It is estimated that in India each million clay bricks consume about 200 tons of coal and emit around 270 tons of CO2; on the other hand, with fly ash bricks production in an energy-free route, there are no emissions.
Dr. N. Subramanian, Consulting Engineer,Gaithersburg, MD, USA


Dr. N. Subramanian, Consulting EngineerFly-Ash Bricks (source: Ref. 1)

The increase in greenhouse gases, of which CO2 is one of the major constituents, increases the global warming potential year after year, leading to increases in flooding, fires, hurricanes, and billions of dollars in annual damage. According to the National Oceanic and Atmospheric Administration, since the start of the Industrial Revolution in about 1750, CO2 atmospheric levels have risen steadily, causing the earth’s temperature to increase at an unusually rapid pace. Due mostly to the burning of fossil fuels, CO2 levels in our atmosphere have risen 69%, from about 280 parts per million (ppm) in 1750 to 416 ppm in April 2021(a 31% increase from the 1958 levels; 280-300 ppm may be considered as the ideal level of CO2 for human life). As a consequence, according to the National Aeronautics and Space Administration, the global average surface temperature rose from –0.07 to 0.98 degrees Celsius between 1900 and 2019—leading to 19 of the 20 warmest years on record, all of which occurred in the past couple of decades.

Although CO2 alone is singled out in many publications, there are other gases like methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (HFCs), that have a much greater effect on global warming than CO2, but their concentration in the atmosphere is less – collectively they are called greenhouse gases (For example, methane is 22 times more potent in global warming effect than CO2). It must be noted that CO2 and other gases, which exist naturally in the atmosphere, retain the Sun’s heat and create an atmosphere that sustains life on earth. The energy consumption in the USA has been broken down into five categories: electricity or power plants (consuming about 40% of the total each year), transportation (28%), industry (21%), residential (7%), and commercial (4%). Overall, CO2 emissions are roughly connected with energy consumption, meaning the largest emitter was the most obvious - electricity.

The current use of fossil fuels, which may be depleted in another 40-50 years, has resulted in the release of huge amounts of green-house gases, especially carbon dioxide (CO2), which is harmful to the environment. In 2015, the global energy-related CO2 emissions were at the level of 49 giga tons per year (Gt/yr), with over 80% coming from fossil fuel combustion. Cement and building material industry is one of the major contributors. Buildings contribute about 40% of global CO2 emission. The CO2 emission is about 90 million tons out of cement and 49 million tons out of clay bricks production in India.

It is estimated that in India each million clay bricks consume about 200 tons of coal (or any other fuel with equal quantity of thermal values) and emit around 270 tons of CO2. Fly ash bricks production in energy-free route saves the emissions totally, befitting the project to qualify under Clean Development Mechanism (CDM), as envisaged by Kyoto Protocol towards the welfare of Mother Earth. The various types of fly-ash bricks are discussed below:

Pulverized Fuel Ash Lime Bricks and Fal-G Bricks
These are made using fly ash in major quantity (conforming to IS 15648:2006), lime, and an accelerator acting as a catalyst. Pulverized fuel ash-lime bricks are generally manufactured by inter-grinding or blending various raw materials, which are then moulded into bricks and subjected to curing cycles at different temperatures and pressures. Crushed bottom fuel ash or sand may also be used in the composition as a coarser material to control water absorption in the final product. Pulverized fuel ash reacts with lime in the presence of moisture to form a calcium-silicate hydrate which acts as a binder. Thus, pulverized fuel ash-lime brick is a chemically bonded brick and hence does not require firing. The specifications for burned clay fly ash bricks are provided in IS 12894:2002. The minimum compressive strength, water absorption, and efflorescence requirements of this kind of brick are similar to that of burned clay fly ash bricks. These bricks are suitable for use in masonry construction just like common burned clay bricks. In addition to the advantages offered by burned clay fly ash bricks, these bricks have the following advantages.
  • As no burning of bricks is involved, saves energy and there is also no pollution. In addition to helping the disposal of fly ash (which is a waste product), it also conserves topsoil.
  • The bricks can be made locally, even at the job site.
  • These bricks have better mechanical properties and more durability.
  • They are about 10–20% cheaper than burned clay bricks.
The FaL-G (Fly ash-Lime-Gypsum) process was developed and patented by Dr Bhanumathidas and Mr. Kalidas and introduced in India during 1991(see www.fal-g.com). In this process, 60% fly ash, 30% sand, and 10% Portland cement are used. In the lime route, the composition is fly ash (62%), slaked lime (8%), anhydrite gypsum (5%), and stone dust/sand (25%). These ingredients are manually fed into a pan mixer, where required amount of water is added and intimately mixed. The mixture is then fed into brick making machines, and the manufactured bricks are dried and water cured for 14 days. The calcium aluminate is converted into calcium alumino-sulphate resulting in a product having high early strength. FaL-G bricks can be produced with compressive strength of 10–35 N/mm2, and water absorption of 8–15% (Bhanumathidas and Kalidas, 2003). It is notable that FaL-G bricks do not need any pressure and are cured at ambient temperature of 20–40oC. By avoiding both pressing and heating chambers, high economy is achieved and this resulted in the proliferation of 18,000 manufacturing units in India as of 2016.

Fly Ash Bricks
These are made using Class C or Class F fly ash and water. They are compressed at 28 MPa and cured for 24 h in a 66oC steam bath, then toughened with an air entrainment agent. Owing to the high concentration of calcium oxide in Class C fly ash, the brick is described as ‘self-cementing’. Use of fly ash to make the bricks results in the elimination of the whole processes of mining, transporting, mixing and grinding, and firing that are necessary in the case of the clay- and shale-based bricks. The manufacturing method saves energy, reduces pollution, and costs 20%less than traditional clay brick manufacturing.

A comparison of the properties of clay/red bricks with fly ash bricks is given in Table 1

Table 1 Comparison of Red/clay bricks with fly ash bricks
Properties

Clay/red BricksIS 1077:1992

Fal-G /fly ash bricksIS 12894:2002

Advantages of fly ash bricks

Colour Vary Uniform Good appearance
Density 15.70 -18.85 kN/m3 10 -18.85 kN/m3 Higher load bearing
Compressive strength > 5.5 MPa 10-30 MPa Higher load bearing
Water absorption 15-20% 15-20% Less dampness seen on walls
Dimensional stability Very low tolerance High tolerance Saving in mortar up to 25%
Wastage during transit Up to 10% Less than 2% savings in  cost up to 8%
Plastering Thickness may vary on both sides of the wall Thickness may be the same on both sides of the wall May result in savings in plaster  cost up to 15%
Environmental advantage Nil Absorbs CO2 from the atmosphere Eco-friendly
As the fly ash bricks may not be smooth like clay bricks, plastering on them is easy.
References
  • https://theconstructor.org/building/fly-ash-bricks/
  • Subramanian, N., Building Materials, Testing and Sustainability, Oxford University Press. New Delhi, 2019, 788 pp.
  • Subramanian, N. (2022), “Achieving Net-Zero CO2 Emissions in the Concrete Industry”, Civil Engineering & Construction Review (CE & CR), Vol. 35, No.4, Apr., pp. 32-41.
Innovative Approaches Driving Sustainable Concrete Solutions
This paper explores the evolving landscape of sustainable concrete construction, focusing on emerging trends, innovative technologies, and materials poised to reshape the industry. Highlighted areas include the potential of green concrete

Read more ...

GGBS: Partial Replacement Of Cement For Developing Low Carbon Concrete
Dr. L R Manjunatha, Vice President, and Ajay Mandhaniya, Concrete Technologist, JSW Cement Limited, present a Case Study on using GGBS as partial replacements of cement for developing Low Carbon Concretes (LCC) for a new Education University

Read more ...

Behaviour of Ternary Concrete with Flyash & GGBS
Evaluating the performance of concrete containing Supplementary Cementitious Materials (SCM) like FlyAsh and Ground Granulated Blast Furnace Slag (GGBS) that can be used in the production of long-lasting concrete composites.

Read more ...

Nanospan’s Spanocrete®: nano-admixture for concrete
Nanospan’s Spanocrete, a Greenpro-certified, award- winning, groundbreaking nano-admixture for concrete, actualizes the concept of “durability meets sustainability”. This product simplifies the production of durable concrete, making it cost-effective

Read more ...

The Underwater Concrete Market in India
India, with its vast coastline and ambitious infrastructural projects, has emerged as a hotspot for the underwater concrete market. This specialized sector plays a crucial role in the construction of marine structures like bridges, ports

Read more ...

The Path to Enhanced Durability & Resilience of Concrete Structures
This article highlights a comprehensive exploration of the strategies, innovations, and practices for achieving concrete structures that not only withstand the test of time but also thrive in the face of adversity.

Read more ...

Self-Curing Concrete for the Indian Construction Industry
The desired performance of concrete in the long run depends on the extent and effectiveness of curing [1 & 2]. In the Indian construction sector, curing concrete at an early age is a problematic issue because of lack of awareness or other

Read more ...

BigBloc Construction an emerging leader in AAC Block
Incorporated in 2015, BigBloc Construction Ltd is one of the largest and only listed company in the AAC Block space with an installed capacity of 8.25 lakh cbm per annum. The company’s manufacturing plants are located in Umargaon

Read more ...

Decarbonizing Cement Industry: Sustainable & Energy-Efficient Measures
Dr. L R Manjunatha (VP), Manoj Rustagi (Chief Sustainability & Innovation Officer), Gayatri Joshi (ASM), and Monika Shrivastava (Head of Sustainability) at JSW Cement Limited, discuss new approaches for Decarbonizing the Cement

Read more ...

Concrete Rheology: Technology to Describe Flow Properties of Concrete
Concrete is a heterogeneous composite complex material, and its hardened property is influenced by its fresh property. Concrete today has transformed into an advanced type with new and innovative ingredients added - either singly or in

Read more ...

Amazecrete ICRETE: Making Concrete Economical & Durable
ICRETE offers many benefits apart from reducing cement content and giving high grades saving to ready-mix concrete companies; it helps reduce shrinkage and permeability in concrete slabs, increases the durability of concrete, and also works

Read more ...

UltraTech Cement & Coolbrook’s RotoDynamic HeaterTM Technology
UltraTech Cement Limited, India’s largest cement and ready-mix concrete (RMC) company, and Coolbrook, a transformational technology and engineering company, will jointly develop a project to implement Coolbrook’s RotoDynamic HeaterTM (RDH)

Read more ...

Plastic Shrinkage and Cracks in Concrete
Plastic shrinkage cracking occurs when fresh concrete is subjected to a very rapid loss of moisture. It is caused by a combination of factors such as air and concrete temperature, relative humidity, and wind velocity at the surface of concrete. These can cause

Read more ...

Dam Rehabilitation With Cutoff Wall for Seepage Control
This paper covers the research work carried out on cement plastering process for internal and external building wall by using spray plastering machine. Objective of study is to experiment and compare the plastering activity by conventional way and

Read more ...

Construction Defects Investigation & Remedies
In recent years, the speed of construction has increased very fast; buildings which used to take 3-5 years are now getting completed in 1-2 years. There is a race to complete projects faster, but due to this speedy construction, the quality of construction is often

Read more ...

Challenges in usage of Hydrogen in Cement Industry
With its zero-emission characteristics, hydrogen has become a promising decarbonization path for the cement industry. While there are several issues that need to be resolved in the use of hydrogen, there are also many advantages, so much so that the growth

Read more ...

Enhancing Corrosion Resistance of Steel Bars in Reinforced Concrete Structures
Reinforced concrete is a composite material which is made using concrete and steel bars. Concrete takes the compressive forces and steel bar takes tensile forces. Concrete around the steel bar protects it from corrosion by providing an alkaline environment

Read more ...

Moving toward workability retention to rheology retention with low viscosity concrete technology
Amol Patil, Sr. Specialist - General Manager (Admixture and Specialty Products), Master Builders Solutions (India), and Nilotpol KAR, Managing Director, Master Builders Solutions (South Asia), present a paper on the concept of low viscosity concrete in

Read more ...

Cement industry innovating eco-friendly packaging
Cement companies are constantly innovating to meet global sustainability standards and improve logistics, shelf life, and utility of cement, while reducing wastage. Thei aim is to reduce their environmental impact without compromising their product

Read more ...

IIT Madras uses Solar Thermal Energy to Recycle Waste concrete
Researchers at the Indian Institute of Technology Madras have developed a treatment process using solar thermal energy to recycle construction and demolition debris. Waste concrete from demolition was heated using solar radiation to produce recycled concrete

Read more ...