Carbon sequestration in cementitious composites using biochar and fly ash – Effect on mechanical and durability properties

Abstract

A possible reduction in high CO2 emission associated with cement production can be achieved by sequestering CO2 as carbonate mineral in hydrated cement matrix. This study aims to investigate application of biochar and its combination with fly ash to improve CO2 uptake and carbonate mineralization in cement mortar. Effect of fly ash and biochar, from waste peanut shell, on carbonate mineralization, strength, permeability and shrinkage of mortar are investigated. Experimental findings show that combination of biochar and fly ash, used to replace 23% of cement by mass, enhances carbon sequestration through mineralization by 7–13 % (by weight of cement) than control. Biochar addition at 3% contributes to higher carbon sequestration than plain mortar, while improving strength and reducing capillary water absorption. Although relatively high content of sodium (42%) and potassium (8%) in the produced biochar lead to 39% higher drying shrinkage than control, addition of biochar reduces the chemical shrinkage associated with only carbonation reaction by 30–60%. 23–25% of carbonation shrinkage in biochar-mortar can be recovered through 4–7 days of rewetting. Overall, the research suggests a strong possibility of developing low carbon building materials using biochar as supplementary admixture, while offering improved mechanical and durability performance.