GGBS: Partial Replacement Of Cement For Developing Low Carbon Concrete

Low Carbon Concretes (LCC)
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 Campus in India.

Case Study on using GGBS
The education sector in India is estimated to be worth US $117 Bn and expected to reach US $313 Bn by FY30. India is set to become a globally prominent education hub. 100% FDI (automatic route) is allowed in the education sector in India. Soon, foreign universities and higher education institutions may be allowed to set up physical campuses in India. These campuses are required to be sustainable and durable by bringing efficiencies in energy generation, consumption and distribution, land and water, waste management, design and occupier comfort, use of resources and materials, and reduction in greenhouse emissions, and in indoor environments, etc.

One of the most important dimensions of sustainability is material and resource efficiency, since brick-and-mortar campuses require a lot of construction materials, which would be explored/sourced from our natural resources. However, the conservation of natural resources is very important for a sustainable future. In a typical modern construction method for mass construction, we require cement, steel, water, aggregates and admixtures, all of which require a significant amount of natural resources and energy, and which can cause a lot of pollution in the environment.

Case Study on using GGBS
Cement is the only binder material in concrete to bind all construction materials like steel and aggregate with a hydration process with water to impart strength to the structure. Production of 1 ton of cement requires 1.5 ton of limestone and emits 1 ton of CO2 in the environment. The SCMs (Supplementary Cementitious Material) like GGBS (Ground Granulated Blast Furnace Slag), is a by-product of the Steel Industry, PFA (Pulverised Fuel Ash) is a by-product of Thermal Power Plants, Silica Fumes is a by-product of Ferrosilicon industry, Metakaolin, and other superfine mineral additives, etc. can be used for partially replacing the OPC Cement and bringing them down the total cement requirement in Concretes.

GGBS is one of the SCMs which is widely used for major infra projects as well as for housing projects in India for building sustainably and durably, and as per India’s Global Sustainability Goals.

Ground Granulated Blast Furnace Slag (GGBS)

GGBS is a by-product of the Iron and Steel industry and is widely used for the replacement of OPC in concrete mixes. Granulated Blast Furnace Slag is obtained by rapidly chilling (quenching) the molten Slag from the blast furnace with the help of water. During this process, the slag gets fragmented and transformed into amorphous granules (glass), meeting the requirement of IS 16714: 2018, as per Fig. 1.

The granulated slag is ground to the desired fineness for producing GGBS. The chemical composition of GGBS is closer to that of cement clinker and permissible replacement levels are in the range of 25%-70% as per IS Codal provisions of 455: 2015. GGBS has more CaO content compared to Fly ash and it is just cement only in chemical properties and thus resembles chemistry in these two aspects with cement clinker, as represented in Fig. 2.

Case Study on using GGBSFigure 1: Blast Furnace & Figure 2: Chemical Composition

GGBS is a non-metallic product consisting of silicates and aluminates of lime, which conforms to IS 16714:2018. Since it is a product manufactured in a controlled environment, consistency and quality are maintained.

GGBS design mix does the pozzolanic and hydraulic reaction in concrete. Calcium silicate hydrates (or C-S-H) are the main products of the hydration of portland cement and are primarily responsible for the strength of cement-based materials and calcium hydroxide (Ca(OH)2 is the by-product of this process which is the weakest component in concrete. GGBS reacts with Calcium hydroxide and produces C-S-H gel which helps to fill microspores in structure and make the structure impermeable to water and air. Resulting in less corrosion in the steel and adding more life to the structure.

The article focuses on the technical specifications, requirements of the project, and the role GGBS plays in the mix to meet the criteria and make the structure sustainable and durable.

Case Study

This paper references the upcoming campus in Devanahalli in Bangalore, where GGBS is proposed to be used as partial replacement of the existing pure OPC cement concrete mixes which were neither cost-effective, durable or sustainable. It is a fast-phase and fast-track project, and the site requirement is to achieve more than 80% strength within 7 days as compared to 67% strength in normal construction sites.

Concerning the existing Design Mix with 100% Pure OPC and 7 days strength criteria, the suggested Design Mix with partial replacement of GGBS for all grades is required for this project. Details are in Table No.1.

Case Study on using GGBSTable 1

After conducting the trail at the site, 7 days and 28 days of results of Compressive Strength were encouraging and easily surpassed the 80% strength requirement. Details are given in Table 2.

Case Study on using GGBSTable 2

The 7 Days and 28 Days Compressive Strength of 100 % OPC Design Mix and partially replaced OPC with GGBS results showed that the GGBS mix gave equally good strength compared to the 100% OPC Design Mix. Details are shown in Fig 3.

Case Study on using GGBSFig 3
The cost comparison between 100% OPC Design Mix and partially replaced OPC with GGBS showed savings of Rs.6.5/m3 in M40 Grade, Rs.54/m3 in M35 Grade, Rs.101/m3 in M25 Grade, and Rs.125/m3 in M7.5 Grade. Details are shown in Table 3.

Apart from the strength, durability, and cost parameters, we studied the sustainability parameters as well. We found that we can replace more than 25000 Mt OPC with GGBS for the 2.5 Lakh Cum concrete requirement for this project. It will help to conserve the 28500 Mt limestone reserves, reduce 18500Mt Co2, save 25000 Mt mass from land dumps, and save 18100 Kcal Thermal Energy, and 2175 KWH Electrical Energy.

Case Study on using GGBSTable 3

Conclusion

The case study showed that the campus can be stronger, more durable, and more sustainable using GGBS in Concrete Mixes. It shows that GGBS Design Mix achieved similar strengths and as per guidelines of Codal Provisions of IS 456 and IS 10262. The overall saving is more than INR15 millons for the entire project and it will help the environment get equal to 25000 trees plantations and afforestation Apart from this, there are other benefits of GGBS in concrete like improved long-term strength, improved flexural strength, better particle packing, enhanced durability, reduced heat of hydration, improved resistance to corrosion, high resistance to chemical, sulphate, and chloride attacks, besides it is eco-friendly and cost-effective.

References

Sengupta L., Dr. Manjunatha LR, Awasthi A., Landage A. (2022), “Use of Industrial By-Products in Concrete Production Achieve Lower CO2 Emission.”
ICCT, January- February 2024
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