Cold-bonded biochar-rich lightweight aggregates for net-zero concrete

16 August 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


An emerging strategy to remove CO2 from the atmosphere and compensate for the greenhouse-gas emissions of cement and concrete is based on incorporating biochar into concrete. With this approach, concrete can be turned into a functional carbon sink (C-sink). Until now, biochar has been used without modification to replace part of the cement or of the aggregates in concrete. However, this technology comes with a number of practical problems, which include the high water absorption of the biochar (due to its high specific surface) and hazards (dust, risk of combustion). In this paper we present an alternative approach in which biochar is first processed into lightweight aggregates in a cold-bonding process. To this end, biochar is pelletized together with a small amount of hydraulic binder and with water and forms round pellets that further harden with hydration time. In this way, carbon-rich lightweight aggregates (C-LWA) are obtained that are easier to handle than the pure biochar. The C-LWA pellets have similar porosity and strength as conventional LWA and can be used for similar applications. Yet, the CO2 emissions from sintering traditional LWA are avoided and the C-LWA are instead an effective C-sink. We demonstrate that it is possible to incorporate in the pellets and eventually in the concrete a sufficient amount of carbon to compensate for the original emissions of concrete. The net-zero emissions concrete obtained with this approach possesses mechanical performance sufficient for typical structural applications in buildings.


Net-zero emissions
Lightweight aggregates


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Comment number 1, Mateusz Wyrzykowski: Dec 06, 2023, 14:50

The peer-reviewed version of the paper has been just published at: