UHPC is considered one of the most innovative cement-based engineering materials in the 20th century. At present, France, Switzerland, Denmark, China, Japan, and the United States are all countries with active UHPC development. These countries are committed to research on related technologies and development trends of common structures, such as single buildings, bridge decks and their joint connections, and bridges. Structural and restoration, balcony, staircase construction, and more.
• Pedestrian bridge and bridge deck applications
In Spain, there are also different types of institutions promoting implementation in this area. In fact, the first application of UHPC in Spain can be traced back to 2003, in the composite structure project of the Reina Sofia Museum in Madrid. Ductal®-AF is used to cast a structure with a height of 16m and a diameter of 32cm. Unfortunately, there is little information about this project, which is also a milestone for UHPC internationally.
The second application of UHPC in Spain came a decade later, in 2013 when a pedestrian bridge across Oveja's Ravine was completed in the Mediterranean city of Alicante. With a span of 43m and a width of 3m, the structure became the world's first truss pedestrian bridge built exclusively with UHPC. The UHPC mix uses locally available materials and has an average compressive strength of 150mpa after air curing.
Since Valencia is an open city, the construction plan was proposed and the final project was realized.
The structure received the 2013 Civil Engineering Award from the Spanish Civil Engineering Association ACHE, as well as the 2019 ACI Architecture Award in recognition of the project's designers' outstanding contribution to the industry. Now, nearly 10 years later, the structure requires no maintenance and remains in perfect condition despite being exposed to an XS1-level environment.
Following this successful experience, two more pedestrian bridges were built in 2014. One is located on the V-21 motorway in Puçol, Valencia, and the other is the Guadassuar pedestrian bridge built in 2016.
The footbridge structure has a span of 30-33m, achieving a more industrial, prefabricated solution allowing it to achieve minimal maintenance costs compared to other options.
The decks of all these footbridges are 35mm thick unreinforced UHPC panels, made from a mix of UHPC and hook-end steel fibres. Since 2016, this solution has been used in many different types of projects as technical flooring in sizes up to 2×3 m.
In 2021, Spain's fourth UHPC pedestrian bridge was installed in Sollana, with a span of 15.4m. Before the end of 2022, a second pedestrian bridge with a span of 35m will be put into use near Valencia.
• Application of floating structures in offshore ranches
In 2015, the local UHPC research and development agency identified a major persistence problem in the aquaculture sector: Galicia has 3,337 floating farms used to harvest mussels, and their lifespan rarely exceeds 10-15 years. Therefore, they decided to design a floating structure similar to UHPC beams. The UHPC beam structure can maintain the same weight, the structure is more adaptable to the impact of waves, and has better durability. Therefore, floating structures made by UHPC came into being. In October 2016, the team installed the first 365㎡ floating raft prototype for AZTI in the Cantabric Sea. This became the world's first UHPC floating structure and the first application of this material in aquaculture.
From a business strategy perspective, the idea of bringing such a product to market may seem crazy, as UHPC floating farms have four clear obstacles:
Fishermen have inherent conceptual barriers: they don't believe in concrete because they see a lot of corrosion in the harbor;
Transportation obstacles: The UHPC product production factory is 1,000km away from Galicia, where the traditional raw material for floating rafts (eucalyptus wood) is abundant, which means that using the new solution will face double difficulties;
Price barrier: UHPC solutions are 25% more expensive than traditional solutions;
Knowledge Barrier: UHPC R&D facilities are experts in advanced materials, but not in seafood farming.
Despite the numerous obstacles above, there is one key fact that allows R&D institutions and practitioners to enter the market: the customers are the maintainers of floating rafts, and they know exactly how much money they spend each year to protect and repair wooden structures. Therefore, the advantage of UHPC floating structures in reducing maintenance costs is highlighted, making it more logical for them to enter the market. There are currently more than 20,000 square meters of UHPC floating raft structures used in Galicia, Valencia, the Adriatic Sea, the North Sea, and the Baltic Sea.
Inspection status of the first UHPC raft 5 years after installation (2016-2021). Despite being in an environmental class of XS3 and withstanding waves up to 1.2m, the structure remains in good condition with no signs of corrosion. UHPC floating rafts can withstand waves up to 3.7m. Taking the floating raft at the Baiona River estuary in Galicia as an example, it is still in perfect condition.
• Highway bridge structural applications
In 2018, Spain's first UHPC road bridge was completed. The project mainly completed the installation of a road bridge deck with a span of 7m (the bridge was damaged by the flow of the Vernissa River in 2007).
The scheme consists of three bi-directional UHPC prefabricated elements (40cm thick) to withstand future high-flow floods and improve durability.
In 2019, a bridge in Alcira (50 kilometers away from the previous one) was hit by a truck, destroying its original two double T-girders. The contractor designed new UHPC beams so that if there were new collisions in the future, the beams would not be damaged. The new UHPC double T-beams are prestressed and manufactured in the factory to the same dimensions as undamaged ordinary concrete beams.
• Building structure repair applications
In 2020, following the global lockdown caused by the coronavirus disease (COVID-2019), UHPC materials offer possibilities for a variety of application scenarios. In 2021, a Spanish company used UHPC to restore a four-story historic building. The building, built in 1900, required increased maximum design loads and had to comply with minimum floor height requirements. Due to height issues, typical concrete or steel floors were not allowed to be installed. Additionally, given the special conservation requirements of this heritage building, some wooden floors needed to be integrated as new floors.
For these reasons, the building was restored using UHPC materials. The solution minimized the weight per square meter of flooring, avoiding overloading the historic building. UHPC delivers 40% performance after 24 hours, so it facilitates project progress and early removal of formwork.
• Development and application of functional components (swimming pool)
In 2021, Casas InHaus, a Spanish prefabricated housing company, designed a 12m-long cantilever structure swimming pool. Increasing the length of the cantilever was the most challenging. The use of UHPC reduces weight by 70% compared to traditional concrete structures, so the thickness of the members is reduced and has greater architectural value. This case illustrates that the lightweight of UHPC structures can not only reduce costs but also provide additional value through aesthetic and artistic effects, allowing customers to choose solutions that cannot be achieved with other materials.
• Solar floating structure applications
In 2022, UHPC components will be used in floating solar plants. This is the first time in the world that UHPC materials are used to solve problems encountered in offshore photovoltaic projects. The patented design protects the UHPC pontoon platform from the impact of waves while serving as a stiffener to minimize the number of moorings to achieve the goal of reducing costs. This solution is currently available on the market. The design is used in the largest artificial lake in the European Union, and the installation is the largest floating solar power plant in a dam in the European Union.
Using UHPC is more competitive than other materials because both durability and lightness provide a competitive advantage in this application. Durability is important due to wear and tear from wet conditions and waves.
The lightness of the solution is reflected in the following aspects:
The average density of a pontoon is less than 1. If the pontoon plate is thinner, the weight is lower, so the density can be kept below 1 by reducing the thickness of the pontoon plate, thereby saving more weight and reducing costs. This makes UHPC pontoons significantly competitive with traditional concrete solutions.
Lightweight members require a reduced draft to float and therefore reduced hydrodynamic forces, which saves mooring points and connection costs.
Transport and operating costs can be significantly reduced, with this case halving transport costs compared to traditional solutions.
• Floating substation structural applications
Durability, lightness, fire resistance, and flexibility are the main advantages of the floating substation at the Alqueva factory. This substation is an ancillary supporting solution for the "Solar Floating Structure" mentioned above, making it the first substation in the world to be completed using UHPC. The size of the substation is 12.3mx 6.5m, the thickness is 1.29m, and a 22t container is designed in the center.
These successful applications prove that Spanish engineers and users have a deeper and deeper understanding of the possibilities of UHPC.
