# Determination of the Optimum Amount of Superplasticizer Additive for Self-Compacting Concrete
## 1 Introduction  
Self-compacting concrete (SCC) was developed to solve durability problems in reinforced concrete structures, which were appearing at the beginning of the nineteen eighties in Japan. These problems were due to the lack of experience of the workers in the construction sector, which had an impact on construction quality and, especially, durability [1]. For this reason, Professor [PERSON] of the University of Tokyo proposed the design of a concrete whose final result depended as little as possible on the construction process, more specifically, to mix a concrete that did not need to be vibrated after pouring [2; 3]. The use of SCC brings a series of advantages that can be classified into two types: logistical and technical. The logistical advantages are a consequence of eliminating the vibration phase for concrete, in other words, the number of operators and the execution time are reduced [4]. In addition, eliminating the vibration phase provides savings in electricity costs and reduces noise pollution. The technical advantages are derived from this concrete's greater flow capacity, which, regardless of the density of the reinforcement, makes it easier to pour and even pump. It can better encapsulate the reinforcements and facilitates the filling of formworks with complex geometries [5; 6]. It is estimated that approximately 10% of man-made CO\({}_{2}\) emissions are from concrete production and transportation [7]. SCC is one of the most eco-friendly types of concrete because waste materialshave always been used in SCC as the mineral powder, such as marble powder or fly ash [8]. This substitution is generalized because SCC requires a high quantity of fine particles and, in order to limit the economic cost by reducing the quantity of cement, other fine particles are used. As an example, [PERSON] et al. [9] found that the optimal cost solutions have quite satisfactory environmental outcomes when using high strength SCC for the construction of precast-prestressed concrete U-beam road bridges. There are three main differences between SCC and conventional concrete are in terms of composition. The first of these is the use of a lower content of coarse aggregate, which usually has a relatively small maximum size, in order to minimize the segregation tendency [10]. Secondly, it has a higher fine particle content, specifically, with fines of less than 125 \(\upmu\)m. Thirdly, and most importantly, it is imperative to use superplasticiser admixtures (SPAs) in order to achieve the workability necessary for a self-compacting concrete [11]. These three conditions must be fulfilled to generate a mixture with an appropriate viscosity/flowability ratio, which allows the fresh mixture to flow, but without allowing any of the concrete components to segregate [12]. SPAs are considered to be the most important element in SCC. The progress, evolution and popularity of SCC in recent years has been driven by progress in the chemical formulation of the latest SPA generation. The polycarboxylate type SPA makes it possible to achieve appropriate workability and flowability in concrete in spite of the high content of fines that these concretes have, making the mixture more viscous and reducing the amount of water by up to 40% [13]. In addition, it has been shown that the use of these SPAs enables the recycled concretes to minimize the property reduction caused by using these recycled aggregates [14; 15; 16]. Nonetheless, as [PERSON] et al. [17] concluded, the optimization of the water content is necessary to balance the extra water required by the high water absorption of the recycled aggregates and the reduction in the effective water/cemet (w/c) ratio required to increase the mechanical properties of recycled concretes. There is no specific tool for determining the optimum amount of SPA for SCC. A lack of SPA in the concrete without enough flowability can lead to serious durability problems in structures. A low flowability can cause high porosity and permeability with a corresponding loss of durability.