Carbon dioxide sequestration in mortars with excavated soil: Engineering performances and environmental benefits

Globally, substantial volume of excavated soils is generated during construction and demolition activities, which can be utilized in the manufacturing stabilized earth-based construction materials. Furthermore, increasing amount of CO₂ is being released into the environment from growing industrial operations that can sequestered in earth-based materials without compromising the engineering properties. This article attempts to explore the effect of CO₂ sequestration through accelerated carbonation curing on engineering properties, micro-structure and phase composition of cement-lime stabilized soil mortars. Lateritic soil (clay content of 42 %) is used to replace 25 % and 50 % of natural sand by mass. The experimental findings demonstrate an increase in CO₂ uptake by 15-23 % and 33-40 % due to addition of 25 % and 50 % soil respectively compared to control (0 % soil). Precipitation of meta-stable calcium carbonates majorly contributes to the total CO₂ uptake, accounting for 62-69 % and 78-87 % of the carbonates formed in 25 % soil-mortars and 50 % soil mortars. These are substantially higher compared to 40-50 % in the case of control mixes. The mentioned finding is attributed to the formation of additional calcium-silicate-hydrate and calcium-aluminate-hydrate due to clay-lime reaction, that binds CO₂ and precipitate meta-stable polymorphs of calcium carbonate. Addition of lime and carbon sequestration are found to substantially enhance 1-day strength of cement-soil and cement-lime-soil mortars by 31-36 %, although no prominent effect at 7-day and 28-day marks are observed. Furthermore, capillary water absorption at 28-day age is reduced by 18-31 % in lime-added cement-soil mortars compared to the ones without lime, that reduces moisture sensitivity of the mortars. Overall, the carbon sequestered mortars demonstrate satisfactory strength (20-37 MPa) and water absorption performance of the stabilized mortars for masonry applications, which will provide a promising means to manufacture low-carbon and more durable construction products.