Building better, for longer, with less:

“holistic” lessons learned from H2020 ReSHEALience project on material concept, structural application and life cycle analysis of Ultra High Performance/Durability Concrete

The recently concluded Horizon 2020 ReSHEALience project has developed a new conceptual design approach for concrete structures exposed to challenging structural scenarios, including extremely aggressive environmental conditions. Ultrahigh Durability Concretes (UHDC), based on Ultra High Performance Fibre Reinforced Concretes (UHPFRC) and Textile Reinforced Concretes (TRC) incorporating nano additives to enhance functionalities, have been developed and validated, under mechanical and aggressive scenarios in lab and on-site. The approach combines, in a holistic life cycle thinking framework, higher and longer lasting performance with enhanced structural functionality and high value aesthetic requirements. The signature of high resilience material concept developed and validated in the project – “branded” as UHDC – also features the possibility of engineering the structural performance over time through its self-healing capacity, i.e. the ability of the material to self-repair without external intervention but thanks to its suitably designed composition cracks and defects. Thanks to this innovative conceptual design approach for structural engineering, concretes are no longer regarded as providers of passive protection only, whose degradation over time has to be delayed as much as possible, but become active players in shaping their own performance as a function of the requirement in the operating scenario while retaining functionality and aesthetics. The conceptual design approach, suitably “nestled” into a life cycle thinking framework, represents a key driver for advanced materials innovation uptake in concrete construction industry. The overall performance assessment must no longer rely on the merely misleading concepts of material unit volume cost and environmental impact at its time of generation. Contrarily, it has to be framed appropriately into a structural functional unit context all along its service life. The project results have demonstrated that up to 60% less amount of material can be used to achieve the same or higher structural and durability performance, with maintenance from five to ten times less frequent all along the reference service life period.
This represents a breakthrough innovation in the approach of concrete construction industry to the use of advanced cement based materials, overcoming the current situation where Ultra High Performance Concretes are very often promoted only through their extremely high compressive strength, whereas their higher durability is simply accepted as a bonus but has hardly been quantified as true benefit in design, construction, maintenance and use stage of buildings and structures.
This new concept has been demonstrated by the project consortium in six full-scale pilot applications serving a broad portfolio of challenging societal needs, also implementing a synergic contribution towards the EU decarbonisation objectives. They include: two tanks, for water (TRL6) and mud (TRL7) collection, in a geothermal power plant in Italy; a floating raft for mussel farming (TRL7) and a floater of an offshore wind tower in Spain (TRL6) (Mediterranean sea); a floating pontoon in Ireland (TRL6) (Atlantic west coast) and the retrofitting of a reinforced concrete heritage structure in Malta (TRL7). The pilots have been and will be continuously monitored also after the project termination to support the validation of the project main concepts and results.
The project, throughout its lifespan, has organized 5 thematic workshop, onw of which in collaboration with Fondazione Politecnico di Milano Innovation House at Expo 2020 Dubai and  more than 60 dissemination events throughout the world, also in synergy with our twin project Endurcrete Project, including more than 10 continuing education workshops for professionals and participation into 6 major international fairs. We have delivered 10 newsletter issues, distributed to more than 1200 subscribers and also in synergy with Smartincs – ITN – H2020 project and one podcast. Our work has been summarized in 35 deliverables and , as of now, in 24 papers published in major peer reviewed journals and one MOOC. The papers and the MOOC are available through our project website www.uhdc.eu
Last but not least, in the framework of the project, 9 PhD theses have been completed or are on their way to be completed and more than 50 MSc theses have been developed and defended by young researchers and engineers. Together with the project consortium partners, these young colleagues will now use and spread in their profession the experience and knowledge garnered in the field of advanced cement based materials, monitoring and durability based design, life cycle analysis and sustainability and continue to demonstrate that WE CAN BUILD BETTER AND FOR LONGER WITH LESS.

Liberato Ferrara.  ReSHEALience Project Coordinator.
Department of Civil and Environmental Engineering, Politecnico di Milano liberato.ferrara@polimi.it

FOCUS ON OUR PILOTS

Water tower restorationand strengthening

Carried out by University of Malta (UoM)

The reinforced concrete water tower is 15m high with a 10m diameter tank having a capacity of 400 m³ of water. The structure suffered severe degradation due to exposure to the sea and the storage of water with high salinity. The structure was assessed in detail through documentation, advanced non-destructive techniques, material experimental analysis, micro-tremor structural assessment and biological assessment. Finite element modelling was exploited for the analysis of the structure and assessment of optimised solutions. Advanced restoration interventions necessary included polymer cement-based repair, corrosion-inhibitors, reinstatement of concrete, electrochemical chloride extraction and re-alkalisation of concrete, bond enhancement and assessment between existing RC and the UHPC. Replica structures were constructed for the testing of the strengthening materials. The complex interventions were developed to support the conservation principles adopted and relied on the optimised solution, through strengthening of the columns using UHPC, with TRC developed for the tank shell elements. It was decided to proceed with a full conservation project to reinstate the Water Tower and bring it back into operation as a useful asset, Industrial heritage in service. A complex scaffolding system was set up, together with a UHPC site production facility supported with a quality management and inspection setup.

A new research station was set up next to the Water Tower, hosting the monitoring station for long-term performance monitoring of the structure. The sensor network system (complex 150 sensor system) is based on three categories: Durability sensor system; Structural Health Monitoring and Environmental monitoring. The sensors are connected to a data logging station and data is stored in the cloud and analysed. The durability sensor system includes galvanic and resistivity sensors developed at the UoM together with Embedded Electrodes and temperature sensors. These sensors were installed in the replica structures for validation and then in the water tower structure, at different heights, in different structural elements (columns, cone, drum) and on different orientations (N,S,E,W) to assess performance. The structural health monitoring system includes strain gauges and accelerometers, installed in different elements / orientation and at different elevations. A weather station was installed next to the water tower to monitor wind direction and intensity, precipitation, insolation, temperature and relative humidity. UHPC Crack width monitoring and healing is also monitored. The water During the 12-month monitoring period, level in the tank and water temperature within is also monitored together with cameras installed on the tower. The restored reinforced concrete structure and the UHPC and TRC applied have performed well, are stable with no corrosion at all points in the structure including high stress points in the columns, after more than 12 months monitoring, with indications of crack healing in UHPC. The advanced system of 150 sensors designed and installed in the WT pilot is measuring successfully allowing the validation of UHPC exposed to a very aggressive and real exposure condition for the structure in service.
The validation of materials is supported through long term experimental analysis of UHPC and TRC,  site NDT analysis including crack monitoring and fibre distribution (magnetic technique). The validation step included the filling up of the tank with water, and emptying of the tank. The accelerometers installed at the base, middle and the top of the structure together with the strain gauges installed in the columns (Vertical) and the tank (Horizontal: in RC and TRC), indicated a good performance of the structure once filled with water, with full recovery. The microtremor analysis was applied before restoration, after restoration with the tank empty and full, recording fundamental frequencies of 2.75, 2.54 and 1,87Hz respectively. This was compared to the advanced numerical modelling. High resolution Lidar Scanning imaging was used for crack recording and monitoring during the filling up and emptying process. Scans of the structure as restored with the UHPC and the TRC strengthening system, were compared to the degraded structure, scanned prior to restoration. The long term monitoring of the structure through the research and control station set up by the University of Malta at the WT, is of fundamental importance for the service life performance assessment of the structure in operation.
Find more info about this pilot here

OUR TEMPER

RESEARCH & DEVELOPMENT CONCRETES

A worldwide reference in UHPC technology

Research and Development Concretes (RDC) is a consultant that provides support to switch from traditional materials to UHPC in a great variety of sectors (industry, renewable energies, civil engineering, blue economy, precast structures, security, etc). Formex^® is the registered UHPC that RDC proposes for these applications, tailoring its mix design for each client to create an efficient, sustainable, and cost-affordable solution. Possibly, UHPC is valuable for many sectors where it is still unknown, or where ordinary concrete is not even used. UHPC extreme capacity allows its use in applications where steel, traditional concrete, plastics, or wood are expensive or insufficient in terms of performance or durability.
For RDC, the moment to change to UHPC is now because….

• The last trends of steel prices have made many new applications using UHPC more economic than using steel or reinforced concrete.
• Specialized workforce is scarcer every day, being logic to replace the steelworks of the precast concrete elements by simply UHPC with steel fibers.
• Fuel and transportation costs are increasing, which is beneficial for UHPC as it reduces the weight of the precast structures by a 50-70% compared to ordinary concrete.
• Administrations have each year less resources for maintenance of infrastructures, so choosing a resilient solution is beneficial for the society.

RDC can evaluate the replacement of the traditional solutions currently used by a tailored premix of Formex^®, one of the most used UHPCs in the world. But RDC is not simply an experienced consultant in UHPC materials and structures: It supports the client to understand the benefits of this innovative technology, it quantifies its advantages under an specific application, it does the technology transfer required to use at industrial scale, and it develops specific projects from the concept stage to the monitoring of the structure. If RDC is one of the very few companies in the world that knows how to design competitive UHPC structures, is because it counts with the following strengths:

1. RDC founders know very well the traditional solutions, as they have more than 25 years of experience managing engineering projects. Thus, they have a realistic picture of the current problems and limitations.
2. RDC team has already 13 years of experience designing (un)reinforced and prestressed UHPC structures of up to 45-m length.
3. RDC owners are also PREFFOR owners, so they have the expertise precasting and commercializing UHPC structures, so they know well what is really demanded by the potential clients.
4. Both RDC and PREFFOR are small and independent companies, so they are flexible and can adapt to the more and more volatile environment.

With this vision and capacity, RDC has achieved since 2015 the following milestones, among others:

• Design of the four UHPC footbridges that exist in Spain, including the first world truss footbridge made only with UHPC.
• Design and patent of the first world UHPC floating farm (2015), which is now market leader in Galicia, the largest EU farming region.
• Design and patent of the 1^st UHPC floaters with integrated solar panels (2021).
• Design and patent of the 1^st UHPC pontoons-stiffeners for floating solar energy systems, which have been used in the largest floating farm in the Iberian Peninsula (Alqueva dam, 5 MW, 2022).
• Design of the 1^st UHPC bridge in Spain, located in Beniarjó, Valencia.

Esteban Camacho.  Research & Development Concretes (RDC)