# Influence of Recycled Precast Concrete Aggregate on Durability of Concrete's Physical Processes
## 1 Introduction  
Although construction has existed since the origin of civilization (Greek and Roman temples serve as an example), construction with structural elements of precast concrete is more recent. The origins of these precast elements date back to the early nineteenth century when, in Chicago, the first blocks based on lime cements and limestone aggregates were used in masonry walls, as an alternative to natural stone. Prefabrication is the industrialized version for construction and its many advantages include greater reliability (quality), dimensional precision, speed of execution, optimization of sections, greater work safety and longer useful life. Hence, in recent decades, many countries, such as the USA, Japan or The Netherlands, are promoting the prefabrication industry, consolidating the use of precast elements. However, and as with other activities related to construction, the precast sector requires a large amount of natural resources, since almost 80% of the total volume of concrete is aggregates. This is leading to a progressive depletion of natural resources, forcing all countries to adopt more sustainable construction. In this regard, it is worth highlighting the \"Precast Sustainability Strategy and Charter\" of the British Precast Concrete Federation [1] where measures to reduce energy consumption, eliminate waste and implement environmental and sustainable management systems were introduced. Furthermore, they have recently approved new targets in line with the Sustainable Concrete industry Strategy targets and the construction industry Low Carbon Route map to 2050. Therefore, taking into account that construction and all activities related to cement consume a large amount of natural resources, the recovery of concrete and its subsequent treatment to re-incorporate as a substitute for natural aggregate has taken on great importance. Since 2011, all precast sector companies in the European Union, complying with EU Regulation 305/2011 [2] have had to use natural resources sustainably. The use of recycled aggregates (RA) from concrete can be an alternative to natural aggregates for the manufacture of different types of concrete, which has a positive impact on the environment by reducing the continuous exploitation of natural aggregate quarries that produce an important environmental impact and also has a favourable impact on the economy. Numerous investigations have been carried out to find ways to use this type of RA in the manufacture of concrete [3; 4; 5; 6; 7; 8; 9], generally observing a decrease in the properties and durability of concrete. A possible cause of this reduction may be a consequence of the greater absorption of the recycled aggregate with respect to the natural aggregate, producing a reduction in the water/cement (_w/c_) ratio, which reduces the workability of the concrete and, therefore, its fresh properties. As has been shown in different studies, the use of superplasticizer additives can be an alternative to correct the workability and can be beneficial in terms of durability and mechanical resistance since it optimizes the _w/c_ ratio [6]. In this regard, [PERSON] [10] analysed the optimal amount of superplasticizer additive in the manufacture for self-compacting concrete. Regarding the use of RA, [PERSON] et al. [8; 11] analysed the possibility of incorporating multi-recycled aggregate for the manufacture of a multi-recycled concrete. The results showed that it was possible to incorporate this type of RA, but limiting recycling to a 3 rd generation aggregate. Regarding the mechanical properties, it has been shown that the quality of the recycled aggregate influences the compressive strength, especially when it is desired to obtain strengths greater than 30 MPa. [PERSON] and [PERSON] [12] showed that when using high quality RA, the results obtained can be better than those obtained for control concrete. The results obtained by [PERSON] when replacing 100% of the aggregate with waste from precast parts were in the same line [13].