Utilization of biochar from olive tree pruning as additive to cement mortars

• Published in: Journal of cleaner production 2024-09, Vol.469, p.143137, Article 143137
• Main Authors: Kalderis, Dimitrios, Anastasiou, Eleftherios, Petrakis, Evangelos, Konopisi, Stavroula
• Format: Article
• Language: English
• Subjects: absorption; agricultural wastes; Biochar; bioeconomics; Building composites; carbon sequestration; Cement; compression strength; durability; Mediterranean region; modulus of rupture; Mortar; Olea europaea; Olive tree pruning; porosity
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2024.143137

Olive tree pruning is the most abundant agricultural waste in the Mediterranean region and a sustainable exploitation pathway has yet to be established. In the framework of circular bio-economy, olive tree pruning was converted to biochar which was then characterized by various elemental and surface analysis methods. The olive tree pruning biochar (OTB) and a commercial biochar sample (SON) were combined with cement, each at rates of 2 and 5 % wt. and had their physical and mechanical properties investigated. A small workability loss was determined for both mortars, which was counterbalanced by slightly increasing the superplasticizer dosage to 1.3 and 1.73 % wt. of cement, for the 2 and 5 % wt. OTB, respectively. OTB addition reduced the final setting times both at 2 and 5% addition rates by 51 and 15 min compared to the reference mortar, respectively. The addition of 2 % wt. OTB resulted in 27.8% reduction in porosity and 27.3% reduction in capillary absorption after 28 days, compared to the reference mortar. Furthermore, a 5% wt. addition of OTB resulted in 12.5 and 29.7% increase in compressive strength after 28 and 56 days, respectively. With respect to the flexural strength, 5% wt. SON exhibited a more positive behavior than 5% wt. OTB, achieving a 24.5% improvement compared to 13.3% achieved from the OTB addition, after 56 days. Overall, considering the high atmospheric emissions from the open-burning of olive tree pruning, the conversion to an added-value material such as biochar contributes to carbon sequestration and at the same time improves the long-term mortar durability and behavior. •Olive tree pruning biochar was valorized as cement additive at 2 and 5 % wt. rates.•2% wt. biochar addition reduced the setting time by 51 min compared to control.•2% wt. biochar addition reduced the mortar porosity by 27.8% compared to control.•5% wt. biochar addition resulted in 29.7% increase in compressive strength.•5% wt. biochar addition resulted in 13.3% increase in flexural strength.