Page 36 - Demo

CONCRETE TECHNOLOGY36 CPI %u2013 Concrete Plant International %u2013 2 | 2026 www.cpi-worldwide.comThis study evaluates concrete mixtures in which 5%, 10% and 20% of the 0%u20134 mm fine aggregate fraction is volumetrically replaced by olive pit biochar and discusses their practical implications for applications in concrete plants. Four mixes were produced using conventional CEM II/A-L cement, natural coarse aggregates and standard plasticizing and superplasticizing admixtures. Compressive strength, splitting tensile strength and static modulus of elasticity were measured at 7 and 28 days. All biochar-modified concretes achieved strength levels within the range of conventional structural concrete classes commonly used for building and general infrastructure slabs, with 28-day compressive strength reductions of about 6%u201314% and a systematic decrease in stiffness as biochar content increased. The 10% replacement level provided the most favourable compromise, combining the highest splitting tensile strength with an adequate modulus for general structural and precast applications. Overall, the results show that olive pit biochar can be integrated into conventional concrete production with limited adjustments, offering a promising route towards lower-carbon concrete applications.Biochar is a carbon-rich material produced from waste biomass and designed to act as a long-term carbon sink. In recent years, several studies have investigated its incorporation into concrete, mainly as a low-dosage cement replacement, reporting that biochar additions up to a few per cent by weight of cement can enhance mechanical performance and reduce water absorption while contributing to carbon sequestration [1, 2].This trend is consistent with the broader shift towards using biomass-derived and secondary raw materials in cementitious composites to improve resource efficiency and reduce the global warming potential (GWP) of concrete [3]. In parallel, policy frameworks such as the European Green Deal promote the reduction of natural aggregate extraction and the valorization of agro-industrial residues [4].Olive-growing regions generate large quantities of residual biomass and processing wastes, which can be upgraded to biochar. Previous research has shown that olive-based ashes and by-products can partially replace natural fine aggregates or cement in mortars and concretes, achieving structural strength levels suitable for different concrete elements while lowering CO2 emissions [5]. This is particularly attractive in construction applications with high material consumption, where any reduction in cement and natural aggregate demand has a direct environmental and economic impact.MethodologyMaterials and mix design for concrete plant implementationOlive pit biochar and conventional constituentsThe key innovative component in this study is an olive pit biochar supplied by an industrial producer. According to the manufacturer, the material has a bulk density of about 0.5 kg/dm%u00b3, moisture content of around 8%, ash content in the range of 3%u20135% and a high fixed carbon content (75%u201385%). This relatively low density and porous internal structure distinguish it from mineral sands and are relevant for both mix design and handling in the plant.The biochar was combined with conventional constituents commonly available to concrete plants: CEM II/A-L 42.5 R cement, natural aggregates graded into 0/4, 4/10 and 10/20 mm fractions, and potable mixing water. The natural aggregates showed an average density of approximately 2.7 kg/dm%u00b3 and water absorption below 1%. Figure 1 compares the particle size distributions of the reference 0/4 sand and the olive pit biochar, both of which fall within acceptable grading limits for fine aggregates, with the biochar being somewhat Effects of olive pit biochar on the mechanical performance of concrete Enhancing sustainabilityn Samantha Hidalgo-Astudillo, Nadia Quijano and Albert de la Fuente, Civil and Environmental Engineering Department, Universitat Polit%u00e8cnica de Catalunya (BarcelonaTECH), Barcelona, SpainHector Bustos-Andrade and Natividad Garc%u00eda-Troncoso, Facultad de Ingenier%u00eda en Ciencias de la Tierra (FICT), Escuela Superior Polit%u00e9cnica del Litoral, ESPOL, Ecuador