# Determination of the Optimum Amount of Superplasticizer Additive for Self-Compacting Concrete
## Materials and Methods
### Concrete Mixer Method  
From each step, the last 50 s were selected (each step has a duration of 180 s), when the step is already considered to be stabilized. In this section, the maximum recorded power value is selected. The decision was made to record the maximum value because this value reflects the moment when the concrete exerts the greatest resistance to the rotation of the blades, i.e., the moment when the concrete is least fluid and therefore the most unfavourable situation for each step (once it has stabilised). Figure 13 shows the evolution of the power consumed by each of the phases during the mixing process for the different partial quantities of the SPA/C. In this graph, each time the SPA/C is increased, there is a corresponding decrease in power or what would be equivalent, a corresponding decrease in viscosity, or increase in fluidity of the mixture. It can be seen that when exceeding 1% of SPA/C, the power tends to stabilize, but it is from 2% onwards that the power becomes constant, which is why 2% of the SPA is defined as the optimum percentage of SPA, also coinciding with the saturation point measured through the Marsh cone test and the rest of the tests on the fresh concrete.  
Figure 12: V-funnel tests results.  
Figure 13: Evolution of the concrete mixer maximum power as a function of the SPA/C ratio.  
Correlation between the Results from the Marsh Cone, Concrete Workability and Concrete Mixer Methods  
A correlation was found between the results obtained using the Marsh cone test and the concrete mixer method. Through both methods, it is possible to determine the same saturation point in terms of the SPA/C value, from either the time, in the case of the Marsh cone test, or the minimum value of the mixer power consumption, in the case of the concrete mixer method. In addition, through both methods, a significantly greater effect can be seen when the SPA/C is less than 1%, from which point the effect decreases until approximately 2%, where the effect is almost zero.  
If concrete mixer method results are correlated with the slump flow test results, it can be seen that results proportional to those of t\({}_{500}\) and inversely proportional to D were obtained. In this test, it is also possible to detect that the effect of the SPA/C is greater up to the value of 2%, a value defined as the saturation point both by the Marsh cone method and by the concrete mixer method.  
If the concrete mixer method results are correlated with the L-box test results, it is not possible to determine a proper correlation. This is because the L-box test evaluates the passing capacity of concrete while the concrete mixer method evaluates the flowability of concrete. For this reason, the concrete mixer method is not a direct alternative for the L-box test, since the concrete mixer method does not enable the evaluation of whether there is segregation. Since segregation implies that either there is an excess amount of water or that the SPA no longer interacts with the concrete but remains on its surface, it is understood that segregation is only possible in the section where the maximum power consumption value is already stabilized. Therefore, if progressively greater quantities of SPA are added, the onset of segregation could be predicted.  
If the concrete mixer method results are correlated with the V-funnel tests results, as both methods evaluate the flowability of concrete, it can be appreciated that there is a direct relationship between the two methods.