Page 38 - Demo

CONCRETE TECHNOLOGY38 CPI %u2013 Concrete Plant International %u2013 2 | 2026 www.cpi-worldwide.comfiner at intermediate sieve sizes. Plasticizing and superplasticizing admixtures were used to achieve adequate workability at a relatively low water%u2013cement ratio.From a plant perspective, the biochar can be stored and handled in a similar way to a fine aggregate, but it requires closer moisture control due to its higher water-holding capacity and very low particle size. In a dry state, the material tends to generate airborne dust, which may increase particulate emissions. Keeping the biochar slightly moist helps to minimize this issue and improves its behaviour during handling and batching. In addition, its lower density means that a given volume of biochar corresponds to significantly less mass than natural sand, so a volumetric, rather than purely mass-based, replacement strategy is advisable in mix design and production control.Volumetric mix design with biochar as sand replacementIn this stage of the experimental program, four concrete mix designs were produced. The reference mix, with 100% natural sand as fine aggregate (C-REF), was proportioned to achieve a normal-weight structural concrete of approximately strength class C40/50 in accordance with EN 206[6]. In addition, three modified mixes were prepared in which 5% (C5B), 10% (C-10B), and 20% (C-20B) of the sand volume were replaced by olive pit biochar. The replacement was specified on a volumetric basis to properly account for the lower density and higher porosity of biochar relative to mineral aggregates as shown in Table 1. This approach is consistent with recent studies on biochar%u2013concrete composites, particularly those in which biochar partially replaces the fine sand fraction, where dosages are defined by 01020304050607080901000,05 0,5 5Percentage passing by mass (%)Sieve size mmFine aggregate 0/4Biochar Olive pitFig. 1: Particle size distribution of the olive pit biochar and sieve test.Table 1: Volumetric mix designs incorporating biochar at various replacement ratiosMaterial U C-REF C-5B C-10B C-20BFine aggregate 0/4 mm m%u00b3 0.309 0.294 0.278 0.248Biochar (Olive pit) m%u00b3 0.000 0.015 0.031 0.061Coarse aggregate 4/10 mm m%u00b3 0.078 0.078 0.078 0.078Coarse aggregate 10/20 mm m%u00b3 0.251 0.253 0.252 0.251CEM II/A-L 42.5R m%u00b3 0.156 0.156 0.156 0.156Water m%u00b3 0.185 0.185 0.185 0.185Plasticizer (%w. of cem.) % 1 1 1 1Superplast. (%w. of cem.) % 1 1 1 1w/c 0.39 0.39 0.39 0.39