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CONCRETE TECHNOLOGY40 CPI %u2013 Concrete Plant International %u2013 5 | 2025 www.cpi-worldwide.comthat the proportion of fine aggregate was kept constant in all mixtures, while the cement and water contents were varied. As the water content or w/c ratio increased, only the coarse aggregate fraction (8/16) was volumetrically reduced to compensate.Figure 2 shows the consistency of different concrete mix designs as a function of water content and maximum aggregate size (8 - 32 mm). As expected, all mixes exhibited a clear increase in consistency with increasing water content. Additionally, a strong dependency on the maximum aggregate size %u2013 and thus the particle size distribution %u2013 is evident. Mixes with a maximum aggregate size of 8 mm require significantly more water to achieve a specific target consistency than those with a maximum aggregate size of 32 mm. This is due to the higher specific surface area associated with finer aggregate blends. As the water content increases (at constant binder content), the paste content in the fresh concrete also increases. These observations align well with the minimum paste content requirements specified in DIN 1045-2:2023:08. According to the standard, the minimum required paste content increases as the maximum aggregate size decreases; For example, for consistency class F4, from 280 L/m%u00b3 (for 32 mm) to 305 L/m%u00b3 (for 8 mm). However, when considering the minimum paste content, it is important to note that these values cannot be directly applied to all types of fresh concrete mixes, since the variability in constituent materials, especially the coarse aggregates and sand, is not fully taken into account. Depending on the specific constituent materials used, each fresh concrete system ultimately has its own necessary minimum paste content, which may deviate from the generalized values provided in DIN 1045-2:2023:08.The consistency of fresh concrete with a maximum aggregate size of 16 mm as a function of water content is shown separately in Figure 3b. A relatively large variation in the results can be observed. For example, at a water content of 204 l/m%u00b3,the consistency values range from 38 cm (S4) to 50 cm (S3).This variation in consistency is solely due to the change in fine aggregate, while the cement content remains constant at 340 kg/m%u00b3. In contrast, changing the cement type while keeping the fine aggregate and water content constant shows significantly less impact on consistency. It can therefore be concluded that the fine aggregate plays a decisive role in determining the consistency of fresh concrete in the conventional 3-component system. These findings confirm the systematic studies described earlier. The composition and granulometry of the aggregate determine the paste demand required to achieve the desired consistency of the fresh concrete.Assuming, in simplified terms, that no binder paste but only water is adhesively bound to the surface of the aggregates in fresh concrete, the amount of water available for fluidizing the fresh concrete (Vw,flow) can be calculated based on the aggregate composition. This is done using the water required for surface wetting (Vw,s), as determined earlier, and the total mixing water added (Vw,z):Vw,flow = Vw,z %u2013 Vw,sFigure 3 shows the consistency of fresh concrete with maximum aggregate sizes ranging from 8 mm to 32 mm as a function of the determined water content Vw,flow, i.e., the effective amount of water available for fluidizing the fresh concrete. This approach allows the influence of the maximum Fig. 2: Water content in fresh concrete (3-component system, without plasticizing admixtures) as a function of the resulting slump flow for different concrete mixes, depending on the maximum aggregate size from 8 mm to 32 mm (a), and for mixes with a maximum aggregate size of 16 mm only (b).a) b)