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CONCRETE TECHNOLOGYwww.cpi-worldwide.com CPI %u2013 Concrete Plant International %u2013 2 | 2026 39the volumetric ratio of biochar to sand rather than by mass [7, 8]. All mixtures were proportioned to maintain comparable workability and target strength, enabling the isolated effect of biochar content on the mechanical response of concrete to be evaluated.This strategy ensures that the effect of increasing biochar content can be isolated while keeping the mix design simple and compatible with typical production practices in concrete plants. In practical terms, a plant adopting this approach would mainly need to (i) introduce an additional fine %u201caggregate%u201d fraction (biochar) controlled volumetrically and (ii) monitor moisture in the biochar to avoid unexpected changes in workability.Mixing procedureAll concrete batches were mixed in a laboratory mixer following standard procedures for structural concrete. Before batching, the required volume of olive pit biochar was pre-wetted with part of the mixing water until a uniform, surface-damp condition was reached, in order to limit water absorption and stabilise workability. The coarse aggregates and sand were first dry-mixed with the cement, then about 70%u201380% of the total water (with plasticizer and superplasticizer) was added, followed by the remaining water to reach the target consistency. Finally, the pre-wetted biochar was added and mixing continued for roughly one extra minute compared with the reference concrete. With this procedure, all mixtures could be produced and placed without significant practical problems, achieving a uniform distribution of the light, porous biochar particles.From a practical plant perspective as can be seen in Figure 2, the following points are especially relevant:%u2022 Pre-wetting of biochar: at the beginning of the experimental work, the olive pit biochar showed a clearly hydrophobic behaviour, so direct addition in dry form led to poor wetting and rapid loss of workability. For this reason, the biochar was first brought to a controlled, surface-damp condition using part of the mixing water, until a uniform, visually consistent state was achieved. This pre-wetting step is advisable in practice to overcome the initial hydrophobicity of the material and to avoid a sudden loss of workability due to water uptake during mixing.%u2022 Mixing time: a modest increase in mixing time (around one extra minute after biochar addition in this study) is recommended, particularly at higher replacement levels, to achieve a homogeneous distribution without modifying the existing mixing equipment. THE KNIELE KKMWeb:Catalogue:Movie:THE ART OF MIXINGMade in Germany