The Alcántara Bridge is one of the most important Roman bridges in the world and has been a Spanish National Monument since 1924. Since its construction, almost two thousand years ago, it has suffered numerous damages due to the passage of time and human action, which has led to different interventions. The most important was that carried out by Millán (1856–1860), for the reconstruction of the arch demolished in 1810. During a visit to the bridge, areas with reinforced concrete were observed. Given the areas where it appears, the geometry of the reinforcement and its configuration, is possible to think that it is a very old intervention, which could date from the same period as that carried out by Millán. If so, it would be the first application of reinforced concrete in Spain and one of the first in the world. The aim of this study is to date the intervention and validate the initial hypothesis. To this end, based on a 3D survey of the rehabilitated areas using a drone, a comparative analysis has been carried out with the plans of Millán's project, as well as sheets and photographs from different periods to establish the date of the interventions. Research was also carried out in the archives of the Real Academia de Bellas Artes de San Fernando to gather information on the interventions on the bridge throughout the 19th century. Finally, the geometry and layout of the reinforcement is analysed in relation to the knowledge of reinforced concrete from its first patents worldwide to its widespread application in Spain. These analyses allow us to conclude that the date of the reinforced concrete repairs on the bridge is undoubtedly 1857, which would be the first application in Spain and the first in Europe on bridges.
Reinforced concrete is the most widely used material in the construction of bridges and buildings during the last 150 years. This new material emerged as the result of the combination of concrete and steel bars strategically placed inside the section of the structural element, which allows it to acquire the advantages of both compressive and tensile strength respectively .
On the other hand, concrete is the result of combining a binder, fine aggregate and coarse aggregate. The most common binders used in the manufacture of concrete have been aerated lime and hydraulic lime, giving rise to common and hydraulic concretes, respectively .
The first scientific studies of hydraulic binders were carried out by Smeathon for the construction of Eddystone's Third Lighthouse (1756–1759) in search of a material that would harden under water . But it was Vicat, at the beginning of the 19th century, who deepened his knowledge of the hydraulicity of limes, laying the foundations of hydraulic cement , the basis of concrete, and therefore of reinforced concrete.
Throughout the first half of the 19th century, natural cement was developed in Europe, which began to be manufactured in Spain in 1835 . Artificial cement, also known as Portland cement, began to be manufactured in France and Great Britain in the second quarter of the 19th century, but its manufacture in Spain did not begin until 1898, more than half a century late .
The Alcántara Bridge is one of the most important Roman bridges in the world due to its size and state of conservation. Since its construction almost two thousand years ago, it has suffered damage because of the passage of time and human action, and therefore, it has required restoration work. During an inspection of the bridge, areas with reinforced concrete were observed, which, due of its typology, suggested that it was a very old intervention. In order to date this intervention, a comparative analysis was carried out between the current situation, the survey plans that Millán made for the repair of the collapsed arch, the sheets from different periods and photographs from different dates. In addition, research has been carried out in the archives of the Real Academia de Bellas Artes de San Fernando on other possible restoration works on the bridge in the 19th century.
Following this research, it can be concluded that the areas of the bridge with reinforced concrete were built during the restoration work carried out by the engineer Millán (1856–1860). Specifically, the application of reinforced concrete was carried out during the year 1857.