Aprovechamiento de escorias blancas (LFS) y negras (EAFS) de acería eléctrica en la estabilización de suelos y en capas de firmes de caminos rurales

El trabajo que recoge la presente Tesis Doctoral estudia la idoneidad de un aprovechamiento integral de las escorias blancas de horno de cuchara (LFS) y de las escorias negras de horno eléctrico de arco (EAFS) en la estabilización de suelos arcillosos de mala calidad y en la formación de las capas del firme de caminos rurales. Para conseguir las propiedades resistentes adecuadas en terrenos naturales arcillosos sobre los que se construyen obras civiles, es preciso mezclarlos con materiales cualificados, como cementos y cales. Asimismo, existen ciertos subproductos que pueden ser empleados con esa finalidad, como las escorias de acería u otros. En este trabajo se han analizado las propiedades de la escoria blanca LFS y de varios suelos arcillosos susceptibles de estabilización. Tras la elaboración de las mezclas entre ambos en distintas proporciones los resultados obtenidos indican un comportamiento similar en las mezclas de suelo con escoria de horno cuchara y las mezclas de suelo con cal, registrándose una mejora de las propiedades del suelo en cuanto a su expansividad, capacidad portante y resistencia. Por otro lado, se ha estudiado las propiedades de la escoria negra EAFS y se ha comprobado que se trata de un subproducto con muchas semejanzas a una zahorra artificial. Se plantean en la Tesis diferentes opciones para la utilización con éxito de escoria EAFS en la formación de capas del firme. Con este planteamiento se pretende contribuir a la sostenibilidad medioambiental; por un lado, eliminando acopios de residuos que degradan las zonas productivas y por el otro, se evita la explotación de canteras y recursos naturales

Simplified calculations of slenderness limit in U.L.S. Of instability: interaction diagrams according to the instruction EHE-08

La introducción de la norma EHE-08 ha llevado consigo varios cambios, tanto conceptuales como paramétricos, en diferentes aspectos de su articulado. Este artículo busca ofrecer una ayuda al proyectista de hormigón, facilitándole los cálculos previos a la comprobación del Estado Límite de Inestabilidad. Se realiza una introducción al significado del límite inferior de esbeltez (incluyendo las propuestas de la ACI-318, el EC-2 y MC-90), para inmediatamente ofrecer una herramienta de aplicación directa que permita su obtención en el caso de la vigente Instrucción de hormigón estructural. Por otra parte, se expone también la formulación para comprobar secciones de soportes armadosRecent EHE-08 code has introduced many changes, both conceptual and parametric, in different aspects of its requirements. This paper seeks to offer support to the concrete designer, enabling pre-test calculations of the instability limit state. Beginning with an introduction to the meaning of the lower limit of slenderness (including ACI-318, EC-2 and MC-90 proposals), to immediately provide an application tool that allows obtaining direct in the case of the current Instruction of Structural Concrete. Moreover, it is also exposed the formulation to test reinforced column sections

Hammer rebound index as an overall-mechanical-quality indicator of self-compacting concrete containing recycled concrete aggregate

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

An alternative experimental methodology to determine the diagonal cracking resistance of steel-reinforced concrete beams

[EN]An alternative experimental method for predicting the diagonal shear cracking resistance of steel-reinforced concrete beams is developed in this paper. Conventional extensometric strain-gauge rosettes are placed on the lateral surfaces of a set of four beams. As diagonal cracking propagates through the beams, the load-strain curves flatten out at a plateau and the mechanical property under consideration may be determined. The method is applied to four beams cast from pumpable and self-compacting concrete mixes with cement types I and IV containing electric arc furnace slag aggregates. The feasibility of applying standard design code formulas to the concretes containing these aggregates may therefore be studied and compared with other recent research works. Accurate experimental results were obtained with this method without having to interrupt the test for subjective visual appraisals of the test specimen.The authors wish to express their gratitude to: the Spanish Ministry MICINN, AEI and ERDF [RTI2018097079BC31; PID2020113837RBI00; 10.13039/501100011033; FPU17/03374] ; the Junta de Castilla y Leon (Regional Government) and ERDF [UIC231, BU119P17] ; Youth Employment Initiative (JCyL) and ESF [UBU05B_1274] ; and the University of the Basque Country [PPGA20/26] and University of Burgos [SUCONS, Y135.GI] for additional funding. Our thanks also go to the Basque Government research group [IT131419] and likewise to CHRYSO and HORMOR for supplying the materials used in this research

Strength performance of low-bearing-capacity clayey soils stabilized with ladle furnace slag

In this paper, the performance of ladle furnace slag (LFS), a by-product of secondary steel refning, is evaluated as a binder to stabilize clayey soils of low bearing capacity. The aim is to defne whether additions of this by-product to clayey soil can stabilize the soil in accordance with the technical specifcations of Spanish standards. To do so, three diferent soils stabilized with 5% LFS were compared with the same soils stabilized with 2% lime and with no stabilization, in order to investigate their diferent behaviors. The chemical and mineralogical characterizations of all the soil mixes were conducted using X-ray fuorescence, X-ray difraction, and scanning electron microscopy. The Atterberg limit test was used to study the plastic behavior of the soils, and the results of compaction, bearing capacity, unconfned compressive strength, and direct shear strength (cohesion and friction angle) tests defned their strength characteristics. The analysis was completed with the pH monitoring of the mixes along the curing time in order to relate the pH changes with the strength evolution. The addition of LFS to the soils has resulted in an increase in the liquid limit and plastic limit, causing therefore a slight decrease in the plasticity index. All the soils showed increases between 30% and 70% in their California Bearing Ratios immediately after mixing with 5% LFS, and after 90 days of curing, improvements of 30–188% in their unconfned compressive strength were noted in comparison with untreated soil, which were higher than the lime-stabilized soils. The cohesion of soils stabilized with LFS at 28 days of curing obtained improvements ranging from 40 to 300% depending on the type of soil. However, the friction angle showed a slight increase of 10% in two of the soils and zero in another. The high initial pH in LFS-stabilized soils was maintained during the curing time, which favored the development of pozzolanic reactions that improve the soil strength. These results confrmed that the substitution of lime with LFS is a feasible option for soil stabilization

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)

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

The study of properties and behavior of self compacting concrete containing Electric Arc Furnace Slag (EAFS) as aggregate

Electric Arc Furnace Slag (EAFS) can be efficiently reused as aggregate in the production of high-volume batches of hydraulic concrete mixes that show interesting properties in both the fresh and the hardened state. Mixtures containing EAFS aggregate in proportions of nearly 50% by volume are prepared for use as pumpable and self-compacting mixes with consistency classes of S4 and SF2, respectively. Characterization of the mixtures is presented, examining practical aspects such as thixotropy, segregation in the fresh state (under 6%), and mechanical and microstructural evolution in the hardened state. The results yielded compressive strengths of approximately 60 MPa and elastic moduli of 38 GPa after one year. Finally, real-scale flexural elements are cast and subjected to sustained loading tests of moderate intensity. Long-term deflection values were approximately 50% (pumpable mixes) and less than 40% (self-compacting mixes) of the maximum admissible values specified in current standards.The authors wish to express their gratitude to: the Vice-Rectorate of Investigation of the University of the Basque Country(UPV/EHU) [PIF 2013]; the Vice-Rectorate of Investigation of theUniversity of Burgos [SUCONS]; the Junta de Castilla y León (Regio-nal Government) for funding the UIC-231 group through projectBU119P17 partially supported by FEDER funds; Project RTI2018-097079-B-C31 (MCIU/AEl/EU) and the UPV/EHU [PPGA19/61].Moreover, we are also grateful to both the Basque Governmentresearch group (IT1314-19) and the companies Chryso Additivesand Hormor-Zestoa for their ongoing collaboration with the pre-sent research 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]