Abstract
The purpose of the work reported in this paper is to assess the performance of recycled ultra-high durability concrete (R-UHDC), produced using different fractions of recycled aggregate obtained from crushed ultra-high durability concrete (UHDC), as a substitute for the natural aggregate. Four different recycled ultra-high durability concrete (R-UHDC) mixes were designed and manufactured with a reference mix based on the natural aggregate and three mixes with the natural aggregate replaced using recycled UHDC according to two percentage replacement values (50 and 100%). The effect of environmental degradation of the recycled parent concrete was also addressed, using recycled aggregates subjected to accelerated carbonation (replacement percentage equal to 50%). The work has been conducted in the framework of the activities of the Horizon 2020 ReSHEALience Project in ultra-high durability concrete. One key objective of the project was to formulate the concept and experimentally validate the performance of ultra-high durability concrete for structures and infrastructures exposed to extremely aggressive scenarios. The ReSHEALience consortium has defined UHDC as a “strain-hardening (fiber-reinforced) cementitious material with functionalizing micro- and nano-scale constituents especially added to deliver high durability in the cracked state under extremely aggressive exposure conditions.” In this context, the research was conducted to investigate the potential of recycling the UHDC mixes, developed and validated in previous research and employing them as a partial or even total replacement of the natural fine aggregate in the production of new UHDC. This supports the cradle-to-cradle approach in life cycle engineering applications. The research confirmed the effective regeneration of new UHDC based on the recycled aggregate obtained from crushed UHDC, attaining the required rheological characteristics, mechanical properties (compressive strength, flexural strength, and toughness), and durability performance (chloride penetration resistance, chloride migration, water capillary suction, and resistivity). This work is intended as the first step toward the sustainability assessment of the end of life of UHDC materials and structures and the potential of recycled UHDC for new structures and retrofit structural applications.
Highlights
The construction industry accounts for about 6% of the world GDP and generates a total revenue of about 10 trillion USD with 3.6 trillion USD added value (Ferrara, 2019)
In all the aforementioned cases, as witnessed by the results reviewed by Pedro et al (Pedro et al, 2018), the improvement of the recycled aggregates (RAs) properties resulted in improved durability of the recycled aggregate concrete (RAC), with reference to water and chloride permeability, carbonation resistance, freeze–thaw resistance, and shrinkage cracking potential
To the authors’ knowledge, the information about recycled ultra-high performance concrete (UHPC) is still scantly available in the literature due to the relative novelty of this broad category of advanced cementitious composites, mainly with reference to their full-scale structural applications, which still have not reached the end of their intended service life, and the case of their disposal and re-use has not yet been presented
Summary
The construction industry accounts for about 6% of the world GDP (and up to 8% in developing countries) and generates a total revenue of about 10 trillion USD with 3.6 trillion USD added value (Ferrara, 2019). The UPV test results, which are numerically coherent with what is expected and reported in the literature for UHPC materials with the measured strength performance, confirm the trend already noted for vacuum saturation permeable porosity, sorption coefficient, and hardened concrete density results as referring to the relative performance of different mixes (Figure 17) They highlight once again the possibility of obtaining, even when integrally replacing natural aggregates with recycled ones, the concrete with a performance as high as the reference one. This can be, once again, rightly attributed to the presence of binder materials attached to the sand particles in the recycled aggregate share, which could have undergone some natural carbonation even during the four-month open-air exposure in which they were left in the lab before the crushing and recycling process started
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