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CONCRETE PRODUCTS & CAST STONE26 CPI %u2013 Concrete Plant International | India Edition %u2013 4 | 2025 www.cpi-worldwide.comWith a cement replacement of 35 wt.-%, the compressive strength decreased by about 30%. The flexural tensile strength decreased by 16% in the same range, indicating a lower effect of the tailings material with respect to tensile stress.The results show that the tailings material can contribute to partial cement replacement at low dosages without significantly impairing the mechanical properties. However, a higher substitution rate leads to a noticeable loss of strength.For a comparative evaluation of mechanical performance, Figure 5 analyses the compressive strength of mixes with 35 wt.-% cement substitution, based on the content of CEM I 52.5 N. Mixes with tailings material (HM) were compared to two reference materials: pulverized coal fly ash (SFA) with a specific surface area of 3,600 cm%u00b2/g and limestone powder (KSM) with 6,300 cm%u00b2/g. Strength tests were conducted after 28 and 56 days.The results show that the mixes containing tailings material exhibited lower compressive strength values compared to the CEM I reference mix and the mix with SFA as a cement substitute, the latter being known for its pozzolanic reactivity. In direct comparison with limestone powder, an inert filler, the tailings material showed higher strength development, which could indicate a limited but existing microstructural contribution during the hardening process.The results confirm that, compared to an active pozzolanic additive, the tailings material does not represent an equivalent cement substitute, but it can be more effective than a purely inert material.The use of tailings material as aggregate replacement in concreteFigure 6 shows the processed tailings material after classification: on the left, the fine-grained material with a particle size of 0-2 mm, and on the right, the coarser material with a particle size of 2-8 mm. Both fractions were obtained by mechanical sieving. They correspond to the particle sizes commonly used as aggregates in concrete and could therefore potentially replace natural aggregate in paving block mix compositions. For the production of the paving blocks, a reference concrete mix was used, consisting of 1000 kg/m%u00b3 aggregate in the 0-2 mm size range, 1000 kg/m%u00b3 aggregate in the 2-8 mm size range, and 250 kg/m%u00b3 CEM III/A 52.5 L. The water/cement ratio was 0.5. The mix was classified as earth-moist, ensuring immediate shape stability after compaction.62,763,352,745,1 44,0015304560750 5 10 15 20 25 30 35 40Compressive strength (MPa)Tailings in relation to cement content (Ma%)6,1 6,15,5 5,2 5,10,01,53,04,56,07,50 5 10 15 20 25 30 35 404-Point flexural strength (MPa)Tailings in relation to cement content (Ma%)Increase in packing density Crystallization nucleusThinning effect clinker content I IIw/G = 0,50Fig. 4: Compressive and flexural tensile strength results of concrete mixes, for which a part of the cement content was substituted by the tailings material.62,7 56,344,035,965,5 69,451,942,401020304050607080CEM SFA HM KSMCompressive strength (MPa)28 days 56 daysFig. 5: Comparison of compressive strength values, pozzolanic and inert materials.