Achieving Net-Zero CO₂ Emissions in the Concrete Industry

Dr. N. Subramanian
Ph.D., FNAE
Gaithersburg, Maryland, USA

Our planet earth is under peril due to severe climatic changes. Increase in population coupled with urbanization has resulted in unprecedented problems to our cities. Unless urgent measures are taken on war footing, these problems will result in catastrophic consequences. The ever increasing demand for energy, due to population and urban growth, has resulted in energy crisis all over the world. 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 tonnes per year (Gt/yr), with over 80% coming from fossil fuel combustion (In April 2021, CO₂ concentration in the atmosphere reached 416 ppm, a 31% increase from the 1958 levels; 280-300 ppm may be considered as the ideal level of CO₂ for human life). Although CO₂ alone is singled out in many publications, there are other gases like methane (CH4 ), nitrous oxide (N2 O), 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 as greenhouse gases (For example, methane is 22 times potent in global warming effect than CO₂ ). It has to 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 primary source of human-generated CO₂ emissions is fossil fuel power plants, which contribute to 35% of all CO₂ emissions. In the USA passenger vehicles and light trucks account for another 20%. The unmindful use of resources has also resulted in huge waste products and only a few reliable and safe methods have been developed to dispose or recycle them.[1] This situation has resulted in the landfills of many countries overflowing, leading to many pollution problems.

Fig.1: Historically Observed and Future (a) Global CO2 Emissions and (b) Temperature Change (Source: science2017. globalchange.gov/downloads/CSSR2017_FullReport.pdf)

Fig.1: Historically Observed and Future (a) Global CO2 Emissions and (b) Temperature Change (Source: science2017. globalchange.gov/downloads/CSSR2017_FullReport.pdf)

Due to the increasing and huge amounts of CO₂ emissions, the temperature of Earth has risen by 0.08°C per decade since 1880. The rate of warming over the past 40 years has more than doubled to 0.18°C per decade. In effect, global temperatures rose about 1.1°C from 1901 to 2020. As per the temperature data of the World Meteorological Organization, the years from 2015 to 2021 are on track to be the seven hottest years on record. The global oceans also act as CO₂ and heat sinks, increasing the surface temperature of oceans, thus endangering polar creatures and threatening coral reefs and fisheries. (www.climate.gov). Land areas have warmed faster than oceans, and the Arctic is warming faster than most other regions (www.climate.gov). Due to these climatic changes several other catastrophic changes are also predicted, which may include reduced snow cover and sea ice which may result in rise in sea level (several cities along the sea shore are at risk- as per current trajectory, sea level rise could exceed 2 m by 2100, which could displace some 630 million people worldwide), regional and seasonal temperature extremes and intensified heavy rainfall (causing drought and flooding), changed habitat for plants and animals (several plants and animals have already become extinct and some are even expanding). Thus, things which are valuable and depended upon by humans such as, water, energy, transportation, wildlife, agriculture, ecosystems, and human health, are all affected. People in many parts of the world are already experiencing such effects and are suffering.

The amount of warming our Earth will experience depends on the amount of carbon dioxide and other greenhouse gases emitted in the coming decades. At present, burning fossil fuels and clearing forests alone are responsible for adding 11 billion metric tons of CO₂ per year in the atmosphere. The amount of CO₂ in the atmosphere has risen by 25% since 1958, and by about 40% since the Industrial Revolution (Fig.1a). According to the 2017 U.S. Climate Science Special Report, if the current trend continues global temperature will be at least 2.78o C warmer than the 1901-1960 average and possibly as much as 5.66o C warmer, by the end of this century (Fig.1b).

Realizing this, our Indian Prime Minister Shri. Narendra Modi committed, in the UN Climate Conference held in Glasgow on Nov. 1, 2021, that India will become net-zero in carbon emissions by 2070. The challenge for India is to finance the transition to net-zero, which will require trillions of dollars of investment. Top-five greenhouse gas emitters and their net-zero target year is shown in Fig. 2.

Construction Industry and the Global Co₂ Emissions
Global share of buildings and construction related CO₂ emissions in 2018 are shown in Fig. 3. Construction industry accounted for 38% of total global energy-related CO₂ emissions.[2] Cement production alone accounts for as much as 7% of global CO₂ emissions. The initiatives to be taken in the concrete industry, in order to achieve net-zero CO₂ emission by 2050 are listed by the Global Cement and Concrete Association (GCCA) as[3]: (1) Efficient Design and Construction Practices, (2) Efficient Production of Concrete, (3) Replacement of OPC with Cementitious Materials, (4) Reduced Use of Clinker, (5) Carbon Capture, Utilization, and Storage (CCUS), (6) Decorbonisation of Electricity, and (7) Concrete as Carbon Sink. These different actions are described briefly.

Fig. 3: Global Share of Buildings and Construction Related CO2 Emissions in 2018 (Source: Energy Technology Perspectives, Buildings Model, www.iea.org/buildings)

Fig. 4: Emissions Caused by Material Production as a Share of Total Global Emissions[4]

Emissions from the production of materials increased from 5 giga ton (Gt) of CO₂ - equivalent in 1995 to 11.5 Gt in 2015, with their share of global emissions rising from 15 % to 23% (Fig. 4). Construction and manufactured goods each account for nearly 40% of the annual global Green- House Gas (GHG) emissions from global materials production.[4] Of those total emissions, building operations are responsible for 28% annually, while building materials and construction (typically referred to as embodied carbon) for an additional 11% annually (Fig. 3). As shown in Fig. 4, most of the material-related emissions stem from the production of bulk materials: iron and steel (41%), cement, lime and plaster (38 %), as well as plastics and rubber (13%).[4] Cement production alone accounts for about 7% of global CO₂ emissions.[3] Hence, only cement and concrete related discussions alone are discussed further.

Achieving Net-Zero Co2 Emissions in the Concrete Industry
According to the Global Cement and Concrete Association (GCCA), around 14 billion m3 (equivalent of 33.6 billion tonnes) of concrete were cast from 4.2 billion tonnes of cement produced during 2020 (www. gccassociation.org). As per the GCCA, the global CO₂ emissions from the cement and concrete sector today are in excess of 2.5Gt. In order to manufacture one tonne of cement, the raw materials are heated in a kiln up to 1,400o C, resulting in the emission of 667 to 990 kg of CO₂ for every 1000 kg of Portland cement produced. This depends on the fuel type, raw ingredients used and the energy efficiency of the cement plant. CO₂ emissions from a cement plant are divided into two source categories: Combustion (40% of emissions) & Calcination (60% of emissions)

Fig. 5: Achieving Net-Zero CO₂ Emissions in Concrete Industry by 2050 as per GCCA
(Adapted from Reference 3)

The combustion-generated CO₂ emissions are related to the fuels used in the cement kiln. The CO₂ emissions due to calcination are formed when the raw materials [limestone (CaCO3 ) and clay] are heated in kilns to more than 1400°C and CO₂ is liberated from the decomposed minerals. Electricity used by the cement plants may contribute to more CO₂ emissions (According to the Department of Energy, cement production accounts for 0.33% of energy consumption in the USA). Concrete usually consumes about 7% and 15% cement by weight depending on the performance requirements for the concrete. As one cubic meter of concrete weighs 2400 kg, the quantity of cement consumed is around 168- 336 kg/m3 . Thus, about 150 to 300 kg of CO₂ is embodied for every cubic meter of concrete produced (6% to 12.5% of the weight of concrete), depending on the mix design.[5] The cement industry was one of the first to take action on CO₂ reduction. Since 1975 it has reduced emissions by about 33%.[6]

The different actions that could be taken to achieve net-zero emissions in the concrete industry at different stages of the life of cement/concrete production and use, are shown in Fig. 5.[5] These seven actions and their percentage reduction in CO₂ emissions are: (1) Efficient Design and Construction Practices (22%), (2) Efficient Production of Concrete (11%), (3) Replacement of OPC with Cementitious Materials (9%), (4) Reduced Use of Clinker (11%), (5) Carbon Capture, Utilization and Storage (CCUS) (36%), (6) Decarbonisation of Electricity (5%) and (7) Concrete as Carbon Sink (6%). These actions will be discussed further.

Efficient Design and Construction Practices
Certain changes in the design, construction, maintenance, and demolition of buildings can reduce the amount or carbon intensity of concrete, decrease the energy used during a building’s operation, extend a building’s lifetime, and make materials and components available for reuse or recycling (thereby reducing the use of virgin materials or new components). For example, buildings that are lighter and designed strictly following the technical specifications use less material and can lower associated emissions. Reducing the mass of cement and concrete used in the construction of buildings is one relatively straightforward strategy for improving material efficiency and reducing GHG emissions. Mandating prefabrication and modular construction can facilitate weight reduction. Prefabricated elements and modular construction also facilitate design for disassembly and component reuse. Using precast concrete components result in savings in materials and better quality of concrete, as they are produced in the factory. Policies to preserve historic buildings that restrict demolition or alteration can limit building energy efficiency.

It is also important to design concrete structures taking into account all probable loads that may act on them, for a minimum design life of 100 years, rather than the currently presumed 50-60 years. This will reduce the quantity of concrete consumed in the long run. Moreover, the concrete mix should be properly designed, using supplementary cementitious materials, taking into consideration the prevailing exposure conditions at the location of the buildings and structures. The concrete should be placed and compacted properly and finally cured for adequate time in order to have flawless concrete with high durability. The detailing should be carefully done and carried out at site with sufficient good quality cover concrete (by adopting quality cover blocks). Good quality of concrete cover will prevent corrosion of reinforcements, which is the main cause of deterioration of majority of concrete structures. The use of selfcompacting concrete, which can flow through congested reinforcement cages and has advantages like reduction of construction noise and good quality of concrete cover is also recommended. All these measures will prolong the life of concrete structures and reduce the CO₂ emissions in the long run. The four material efficiency techniques to reduce the use of cement and concrete in buildings were found to be[4] (1) use of post-tensioning floor slabs, (2) using more precast frame elements, (3) reducing the cement content of concrete and (4) reducing over-design.

Designers of buildings could also achieve further reductions in CO₂ emission through their choice of concrete floor slab geometry and system (precast and prestressed hollow-core slabs with cast-inplace concrete toppings are not only economical but result in faster construction), choice of concrete column spacing, and optimization of concrete strength/element size/reinforcement percentage, without compromising on the performance. Carbon footprint reduction in 2019 accounts for one-third of the points toward LEED certification, and material efficiency is considered a part of the mitigation strategy considered in such initiatives.

Efficient Production of Concrete
Traditionally concrete was produced at site and the water/binder ratio was not strictly followed and resulted in wastage of material. With the increasing demand for higher speed of construction during the past two decades, the erstwhile practice involving the use of labour-intensive site-mixed concrete construction is diminishing, especially in big cities. Ready-mixed concrete (RMC) and powerful pumps are now used to place large volumes of concrete in big-size pours in the major cities of India. Use of RMC usually results in better quality of concrete, as RMC is properly designed and mixed to achieve the specified strength in a modern plant having computerized controls on the entire production process. The RMC industry in India is reportedly growing at the rate of about 20% and has a market share of about 15-20% (In developed countries like the USA, however, the market share of RMC is around 75%). Such use of RMC plants offers significant reduction in CO₂ emissions because of the adoption of proper mix specifications and quality control.

In addition, use of admixtures and improved processing of aggregates may offer additional reduction in CO₂ emissions in concrete production. Although such reductions have already been achieved in many parts of the world, a broader application of these will deliver further savings.

Replacement of OPC with Supplementary Cementitious Materials (SCMs)
The concrete industry already uses a significant amount of waste industrial byproducts such as fly ash (obtained by burning coal in thermal power plants), ground granulated blast furnace slag (GGBS) (byproduct of iron manufacture), silica fume (by product of processing quartz into silicon or ferro-silicon metals in an electric arc furnace), high-reactivity metakaolin (HRM) and glass powder as partial replacement of ordinary Portland cement in concrete. These industrial waste products, which would otherwise end up in landfills, are called supplementary cementitious materials (SCMs). A plethora of R&D work done all over the world including India, has proved beyond doubt that these SCMs help in improving a variety of properties of concrete, mainly its long-term durability and reduced heat of hydration of concrete. Additionally, the use of SCM with modern-day cement also reduces the increase in the peak temperature of concrete (often limited to 70°C) and its early occurrence. Further, as many researchers have pointed out, the resulting microstructure of concrete with SCM is far superior to that of pure OPC concrete. Several researchers have also found that adding small quantities silica fume or nanosilica (3-5%) is found to reduce the porosity of interfacial transition zone (ITZ) and may even increase the concrete strength. In addition to silica fume, the use of ultrafine GGBS, which provides properties more or less similar to those of silica fume concrete, is gaining ground in India.[7].

SCMs such as slag can be used as high as 50% or even higher as replacement of Portland cement resulting in a significant reduction of the embodied carbon of concrete.[8] However, the varying chemical and physical property of SCMs due to their source and/or location may pose huge quality control challenges on their use in concrete. Hence, developing quality control systems to identify the quality of various types of SCMs is necessary before using these materials in more applications.[9].

Reduced Use of Clinker Content and Savings in Clinker Production
This strategy of CO₂ reductions is through the use of waste materials to replace limestone in the kilns, energy efficiency measures, use of alternative fuels to replace fossil fuels, use of hydrogen and renewable electricity for heating the kilns, and reducing the clinker content in the cement.[3]

Fig. 6: Co-Processing CO2 Emissions Vs Incineration/Landfill CO2 Emissions[10]

The cement industry has already replaced some of its raw natural resources with waste and by-products from other industrial processes. These materials should contain elements such as calcium, silica, alumina and iron.[10] They can be used in the kiln, replacing natural raw materials such as limestone, shale and clay. Some of these waste materials will have both useful mineral content and recoverable calorific value. For example, sewage sludge has a significant calorific value, and yields ash that could be used to make clinker. Ashes from lignite or coal, cement paste from demolition waste, air-cooled blast-furnace slag and waste lime could also be used.[10] As these materials have already been decarbonated, their use as alternative to ‘virgin’ limestone will reduce CO₂ emissions in the production process. About 3-4% of raw materials used in the production of clinker in Europe consisted of such alternative raw materials, totaling about 14.5 million tonnes per year.[10] CEMBUREAU envisages up to 3.5% reduction of process CO₂ using decarbonated materials by 2030 and up to 8% reduction by 2050.[10]

On an average, to produce one ton of cement, 3.4 GJ of thermal energy (in dry process) and 110 kWh of electrical energy are needed.[11] Typically, energy consumption accounts for 20-40% of production costs. Most of the cement kilns are already working at 70 to 80% efficiency. However, the thermal efficiency of some kilns can be improved by converting preheater and other types to precalciner type and by recovering heat from the cooler to generate up to 20% of the electricity needs of the cement plant.[10]

Research is being conducted to use electrical heating or solar energy to calcine the raw materials which could result in the reduction of 55% CO₂ due to the fuel. Such renewable electricity usage combined with the use of hydrogen and biomass fuels for the clinker process may result in near zero fuel CO₂ emissions.[10]

As stated earlier, fuel emissions account for 40% of the total CO₂ emissions from cement manufacturing. Many cement plants simultaneously recover energy and recycle minerals from a variety of waste streams (co-processing) and also use biomass. Such co-processing results in circular economy, and helps local municipalities in their waste management.[10] Thus, not only the replacement of fossil fuels saves CO₂ emissions, but also the CO₂ emissions through incineration and methane emissions from landfill could be avoided, as shown in Fig.6.[10] In 2017, the alternative fuel used in Europe accounted for 46% of the total fuel used, of which 16% was biomass.[10] It is technically feasible to use of alternative fuels to over 90%, if they are locally available. Examples of such plants include those in Allmendingen, Germany and Retznei, Austria which use 100% alternative fuels and 12% alternative raw materials.[11] It is to be noted that with an increase in use of alternative fuels, there can be a slight decrease in the thermal energy efficiency. This can be overcome by considering parameters such as burnability, moisture content, design and size of the plant.

Fig. 7: Components of LC3 Cement
(Source: https://lc3.ch/the-material/)

The strategy of reducing clinker content revolves around partial substitution of clinker with supplementary cementitious materials such as fly ash at the cement plant and the use of alternative materials such as calcium sulfoaluminate cement or geopolymer concrete entirely. The strategy of reducing CO₂ emissions from concrete by reducing the cement content includes analyzing the design mixture of concrete, binder phase, and the quality and quantity of aggregates including recycled materials. With increasing focus on sustainability, more and more coal-fired power plants and steel production plants are expected to be closed. Also, with the increasing popularity of renewable energy and cleaner forms of fuel like natural gas, availability of quality fly ash and GGBS is becoming an issue.

To alleviate the problem, the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland collaborated with researchers at Universidad de las Villa (UCLV) in Santa Clara, Cuba, Technology and Action for Rural Advancement (TARA), New Delhi, India, IIT Delhi, IIT Madras, and IIT Bombay, to conduct research to produce a blended cement having reduced clinker, calcined clay, ground limestone and gypsum, with proportions as shown in Fig. 7. This cement termed as LC3 (Limestone calcined clay cement) has proven successful through industrial trials carried out in Cuba and India.[12] The first permanent large-scale production of LC3 started in Colombia in 2020. The cements produced had mechanical performance similar to the CEM I Portland cement, with clinker content more than 90%. Unlike industrial byproducts like fly ash and GGBS, calcined clay relies on clay deposits that are geographically spread and sufficiently abundant to meet projected demand. LC3 binder is found to produce durable concrete, even in a chloride laden environment.

The major reason for the better performance was attributed to the more compact and dense microstructure of the concrete with LC3 binder.[12]

Carbon Capture, Utilization and Storage (CCUS)
Innovation in carbon capture, utilization, and storage (CCUS) technologies enable captured carbon dioxide (CO₂) emissions to be injected back into concrete to strengthen it, reducing the need for cement. This technology can be used along with the use of SCMs in concrete to reduce dependency on fly ash. CCUS may become significant after about 2030 when commercial viability and necessary infrastructure is expected to be established. CCUS is the only large-scale mitigation option available to make significant reductions in the CO₂ emissions from industrial sectors such as cement, iron and steel, chemicals and refining. The carbon capture technologies are envisaged to include absorption, adsorption, membrane, biological capture, and cryogenic separation. In cement production, the suitability of membranes and solid absorption processes for CO2 capture is expected to be tested at pilot scale, along with new production processes for industrial products that integrate low-cost CO₂ capture.[13] Captured CO₂ can be stored into geological formations such as deep saline aquifers which have no other practical use, and oil or gas reservoirs. Geological storage is at present considered to be the most viable option for the storage of the large quantities of CO₂ . Norcem Brevik plant in Norway, operated by Heidelberg Cement may be the first industrial-scale CCS project in the world, with full scale carbon capture of 400,000 tonnes of CO₂ per year and transporting it for permanent storage. There are now 19 large-scale CCS facilities in operation globally, with four more under construction. US-based Solidia plans to capture CO₂ and use it to dry out the concrete mix, minimizing the amount of water needed in production. In Canada, CarbonCure has developed a technology in which liquefied CO₂ is injected into wet concrete in order to improve its strength and performance. This technology can be easily installed in any ready mix concrete plant. These improvements enable concrete producers to realize cost savings through mix optimization.[14, 15] Other permanent CO₂ capture techniques include the use of recycled concrete aggregates and minerals (such as olivine and basalt).[10] Algae can also be used to absorb CO₂ and grow biomass, which can later be used to fuel the kiln.[10] CCS also has the potential to generate ‘negative emissions’, removing CO₂ from the atmosphere.

Decarbonisation of Electricity
Decarbonisation of electricity means reducing its carbon intensity; i.e., reducing the emissions per unit of electricity generated. Decarbonisation is being achieved by increasing the share of low-carbon energy sources, particularly renewable energy and a corresponding reduction in the use of fossil fuels. Worldwide, renewable energy produced 29% power capacity in 2020.[16]

Concrete as Carbon Sink
The natural process of carbonation of concrete surfaces due to the CO₂ present in the atmosphere is well known to structural engineers. In structural concrete, carbonation is considered a deterioration mechanism, as it decreases pH of concrete (from about 13 to about 8.5)[17] and increases its susceptibility to corrosion. However, in non-structural concrete like pavements and dams, carbonation can uptake CO₂ from the atmosphere into the concrete, to make up for partial emissions generated by cement production. Carbonation reaction, and consequently CO₂ uptake occurs throughout concrete structure lifetime and can even continue after demolition.

Only recently it was considered to take this factor into the carbon accounting. This permits recarbonation of about 20% to the theoretical maximum carbonation possible for a tonne of clinker (525kg CO₂ /tonne), i.e. 105kg CO₂ /tonne clinker. From 2020 to 2050, the clinker binder ratio decreased (Globally, the current average clinker binder ratio is 0.63; It is projected to reduce to 0.58 and 0.52 by 2030 and 2050 respectively.[3]) The reduced clinker per m3 of concrete and total clinker volume globally may result in a slight decrease in the value of recarbonation. The detailed evaluation of recarbonation and efforts to enhance recarbonation through active exposure of crushed concrete to CO₂ at end of life is not yet available. A conservative forecast for global recarbonation is 318 and 242 MT of CO₂ in 2030 and 2050 respectively.[3]

Other Technologies
A few other technologies which when used will reduce the carbon emissions are discussed below:

Geopolymers: In cement manufacture, the clinker is made by calcining calcium carbonate (limestone) at high temperatures, which releases CO₂ into the atmosphere. On the other hand, geopolymers, can be made from inorganic alumino-silicate compounds. An inorganic polycondensation reaction results in a three-dimensional structure, like that of zeolites. It can be produced by blending three elements, i.e. calcined alumino-silicates (from clay), alkali-disilicates and granulated blast furnace slag or fly-ash.[18] Geopolymer cements harden at room temperatures and provide compressive strengths of 20 MPa after 4 hours and up to 70-100 MPa after 28 days, while they also have high fire resistance. Geopolymer cements use hydroxide or sodium silicates as activators instead of lime, therefore eliminating process CO₂ emissions. It has been estimated that geopolymer production will consume 3/5 less energy than the production of Portland cement. The first industrial geopolymer plant is being built in Australia, Zeobond Pty Ltd. and its CO₂ emissions can be as low as 10-20% of those of Portland cement binders. Although considerable interest is evinced in the technology of geopolymer concrete in the academic sphere, its commercialization is yet to pick up in India.

3-D Printing: Digital printing of concrete is based on the principle of 3D printing technology or additive manufacturing. The prevalent processes of digital printing are extrusion-based printing, binder jetting, mesh mould approach (cutting and welding), smart dynamic casting, etc. Among all the processes, the most widely used method is the extrusion-based printing. One of the major advantages of this printing technique can be attributed to less or no use of formwork. Even in modular structures, the geometric freedom possible in 3D printing can allow for structural optimization to achieve material and cost-saving as compared to conventional construction, thereby reducing the CO₂ emissions.[19]

Use of BIM: Building Information Modeling (BIM) is complex software developed by Autodesk Corporation and used in the architecture, engineering, and construction (AEC) industry. The BIM is used to achieve connecting teams, workflows, and data across the entire project lifecycle-from design and engineering to construction and operations. The use of BIM in the design and construction processes will result in the following benefits:
– Cost and resource savings
– Greater efficiency and shorter project lifecycles
– Improved communications and coordination
– More opportunities for prefabrication and modular construction
– Higher quality results
– Because of these above benefits, reduction in CO₂ emissions could be achieved.

Summary and Conclusions
Due to the huge amounts of CO₂ emissions by different industries, our planet earth is experiencing severe climatic changes mainly due to the rise in the average temperature of earth. In an effort to contain the CO₂ emissions to the pre-industrial levels, India has recently committed to the world that it will attain net-zero CO₂ emissions by 2070. Cutting the CO₂ emissions to attain net-zero levels requires urgent action by different countries to be taken on war footing and also huge research investments. Recently the Global Cement and Concrete Association (GCCA) developed a plan of action to achieve net-zero emissions of the concrete industry. This plan of action requires the following actions: (1) Efficient Design and Construction Practices, (2) Efficient Production of Concrete, (3) Replacement of OPC with Cementitious Materials, (4) Reduced Use of Clinker, (5) Carbon Capture, Utilization, and Storage (CCUS), (6) Decarbonisation of Electricity, and (7) Concrete as Carbon Sink. These actions are briefly elaborated and some possible solutions are suggested.

Reference

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2. UNEP (2019) Global Status Report for Buildings and Construction-Towards a zero-emissions, efficient and resilient buildings and construction sector, Global Alliance for Buildings and Construction, International Energy Agency and the United Nations Environment Programme, 41 pp.

3. https://gccassociation.org/concretefuture/getting-to-net-zero/

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15. http://go.carboncure.com/rs/328-NGP-286/images/Calculating%20 Sustainability%20Impacts%20of%20CarbonCure%20Ready%20Mix. pdf

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18. Davidovits, J. (2013), Geopolymer Cement a review, published in Geopolymer Science and Technics, Technical Paper #21, Geopolymer Institute Library, www.geopolymer.org

19. Bhattacherjee, S., Rahul, A. V., and Santhanam, M. (2020) “Concrete 3D Printing –Progress Worldwide and in India”, The Indian Concrete Journal, Vol.94, No. 9, pp.8-25.