable served as a precursor to the Construction Technology Show 2026, scheduled for 19–20 August 2026 at NESCO, Mumbai.

A platform to move from discussion to deployment

Opening the session, Pratap Padode, Founder and Editor-in-Chief, ASAPP Info Global Group, said construction technology has long remained close to his heart, especially given the sector’s traditionally slow pace of technology adoption. He noted that over the years, the Construction Technology Summit had steadily built interest, and the next step was now to expand it into a larger, more meaningful platform that could bring together technology providers, users, startups and innovators under one roof.

Padode said the vision for CTS is not limited to software alone. The platform aims to embrace all forms of technology that can improve construction efficiency, quality and execution—from digital tools and project management systems to lean construction, off-site fabrication and startup-led innovation. He also highlighted plans to deepen startup participation and create space for young companies to showcase emerging construction solutions.

Industry at a turning point

Moderating the roundtable, Naushad Panjwani, Chairman, Mandarus Partners, set the context by pointing out that the global construction industry, despite being a multi-trillion-dollar sector, continues to lag in productivity. He noted that while manufacturing has consistently improved efficiency, construction has remained slow to modernise.

Referring to both global and Indian trends, Panjwani underlined that the industry is now at a decisive moment. India, he said, is entering a major build cycle, and delivering the next phase of infrastructure and real estate growth through traditional methods alone is no longer viable. The goal of the roundtable, therefore, was not to debate technology in isolation, but to identify the most critical conversations that would bridge the gap between innovation and implementation.

His central message was clear: CTS 2026 must be shaped around themes that make CEOs, CIOs and CTOs feel they cannot afford to miss the event.

From BIM to AI, data to governance

A major theme that emerged through the discussion was the need for better data, better visibility and better decision-making. Dr Venkata Santosh Kumar of IIT Bombay echoed this, saying that the underlying data infrastructure itself needs attention. Construction projects, particularly remote ones, often face issues around connectivity, data collection and data use. Without this foundation, more advanced technologies cannot deliver their full value.

Chandra Vasireddy, CEO & Co-founder, Inncircles, expanded the discussion to governance, arguing that technology must help connect the many moving parts of a construction business. For him, the real value of digital transformation lies in creating better governance, clearer visibility and stronger business outcomes.

Tejas Vara of Inncircles stressed the importance of timely site data for leadership teams, especially in large and remote projects where decisions on materials, machinery and manpower often get delayed because information does not reach headquarters in time.

The role of AI also featured prominently. Rushabh Mamania, Partner and CBO, Roadvision said that while AI and machine learning are now common terms, vision intelligence and language intelligence have still not deeply penetrated the construction sector. He emphasised that startups in India are building relevant AI-led solutions and are already attracting international interest, showing that innovation need not be imported—it can be built locally and scaled globally.

Industrialised construction gains ground

The roundtable also placed strong emphasis on industrialised construction methods. Kalyan Vaidyanathan, CTO – Construction & R&D, Tvasta, called for greater focus on off-site fabrication and the broader industrialisation of construction. Bhargav Jog, General Manager, Dextra, highlighted precast technology and alternative sustainable materials as areas with immediate relevance.

Several participants agreed that modular, precast and pre-engineered approaches are no longer niche ideas. They are increasingly becoming practical responses to the sector’s challenges around labour shortage, timelines, quality control and predictability.

Anup Mathew, Sr VP & Business Head, Godrej, argued that the industry needs a fully integrated approach—from design and procurement to execution and asset management. Unless these are connected, technology adoption will remain fragmented and sub-optimal. He pointed to pre-engineered and modular systems as examples of how industrial thinking can compress timelines, improve quality and reduce dependence on difficult on-site conditions.

Adoption remains the biggest hurdle

While there was broad agreement on the promise of technology, the discussion repeatedly returned to one fundamental challenge: adoption.

Abhishek Kumar, COO, LivSYT, observed that the market is crowded with solutions, but many buyers still struggle to evaluate which technology suits which use case. According to him, the industry needs clearer frameworks to help users select, compare and adopt solutions, rather than expecting a single platform to solve every problem.

Dr Tenepalli JaiSai, Associate Professor, School of Construction(SoC), NICMAR University, noted that isolated technologies will not solve the productivity problem by themselves. What is required is an integrated Construction 4.0 approach, where digital, physical and cyber-physical systems work together rather than in silos.

That concern around silos was reinforced by Subodh Dixit, former Director, Shapoorji Pallonji, who said the issue is not just that technologies are disconnected, but that stakeholders are as well. Clients, consultants, contractors and partners often operate with different priorities. Unless these silos are broken, technology will struggle to percolate across the full project value chain.

Harleen Oberoi, Project Management, Tata Realty shared a practical perspective from the client side, saying that successful BIM implementation requires investment across the ecosystem, not just within one organisation. Trade partners, vendors and other stakeholders must also be trained and aligned if the technology is to deliver its intended results.

Beyond buzzwords

A notable takeaway from the session was that the industry is moving past the phase of treating technology as a buzzword. Participants repeatedly stressed that the real question is not whether technology should be used, but where it creates measurable value and how that value can be scaled.

The conversation also expanded beyond mainstream themes to include repairs and rehabilitation, construction and demolition waste, sustainability, circular economy, green sourcing, carbon measurement, design interoperability, generative design, robotics, and the role of horticulture and greener built environments.

Setting the agenda for CTS 2026

By the close of the session, the roundtable had surfaced a strong set of themes for the upcoming show: BIM and digital twins, AI and data platforms, industrialised construction, startup innovation, governance-led technology adoption, robotics, sustainable materials, and integrated project delivery.

More importantly, the session established CTS 2026 as more than an exhibition. It is shaping up to be a serious industry platform where users, technology providers, researchers and policymakers can collectively define the future of construction.

As Padode noted in his closing remarks, the conversation will continue through further consultations and possibly webinars in the run-up to the show. If the roundtable is any indication, CTS 2026 will aim not merely to showcase technology, but to push the industry towards meaningful adoption at scale.