Structural validation of geothermal water basins constructed with durability enhanced ultra high performance fiber reinforced concrete (Ultra High Durability Concrete)

Ultra-High Performance Concrete (UHPC) proved to be very durable in harsh environments, primarily because of the extremely low porosity of the matrix (uncracked). However, the limited availability of design standards is still a barrier to widespread applications of UHPC, together with still limited knowledge of its durability in the real (cracked) service conditions. In this paper, the use of tailored UHPC is introduced, whose composition has been specifically designed to achieve enhanced durability in the cracked state combined with extremely aggressive environments. Validation of the material and structural design concept on a full scale structure is presented, with reference to a tank intended to contain geothermal water from the cooling tower at a geothermal power plant. This pilot structure was designed and constructed using both ordinary reinforced concrete and durability enhanced UHPC, which is called hereafter Ultra High Durability Concrete (UHDC), for comparative assessment purposes. Upon the completion of the pilot construction and entering its service life, periodic assessment and validation tests have been carried out to validate the structural design assumptions and to check the serviceability requirements. Results of these tests, performed over the span of two years are reported in detail in this paper to validate the material and structural concepts. The study highlights the most important parameters that could affect the performance of UHPC structures during casting and service life. The overall project framework presented in this paper has to be intended as a pioneer study in moving towards a performance based durability-design approach for UHPC structures.