Assessment of mechanical and ecotoxicological properties of mortar with wood waste biochar as partial cement replacement

Legan, Maša (author), Štukovnik, Petra (author), Zupan, Klementina (author), Žgajnar Gotvajn, Andreja (author)

For several decades, cement production has caused concerns about CO$_2$ emissions. As the production of concrete has increased over the years, the fact that cement is its key component additionally raises a concern. By partially replacing cement with waste material such as biomass waste biochar, the reduction in waste and the reduction of CO$_2$ emissions could be addressed at the same time but raises a concern about the ecotoxicological potential of biochar-containing cementitious composites. During their use, recycling and disposal of biochar-containing mortars could pose hazardous environmental impacts due to their exposure to rain and other environmental conditions. The aim of the study was to determine the early-age mechanical properties of mortars with 5%, 10%, and 15% biochar as partial cement replacement. The environmental impact of biochar-containing mortars in terms of carbon footprint reduction and ecotoxicological potential was addressed simultaneously. The biochar used was prepared from waste wood biomass as carpentry waste wood. Results showed that added biochar caused no significant changes in flowability and fresh density of fresh mortar mixture. The strength tests revealed mortars with 5% and 10% biochar had higher 3-day flexural strength, while only mortar with 5% biochar had higher 7- and 28-day compressive strength (4% and 6%) than the conventional mortar. The X-ray diffraction (XRD) analysis detected five main crystalline phases in biochar-containing mortars. SEM-EDS showed the strong embedment of biochar particles in cement paste. Ecotoxicological assessment based on acute toxicity tests with mortar leachates using duckweed and mustard seeds showed low toxicity of leachates with the highest inhibition values around 50%. The calculations of the total CO$_2$-equivalent emissions for selected mortars revealed mortars with biochar as partial cement replacement had lower CO$_2$-equivalent emissions than the conventional mortar and can contribute to carbon footprint reduction and at the same time to natural resource conservation.

• Language: English
• Keywords: biochar, carbon footprint reduction, ecotoxicological properties, fresh mortar properties, hardened mortar properties, leachates, partial cement replacement
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FKKT - Faculty of Chemistry and Chemical Technology; FGG - Faculty of Civil and Geodetic Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2025
• Number of pages: 21 str.
• Numbering: Vol. 18, iss. 4, art. 876
• PID: 20.500.12556/RUL-167549
• UDC: 666.971.4:502/504
• ISSN on article: 1996-1944
• DOI: 10.3390/ma18040876
• COBISS.SI-ID: 227528195
• Publication date in RUL: 27.02.2025

Record is a part of a journal

• Title: Materials
• Shortened title: Materials
• Publisher: MDPI
• ISSN: 1996-1944
• COBISS.SI-ID: 33588485

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: biooglje, zmanjšanje ogljičnega odtisa, ekotoksikološke lastnosti, lastnosti svežih malt, lastnosti strjenih malt, izlužki, delni nadomestek cementa