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

di Summa D., Tenório Filho J.R., Snoeck D., Van den Heede P., Van Vlierberghe S., Ferrara L., De Belie N.

Due to the increasing awareness and sensitivity towards the environmental and economic sustainability issues, the concrete industry has to deliver innovative solutions, in terms of materials, products and structural concepts, to achieve higher durability of engineering feats in real service scenarios. The inclusion of SuperAbsorbent Polymers (SAPs) into the concrete mix, can not only stimulate the autogenous crack healing, but is also able to reduce the shrinkage cracking through internal curing. In this paper, Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) analysis have been performed to assess both the ecological and economic profile, in real scale, of conventional reinforced concrete structures , made with concrete containing SAPs, in comparison to a reference solution without any addition. For this purpose, the corrosion of reinforcement has been regarded as the main degradation mechanism and different corrosion models have been considered and combined with the structural analysis principles to obtain reliable Service Life (SL) estimations. Four different scenarios, with a SL ranging from 50 up to 100 years, have been analyzed to assess the potential benefits of a wall, cast with SAP-containing concrete (Wall_SAP). Both Wall_SAP and a reference wall without SAP (Wall_Ref) are subjected to the concrete cover replacement as main maintenance activity while for the Wall_Ref also the crack filling by means of polyurethane resin is considered as an option (Wall_Resin). The adopted CML impact-assessment method, developed by the Center of Environmental Science of Leiden University, shows the advantage of using SAPs, since the environmental burdens were reduced up to 20% in the case of Fresh Water Aquatic Ecotoxicity impact category in comparison to the reference for the fourth scenario. In this scenario a hemispherical corrosion pit model for the steel bars and a service life of 100 years were taken into account. Furthermore, the economic assessment developed for the same scenario, pointed out for the SAPs based solution, there identified as Wall_SAP_M2_100, a consistent reduction in terms of costs up to 14% if compared to the reference, there named as Wall_Ref_M2_100. The outcomes definitely highlight the potential of the analyzed technology that can fulfil the future needs of the stakeholders involved in the construction sector.

Caruso M.C., Pascale C., Camacho E., Ferrara L.

This paper aims to compare the environmental and social impacts of three types of rafts for mussel farming in Spain. These structures, traditionally made of wood, have a short lifespan and, because of their service conditions, require frequent maintenance in order to be fully operational. An innovative solution made with ultra-high performance concrete (UHPC) was developed in 2016 by RDC, being at the base of the pilots of the EU-funded project ReSHEALience (H2020-GA760824). In order to quantify the environmental and social impacts generated by alternative solutions for the aquaculture raft, a life cycle approach has been used. The life cycle assessment methodology, according to ISO 14040 and ISO 14044 standards, has been used for the evaluation of the environmental impacts, while the social life cycle assessment (SLCA) methodology, according to the Guidelines for SLCA of Products and the social impact assessment method developed by Ciroth and Franze (2011), has been used for the evaluation of the social impacts: the same functional unit and the same stages of the life cycle to be included in the study has been set for the alternative solutions. Based on the LCA results, derived from the system boundary described in the “Goal and scope” section for the mussel aquaculture structures, the highest environmental impacts in the cradle-to-grave analysis are generated by the Traditional Raft with maintenance based on the periodic application of paints; the lowest environmental impacts are generated by the Traditional Raft with maintenance based on the progressive replacement of the damaged logs, while the Innovative Raft has an intermediate behavior in terms of environmental impact generation. Based on the S-LCA results, it can be stated that both the solutions generate high impacts; nevertheless, the Innovative solution has a slight lower impact than the Traditional solutions, which could be lowered if some precautions in the society policy are taken. Social hot-spots are identified in order to help reducing the overall social impacts. In conclusion, it can be stated that, from both the environmental and social points of view, the Traditional Solutions for the aquaculture raft are the most “impactful,” especially when the maintenance is based on paint application. The use of innovative concretes allows to build longer lifespan rafts with minimum (or no) need of maintenance. Moreover, the behavior of new companies is more attentive to social aspects related to their activities and has a margin of improvement, when compared to traditional companies.

Cuenca E., Lo Monte F., Moro M., Schiona A., Ferrara L.

Chloride diffusion and penetration, and consequently chloride-induced corrosion of reinforcement, are among the most common mechanisms of deterioration of concrete structures, and, as such, the most widely and deeply investigated as well. The benefits of using Ultra-High Performance (Fiber-Reinforced) Concrete—UHP(FR)C to extend the service life of concrete structures in “chloride attack” scenarios have been addressed, mainly focusing on higher “intrinsic” durability of the aforementioned category of materials due to their compact microstructure. Scant, if nil, information exists on the chloride diffusion and penetration resistance of UHPC in the cracked state, which would be of the utmost importance, also considering the peculiar (tensile) behavior of the material and its high inborn autogenous healing capacity. On the other hand, studies aimed at quantifying the delay in chloride penetration promoted by self-healing, both autogenous and autonomous, of cracked (ordinary) concrete have started being promoted, further highlighting the need to investigate the multidirectional features of the phenomenon, in the direction both parallel and orthogonal to cracks. In this paper, a tailored experimental methodology is presented and validated to measure, with reference to its multidirectional features, the chloride penetration in cracked UHPC and the effects on it of self-healing, both autogenous and stimulated via crystalline admixtures. The methodology is based on micro-core drilling in different positions and at different depths of UHPC disks cracked in splitting and submitted to different exposure/healing times in a 33 g/L NaCl aqueous solution. Its validation is completed through comparison with visual image analysis of crack sealing on the same specimens as well as with the assessment of crack sealing and of mechanical and permeability healing-induced recovery performed, as previously validated by the authors, on companion specimens.

Singh V.K., Shukla A., Sahani R.K., Shekhar A.R., Singh R.

This paper presents the behavior of recycled aggregate concrete (RAC) made using field demolished concrete as aggregate. The experimental investigations were conducted on M25 grade concrete, 30 no. of cubes of size 150 mm × 150 mm × 150 mm and 15 no. of beam of size 700 mm × 150 mm × 150 mm from which 20 cubes and 10 beams were prepared with 15 and 30% replacement of natural aggregate with recycled aggregate (RA) and rest with 0% replacement. The test parameters were specific gravity, water absorption, bulk density for aggregate and workability, compressive strength and flexure strength for RAC and natural concrete (NC). It was found that specific gravity of recycled concrete aggregate (RCA) was lower than natural aggregate (NA), water absorption of RCA was higher than NA and workability of fresh RAC was also low when compare to the NC. Test result shows the concrete needs increase in 3% of water for the use of RA. It was also investigated that for RAC with 15% replacement of NA with RCA, decrement in compressive strength is relatively lower than the RAC with 30% replacement and flexural strength of RAC was also got decrease as the percentage of RA in concrete increase. The result show that however, presence of RA decreases the strength of concrete but with limited replacement of concrete rubble could be transformed into useful RAC which not only make the construction economical, additionally it can be very useful in environment protection and also can be a major solution for the disposal problem of demolished concrete waste.

Al-Obaidi S., Bamonte P., Animato F., Lo Monte F., Mazzantini I., Luchini M., Scalari S., Ferrara L.

The structure presented in this paper is intended to be used as a prototype reservoir for collecting water coming from the cooling tower of a geothermal plant, and is primarily designed to compare the performance of different materials (traditional reinforced concrete and Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC)) as well to assess the performance of different structural solutions (wall with constant thickness versus wall provided with stiffening buttresses). In the absence of specific code provisions, given the novelty of the UHPFRC used, the main properties used for the design were determined through a dedicated experimental campaign (tensile/flexural properties and shrinkage). The main focus of the design was on the Serviceability Limit States, more specifically the requirements regarding water tightness. Given the rather simple structural layout, especially in the compartments where no stiffening buttresses are present, linear elastic analysis was used to determine the internal actions. The nonlinear behavior ensuing from the peculiar tensile constitutive response of the material was taken into account locally, in order to determine the stress level, the depth of the compression zone and the crack width. The performance was finally compared with the reference compartment (made with ordinary reinforced concrete), through on-site observations and measurements.

Sabău M., Remolina Duran J.

This paper presents the mechanical behaviour of concrete mixes made with recycled aggregate by replacing the natural aggregate with crushed concrete from pavement demolition. The purpose of this study was to determine the feasibility of using recycled aggregate from pavement demolition to make new concrete for pavement applications. Considering a control mix without recycled aggregate (RCA0) designed for a compressive strength of 34 MPa, two types of concrete mixes with 50% (RCA50) and 100% (RCA100) replacement percentage of natural coarse aggregate by recycled aggregate were made. The resulting concrete specimens were tested at three different curing ages, 7, 14, and 28 days. The results of this study showed that the compressive and flexural strengths decreased for all two mixes as the recycled aggregate content increased, while the density was slightly affected. A new model based on multiple linear regression analysis of the data from this study and other 14 studies from the literature was developed. The model can be used to predict the compressive strength of general-use concrete mixes with recycled aggregate (20–40 MPa) considering both the recycled aggregate content and the curing age of concrete. A good correlation was found between the compressive strength and the two parameters investigated. Given the predictions of this model, it is recommended not to use more than 30% recycled concrete aggregate in the production of new concrete in order not to affect its strength.

Borg R.P., Cuenca E., Garofalo R., Schillani F., Nasner M.L., Ferrara L.

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.

Lo Monte F., Ferrara L.

• The adoption of strain-hardening cement composites significantly promotes self-healing. • Multi-test approach for self-healing assessment appeared to be robust in durability monitoring. • Self-healing is very effective already after 1 month of curing for the UHDC studied. • The mixes showed sizable self-healing with even almost full crack-sealing after 6 months. • Re-cracking has a detrimental effect in self-healing for all the considered parameters. Within the framework of the Research Project ReSHEALience, new advanced Ultra High-Performance Fibre-Reinforced Cement Composites with enhanced durability, hereafter denoted as Ultra High Durability Concretes, are under investigation to characterize their tensile behaviour and durability performance in aggressive conditions, devoting particular attention to the phenomenon of self-healing. Three different mixes are under scrutiny, based on the combination of cement (CEM I or CEM III), slag, small aggregates (sand with a maximum size of 2 mm), and steel or metallic-alloy amorphous fibre. Self-healing capability has been investigated in aggressive environment (namely, under immersion in geothermal water) via 3 different test setups: (1) water permeability test on pre-cracked concrete disks, (2) 4-Point Bending Test – 4PBT on 100 × 100 × 500mm 3 prismatic beam specimens and (3) on 25 × 100 × 500mm 3 thin beams. In the case of beams, self-healing has been assessed via visual inspection of cracks trough digital microscope and via mechanical re-loading, so to investigate both crack-sealing capability and mechanical recovery. The results of this assessment aim at providing the starting point for a data base finalized at defining a design approach explicitly taking into account self-healing in the evaluation of structural durability. In particular, it has been observed as the adoption of strain-hardening cement composites significantly promotes self-healing phenomenon, thanks to smeared cracking in the tensile region and to consequent low values of crack opening. Self-healing proved to be very effective already after 1 month of curing.

Lo Monte F., Ferrara L.

Within the framework of the European Programme Horizon 2020, the Research Project ReSHEALience is currently running with the objective of developing a new approach for the design of structures exposed to extremely aggressive environments, based on Durability Assessment based Design and Life Cycle Analysis. To this aim, new advanced Ultra-High Performance Fibre Reinforced Cementitious Composites with improved durability, called Ultra-High Durability Concretes, are under investigation to characterize their tensile response in both ordinary and very aggressive conditions. In this context, the first step is to develop an effective approach for identifying the main parameters describing the overall behaviour in tension. In the present study, indirect tension tests have been performed via two techniques, based on Double Edge Wedge Splitting and 4-Point Bending Tests. Starting from the test results, a combined experimental-numerical identification procedure has been implemented in order to evaluate the effective material behaviour in direct tension in terms of stress–strain law. In the paper, the mechanical characterization for the reference mix is reported so to describe the identification procedure adopted.

Al-Obaidi S., Bamonte P., Luchini M., Mazzantini I., Ferrara L.

This paper provides the formulation and description of the framework and methodology for a Durability Assessment-based Design approach for structures made of the Ultra-High-Durability Concrete materials conceived, produced and investigated in the project ReSHEALience (Rethinking coastal defence and Green-energy Service infrastructures through enHancEd-durAbiLity high-performance cement-based materials) funded by the European Commission within the Horizon 2020 Research and Innovation programme (Call NMBP 2016–2017 topic 06-2017 GA 780624). The project consortium, coordinated by Politecnico di Milano, gathers 13 partners from 7 countries, including 6 academic institutions and 7 industrial partners, covering the whole value chain of the concrete construction industry. The innovative design concept informing the whole approach herein presented has been formulated shifting from a set of prescriptions, mainly referring to material composition and also including, in case, an allowable level of damage defined and quantified in order not to compromise the intended level of “passive” protection of sensitive material and structural parts (deemed-to-satisfy approach; avoidance-of-deterioration approach), to the prediction of the evolution of the serviceability and ultimate limit state performance indicators, as relevant to the application, as a function of scenario-based aging and degradation mechanisms. The new material and design concepts developed in the project are being validated through design, construction and long-term monitoring in six full-scale proofs-of concept, selected as representative of cutting edge economy sectors, such as green energy, Blue Growth and conservation of R/C heritage. As a case study example, in this paper, the approach is applied to a basin for collecting water from a geothermal power plant which has been built using tailored Ultra-High-Durability Concrete (UHDC) mixtures and implementing an innovative precast slab-and-buttress structural concept in order to significantly reduce the thickness of the basin walls. The geothermal water contains a high amount of sulphates and chlorides, hence acting both as static load and chemical aggressive. The main focus of the analysis, and the main novelty of the proposed approach is the prediction of the long-term performance of UHDC structures, combining classical structural design methodologies, including, e.g., cross-section and yield line design approaches, with material degradation laws calibrated through tailored tests. This will allow us to anticipate the evolution of the structural performance, as a function of exposure time to the aggressive environment, which will be validated against continuous monitoring, and pave the way towards a holistic design approach. This moves from the material to the structural durability level, anticipating the evolution of the structural performance and quantifying the remarkable resulting increase in the service life of structures made of UHDC, as compared to companion analogous ones made with ordinary reinforced concrete solutions.

Qian D., Yu R., Shui Z., Sun Y., Jiang C., Zhou F., Ding M., Tong X., He Y.

Recycled construction waste cementitious material (RCWCM) can be considered as a kind of waste solid with potential cementitious characteristics. In the past, landfill and stacking methods were generally used for treating this type of wastes, which is harmful for the sustainable development of construction industry. Hence, based on this premise, an effective method for developing a green Ultra-High Performance Concrete (UHPC) by incorporating RCWCM is addressed in this study. Specifically, dehydrated cementitious powder (DCP) is obtained from heating treatment of RCWCM. Then, the DCP is used to gradually replace the cement and included in the design of UHPC based on Modified Andreasen & Andersen (MAA) particle packing model. Afterwards, the physical and chemical characteristics of the newly produced UHPC are evaluated. The results show that when DCP is used to replace up to 25% cement, the variation of UHPC compressive strength is difficult to be noticed. Corresponding to that, the microstructure and durability of the developed green UHPC are also advanced when the added DCP content is less than 25%. Additionally, the ecological assessment shows that the UHPC incorporating DCP has a relatively small impact on the environment, which provides a broad prospect for the future sustainable development of UHPC.

Bai G., Zhu C., Liu C., Liu B.

The difference between the properties of recycled aggregate (RA) and natural aggregate (NA) are caused due to the old mortar attached to RA. In this review, the quantitative relationships were represented about the content of old attached mortar and the performance of RA at the material level. In term of the component level, the influence of replacement ratio of RA on the mechanical properties of concrete was summarized. Finally, some researches have focused on ways to improve the properties of aggregate. The results show that the method of stripping old mortar to improve the performance of recycled aggregates was not the only way to promote the application of recycled aggregates. However, by evaluating some simple and economical methods such as controlling the water-cement ratio, adjusting the aggregate moisture content and the different mixing method can improve the performance of recycled concrete in order to meet the requirement of concrete quality. Three aspects of the performance prediction, application range and reinforcement method for RAs were illustrated in the article. It was believe that the results could promote the accurate application for RAs with different quality in engineering, thus the application range of RAs was expanded.

López Ruiz L.A., Roca Ramón X., Gassó Domingo S.

Construction and demolition waste (CDW) is a priority for many policies at global level. This is due to the high volume of CDW that is produced and its inadequate management. This situation leads to serious environmental effects, which are mainly associated with manufacturing processes for new building materials because of low product recovery rates. In this context, the concept of Circular Economy (CE) is a potential solution in many sectors, as it involves more efficient use of resources and energy, which leads to waste minimization and reduction of the environmental impacts of product cycles. Moreover, it represents potential economic opportunities. The main aim of this study was to identify factors that could influence the adoption of the Circular Economy concept in the construction and demolition sector. A systematic literature review was conducted to understand the main strategies involved in the development of integral circular strategies. The main contribution of this paper is a theoretical framework for the Circular Economy in the construction and demolition sector. The framework is comprised of 14 strategies within the five lifecycle stages of construction and demolition activities. Particularly, the framework emphasizes waste management and recirculation of recovered materials for their use as secondary building materials.

Villoria Sáez P., Osmani M.

Construction and demolition activities in the European Union (EU) are responsible for generating 850 million tonnes of construction and demolition waste (CDW) per year. As a result, the Waste Framework Directive (WFD) set a recovery target to attain 70% CDW recycling by 2020. CDW management in individual EU Member States (MS) has been widely explored by previous researchers, however little attention has been paid to investigate the association of CDW arising with national economic, social and technological factors across different countries. Hence, this paper set out to examine and compare CDW generation across EU MS in correlation with their respective national construction turnover, gross domestic product and capita. It also assesses policy framework and CDW recovery performance of each MS against the WFD recovery target. Statistical data reported by Eurostat were collected and further analysed. A critical assessment of Eurostat CDW data reliability was carried out. A novel approach was adopted by ranking MS in respect to the amount of CDW generated per ‘construction turnover, GDP and capita’ (CDW-TGC). Results show that Austria, Germany, Netherlands, Belgium and France were found to be the highest CDW-TGC producers, whereas Croatia, Slovenia, Slovakia, Poland, Portugal and Spain were found to be the lowest. Further, most MS rely on ‘waste management plans’ rather than specific national CDW regulations. No correlation was found between landfill taxation and CDW landfilled or recovered. Eleven MS still need to improve their recovery performance to achieve the WFD target. Finally, four key CDW recovery challenges were identified: ineffective CDW regulations, incoherent data quality, undeveloped reverse logistics and a low market readiness for secondary materials

Silva R.V., de Brito J., Dhir R.K.

In the light of the ever-increasing need of circular economy in the construction industry and of the recent advances in research and development on the use of recycled aggregates, produced from construction and demolition waste, in new construction materials, this paper presents a compilation of representative case studies of several applications, namely recycled aggregates in unbound, hydraulically-bound and bitumen-bound applications, as well as in (non-)structural concrete in road and building construction. Experience has shown that, in spite of the positive outcomes and comprehensive know-how gained over the course of several years in those exploratory studies, there is a considerable underuse of recycled aggregates mostly due to lack of confidence in the material amongst contractors and designers. This paper, using a range of case studies undertaken in several countries worldwide, highlights the technical viability and appropriateness of using recycled aggregates in a broad range of construction applications.

di Summa D., Camacho E., Ferrara L., De Belie N.

In response to the ever-evolving demands of end-users within the construction sector, also due to the heightened global awareness regarding the pivotal role of the construction industry in sustainability ramifications, it has become imperative to wield strategic tools to steer the market toward farsighted choices. A notable example is represented by innovative cementitious materials, which are progressively captivating market interest due to their potential for enhanced overall sustainability performance. Henceforth, a crucial role is played not only by sustainability evaluation tools like Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) analyses but also by the integration of the latter into a more comprehensive approach able to promptly gauge the ecological and economic performance of the intended structural application. Some investigations have started exploring this opportunity, positing novel approaches that proffer immediate evaluations. These methods center around a range of indices that pivot upon ecological implications, along with performance indicators such as compressive strength. In light of this, the current study introduces a pair of novel indices with a more inclusive purview, encompassing not only environmental considerations but also costs and durability performance. One index, aimed at evaluating the feasibility of utilizing advanced construction materials as an alternative to traditional and consolidated options includes the aforementioned parameters on a cubic meter scale. In pursuit of this objective, part of the investigation is focused on the comparison between the mix designs of Ordinary Portland Cement Concrete (OPCC) and Ultra High Performance Concrete (UHPC), with CEM I or CEM III alternatively. The outcome revealed the limits of this first approach as it does not include some essential parameters, and OPCC performed better than UHPC in general. On the other hand, a complementary index has been proposed, seeking to optimize the mix design to be used to build structural elements or components and scale up to the level of the structural application. Thus, to check the consistency of the latter, UHPC roof panels, constructed by employing CEM I or CEM III alternatively, are then compared to panels made with ordinary reinforced concrete. The option containing CEM III registered better results in terms of holistic sustainability. The overall scope of this study is to encourage a more comprehensive, immediate, and all-encompassing evaluative approach, favouring the spread of advanced construction materials within the entire supply chain of the construction industry.

Cibelli A., Ferrara L., Di Luzio G.

Davolio M., Cuenca E., Borg R.P., Ferrara L.

Strategic structures can benefit from the characteristics of Ultra High-Performance Concretes (UHPC) to achieve long term durability without substantial maintenance. However, in some cases the aforesaid structures may still need to be dismantled. Thus, the possibility to recycle UHPC can significantly affect the environmental impacts associated with the use of this category of materials, given the high binder content and embodied energy. This study has investigated the self-healing performance of a UHPC made with recycled UHPC. Two different mixes were studied, with total replacement of sand and partial replacement of cement by recycled UHPC aggregates and recycled UHPC aggregates and fines respectively. The self-healing capacity of the mixes was addressed with mechanical and durability tests up to six months, with continuous exposure to a chloride-rich solution, simulating the marine environment. The unhydrated cement particles preserved the self-healing capacity of the parent UHPC. Both mixes proved their crack-sealing potential even with repeated damage-healing cycles, exhibiting a slight decrease only after six months of exposure and cracking. The crack closure resulted in a constant mechanical performance which was maintained over time.

Monte F.L., Harmon J., Andrade J., Ferrara L.

The construction industry is a key sector worldwide thanks to its huge social and economic impact. Considering that concrete is the most used construction material all over the world, its role is of paramount importance, with the demand of more efficient concrete structures obviously promoting an increase in terms of sustainability in order to accompany the social and economic transition. This makes (High-Performance) Fiber-Reinforced Concrete – (HP)FRC a promising solution, allowing for more efficient harvesting and storage processes with the possible implementation of digital fabrication, and for structures with improved durability and increased service life. FRC systems represent a promising solution not also towards ordinary reinforced concrete systems, but also with respect to steel structures thanks to the lower maintenance demand for both durability and fire performance. In the present paper, the adoption of HPFRC for an innovative Gravity Energy Storage System is briefly described, starting from the material mechanical characterization, following with full-scale tests and structural design. The results highlight the efficiency of the structural system adopted, enabling significant reductions in traditional reinforcement, and the reliability of Model Code 2010 as a basis for design.

D'Alessandro A., Meoni A., Rodríguez Romero R., García-Macías E., Viviani M., Ubertini F.

Abstract Civil constructions significantly contribute to greenhouse gas emissions and entail extensive energy and resource consumption, leading to a substantial ecological footprint. Research into eco-friendly engineering solutions is therefore currently imperative, particularly to mitigate the impact of concrete technology. Among potential alternatives, shot-earth-concrete, which combines cement and earth as a binder matrix and is applied via spraying, emerges as a promising option. Furthermore, this composite material allows for the incorporation of nano and micro-fillers, thereby providing room for enhancing mechanical properties and providing multifunctional capabilities. This paper investigates the damage detection capabilities of a novel smart shot-earth concrete with carbon microfibers, by investigating the strain sensing performance of a full-scale vault with a span of 4 meters, mechanically tested until failure. The material's strain and damage sensing capabilities involve its capacity to produce an electrical response (manifested as a relative change in resistance) corresponding to the applied strain in its uncracked state, as well as to exhibit a significant alteration in electrical resistance upon cracking. A detailed multiphysics numerical (i.e. mechanical and electrical) model is also developed to aid the interpretation of the experimental results. The experimental test was conducted by the application of an increasing vertical load at a quarter of the span, while modelling of the element was carried out by considering a piezoresistive material, with coupled mechanical and electrical constitutive properties, including a new law to reproduce the degradation of the electrical conductivity with tensile cracking. Another notable aspect of the simulation was the consideration of the effects of the electrical conduction through the rebars, which was found critical to accurately reproduce the full-scale electromechanical response of the vault. By correlating the outcomes from external displacement transducers with the self-monitoring features inherent in the proposed material, significant insights were gleaned. The findings indicated that the proposed smart-earth composite, besides being well suited for structural applications, also exhibits a distinctive electromechanical behaviour that enables the early detection of damage initiation. The results of the paper represent an important step toward the real application of smart earth-concrete in the construction field, demonstrating the effectiveness and feasibility of full-scale strain and damage monitoring even in the presence of steel reinforcement.

Gu L., Liu Y., Zeng J., Zhang Z., Pham P.N., Liu C., Zhuge Y.

Cuenca E., Del Galdo M., Aboutaybi O., Ramos V., Nash W., Rollinson G.K., Andersen J., Crane R., Ghorbel E., Ferrara L.

This paper presents the results of an extensive experimental campaign related to the use of Coal Mining Waste Geomaterials (CMWGs) as recycled constituents (fine and coarse aggregates) in Ordinary Portland Cement mortars and concretes. To this purpose, a reference mix and other mixes with different percentages of replacement of natural aggregates by CMWGs, up to 40% by volume, were investigated. CMWGs came from different providers: Central Mining Institute (GIG), POLTEGOR, both in Poland, and SUBTERRA in Spain and tests were performed at two different laboratories working on similar, but not identical, compositions. This represents a novelty in the literature, generally focusing on one single-source waste and single-lab results. The physical and mechanical properties of all the mixes were evaluated and correlated with respect to the percentage of replacement of natural aggregates by CMWGs. While the presence of CMWGs, likely because of their grain size distribution, reduced the porosity of mortars (decrease of 9.5 and 20.4% for 10 and 20% of replacement respectively) and concretes (70% reduction for concretes with 10% of fines and 30% of coarse aggregates replaced by CMWGs), the mechanical properties decreased when natural aggregates were replaced with CMWGs, likely because of the reduced strength of the CMWGs aggregates. This decrease was found to be roughly proportional to the percentage of replacement of aggregates (for instance, a 12–23% reduction of flexural strength in mortars with 25% replacement of sand and, a decrease of 25% in concretes for a 25% replacement of fine and coarse aggregates); nonetheless the concrete performance remained in the range of applicability for several civil engineering applications without affecting their functionality. In conclusion, the replacement of natural aggregates by CMWGs has resulted an interesting option for real applications providing an added value to the implementation of circular economy concepts in the management and up-cycling of coal mine tailings and CMWGs.

Wan Z., Xu Y., He S., Schlangen E., Šavija B.

This paper presents a state-of-the-art review on the application of additive manufacturing (AM) in self-healing cementitious materials. AM has been utilized in self-healing cementitious materials in three ways: (1) concrete with 3D-printed capsules/vasculatures; (2) 3D concrete printing (3DCP) with fibers or supplementary cementitious materials (SCMs); and (3) a combination of (1) and (2). 3D-printed capsules/vascular systems are the most extensively investigated, which are capable of housing larger volumes of healing agents. However, due to the dimension restraints of printers, most of the printed vasculatures/capsules are in small scale, making them difficult for upscaling. Meanwhile, 3DCP shows great potential to lower the environmental footprint of concrete construction. Incorporation of fibers and SCMs helps improve the autogenous healing performance of 3DCP. Besides, 3D-printed concrete with hollow channels as the vasculature could further improve the autonomous healing and scalability of self-healing cementitious materials. Finally, possible directions for future research are discussed.

Lo Monte F., Repesa L., Snoeck D., Doostkami H., Roig-Flores M., Jackson S.J., Alvarez A.B., Nasner M., Borg R.P., Schröfl C., Giménez M., Alonso M.C., Ros P.S., De Belie N., Ferrara L.

The huge benefits brought by the use of Ultra High-Performance Fibre-Reinforced Cementitious Composites (UHPFRCCs) include their high “intrinsic” durability, which is guaranteed by (1) the compact microstructure and (2) the positive interaction between stable multiple-cracking response and autogenous self-healing capability. Hence, self-healing capability must be properly characterized addressing different performances, thus providing all the tools for completely exploiting such large potential. Within this context, the need is clear for a well-established protocol for self-healing characterization. To this end, in the framework of the Cost Action CA15202 SARCOS, six Round Robin Tests involving 30 partners all around Europe were launched addressing different materials, spanning from ordinary concrete to UHPFRCC, and employing different self-healing technologies. In this paper, the tailored experimental methodology is presented and discussed for the specific case of autogenous and crystalline-admixture stimulated healing of UHPFRCC, starting from the comparison of the results from seven different laboratories. The methodology is based on chloride penetration and water permeability tests in cracked disks together with flexural tests on small beams. The latter ones are specifically aimed at assessing the flexural performance recovery of UHPFRCCs, which stands as their signature design “parameter” according to the most recent internationally recognized design approaches. This multi-fold test approach allows to address both inherent durability properties, such as through-crack chloride penetration and apparent water permeability, and more structural/mechanical aspects, such as flexural strength and stiffness.

di Summa D., Parpanesi M., Ferrara L., De Belie N.

AbstractThe development of innovative cementitious materials such as Ultra High Performance Concrete (UHPC) requires tailored approaches to assess both the environmental and economic impact of structural applications employing them. For this purpose, in this paper, Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) methodologies are integrated into a Durability Assessment‐Based Design (DAD) workflow which combines structural design algorithms for UHPC with the assessment of the durability performance, with the aim of predicting the evolution of the structural performance all along the service life (SL) in the intended scenarios. As a case study a water tank made of UHPC has been herein selected and compared to a reference made of ordinary reinforced concrete (ORC). While the ORC solution was designed with cantilever cast in situ walls, two different design concepts were assessed for the UHPC basin: one with cast in situ walls and one with precast slabs supported by ORC columns. Moreover, two different mix designs (mainly differing on the alternative presence of silica fume or slag) have been investigated for the UHPC basin and a SL equal to 50 years has been taken into account for each structure. The optimized design, together with the reduced frequency of the maintenance activities for the UHPC structure, allowed by the UHPC superior material and structural durability, resulted into consistent reductions of environmental impacts, up to 76% as for Human Toxicity and Fresh Water Aquatic Ecotoxicity in comparison to the ORC solution. In addition to this, an assessment of the overall construction and maintenance costs that occur during the lifetime of the structures showed a cost reduction higher than 40% for both UHPC solutions, mainly due to a reduction of up to 6% during the construction phase and 91% for the maintenance activities. This also highlights the importance of the correct metrics in evaluating the sustainability of UHPC structural applications, which has to move forward from the units volume or mass of material and its individual constituents to functional units, representative of the benefits of using advanced cement based materials in structurally and environmentally challenging service scenarios.

Ferrara L., Borg R.P., Cuenca E., El-Sayed M., Vassallo C.

The work reported in this paper aims at assessing the performance of Recycled Ultra High Performance Concrete (R-UHPC), produced using different fractions of recycled aggregates and fines obtained from crushed Ultra High Performance Concrete (UHPC), as a substitute of the both the natural aggregates, as customary in recycled aggregate concrete, and of cement. Three different (R-UHPC) mixes were designed and manufactured with a reference mix based on natural aggregate and two mixes with the natural aggregate totally replaced by recycled UHPC and 30% cement replacement either with recycled UHPC fines or with recycled UHPC aggregates as well, under the assumption of exploiting the paste halo around the recycled interface particles as a binder since it can consist of significant quantity of uh-hydrated cement. The possibility of totally replacing new fibres with recycled ones, reclaimed after UHPC crushing, was also addressed. This supports the cradle-to-cradle approach in life cycle engineering applications. The research confirmed the effective regeneration of new UHPC based on recycled aggregate obtained from crushed UHPC, attaining the required rheological, mechanical (compressive, flexural strength and toughness) and durability performance (chloride penetration resistance, chloride migration, water capillary suction and resistivity) as well as the capacity to maintain the overall performance upon the recycling process. This work is intended as the first step towards the sustainability assessment of the potential of R-UHPC for new and retrofit structural applications. The work has been conducted as a follow up of the activities of the H2020 ReSHEALience Project. One key objective of the project was to formulate the concept and experimentally validate the performance of UHPC for structures and infrastructures exposed to extremely aggressive scenarios, employing 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 UHPCs, developed and validated in previous research and employing them as a partial or even total replacement of natural fine aggregate in the production of a new UHDC.

ALOBAIDI S., Al-Obaidi S., He S., Schlangen E., Ferrara L.

Abstract This study investigates the bond-slip behavior of micro steel fibers embedded into an Ultra High-Performance Concrete (UHPC) matrix as affected by the self-healing of the same matrix in different exposure conditions. The UHPC matrix contains a crystalline admixture as promoter of the autogenous self-healing specially added to enhance the durability in the cracked state. To the aforesaid purpose, some samples were partially pre-damaged with controlled preload (fiber pre-slip at different levels) and subjected to one-month exposure in 3.5% NaCl aqueous solution and in tap water to study the fiber corrosion, if any, and the effects of self-healing; after that, they were subjected to a pull-out test, to be compared with the behavior of analogous non pre-slipped samples undergoing the same curing history. Moreover, some samples were cured in the chloride solution, intended to simulate a marine environment, to study the effect of marine curing on the pull-out behavior of steel fiber. The steel fiber corrosion and self-healing products attached on the surface of steel fiber were analyzed via the Scanning Electron Microscopy (SEM), and Energy -Dispersive Spectroscopy (EDS). The results indicate that the new healed particles formed on the highly damaged fiber-matrix interface significantly enhance the friction phase of the bond-slip behavior and result into a significant residual capacity compared to non-pre-slipped specimens. On the other hand, the self-healing effect in specimens subjected to low damage pre-slip contributed more to the chemical adhesion region of the bond-slip behavior. Owning to the dense microstructure of the matrix, curing in 3.5% NaCl aqueous solution was not found to significantly affect the pull-out resistance as compared for the samples cured in tap water.