Assessment of Sustainability and Self-Healing Performances of Recycled Ultra-High-Performance Concrete

This research focuses on the evaluation of the sustainability of recycled ultra-high-performance concrete (R-UHPC) in a life cycle analysis (LCA) perspective, and with reference to a case study example dealing with structures exposed to extremely aggressive environments. This involves the assessment of the self-healing capacity of R-UHPC, as guaranteed by the R-UHPC aggregates themselves. Recycled aggregates (RA) were created by crushing 4-month-old UHPC specimens with an average compressive strength of 150 MPa. Different fractions of recycled aggregates (0 to 2 mm) and two different percentages (50 and 100%) were used as a substitute for natural aggregates in the production of R-UHPC. Notched beam specimens were pre-cracked to 150 [micro]m using a three-point flexural test. The autogenous self-healing potential of R-UHPC, stimulated by the addition of a crystalline admixture, was explored using water absorption tests and microscopic crack healing at a pre-determined time (0 days, 1 month, 3 months, and 6 months) following pre-cracking. Continuous wet/dry healing conditions were maintained throughout the experimental campaign. The specimens using R-UHPC aggregates demonstrated improved self-healing properties to those containing natural aggregates, especially from the second to the sixth month. To address the potential environmental benefits of this novel material in comparison to the conventional ones, an LCA analysis was conducted adopting the 10 CML-IA baseline impact categories, together with a life cycle cost (LCC) analysis to determine the related economic viability. Both LCA and LCC methodologies are integrated into a holistic design approach to address not only the sustainability concerns but also to promote the spread of innovative solutions for the concrete construction industry. As a case study unit, a basin for collection and cooling of geothermal waters was selected. This is representative of both the possibility offered, in terms of structural design optimization and reduction of resource consumption, and of reduced maintenance guaranteed by the retained mechanical performance and durability realized by the self-healing capacity of R-UHPC. Keywords: life cycle assessment; recycled aggregate; self-healing; sustainability; ultra-high-performance concrete (UHPC).