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CONCRETE PIPES AND MANHOLES134 CPI %u2013 Concrete Plant International %u2013 5 | 2025 www.cpi-worldwide.comterial%u201d is then separated into the various fractions by a sieve system. The cement paste, ground into powder, leaves the mill with the air and is separated by a filter system. If desired, in a separate second step, the powder can be carbonated with CO2 in batches in a special reactor. The amount of CO2bound in this process, approximately 50-60 kg per ton of powder, is measurable and can therefore be certified.Laboratory tests to determine the concrete conceptAs part of a pilot project with the Federal Association of Concrete Sewer Systems (FBS) and the R%u00f6ser Group, pre-crushed concrete pipes were treated using Sika%u2019s reCO2ver process at the pilot plant in Weiach, Switzerland, to produce new pipes with the recovered materials at the R%u00f6ser II site in Krauchenwies. Since there was no experience with the industrial application of reCO2ver material in semi-dry concrete at that time, the concrete was designed and tested for its production and quality properties in laboratory tests. The following steps were carried out in Sika%u2019s special laboratory for semi-dry concrete technology in Leimen:1 Characterization of the aggregates2. Development of the concrete concept3. Comparison of fresh and hardened concrete dataIn the first step, both the original material and the reCO2ver material were examined for density, water absorption, grading curve, and grain shape. Visual inspection of the reCO2ver material revealed only a few cement-stone residues on the grain surface (Fig. 2). Analysis using the Sika Sand-App revealed a grain shape comparable to the original grain (Fig. 3). The density of the reCO2ver material was slightly lower than that of the original material, which can be explained by the remaining cement-stone residues. The water demand increased only slightly, from 0.7 mass% (concrete suction water 13 l/m%u00b3) to 2.1 mass% (concrete suction water 39 l/m%u00b3) with 100% reCO2ver material.Using the data obtained, a grading curve comparable to the original material was created with the two fractions sand 0/4 (35%) and gravel 4/8 (65%). In the first concrete design, a 100% volumetric replacement of the original aggregates Fig. 2: Visual comparison of the original aggregate with the recycled aggregate treated with the reCO2ver processFig. 3: Comparison of the grain shape of original aggregate and recycled aggregate treated with the reCO2ver process%u00a9 Sika Deutschland CH AG & Co KG %u00a9 Sika Deutschland CH AG & Co KG