# Susceptibility to Expansive Reactions of a _Greener_ Uhpc: Micro to Macro-Scale Study
###### Abstract  
Nowadays, in Europe, several infrastructures, such as bridges, viaducts, and maritime structures, are in an advanced state of degradation. Therefore, novel repair/rehabilitation techniques are sought. Recent advances in ultra-high-performance fibre-reinforced cement-based composites (UHPFRC) represent a significant step towards resilient structures. In addition to their remarkable mechanical properties (compressive strength \(>\) 150 MPa), they present extremely low permeability and, as a premise, very high durability. Despite their relatively high cost, UHPFRC can be a competitive solution for rehabilitation/strengthening applications where smaller volumes are needed. UHPFRC applied in thin layers (with or without reinforcement) can replace carbonated and/or cracked concrete acting as a protective watertight and/or strengthening layer. The structural capacity increases (stiffness, ultimate strength), and the durability is expected to improve significantly while keeping cross-sectional dimensions. Additional advantages are expected, such as reduced intervention time, fewer maintenance routines, reduced life-cycle cost, and longer service life. Although much of the focus on UHPFRC has centred on mechanical and/or structural performance, durability is inevitably linked with mechanical properties. The current work evaluated the durability of non-property and greener UhPC concerning expansive reactions, alkali-silica reactions and expansion due to external sulphates, by macro and micro-scale integrative study. Linear expansion tests were performed in UhPC specimens according to ASTM C 1260 and LNEC E\(-\)364. At the macro level, no deleterious expansion due to ASR or external sulphate occured. Expansion due to ASR was 0.0018% after 14 days of immersion in an alkali-rich environment, and no expansion was recorded regarding sulphate attack. However, SEM analysis reveals reactive products of ASR and sulphate attack, namely, ASR gel and ettrinigle, respectively, in UhPC specimens. UhPC; durability; ASR; external sulphate attack; SEM +
Footnote †: journal: Applied Sciences  
and improving tensile strength. The academy, the technical community, and industries worldwide have made significant research efforts to manufacture ultra-high-performance fibre-reinforced cement-based composites (UHPRC). Additionally, private companies and governmental figures are increasing their attention and initiatives toward the performance advantages of UHPFRC as a solution for more sustainable and resilient construction [3; 4; 5; 6; 7]. Most UHPFRC advances have been performed in Japan, France, Switzerland, Germany, Denmark, and the USA. Some of them give rise to commercial UHPFRC blended mixtures, as presented in Appendix A. Usually, UHPFRC tensile strength exceeds 10 MPa, such as DUCTAL(r) (12 MPa) [8], the \"High-Performance Hybrid-Fibre Concrete\" (12 MPa) [3], and, more recently, the \"Ultra-High Performance Fiber Reinforced Concrete with Low Fiber Contents\" (13 MPa) [9]. In Europe, UHPFRC has been used in bridges in Germany, Austria, Croatia, France, Italy, The Netherlands, Spain, and Switzerland [3; 10]. Using UHPFRC for architectonic purposes can also be seen in facades of MuCEM in France, Centre bus RATP de Thiais, Jean Bouin Stadium, and SWATCH Building in Swiss. In the USA, UHPFRC has been applied in precast concrete deck panels, pre-stressed concrete girder simple-span bridges, and cast \"in-situ\" UHPC to connect prefabricated bridge components [11]. An exhaustive list of UHPFRC applications worldwide can be found elsewhere [12; 13]. Despite its relatively high cost, UHPFRC can be a very competitive solution for the rehabilitation and/or reinforcement of specific areas of reinforced or pre-stressed concrete infrastructures (bridges, viaducts, and maritime structures). This concept was proposed at the Laboratory of Maintenance and Safety of Structures (MCS) in EPFL, by Prof. Dr. [PERSON], in 1999, in the scope of the project SAMARIS work package 14 \"HPFRCC for rehabilitation\", whose contributors included MCS-EPFL [14].