## 1 Introduction  
In recent times, the problem of preservation of reinforced and pre-stressed concrete structures has been developing rapidly. In fact, nowadays, as a consequence of the use of a bad mix design and inaccurate casting and execution of structures that occurred around the fifties, many structures present serious degradation phenomena. Moreover, there is a higher concentration of industrial and natural aggressive factors in the environment that can cause material degradation when compared to about forty years ago [1]. With a correct mix design, the appropriate use of super-plasticizers, low water/cement ratios, and, especially, the addition of materials constituted by very small granules obtained from the pozzolanic activity, it is possible to reduce the empty spaces in the particles of the concrete mix and get waterproof concretes with good mechanical strength characteristics. The field of concrete technologies and its production is a current research topic. In recent years, recycling and re-use have become critical issues to develop concrete technologies and build reinforced concrete structures with a long service life and that, at the same time, are able to satisfy economic and environmental issues [2,3]. As a consequence, the use of industrial by-products or solid wastes in concrete production, such as fly ashes (FA), blast-furnace slag, and silica fume (SF) is increasing. Quite good mechanical properties, in fact, are obtained from concretes that use as aggregates calcareous rubble and, in total substitution of sand, blast-furnace slag [4]. Slag is constituted by scoriae at the liquid state; they remain in the furnace and are eliminated during the cast iron production. Approximately 300 kg of slag is generated per ton of pig iron. In particular, the slag cools in extremely quickly and prevents the crystallization process. As a consequence, it solidifies in glass granules mixed with foamy fragments [5; 6]. From this process it is possible to obtain the so-called granulated blast slag, an industrial by-product, which can be classified as waste [7], thus increasing problems associated with environmental pollution. Therefore, the aim of this study is to try to increase its possible uses, especially in the field of construction [8; 9]. Due to its low iron content it can be safely used in the manufacturing of cement. Two types of blast furnace slag, air-cooled slag and granulated slag, are being generated from the steel plants. The color of granulated slag is whitish. The air-cooled slag is used as aggregate in road making, while the granulated slag is used for cement manufacturing. Although it has no behavioral problems, its use as aggregate in concrete is not very common and there has been little research work done on the subject. The optimum cement replacement level with granulated blast-furnace slag is often quoted to be about 50% and sometimes as high as 70% and 80% to get an improvement of the mechanical and durability properties of concrete and to generate less heat of hydration. On the other hand, concrete based on Portland cement is the most widely used material in the world. Compared to other materials like steel, aluminum and plastics, it is the most viable option for the construction industry considering economic and environmental costs. Nonetheless, it is estimated that 7% of anthropogenic CO\({}_{2}\) corresponds to the ordinary Portland cement production; considering the current global environmental situation, it is obvious that cement and concrete specialists must search for ways to reduce that figure, or at least to avoid its growth. One of the possibilities is the massive usage of industrial wastes like blast-furnace slag, to turn them into useful environmentally friendly and technologically advantageous cementitious materials [10]. In a previous study, the slag partially replaced 30%, 50% and 70% of Portland cement, and the cement's strength reduced as the amount of slag increased [11].