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CONCRETE PRODUCTS & CAST STONE72 CPI %u2013 Concrete Plant International %u2013 4 | 2025 www.cpi-worldwide.comthe saturation curve, indicating pronounced pozzolanic reactivity. In contrast, the tailings material and limestone powder lie above the saturation curve, confirming their non-reactive, inert nature.As part of the investigations, the influence of the tailings material on the mechanical properties of concrete mixes was analyzed after partially substituting the cement content. The mixes were prepared and tested in accordance with DIN EN 196-1:2016. The reference mix consisted of 450 kg/m%u00b3 CEMI 52.5 N with a water/cement ratio of 0.50. Figure 4 shows the results of the compressive and flexural tensile strength tests after 28 days.At low substitution levels between 5 and 15 wt.-% based on the cement content, an increase in strength was observed compared to the reference mix. This effect is attributed to an increased packing density in the fine particle range as well as the function of the tailings material as a crystallization nucleus during cement hydration.With 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, 05101520253030 40 50 60 70 80 90 100CaO (mmol/l)OH- (mmol/l)Puzzolanic Non-puzzolanic Limestone powder Tailings MetakaolinCEM I Fly ash Saturation curveFig. 3: Frattini-Test according to EN 196-5.62,763,352,745,1 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.