Ellis Davies takes a look at the materials and construction techniques used in the Basilica de la Sagrada Família.
On 19 March 1882, the first stone of the Sagrada Família was laid during a ceremony delivered by the Bishop of Barcelona, Josep Urquinaona. Since the placing of that single stone, the famous Basilica has slowly climbed to a height of 172m, making it the tallest church in the world, covering around 9,000m2 of central Barcelona – and it’s not done yet. The landmark will not be completed until 2026, at which point its construction time will total 144 years.
The lengthy construction means that the Sagrada Família has seen an array of materials and methods, and therefore offers a unique look at how technology and understanding has progressed over the last century. A multitude of architects have also worked on the project, all stemming from Antoni Gaudí, the first chief architect of the Basilica.
The Gaudí era
In 1883, the project was handed over to Gaudí, who set about designing the Basilica to express Christian belief through architecture in the hope of combining religious iconography with form. The 18 towers of the Sagrada Família are each dedicated to a religious figure, such as Jesus Christ (the middle tower) and the Virgin Mary (the star crowned tower). Gaudí famously said, in relation to the time taken to build the Basilica, ‘My client can wait,’ as he believed that it was God that the project was being built for.
From 1914, Gaudí concentrated exclusively on the Expiatory Temple of the Sagrada Família, even going as far as to live close to his studio workshop at the site for the final few months of his life. Gaudí would only see the completion of the Saint Barnabus tower
in 1925, before he sustained fatal injuries in an accident involving a tram – he is buried in the Chapel of Our Lady of Mount Carmel in the crypt of the Sagrada Família.
The project was handed over to Domènec Sugrañes, who had collaborated closely with Gaudí. Sugrañes oversaw the finishing of the bell tower on the Nativity façade, as well as the faith portal and central cypress tree. Following an attack by Spanish revolutionaries during the Spanish Civil War, a fire in the crypt of the Sagrada Família destroyed many original plans and models, which hampered the progress of the project significantly.
Towers, towers, towers
The bell towers that were constructed during Gaudí’s lifetime are made from Montjuïc sandstone, which creates a supply issue today – the quarry from which this stone was extracted has shut down, meaning that the material can only be obtained from demolished buildings. David Puig, Technical Architect at the Sagrada Família, told Materials World, ‘For this reason, extensive research was done to find materials similar in character and properties. Several stones have been found that meet the requirements of durability, resistance and colour. The solution is a combination of several stones that emulate the original closely.’
The towers are largely made from granite. These include the Jesus, Mary and the four evangelist towers. Vladimir Marinov, former Senior Engineer at Arup, UK, spoke about the company’s involvement in the construction of these remaining towers at the Materials 2017 conference. ‘What's interesting about the structure of the Mary tower is that it's not just granite masonry – that would not have worked at such a height. The way the structure works is that the granite is post-tensioned with ultra-high-strength stainless steel rods up to 400 kilonewtons, and the masonry is then reinforced by stainless steel columns necessary to reach such a height, particularly in the seismic area that Barcelona is,’ he said. The Mary tower stands at 120m, five metres shy of the evangelist towers.
As you would expect, the tallest central tower is devoted to Jesus. Reaching 172m, it will be topped by a 30m-tall cross, which will be accessible upon completion as a viewing gallery. The Jesus tower shares a similar construction to the Mary, but also features a parabolic staircase to allow visitors to access the spire. The staircase is 60m high with a platform at the top, and is a post-tension granite structure, which counter-levers from a post-tension granite core. Restrained to this is a glass elevator, which navigates a hanging glass cylinder that has minimal steelwork – only at connection points. The load of the structure is borne by the glass and silicone – each piece of glass is roughly 1 x 2.5m and the joint in the glass occurs where the staircase begins to spiral.
Marinov highlighted the doors of the lift as a particular point of interest. ‘The doors to the lift use something that has never been done before. This is a cylindrical titanium insert, and to laminate this in, the glass is first of all slumped, and then 3D scanned. Based on the scan, the piece of titanium is made to the correct geometry and laminated in,’ he said.
The platform of the Jesus tower will also have a double helix staircase, which will ascend to the cross viewing platform. The opening of the cross is around 1m wide, so will be an exclusive vantage point. Visitors will ascend to the platform in the lift, use the double helix staircase to gain entrance and exit the cross, and descend via the spiral staircase to ease congestion.
The Sagrada Família has been constructed using a large amount of concrete throughout, a material that Gaudí first used for the pinnacles of the Nativity façade. The first use of high-strength concrete was in 1998 in the construction of the columns of the transepts that support the evangelist towers and the central dome. In 2008, Josep Gómez, Ramon Espel and Chief Architect Jordi Faulí produced a report that highlighted the construction techniques and materials used in the Sagrada Família, including the use of reinforced, high-strength and white concrete. ‘The project requires structures that will be able to withstand the compression loads and will also respect the shapes and diameters set forth by Gaudí. Increasing the strength of the concrete decreased the amount of steel needed in the dense reinforcements, facilitated the construction process and prevented the builders of the Sagrada Família from having to bulk up the diameter of the columns,’ they said.
Hanson, part of the Heidelberg Cement Group, Germany, has been the exclusive supplier of white concrete to the Sagrada Família since 2010, providing around 500m3 of material. Carlos Sanchez of Hanson told Materials World, ‘The white concrete – branded as H-Blanc – supplied to Sagrada Família is not only aesthetic, but structural. It was used for the base of the future large central tower (the concrete was poured at 80m height). The importance of this product is based on a type of white concrete that, after many tests, is similar to the original stone used by Gaudí.’ This concrete has also been used in the large pilasters of the new façades, which were later covered by stone or bricks. Sanchez highlighted the need for high-strength concrete for this construction.
The decision was made to use white concrete poured in situ, whereas the concrete columns in the main nave are prefabricated architectural concrete, which cannot hold as much – 35MPa rather than 80. The team also took into account performance goals when choosing the concrete, including on-site workability, low porosity, good durability and an appropriate colour. The concrete is produced with white cement, non-coloured additive and limestone from Hanson’s quarries. It is fast hardening, and has a seven-day compressive strength of 45MPa. White concrete was used for pillars and the surrounding walls, whereas high strength concrete is used for pilasters, foundations and pavements. ‘Due to the height, white and high-strength concrete were poured into a concrete bucket and then elevated with the help of a crane. Standard concrete, for floorings or filling, was pumped and then vibrated and compacted,’ Sanchez explained.
Concrete is also used in the vaults, which are 30m above ground level and were built using moulds as a framework to make the replication of many elements an easier task.
The modules are modelled with plaster in a workshop and polyester moulds produced, which are pneumatically sprayed with gunite mortar, fitted and concreted.
The construction techniques employed at the Sagrada Família have evolved over the many years of the project. Gaudí‘s early work can be identified by the more traditional ashlar stonewalls carved with irregular filling in the middle, whereas his later work takes a different approach. ‘In the last years of his life, building the terminal faces of the towers of the Nativity, he used a completely different approach, applying the then-novel reinforced concrete, which used prefabricated Venetian glass. This technique allows you to streamline the process and reduce the number of operations at height,’ Puig said.
In recent years, prefabrication has been more widely used at the site to increase speed and minimise risk. ‘This is a process of changing from completely handmade production, which was
done with the abundant skilled labour that existed at the time of Gaudí, to an increasingly industrialised form of production. There are two reasons for this change – there are fewer skilled workers and the adjustment to the industrialised world makes it possible to increase the production rate,’ Puig said. Some techniques have, however, remained, such as the use of models. The models used by the modern day team are created using computer-aided design (CAD) software, but Puig says that the need for physical modelling is still an essential part of the design process, as it was for Gaudí.
CAD was first used on the project in 1991 by a team led by Josep Gomex Serrano, who used CADD-S5 to draft new designs for the Basilica. The use of 3D modelling allows for a precise design, which can also reduce cost and time significantly. This technique has become a staple of the project, as Marinov described, ‘Nothing goes on paper, it goes directly from the model to a robotic arm and the [materials] are then cut precisely to shape and size. What's interesting is that because of this we can engineer the stone and steel very precisely.’
The development of materials has also had an effect on the plans for the Basilica. Materials such as modern high-strength concrete, various types of mortar and stainless steel were not available to Gaudí, and materials that are the result of more industrialised construction such as engineered wood, glass and light metal elements have also been used. Modern builds have to adhere to a different concept of performance and comfort that they did in the early 20th Century, and ‘the Sagrada Família therefore adapts to provide valid solutions for the project. As examples we can mention the requirements for evacuation, protection and comfort facilities,’ Puig explained.
Currently 70% complete, the Basilica de la Sagrada Família is an eclectic mix of traditional and modern architecture, while holding true to Gaudí’s broadly defined project. The original intention to use materials now unavailable or not fit for purpose has provided aesthetic and engineering challenges, but has likely improved the overall construction of the church. Even unfinished, the Basilica is one of the most popular tourist attractions in Europe, allowing the construction to be almost entirely paid for by ticket sales. The Basilica is unique, from its architecture to its place in Spanish history.