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CONCRETE TECHNOLOGY48 CPI %u2013 Concrete Plant International %u2013 5 | 2025 www.cpi-worldwide.comFigure 9 shows the determined slump flow diameters of the individual concrete mixes, depending on the type of fine aggregate used and the water content. With a water content of 176 l/m%u00b3, the target consistency of 52 %u00b1 3 cm couldbe achieved for all concretes, regardless of the sand type. However, when the water content was reduced to 162 l/m%u00b3,it was not possible to achieve the target consistency when using Sand S4. The addition of plasticizing admixtures did not result in sufficient liquefaction but rather led to pronounced segregation. Similar behaviour was observed when the water content was further reduced to 146 l/m%u00b3 with Sand S1. This is due to the physical properties of the mix (i.e., the system-dependent minimum paste content) and the exceeding of the saturation point. The characteristics of the different sands mean that at the given water content, there is not enough available paste to enable proper liquefaction (see [6]).When comparing the results to the estimated minimum water contents determined in Figure 7, a strong correlation is observed (see Figure 10). Concretes with a water content above the estimated minimum were consistently able to reach the target slump flow of 52 %u00b1 3 cm when using plasticizing admixtures. In contrast, for concretes below the estimated water content (marked in red), liquefaction was not possible with Sands S1 and S4 due to the system-dependent minimum paste content and the exceeding of the saturation point (indicated by dark-filled symbols in Fig. 10). The only exception is the concrete with Sand S3 and a water content of 147 l/m%u00b3.Despite being below the estimated minimum water content of 155 l/m%u00b3, this fresh concrete could still be liquefied using plasticizing admixtures without any segregation, and the target consistency of 52 %u00b1 3 cm was reliably achieved (indicated by a white-filled symbol in the red area in Fig. 10). It should be noted that the estimated minimum water content is not a strict threshold, but rather a guideline value. Therefore, even below this value, it is still possible to produce stable, flowable concretes, depending on the specific raw materials used.7 Summary Based on systematic investigations, this article described and discussed the influence of different granulometric properties of fine aggregates on the workability and water demand of fresh concrete. In addition to common physical properties, the water demand required to wet the surface of the aggregate was experimentally determined. The experimentally obtained values clearly show that the grain composition of the aggregate is particularly decisive for the workability and consistency of the fresh concrete, considering a constant water content in the classic three-component system.Building on the experimental investigations, a concept was developed to estimate the minimum possible water content of a specific concrete mix, taking into account the addition of plasticizing admixtures. To achieve the desired consistency with plasticizing admixtures, a sufficient paste content in the fresh concrete is required. If there is insufficient paste and the voids between the aggregate grains are not fully filled, increasing the amount of plasticizing admixture will not lead to liquefaction of the fresh concrete but will cause segregation and instability due to exceeding the saturation point of the chosen concrete composition. Using established testing Fig. 9: Slump flow of the investigated concrete mixes with varying water content (176 - 147 l/m%u00b3) at a constant cement content of 360 kg/m%u00b3.Fig. 10: Water content in fresh concrete (three-component system, without plasticizing admixtures) as a function of the resulting slump flow for different concrete mixtures to determine the %u201czero-consistency%u201d (WNullk,38cm).