Numerous test results at laboratory scale confirm the utility of Recycled Aggregate (RA) for the development of
concrete that demonstrates durability and adequate in-fresh and mechanical behavior. However, feasibility
evaluations of the use of RA in real industrial applications are necessary, before any large-scale industrial
application of these products can begin. In this research, the feasibility of producing precast-concrete components containing large amounts of coarse RA at a precast-concrete plant is analyzed. Two Self-Compacting
Concretes (SCC) were produced incorporating 0% and 100% coarse RA, respectively, at both laboratory scale
(0.08 m3
) and industrial scale (2 m3
). Work took place at the industrial-scale facilities of a precast-concrete
company that was collaborating in this study. Flowability and mechanical behavior were maintained as concrete production volumes increased, and concrete strength even increased after adding coarse RA, due to a
careful mix design. However, the durability performance worsened by around 20% when produced at industrial
scale, being this worsening higher whether coarse RA was used. A Multi-Criteria Decision-Making (MCDM)
analysis, in which the criteria of the precast-concrete company defined the relative importance of each concrete
property, showed the feasibility of manufacturing precast-SCC components containing coarse RA for interior
usage, whose fundamental requirement is adequate mechanical strength. The results of the MCDM analysis also
underlined the lower cost of coarse RA, making its use in SCC components cast with large concrete volumes
advisable. Overall, the addition of coarse RA in the precast-concrete industry is recommended in the interests of a
greener construction sector., The authors wish to express their gratitude for funding this research work to the Spanish Ministry of Universities, MICINN, AEI, EU, ERDF and NextGenerationEU/PRTR [PID2020-113837RB-I00; 10.13039/ 501100011033; TED2021-129715B-I00; FPU17/03374]; the Junta de Castilla y Leon ´ (Regional Government) and ERDF [UIC-231]; and the University of Burgos [SUCONS, Y135.GI]. In addition, Priyadharshini Perumal acknowledges the financial support received from the project DeConcrete [grant # KO 4068: Eco-efficient Arctic technologies cooperation] funded by the Kolarctic CBC initiative of the European Union. Finally, the support and assistance of ARTEPREF S.A. for the development of this study is also highly appreciated.

Recycled Aggregate (RA) usually increases porosity and weakens Interfacial Transition Zones (ITZs) of concrete,
which favors the appearance of internal thermal damage. Four Self-Compacting Concrete (SCC) mixes with
coarse and fine RA were subjected to positive and negative cyclic temperature variations to characterize their
thermal damage and quantify its effects. Two damage mechanisms were found. On the one hand, micro-cracks
appeared in the ITZs. On the other hand, micro-cracks arose from the micro-pores and propagated through the
cementitious matrix. Both damage mechanisms were promoted by the use of coarse and fine RA, respectively.
The damage was most notable at sub-zero temperatures and when adding coarse RA. Furthermore, it primarily
affected compressive strength, although ultrasonic pulse velocity and hardened density also decreased, which
served as non-destructive indicators to indirectly quantify the level of thermal internal damage of SCC., This work was funded by MICINN, AEI, EU, ERDF and NextGenerationEU/PRTR [PID2020-113837RB-I00; 10.13039/501100011033; TED2021-129715B-I00; FPU17/03374]; JCyL and ERDF [UIC-231]; and the University of Burgos [SUCONS, Y135.GI].

The hammer rebound index has traditionally been solely and exclusively used to estimate the compressive
strength of vibrated concrete. Its use has recently been extended to the prediction of the compressive strength of
Self-Compacting Concrete (SCC) and concrete produced with Recycled Concrete Aggregate (RCA). The conventional use of the hammer-rebound test is further developed in this paper, by demonstrating how it can be used
to estimate the overall mechanical behavior of SCC containing RCA. To do so, nine SCC mixes with different
contents and fractions (coarse, fine, and powder) of RCA are analyzed. Following a simple-linear-regression
validation and property standardization procedure, the hammer rebound index is then expressed as a linear
combination of four mechanical properties, adjusted through a multiple regression. The hammer rebound index
is therefore expressed as a weighting of both the mean value of compressive behavior (arithmetic mean of
compressive strength and modulus of elasticity) amounting to a weight of 72.8%, and the mean value of bendingtensile behavior (arithmetic mean of splitting tensile strength and flexural strength) amounting to a weight of
27.2%. The hammer rebound index can therefore be construed as an overall-mechanical-quality performance
indicator of the SCC containing RCA, which can also yield predictions of every mechanical property. In this way,
the application of the hammer rebound index could likewise be of use in rehabilitation, pathology, and healthmonitoring works where a full characterization of the mechanical performance of SCC with RCA is required,
facilitating the use of SCC with RCA in real structures., The authors wish to express their gratitude to the following government ministries, agencies, and universities for funding this research: the Spanish Ministry of Universities, MICIN, AEI, EU, ERDF and NextGenerationEU/ PRTR [PID2020-113837RB-I00; 10.13039/501100011033; TED2021- 129715B-I00; FPU17/03374; PRX21/00007]; the Junta de Castilla y León (Regional Government) and ERDF [UIC-231, BU119P17]; the University of Burgos [SUCONS, Y135.GI]; and, finally, the University of Padova.

Adding sustainable raw materials to Self-Compacting Concrete (SCC) modifies its flowability
behavior. Furthermore, the use of these raw materials may at the same time even improve one
fresh property while worsening another. An accurate flowability description of SCC containing
sustainable raw materials therefore requires a multi-parametric classification that simultaneously
covers all fresh properties (slump flow, viscosity, and blocking ratio) for an accurate description
of its potential applications. Existing classifications consider each fresh property independently.
In this paper, a multi-parametric flowability classification of SCC containing sustainable raw
materials is proposed. The effects of multiple sustainable raw materials on SCC flowability are
compiled in a dataset serving as a knowledge base with information on 663 SCC mixes containing
sustainable aggregates and binders. The statistical analysis of the dataset led to the definition of
three types of flowability zones. Firstly, the overall-flowability zones, in which SCC flowability is
described in absolute terms: the better the in-fresh properties, the better the overall-flowability
zone. Secondly, the flowability-balance zones reflect the balance between free flow (slump
flow and slump-flow viscosity) and flow around obstacles (V-funnel emptying time and L-box
blocking ratio). Finally, SCC is classified within flowability-predominance zones, which define the
main characteristic of SCC flowability, rate of flow (viscosity) or uniformity of flow (spreading).
The variability of the effect of each sustainable raw material on the flowability of SCC makes this
classification useful, in so far as it offers a complete picture of the fresh behavior of SCC in which
all fresh properties are simultaneously considered. Furthermore, based on the description in the
proposed classification of overall flowability and the balance between free flow and flow around
obstacles, the application fields are defined for which the use of each SCC mix with sustainable
raw materials is recommended., This research work was supported by the Spanish Ministry of Universities, MICINN, AEI, EU, ERDF and NextGenerationEU/PRTR [grant numbers PID2020-113837RB-I00; 10.13039/501100011033; TED2021-129715B–I00; FPU17/03374]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231]; and, finally, the University of Burgos [grant number SUCONS, Y135. GI].

Ultrasonic pulse velocity (UPV) is a non-destructive measurement technique with which
the quality of any concrete element can be evaluated. It provides information on concrete health
and for assessing the need for repair in a straightforward manner. In this paper, the relationship
is studied between UPV readings and the mechanical behavior of self-compacting concrete (SCC)
containing coarse, fine, and/or powdery RA. To do so, correlations and simple- and multipleregression relationships between compressive strength, modulus of elasticity, splitting tensile strength,
flexural strength, and UPV readings of nine SCC mixes were assessed. The correlations showed that
the relationship of UPV with any mechanical property was fundamentally monotonic. The inverse
square-root model was therefore the best-fitting simple-regression model for all the mechanical
properties, although for bending-tensile-behavior-related properties (splitting tensile strength and
flexural strength) the estimation accuracy was much lower than for compressive-behavior-related
properties (compressive strength and modulus of elasticity). Linear-combination multiple-regression
models showed that the properties related to bending-tensile behavior had a minimal influence on
the UPV value, and that their introduction resulted in a decreased estimation accuracy. Thus, the
multiple-regression models with the best fits were those that linked the compressive-behavior-related
properties to the UPV readings. This therefore enables the estimation of the modulus of elasticity
when the UPV and compressive strength are known with a deviation of less than ±20% in 87% of the
SCC mixes reported in other studies available in the literature., This research was funded by the Spanish Ministry of Universities, MICIN, AEI, EU, ERDF, and NextGenerationEU/PRTR, grant numbers PID2020-113837RB-I00, 10.13039/501100011033, and TED2021-129715B-I00; the Junta de Castilla y León (Regional Government) and ERDF, grant number UIC-231; and the University of Burgos, grant numbers SUCONS, Y135.GI.

Raw-crushed wind-turbine blade (RCWTB), a waste from the recycling of wind-turbine blades, is used as a raw material in concrete in this research. It contains not only fiberglass-composite fibers that bridge the cementitious matrix but also polyurethane and balsa-wood particles. Therefore, concrete containing RCWTB can be notably affected by moisture and temperature fluctuations and by exposure to high temperatures. In this research, the performance of five concrete mixes with 0.0%, 1.5%, 3.0%, 4.5%, and 6.0% RCWTB, respectively, is studied under moist/dry, alternating-sign-temperature-shock, and high-temperature-shock tests. Two damage mechanisms of RCWTB within concrete were found through these tests: on the one hand, micro-cracking of the cementitious matrix, which was verified by microscopic analyses and was dependent on concrete porosity; on the other, damage and degradation of the RCWTB components, as the polyurethane melted, and the balsa-wood particles burned. Both phenomena led to larger remaining-strain levels and reduced concrete compressive strength by up to 25% under temperature and humidity variations, although the bridging effect of the fiberglass-composite fibers was effective when adding RCWTB amounts higher than 3.0%. The compressive-strength loss after the high-temperature-shock test increased with the RCWTB content, reaching maximum values of 8% after an exposure time of 7 days. Statistical analyses revealed that effect of the RCA amount in the concrete was conditioned by the exposure times in all the tests. The accurate definition of those times is therefore key to set an RCWTB content in concrete that ensures its suitable behavior under the environmental conditions analyzed., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This research work was funded by the Spanish Ministry of Universities, MICINN, AEI, EU, ERDF, and NextGenerationEU/PRTR [grant numbers PID2020-113837RB-I00, PID2023-146642OB-I00,https://doi.org/10.13039/501100011033, TED2021-129715B-I00, and FPU21/04364]; the Junta de Castilla y León (Regional Government) and ERDF [grant numbers UIC-231, BU033P, and3; BU066-22]; and, finally, the University of Burgos [grant number SUCONS, Y135.GI].

Recycled Concrete Aggregate (RCA) and Raw-Crushed Wind-Turbine Blade (RCWTB) are waste materials obtained from decommissioned wind turbines after crushing their foundations and blades, respectively. Their use as raw materials in concrete allows their recycling. RCA increases concrete sustainability, while the fibers of Glass Fiber-Reinforced Polymer (GFRP) in RCWTB (66.8 % wt.) improve its bending performance. Nevertheless, only balanced waste combinations provide an adequate concrete behavior. Following a characterization of concrete in terms of fresh and strength performance, Response Surface Method (RSM) was conducted based on the experimental results to define the optimum waste combinations to reach a concrete strength performance adequate for engineering applications. RSM highlighted the need to limit the RCWTB content to 3 % to reach a compressive strength higher than 45 MPa, while amounts below 3 % and above 7 % would allow obtaining a flexural strength over 5.5 MPa. In both cases, the maximum content of coarse RCA should be 80 %. 70 % coarse RCA and a RCWTB amount between 6 % and 10 % would enable to develop concrete mixes with conventional strengths of 30–40 MPa under compression and 5 MPa under bending. RSM results revealed that RCWTB and their GFRP fibers properly behave in concrete with coarse RCA., This research work was supported by the Spanish Ministry of Universities, MICINN, AEI, EU, ERDF and NextGenerationEU/PRTR [grant numbers PID2020-113837RB-I00; 10.13039/501100011033; TED2021-129715 B–I00; PID2023-146642OB-I00; FPU21/04364]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231; BU033P23; BU066-22]; and, finally, the University of Burgos [grant number SUCONS, Y135. GI].

Selectively Crushed Wind-Turbine Blade (SCWTB) is obtained through knife crushing of panels from wind-turbine blades. Two thirds of SCWTB weight consist of GFRP-composite fibers, which may improve both dimensional stability and high-temperature resistance of concrete. In this investigation, the evaluation of such aspects in concrete containing 1.5 %, 3.0 %, 4.5 % and 6.0 % SCWTB by volume is addressed. For this purpose, plastic shrinkage, drying shrinkage, total shrinkage, and thermal expansion were evaluated regarding dimensional stability, while resistance to high temperatures was assessed through accelerated-aging and thermal-shock tests. The results revealed that 6.0 % SCWTB reduced by half concrete plastic shrinkage, and total shrinkage by 40–50 % at 7 days and by 10–20 % at 91 days. Furthermore, the initial thermal strain was decreased from SCWTB contents of 3.0 %, which in turn reduced the linear thermal expansion coefficient, which had a value of 1.49·10−5 °C−1 in concrete with 6.0 % SCWTB. Finally, concrete with SCWTB maintained adequate compressive strength after accelerated aging and air-heating thermal shock, reaching values above 40 MPa, and halved the loss of flexural strength when added in a content of 6.0 %. Scanning electron microscopy revealed that high temperatures caused micro-cracks that started in weak zones and propagated along the glass fibers of GFRP, but the bond between the cementitious matrix and the GFRP-composite fibers was ideal, so the matrix fractured instead of the fibers slipping when loading. The improvements induced by SCWTB were statistically significant, so this waste can be considered a value-added material in terms of the concrete behavior analyzed., This research work was supported by the Spanish Ministry of Science, Innovation and Universities MICIU, AEI, EU, ERDF and NextGenerationEU/PRTR [grant numbers PID2023-146642OB-I00; 10.13039/501100011033; TED2021-129715B-I00; FPU21/04364]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231; BU033P23; BU066-22]; and, finally, the University of Burgos [grant number SUCONS, Y135.GI].

Nonselective crushing of wind turbine blades results in raw-crushed wind turbine blade (RCWTB), a material that can be used in concrete production. Wind farm decommissioning can also generate coarse recycled aggregate (CRA) from the demolition of wind turbine concrete footings. This paper proposes a first approach for the joint management of both wastes through their simultaneous use in low-strength concrete, with a target compressive strength of 25 MPa. Mixes with 50% and 100% CRA, and 0% and 10% RCWTB as a cement addition, were designed, with the effect of CRA content not being statistically significant, to analyze its interaction with RCWTB. The results showed that, on the one hand, RCWTB reduced strength and stiffness under compression by a maximum of 9%–15%, although the target strength was achieved in all mixes; the presence of balsa wood and polymer particles in RCWTB, with high flexibility, could explain these reductions. On the other hand, the stitching effect of the glass fiber–reinforced polymer fibers present in RCWTB largely improved the bending-tensile mechanical properties. For example, flexural strength was almost doubled (from 2.51 to 4.99 MPa) when RCWTB was combined with 50% CRA. Additionally, RCWTB reduced both the embodied carbon and cost of low-strength concrete, resulting in doubled flexural-strength efficiency (flexural strength per unit of embodied carbon and cost), regardless of the CRA content. Overall, the best interaction was observed with 10% RCWTB and 50% RCA. Therefore, this study opens the possibility of simultaneously using RCWTB and CRA in low-strength concrete for applications where bending stresses predominate., This research work was supported by the Ministerio de Ciencia, Innovación y Universidades (MICIU), Agencia Estatal de Investigación (AEI), European Union (EU), European Regional Development Fund (ERDF), and NextGenerationEU/PRTR (Grant Nos. PID2020-113837RB-I00, PID2023-146642OB-I00, 10.13039/501100011033, TED2021-129715B-I00, and FPU21/04364); the Junta de Castilla y León (Regional Government) and ERDF (Grant Nos. UIC-231, BU033P23, and BU066-22), and, finally, the University of Burgos (Grant No. SUCONS, Y135.GI). Authors Nerea Hurtado-Alonso and Javier Manso-Morato contributed equally to this paper.

Fiber-Reinforced Concrete (FRC) was manufactured by the addition of high percentages of mechanically recycled wind-turbine blades, known as Raw-Crushed Wind-Turbine Blade (RCWTB). This sustainable material was added as aggregate replacement up to 10 % vol., while keeping the cement content equal for all mixes, and the effects on several fields were evaluated. First, strength (compressive, tensile splitting and flexural testing) and stiffness were evaluated at 7, 28, 90 and 180 days of age. Results showed that low RCWTB contents improved compressive (above 60 MPa) and tensile strengths (over 6.50 MPa under bending) due to enhanced matrix compactness. Nevertheless, the large proportions of deformable particles when using high RCWTB contents slightly hindered mechanical performance. Second, temporal strength development mechanism was evaluated through Scanning Electron Microscopy (SEM) on specimens that underwent mechanical testing and explained through schematics by the authors. This analysis revealed that the porous particles of RCWTB, acting as water reservoirs, accelerated matrix hydration and improved Interfacial Transition Zones (ITZ) around the Glass Fiber-Reinforced Polymer (GFRP) fibers of RCWTB, globally enhancing early-age strength. Third, low RCWTB levels improved abrasion resistance (up to 14.73 %), while high contents reduced surface quality but maintained acceptable performance. Finally, thermal conductivity remained stable following RCWTB incorporation at low levels and increased at higher contents (up to 35.75 %) but remained within typical FRC ranges. Therefore, this research ensures proper early-age and long-term overall performance of FRC produced with RCWTB, enhancing sustainability while yielding an improved concrete material suitable for a wide variety of applications., This research work was supported by the Spanish Ministry of Science, Innovation and Universities MICIU, AEI, EU, ERDF and NextGenerationEU/PRTR [grant numbers PID2023-146642OB-I00; 10.13039/501100011033; TED2021-129715B-I00; FPU21/ 04364]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231; BU033P23; BU066-22]; and, finally, the University of Burgos [grant number SUCONS, Y135.GI].

The use of Coarse Recycled Aggregate (CRA) in Low-Strength Concrete (LSC), suitable for pavements, allows the sustainable revaluation of this waste material, but worsens its performance. Recycled fibers of Glass Fiber-Reinforced Polymer (GFRP) present in Raw-Crushed Wind-Turbine Blade (RCWTB) may counterbalance the detrimental effects caused by CRA addition. This research analyzes the mechanical properties, durability, cost and carbon footprint of LSC mixes with 50 % and 100 % CRA combined with 0 % and 10 % RCWTB. Stitching of the cementitious matrix by GFRP fibers improved flexural strength and energy absorption of LSC containing CRA. In addition, these fibers exerted a barrier effect against water passage and exhibited higher surface hardness, the addition of RCWTB therefore did not affect the water-absorption rate and effective porosity and increased the abrasion resistance of LSC. Finally, RCWTB also reduced the cost and carbon footprint of LSC. These enhancements caused by RCWTB were analyzed through Multi-Criteria Decision-Making (MCDM) and Response Surface Methodology (RSM), approaches novel in the literature. According to them, the joint use of CRA and RCWTB in LSC was recommended. PROMETHEE II algorithm indicated that the use of 10 % RCWTB combined with 100 % CRA was the best option due to economic and environmental advantages, as this algorithm only considered which LSC mixture was the best for each property. ELECTRE algorithm showed indifference between both CRA contents, due to the better mechanical and durability performance of 50 %-CRA LSC. TOPSIS algorithm and RSM models revealed a preference for 50 % CRA and 10 % RCWTB following quantitative calculations based on the magnitudes of the property differences between the mixes. This research demonstrates the broad suitability of LSC containing both CRA and RCWTB in construction applications, mainly regarding pavements., This research work was supported by grant TED2021-129715B-I00 funded by MICIU/AEI/10.13039/501100011033 and by European Union NextGenerationEU/PRTR; grant PID2023-146642OB-I00 funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU; grants UIC-231 and BU033P23 funded by the Junta de Castilla y León (Regional Government) and ERDF/EU; and grant SUCONS, Y135.GI funded by the University of Burgos.