Environmental Pollution and Health Hazards

Statement of the Problem: Construction and Demolition waste (C&D waste) is one of the biggest waste streams in most countries. The heavy inorganic part (from concrete and masonry) could be processed and refined into recycled aggregates. This type of aggregates could substitute natural aggregates in a range of user applications like road construction, landscaping and concrete production. This will save natural resources,

decrease transportation, reduce landfilling and bind CO2 through increased carbonation. The purpose of the study is to calculate the binding potential in the Indian concrete.

Methodology & Th eoretical Orientation: Carbonation of concrete normally occurs when air or water-borne CO2 dissolves in the concrete pore water and react with Ca2+ to form stable CaCO3. Upon carbonation, the pH of the concrete pore water is decreased

to around 9. Carbonation mainly involves decalcifi cation of the Ca-bearing hydrate phases when diff erent polymorphs of CaCO3 are formed. In addition, the Mg-bearing hydrate phases (OH-hydrotalcite and CO3-hydrotalcite) will also carbonate by

forming MgCO3 and Al(OH)3.

Findings: Applying the cement chemistry of the hydrate phases, a realistic binding of 200 kg CO2/ton cement has been calculated for Indian concrete. It has been assumed an average clinker factor of 0.75. Furthermore, accounting for a total annual Indian cement consumption of 300 million tons, the emission during cement production is 180 million tons, i.e. 600 kg CO2/ton cement. Due to carbonation, 10-20% of the emission are re-absorbed in service life, i.e. the remaining binding potential is around 18-36 million tons. If 10% of the cement consumed in concrete is recycled, minimum 5 million tons of CO2 may potentially be bound due to the recycling.

Conclusion & Signifi cance: Th e binding of CO2 to concrete materials due to carbonation is signifi cant. Th e CO2 binding

potential can be further utilized by recycling of C&D waste.