Exploring Indian SCM Usage

Due to rapidly expanding urbanisation, environmental sustainability in the construction industry is facing serious challenges. To put it into perspective, concrete preparation requires a significant quantity of natural reserves worldwide and necessitates the development of alternative materials and sources.

Global concrete production requires around 27 billion t of raw material, representing nearly 4 t per person, per year!

By 2050, concrete production will be four times higher than in 1990. Aggregates and cement represent around 60 – 80% and 10 – 15% of the total weight of concrete, respectively.

Along with processing a substantial quantity of aggregates and around 3.5 billion tpy of cement, concrete generates approximately 5 – 7% of the global total carbon dioxide emissions.

By 2025, around 4 billion t of carbon dioxide is estimated to be released into the atmosphere during cement production. A possible solution for more sustainable production could be to explore and develop SOPs for utilising locally-available waste materials or recyclable materials.

The abundance of these materials and their different chemistries and physics compel the development of a common strategy for their application in concrete production.

Numerous solid industrial byproducts containing calcareous, siliceous, and aluminous materials (fly ash, ultrafine fly ash, silica fume, etc.), along with some natural pozzolanic materials (volcanic tuffs, diatomaceous earth, sugarcane bagasse ash, palm oil fuel ash, rice husk ash, mine tailings, etc.) can be used as supplementary cementitious materials or SCMs.

Sewage sludge ash (SSA) is an urban waste that may be used as fertilizer, as well as a cement substitute. SSA was not only considered as an SCM in blended cements but also in a wide range of building materials like paving-stones, tiles, bricks, and light aggregates production.

Marble dust could also be explored as one of these SCMs. Marble is a finely crystallised metamorphic rock originating from the low-intensity metamorphism of calcareous and dolomitic rocks. Calcium carbonate (CaCO₃) can form up to 99% of the total amount of this carbonated rock. Additional phases may also include SiO₂, MgO, Fe₂O₃, Al₂O₃ and Na₂O and, in minor ratio, MnO, K₂O, P₂O₅, F, Cu, S, Pb, and Zn.

Construction and demolition debris (CDD) constitute one of the massive flows of solid waste generated by modern municipal and commercial activities. Usually, CDD comes in the form of brick fragments, mortars, aggregates, concrete, glass, ceramic tiles, metals and even plastics.

It is imperative that new SCMs such as these are reviewed for their impact on the environmental footprint of cement and concrete.

The role of SCMs

SCMs play a very significant role in the performance of concrete, especially in imparting additional durability. They encompass a wide spectrum of alumino-silicious materials, including natural or processed pozzolans and industrial byproducts like ground granulated blast furnace slag (GGBS), fly ash (FA), ultra-fine fly ash (UFFA), and silica fume (SF). Though there is higher fluctuation both in properties and chemistry across the various types of SCMs, they share a common capacity to chemically react in concrete and form cementitious binders replacing those obtained in OPC hydration. The key feature of SCMs is their pozzolanicity, i.e. their capability to react with calcium hydroxide (portlandite, CH) aqueous solutions to form calcium silicate hydrate (C–S–H).

In the right proportion, SCMs can improve the fresh and hardened properties of concrete, especially long-term durability.

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