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The glass fiber-reinforced polymer (GFRP) materials of wind turbine blades can be recovered and recycled by crushing, thereby solving one of the most perplexing problems facing the wind energy sector. This process yields selectively crushed wind turbine blade (SCWTB), a novel waste that is almost exclusively composed of GFRP composite fibers that can be revalued in terms of their use as a raw material in concrete production. In this research, the fresh and mechanical performance of concrete made with 1.5%, 3.0%, 4.5%, and 6.0% SCWTB is studied. Once incorporated into concrete mixes, SCWTB waste slightly reduced slumps due to the large specific surface area of the fibers, and the stitching effect of the fibers on mechanical behavior was generally adequate, as scanning electron microscopy demonstrated good fiber adhesion within the cementitious matrix. Thus, despite the increase in the content of water and plasticizers when adding this waste to preserve workability, the compressive strength only decreased in the long term with the addition of 6.0% SCWTB, a value of 45 MPa always being reached at 28 days; Poisson's coefficient remained constant from 3.0% SCWTB; splitting tensile strength was maintained at around 4.7 MPa up to additions of 3.0% SCWTB; and the flexural strength of mixes containing 6.0% and 1.5% SCWTB was statistically equal, with a value near 6.1 MPa. Furthermore, all mechanical properties of the concrete except for flexural strength were improved with additions of SCWTB compared to raw crushed wind turbine blade, which apart from GFRP composite fibers contains approximately spherical polymer and balsa wood particles. Flexural strength was conditioned by the proportion of fibers, their dimensions, and their strength, which were almost identical for both waste types. SCWTB would be preferable for applications in which compression stresses predominate. [ABSTRACT FROM AUTHOR]

The addition of Ladle Furnace Slag (LFS) to concrete modifies its compressive strength and modulus of elasticity and consequently impacts their relationship. This research evaluated both properties at 28, 90, and 180 days in concrete mixes produced with 5%, 10%, and 20% of two LFS types, both stabilized and non-stabilized. The relationship between them was then analyzed through these experimental results by adopting a statistical approach. A three-way analysis of variance revealed that both properties were affected by LFS differently. Thus, the effect of each LFS content on both features varied depending on its composition and pre-treatment. Furthermore, the effect of the LFS content on the compressive strength was also influenced by the age of the concrete. These facets implied that when analyzing the relationship between both mechanical properties, the monotonic correlations were stronger than the linear ones, reaching values between 0.90 and 1.00. Therefore, the double reciprocal regression models were the most precise ones for expressing the modulus of elasticity as a function of compressive strength. The model accuracy was further enhanced when discriminating based on the LFS type and introducing concrete age as a predictive variable. With all these considerations, the average deviations between the estimated and experimental values of 1–3% and the maximum deviations of 4–7% were reached, as well as R2 coefficients of up to 97%. These aspects are central to the further development of LFS concrete models. [ABSTRACT FROM AUTHOR]

• Concept of raw-crushed wind-turbine blade as waste material defined. • Solution for recycling wind-turbine blades to be dismantled in the next years. • Waste composed of glass fibers and spherical particles of balsa wood and polyurethane. • Good concrete workability by five-stage mixing process and plasticizer adjustment. • Waste provided load-bearing capacity to concrete, and reduced its carbon footprint. Many of the first wind-turbine installations are reaching the end of their useful life, so their blades have to be replaced. Inexpensive, sustainable, and straightforward recycling solutions are therefore needed. The conversion of turbine blades into raw materials for concrete solutions is proposed in this paper, through a novel recycling process entailing non-selective cutting, crushing, and sieving of the blade walls, without component separation. The material, Raw-Crushed Wind-Turbine Blade (RCWTB), consists of fiberglass-composite fibers, polyurethane, and balsa-wood particles. It serves as concrete fibers and aggregates, according to its physical and microscopic characterizations. A customized concrete mix design and a five-stage mixing procedure with up to 6% RCWTB achieved suitable workability levels. The compressive strength of the RCWTB concrete was 40 MPa, and it had a higher load-bearing capacity and a lower carbon footprint than ordinary concrete. The results encourage research on the overall performance of RCWTB concretes. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • 15 SCC subjected to continuously-increasing-load and loading/unloading tests. • Stress–strain curves in both directions and ratio between their strains obtained. • Yield step and cracking by vertical splitting highly affected transverse behavior. • Recycled SCC transverse damaged after cyclic elastic loading of increasing severity. • Advisable SSC design according to serviceability conditions in compressed elements. Plastic strain behavior in the transversal direction to the axis of loading has often been underestimated in concrete design and its strength performance. However, as this article demonstrates, it is fundamental to define the viability of using concrete of a certain composition in real applications. In this study, 15 Self-Compacting Concrete (SCC) mixtures produced with Recycled Concrete Aggregate (RCA) and Ground Granulated Blast Furnace Slag (GGBFS) were subjected to a monotonic-load test and a 5-cycle loading/unloading test with increasing maximum loads. Continuous monitoring of the applied loads and the SCC strain was performed. In the transversal direction, these tests caused the appearance of a yield step, cracking by vertical splitting, and higher levels of deformability than in the longitudinal direction. It was concluded that the RCA content of SCC should be defined according to serviceability conditions when used in compressed elements, to safeguard against failure due to transversal plastic strain. [ABSTRACT FROM AUTHOR]

The addition of by-products, such as recycled concrete aggregate and ground granulated blast furnace slag, modify the in-fresh flowability of ordinary self-compacting concrete both initially and over time. A detailed study is presented in this paper of 18 mixtures (SF3 slump-flow class) containing 100% coarse recycled concrete aggregate, two types of cement (CEM I or CEM III/A, the latter with 45% ground granulated blast furnace slag), different contents of fine recycled concrete aggregate (0, 50, or 100%), and three different aggregate powders (ultra-fine limestone powder <0.063 mm, limestone fines 0/0.5 mm, and recycled concrete aggregate 0/0.5 mm). The temporal evolution of slump flow, viscosity, and passing ability, and the values of segregation resistance, air content, fresh and hardened density, and compressive strength were evaluated in all the mixtures. The addition of fine recycled concrete aggregate and CEM III/A improved initial slump flow and passing ability by 6%, due to their higher proportion of fines. Nevertheless, the temporal loss of flowability within 60 min was 5.8% lower when adding natural aggregate and CEM I. Viscosity and air content increased 26% on average following additions of fine recycled concrete aggregate, unlike with additions of ground granulated blast furnace slag. Flowability and strength increased with the addition of limestone fines 0/0.5 mm. According to multi-criteria analyses, the mixtures with CEM III/A, 50% fine recycled concrete aggregate, and limestone fines 0/0.5 mm showed an optimal balance between their flowability (SF2 slump-flow class 60 min after the mixing process), compressive strengths (around 60 MPa), and carbon footprints. [Display omitted] • Effect of binder type, RCA, and powder on temporal flowability evolution of SCC. • GGBFS and fine RCA improved initial flowability and worsened it in the long term. • Loss of flowability statistically predicted from aggregates' water absorption. • Placement of SCC with high amounts of waste 60 min after production is feasible. • Optimum balance between sustainability and SCC behavior with GGBFS and 50% fine RCA. [ABSTRACT FROM AUTHOR]

[Display omitted] • 24 Highly SCC mixes with high contents of Recycled Concrete Aggregate (RCA) • 2592 Hammer rebound index and 864 UPV analysis performed. • Conventional models invalid for compressive strength estimations of RCA SCC. • Non-destructive testing suitable to estimate strength regardless of SCC composition. • Safe and precise models developed through rebound index and UPV for SCC. Indirect estimation of compressive strength through non-destructive testing is key to monitoring the strength of structural concretes used in construction and rehabilitation works. However, no models are available to perform this estimation in highly Self-Compacting Concrete (SCC) with Recycled Concrete Aggregate (RCA). To fill this gap, two indirect measures were tested in this paper, the hammer rebound index and Ultrasonic Pulse Velocity (UPV), to predict the compressive strength of highly SCC. To do so, 24 SCC mixes were developed with different aggregate powders, binders, such as Ground Granulated Blast Furnace Slag (GGBFS), and contents of fine RCA. Compressive strength, and both indirect measures of all mixtures were determined at 1, 7, 28, and 90 days. The development of specific models for highly SCC responded to the inappropriateness of conventional models that are not adapted to its high fines content. Modelling as a function of either UPV or the hammer rebound index yielded accurate predictions, although the UPV model proved more sensitive to compositional changes and presented higher uncertainty. The best predictions were modelled by combining both indirect measures. The models provided safe and accurate indirect estimations of the compressive strength of high flowability SCC in real structures. [ABSTRACT FROM AUTHOR]

A suitable content of powdery Ladle Furnace Slag (LFS) has to be selected to balance its hydraulic and expansive properties when added to concrete. In this study, the performance of concrete containing two powdery LFS is studied: H -type LFS, stabilized before use, and N -type LFS, used in its original state. Lower expansiveness was observed in the H -type LFS, and strength development was assisted by the formation of calcium-silicate-hydrates. Therefore, it increased the modulus of elasticity, the splitting tensile strength, and the flexural strength of concrete. Higher hydraulicity and expansiveness were found in the N -type LFS, which improved compressive-behavior-related properties up to a content of 10% but reduced tensile-related properties. These aspects were confirmed through scanning electron microscopy. In general, the H -type LFS improved the mechanical properties and carbon footprint of concrete, and its use is recommended in a multi-criteria approach, although the difference between both LFS was only statistically significant at advanced ages. [Display omitted] • Concrete produced with Ladle Furnace Slag (LFS) from two different sources. • H -type LFS stabilized before concreting, whereas N -type LFS used in original state. • H -type LFS improved all properties except compressive strength, which held constant. • Up to 10% N -type LFS improved compressive behavior, not tensile properties. • H -type LFS recommended, but difference significant only at advanced concrete ages. [ABSTRACT FROM AUTHOR]

[Display omitted] • Recycled aggregate HPC manufactured with 10% reactive MgO as cement replacement. • MgO slightly worsened mechanical behaviour, especially when high amount RA added. • MgO's expansion reduced autogenous shrinkage, higher decrease in mixes with RA. • Additional water when using MgO enlarged drying shrinkage and compensated expansion. • MgO's effectiveness in total-shrinkage reduction lower when increasing RA content. The high strength and durability of high-performance concrete (HPC) may be significantly reduced by shrinkage cracking. The use of reactive magnesium oxide (MgO) can reduce shrinkage of cement-based materials due to its expansive properties. This study intends to analyse the validity of MgO as shrinkage-reducing agent in recycled aggregate HPC. To do so, ten HPC mixes with 0%, 25%, and 100% of both early-age (7-days air curing) and matured (6-month air curing) RA were produced. In half of the mixes, 10% ordinary Portland cement was replaced with MgO. The use of MgO slightly worsened the mechanical behaviour of HPC, especially when combined with large amounts of RA. On the other hand, the expansion of MgO fully offset the autogenous shrinkage of HPC and reduced total shrinkage by around 20–40%. Water storage of RA, and its deferred release over time, produced a more efficient hydration of MgO, which in turn led to a further reduction of autogenous shrinkage. However, the increase of drying shrinkage caused by RA was greater than this decrease of autogenous shrinkage due to MgO, so the higher the RA content of HPC the lower the total shrinkage reduction when adding MgO. Thus, the decrease of total shrinkage caused by MgO was compensated by the shrinkage increase because of RA when adding amounts above 35% early-age RA and 42% matured RA. Therefore, despite the suitability of MgO as shrinkage-reducing agent in recycled aggregate HPC, its effectiveness was reduced with increasing amounts of RA. [ABSTRACT FROM AUTHOR]