ORALS

In recent years, the “greening” of cement and concrete has taken on a different path with a sharper focus on reducing carbon footprint while enabling companies and countries to benefit from carbon credits. It is only in 2012 that the first academic paper on the use of biochar – the solid by-product of pyrolysis or gasification – was published. In the following 9 years, biochar concrete has taken an upward trajectory in terms of academic research and commercial consideration. Two of the key reasons accounting for this popularity are that biochar is potentially a carbon negative material from the life-cycle accounting perspective [1], and that biochar is a widely available material that has primarily been used in agriculture (for soil enhancement) and for water purification. This talk aims to demystify the near-decade long development of this young field of research, and summarize the key milestones in the growth path of this sustainable construction material. The different technical ideas and scientific technique used to achieve these milestones will be elaborated. For example, it was found that coating polypropylene fibers with biochar, and deploying these fibers to reinforce mortar, decreases water sorptivity of the mortar by about 44%, and water penetration by about 62%. Correspondingly, it increases 7-day and 28-day compressive strength by about 11% and 4.3% respectively [2]. When biochar was deployed evenly in the mortar mix without any fibers, biochar reduces water penetration by about 58.8% and increases 7-day compressive strength by about 13.8% [3]. Methods used for these studies include ASTM C1585-04 (Standard Test Method for Measurement of Rate of Absorption of Water by Hydraulic-Cement Concretes) and different characterization methods, such as Fourier Transform Infrared analysis for studying the surface chemical species found on biochar, and Brunauer-Emmett-Teller method for measuring pore size distribution of mortar samples containing different quantities of biochar. These efforts have created several important areas of research, including the potential of using biochar as a mean of enhancing accelerated carbonation curing of concrete; that is, using biochar to increase the total amount of CO₂ that can be removed from the atmosphere through the process of carbonation of the calcium hydroxide and calcium silicate hydrate found in curing mortar mixture [4]. Latest evidence for the effectiveness of specially made biochar in improving electromagnetic wave (GHz) shielding of mortar tiles and application of biochar concrete under extreme environmental conditions (for example, using biochar to reduce the infusion of sulfate and chloride ions into mortar submerged in aqueous medium [5], and for increasing the “crack-resistance” of concrete operating under high temperature [6]) will also be presented. This talk will end by boldly charting the future directions of biochar concrete and how it can continue to stay abreast and relevant, by addressing some of the most challenging sustainability-related problems facing the construction industry the world over.

References:
[1] Roberts K.G., Gloy B.A., Joseph S., Scott N.R., Lehmann J., Life cycle assessment of biochar systems: estimating the energetic, economic, and climate change potential, Environ. Sci. Technol. 44 (2) (2009) 827–833.
[2] Gupta, S., Kua, H.W. and Cynthia, S.Y.T., 2017. Use of biochar-coated polypropylene fibers for carbon sequestration and physical improvement of mortar. Cement and Concrete Composites, 83, pp.171-187.
[3] Gupta, S., Kua, H.W. and Low, C.Y., 2018. Use of biochar as carbon sequestering additive in cement mortar. Cement and concrete composites, 87, pp.110-129.
[4] Gupta, S., Muthukrishnan, S. and Kua, H.W., 2021. Comparing influence of inert biochar and silica rich biochar on cement mortar–Hydration kinetics and durability under chloride and sulfate environment. Construction and Building Materials, 268, p.121142.
[5] Gupta, S., 2021. Carbon sequestration in cementitious matrix containing pyrogenic carbon from waste biomass: A comparison of external and internal carbonation approach. Journal of Building Engineering, 43, p.102910.
[6] Gupta, S. and Kua, H.W., 2020. Application of rice husk biochar as filler in cenosphere modified mortar: preparation, characterization and performance under elevated temperature. Construction and Building Materials, 253, p.119083.