Assessment of longitudinal and transversal plastic behavior of recycled aggregate self-compacting concrete: A two-way study

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.Spanish Ministry MCIU, AEI and ERDF [grant numbers FPU17/03374 and RTI2018-097079-B-C31; 10.13039/501100011033]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231, BU119P17]; Youth Employment Initiative (JCyL) and ESF [grant number UBU05B_1274]; the University of Burgos [grant number SUCONS, Y135.GI], UPV/EHU (PPGA20/26) and, finally, our thanks also to the Basque Government research group IT1314-19

Self-compacting concrete containing coarse recycled precast-concrete aggregate and its durability in marine-environment-related tests

Marine environments are extremely challenging for the long-term durability of concrete. Prior validation of concrete durability is therefore a prerequisite to guarantee its adequate performance under marine environmental conditions. In this study, the performance of Self-Compacting Concrete (SCC) with variable contents of coarse Recycled Precast-Concrete Aggregate (RPCA) and two different cement contents is assessed in terms of capillary water absorption, natural and accelerated carbonation, resistance to SO2 attack, and moist/dry performance in drinking water, marine water, and sulfate water. These tests are intended to simulate the conditions of a marine environment. In general, the results showed that an SCC containing coarse RPCA of adequate durability under marine conditions could be produced. On the one hand, porosity due to the presence of RPCA increased less as the cement content was increased, which in turn reduced water absorption and SCC carbonation. For example, the effective porosity of the SCC was reduced by 25 % between day 28 and day 180, following the addition of 100 % coarse RPCA. On the other hand, both the SO2-attack and the moist/dry tests revealed that the weight of the SCC with RPCA underwent greater variations, due to the reactions of the cementhydration products with chlorides and sulfates, as well as salt deposition. However, SCC compressive strength was never adversely affected, as the concrete strength increased up to 8 MPa after the drinking-water and the sulfate-water moist/dry tests when using RPCA. According to both Fick's and Parrot's models, the projected service life of all the mixes was over 100 years, regardless of the coarse RPCA content, making this sort of SCC a feasible option for construction in marine environments.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]; 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]

Simultaneous addition of slag binder, recycled concrete aggregate and sustainable powders to self-compacting concrete: a synergistic mechanical-property approach

The behavior of Self-Compacting Concrete (SCC) is very sensitive to the use of by-products in replacement of conventional cement or finer aggregate fractions. The high proportions of these raw materials in SCC can in great part explain this performance. 18 SCC mixes of slump-flow class SF3 were prepared for a thorough evaluation of different sustainable materials and for the prediction of their effects as binder or fine/powder aggregate on the mechanical properties of SCC. The mixes incorporated 100% coarse Recycled Concrete Aggregate (RCA); different amounts (0%, 50% or 100%) of fine RCA; CEM I ordinary Portland cement and CEM III/A (with 45% ground granulated blast furnace slag); and more sustainable powders compared to conventional limestone filler <0.063 mm (such as limestone powder 0/0.5 mm and RCA powder 0/0.5 mm). Flowability, hardened density, strength under compression, tensile and bending stresses and modulus of elasticity were all studied. The addition of 50% fine RCA yielded an SCC of adequate strength, stiffness and flowability. SCC manufactured with limestone powder 0/0.5 mm showed the best overall performance, while SCC behavior was improved when adding CEM III/A by adjusting the mix composition. The experimental results of all the mechanical properties were compared with the values predicted by the compressive-strength-based formulas from the European and USA standards. Overall, the values resulting from those expressions overestimated all the mechanical properties. Therefore, since all these properties followed the same simple-regression trend, a statistical analysis was performed to develop a global model capable of accurately predicting them all.The authors wish to express their gratitude for funding this research work to: the Spanish Ministry of Universities, MICINN, AEI, EU, and ERDF [PID2020-113837RB-I00; 10.13039/501100011033; FPU17/03374; PRX21/00007]; the Junta de Castilla y León (Regional Government) and ERDF [UIC-231, BU119P17]; and the University of Burgos [SUCONS, Y135.GI] and the University of Padova

Microstructure and Dimensional Stability of Slag-Based High-Workability Concrete with Steelmaking Slag Aggregate and Fibers

Four high-workability (pumpable and self-compacting) concretemix designs are presented that incorporate steelmaking slagswith additions of both metallic and polymeric fibers. Electric arcfurnace slag (EAFS) as aggregate, and ladle furnace slag (LFS) andground granulated blast furnace slag (GGBFS) as supplementary cementitious material (SCM) are applied to optimize the sustainability ofthe mix design. The main variables in the microstructural analysis, theporosity and the pore structure of the hardened mixes, were assessedwith mercury intrusion porosimetry (MIP), X-ray computed tomography (XCT) and water capillary penetration analysis. Moreover,shrinkage was observed to decrease when adding metallic fibers and LFS. In general, scanning electron microscopy (SEM) observationsrevealed good quality concrete microstructures. Accelerated aging tests at a moderate temperature (72°C) produced a slight lengthening,which affected the dimensional stability of all the mixtures, which was also conditioned by their micro-porosity. The internal damageinduced by this test decreased the brittle fracture strength of the concrete mixes, although the use of GGBFS and LFS moderated thatdamage, due to the increased compliance of the cementitious matrix.The authors wish to express their gratitude for funding this researchwork to the Spanish Ministry of Universities, MInisterio de Cienciae INNovaci ́on (MICINN), Agencia Estatal de Investigaci ́on (AEI),European Union (EU), and European Regional Development Fund(ERDF) (PID2020-113837RB-I00, PID2021-124203OB-I00,RTI2018-097079-B-C31, 10.13039/501100011033, FPU17/03374);ERDF and the Junta de Castilla y Le ́on (BU119P17; UIC-231);European Social Fund (ESF) and Youth Employment Initiative(JCyL) (UBU05B_1274); Sustainable And Resilient ENvironment(SAREN) research group (IT1619-22, the Basque Government);and the University of Burgos [Y135.GI]. Our thanks also go to thecompanies Chryso Additives and Hormor-Zestoa for their ongoingcollaboration with research group members

Shear strength assessment of reinforced concrete components containing EAF steel slag aggregates

Electric Arc Furnace (EAF) slag can be reused as aggregate in Portland cement concrete mixes. The addition of EAFS and other waste co-products (fly ash, blast furnace slag) will modify the binding properties and will, importantly, enhance the global sustainability of such concretes. These mix designs offer acceptable pumpability and self-compaction in the fresh state and can be reinforced with fibers. In this study, eight different concrete mixes are designed within the range of medium-strength concretes (30–50 MPa) and are characterized in both the fresh and the hardened state. Large concrete volumes are used to pour reinforced beams, which are then subjected to small-span high-load tests to evaluate their resistance to shear stress, by analyzing two types of transversal (shear) reinforcement. The tests yielded promising results, contributing additional evidence on the viability of using recycled EAFS aggregate in structural applications. The mechanical behavior of these concretes was closely correlated with the strength predictions calculated with the formulas listed in various international standards.Spanish Ministry of Universities, MICINN, AEI, EU and ERDF [PID2020-113837RB-I00; RTI2018-097079-B-C31; 10.13039/501100011033; FPU17/03374]; the Junta de Castilla y León and ERDF [UIC-231, BU119P17]; Youth Employment Initiative (JCyL) and ESF [UBU05B_1274]; the University of Burgos [grant number SUCONS, Y135.GI], and, finally, our thanks also go to the SAREN research group (IT1619-22, Basque Government)

Raw-crushed wind-turbine blade: Waste characterization and suitability for use in concrete production

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.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]; 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]

Multi-criteria feasibility of real use of self-compacting concrete with sustainable aggregate, binder and powder

Replacing natural raw materials with industrial by-products can increase the sustainability of Self-Compacting Concrete (SCC), although its fresh and hardened behavior will usually worsen. The benefits of increased sustainability must therefore outweigh any reduction in concrete flowability and strength. These aspects can be analyzed through Multi-Criteria Decision-Making (MCDM) algorithms. In all, 19 SCC mixes were studied. One reproduced commercial SCC (limestone filler and conventional cement), the others were produced with more sustainable materials: 100% coarse Recycled Concrete Aggregate (RCA); 0%, 50% or 100% fine RCA; 45% Ground Granulated Blast-furnace Slag (GGBS); and sustainable aggregate powders such as limestone fines 0/0.5 mm and RCA powder 0/0.5 mm. Decreased flowability at 15 and at 60 min, compressive strength, modulus of elasticity, carbon footprint, and cost of mix were all studied. Both the carbon footprint and the cost were calculated considering only the composition of the SCC, without including aspects that depend on each particular case study, such as transport distances. These aspects constituted the decision-making criteria of the MCDM analysis, under which 14 scenarios were evaluated with different requirements for SCC, using 3 different algorithms (TOPSIS, AHP, and PROMETHEE). The results suggested that the ideal choice for fast concreting is a combination of GGBS, 100% coarse RCA and limestone fines, although if SCC has to be transported to the concreting point, then conventional cement should be used. Strength and stiffness can be maximized by limiting the fine RCA content to 50%. Finally, considering a versatile choice, only SCC with coarse RCA, limestone fines, GGBS and 0% fine RCA could compete with conventional SCC. Adapting the design to minimize the detrimental effects of by-products is therefore essential to promote sustainable SCC that is also commercially competitive.Spanish Ministry MCIU, AEI and ERDF [grant numbers PID 2020-113837RB-I00; 10.13039/501100011033; FPU17/03374]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231, BU119P17]; Youth Employment Initiative (JCyL) and ESF [grant number UBU05B_1274]; and, finally, the University of Burgos [grant number SUCONS, Y135.GI]

Multi-parametric flowability classification of self-compacting concrete containing sustainable raw materials: An approach to real applications

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]

Student Perceptions of Formative Assessment and Cooperative Work on a Technical Engineering Course

Formative Assessment and Cooperative Work (FACW) is a teaching methodology that promotes student learning based on peer support, both in solving problems and identifying the mistakes made through feedback. The perceptions of 49 mechanical engineering students at the University of Burgos are analyzed in this article with regard to their first practical experience of FACW methodology in a technical subject, characterized by a highly complex content and a strong link between theoretical and practical concepts. The responses of the students to two blocks of open questions were evaluated in a qualitative, mixed, and statistical analysis. Various aspects that the students raised in relation to FACW could therefore be studied, such as their points of view towards: (1) The usefulness of FACW teaching modality; and (2) their preferences regarding the optimum teaching modality. The results showed that, although the students expressed favorable opinions towards FACW, they did not consider, in general, that teamwork was necessary for optimal learning, revealing a clear dependence on formal classroom presentations for the explanation of theoretical concepts. Students considered that theoretical concepts could not be autonomously acquired. Therefore, the application of the FACW teaching methodology to these courses could be especially beneficial to favor autonomous learning and to develop teamwork skills, training engineers with the right knowledge and skills today for tomorrow’s world.This research was funded by the following entities and grants: Spanish Ministry MCI, AEI, EU, and ERDF, grants PID2019-106635RB-I00, 10.13039/501100011033, and FPU17/03374; the Junta de Castilla y León and ERDF, grant BU119P17 awarded to research group UIC-231; Youth Employment Initiative (JCyL) and ESF, grant UBU05B_1274; and the University of Burgos through grant Y135 GI awarded to the SUCONS group

Effect of fine recycled concrete aggregate on the mechanical behavior of self-compacting concrete

The high flowability of Self-Compacting Concrete (SCC) is achieved by adding large amounts of fine aggregate. Therefore, the addition of fine Recycled Concrete Aggregate (RCA) in this type of concrete can very noticeably change its behavior. SCCs with different percentages of fine RCA (0%, 25%, 50%, 75%, and 100%) and 100% coarse RCA were manufactured in this study, to evaluate their performance, and to analyze the effect of fine RCA in an SCC when a high amount of coarse RCA is also added. Both the fresh properties (flowability, density, and air content) and their mechanical behavior (strengths, non-destructive tests, stress–strain curves, and Poisson coefficient) at different curing ages were studied. These mechanical properties were compared with the values calculated using the formulas from two of the most common structural design standards. High values of strength and modulus of elasticity were obtained up to a fine RCA content of 50%. Additionally, any increase in fine RCA increased flowability and elastic and plastic deformability of the SCC. The theoretical values overestimated the experimental ones by around 25%. From the mechanical point of view, SCC with up to 50% fine RCA could be used for structural applications, although service requirements regarding deformability recommend that its content should be limited to 25%.The authors wish to express their gratitude to: the Spanish Ministry MCI, AEI, EU and ERDF [grant number FPU17/03374]; the Junta de Castilla y León (Regional Government) and ERDF [grant numbers UIC-231, BU119P17]; Youth Employment Initiative (JCyL) and ESF [grant number UBU05B_1274]; and finally, the University of Burgos [grant numbers SUCONS, Y135.GI]