Continuing with the use of ceramics in the construction of railway housing, regarding the floor slabs, in the first period analysed, corresponding to the construction of housing by RENFE, the so-called “autarkic” floor slabs prevailed, imposed by the restriction on the use of iron in construction (Decree 11 March 1941 (BOE no. 71 of 12 March 1941) in force until the publication of the Decree of derogation of 19 January 1956 and, subsequently, the approval of the MV 101/1962 standard, on “Actions in construction”. It should be pointed out that, despite the repealing decree, another subsequent decree was issued (Decree of 26 July 1957) which warned against the excessive use of metallic materials and that it would be advisable to issue a provision regulating their use, given the scarcity of the material. The policies of the time, in addition to the restrictions imposed, stressed the need to use traditional techniques. Along these lines, the General Directorate of Architecture called in its bulletin in 1947 for the use of traditional materials and techniques. Given the precariousness of materials and labour, the possibility of a certain guarantee and quality, albeit minimal, was seen in ceramic materials. The information bulletins of the Directorate General of Architecture (BIDGA) were published quarterly from December 1946 to the first quarter of 1957 (Pérez Escolano, 2013) and served as a chronicle of the architectural practice of the time. Essentially, these are slabs that were made with ceramic lightening elements and in situ or ceramic ribs with little reinforcement on the tensile side (one or two steel bars). The top slab, then called the “compression layer”, was 4 or 5 cm thick and had no reinforcement. There was also a variant of these slabs without an upper compression layer, which could be assembled on site or in the workshop (Muzquiz de Miguel, 1945). From the 1960s onwards, once the period of restriction had been overcome and, in our case, coincided with the dwellings built by the railway cooperatives, the type of slab that became the norm was made up of prestressed concrete joists. Between one period and another, around the 1950s and 1960s, the use of calcium aluminate cement (aluminous cement) became popular, especially in joists, which was banned for this use from 1979 onwards. To date, we have not detected its use in any of the projects analysed. In the cases under study from this first period, slab edges of between 13 and 20 cm are observed. Although the most commonly used solution is the 15 cm edge. They are made up of hollow bricks arranged every 25 cm (length), leaving a space of 5 cm for the ribs reinforced with a 12-14 mm steel bar on the lower face. The grooving of the brick walls was a guarantee of adhesion with the mortar. The most repeated dosage of mortar used was 1:2:3, using 340 kg of cement per cubic metre, and the coatings did not reach a centimetre, which is one of the most common causes of pathology detected in these slabs due to the lack of protection of the reinforcement. The regulatory requirements of the period meant that, in projects prior to 1957, any type of prefabricated slab was explicitly disdained because it was considered that “they were only weakly reinforced for rigidity before being placed in their definitive position, the reinforcement being completed afterwards with the small ribs that join them together. This, which is theoretically perfect, has the risks of prefabrication imperfections and failures due to deformations when the joists are raised to the floors”. However, the reality is that the limitations imposed on the use of iron during the post-war period led to the lowest quality moment in the construction of floor slabs (Azpilicueta Astarloa, 2004).
Illustration 1. Self-supporting slab section of the RENFE housing group in Las Matas (Madrid). AMF, project M-5476-VP.