Suchergebnisse

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. ; Spanish Ministry MCIU, AEI and ERDF [grant number 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].

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).

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].

Predicting the mechanical properties of Self-Compacting Concrete (SCC) containing Recycled Concrete Aggregate (RCA) generally depends, in great part, on the RCA fraction in use. In this study, predictive equations for estimating SCC mechanical properties are developed through SCC porosity indices, so they are applicable to any RCA fraction and amount that may be used. A total of ten SCC mixes were prepared, nine of which containing different proportions of coarse and/or fine RCA (0%, 50% or 100% for both fractions), and the tenth mixed with 100% coarse and fine RCA, and RCA powder 0–1 mm. The following properties were evaluated: compressive strength, modulus of elasticity, splitting tensile strength, flexural strength, and effective porosity as measured with the capillary-water-absorption test. Negative effects on the above properties were recorded for increasing contents of both RCA fractions. The application of simple regression models yielded porosity-based estimations of the mechanical properties of the SCC with an accuracy margin of ±20%, regardless of the RCA fraction and amount. The results of the multiple regression models with compressive strength as a secondary predictive variable presented even greater robustness with accuracy margins of ±10% and almost no significant effect of accidental porosity variations on prediction accuracy. Furthermore, porosity predictions using the 24-h effective water also yielded accurate estimations of all the above mechanical properties. Finally, comparisons with the results of other studies validated the reliability of the models and their accuracy, especially the minimum expected values at a 95% confidence level, at all times lower than the experimental results. ; Spanish Ministry of Universities within the framework of the State Program for the Promotion of Talent and its Employability in R + D + i, State Mobility Subprogram, of the State Plan for Scientific and Technical Research and Innovation 2017–2020 [PRX21/00007]; the Spanish Ministry MCI, AEI, EU and ERDF [grant numbers PID2020-113837RB-I00; 10.13039/501100011033; 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] and the University of Padova.

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.

AbstractIn this paper, the performance of ladle furnace slag (LFS), a by-product of secondary steel refining, is evaluated as a binder to stabilize clayey soils of low bearing capacity. The aim is to define whether additions of this by-product to clayey soil can stabilize the soil in accordance with the technical specifications of Spanish standards. To do so, three different soils stabilized with 5% LFS were compared with the same soils stabilized with 2% lime and with no stabilization, in order to investigate their different behaviors. The chemical and mineralogical characterizations of all the soil mixes were conducted using X-ray fluorescence, X-ray diffraction, 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, unconfined compressive strength, and direct shear strength (cohesion and friction angle) tests defined 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 unconfined 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 confirmed that the substitution of lime with LFS is a feasible option for soil stabilization.

The environmental conditions to which a concrete may be exposed will condition its real range of use. Thus, concrete behavior must, at all times, be verified under a wide variety of environmental conditions, in order to ensure its real applicability. In this study, the real strength development and durability behavior of a fiber-reinforced self-compacting concrete is analyzed. This particular concrete incorporates 100% coarse (4/12 mm) and fine (0/4 mm) Electric Arc Furnace Slag (EAFS) as aggregate, as well as limestone fines as aggregate powder (0/1.18 mm). Furthermore, Ground Granulated Blast Furnace Slag (GGBFS) was also added as binder. Four mixtures with and without either metallic or synthetic fibers, and different GGBFS contents were designed. Real strength development was evaluated in all the mixes by comparing the strength development of both cores extracted from full-scale beams and wet-cured laboratory specimens. The durability behavior was analyzed by Mercury Intrusion Porosimetry (MIP), freeze/thaw, moist/dry, sulfate-attack, chloride-penetration, carbonation, and SO2-attack tests. On the one hand, the long-term mechanical properties of the cores (real conditions) were similar to the properties of the specimens cured in a moist chamber for 90 days in all the mixes. On the other, the increase in water content when adding fibers to maintain flowability, as well as the addition of GGBFS, resulted in an increase in MIP porosity. Therefore, the use of fibers, both metallic and synthetic, slightly worsened the durability behavior of the concrete, facilitating the entry of aggressive external agents. Nevertheless, the increased flexibility of the cementitious matrix when adding GGBFS was beneficial against moist/dry and sulfate-attack phenomena, despite the increase in porosity. Overall, the mixes complied with the regulatory requirements for use in aggressive environments, although the amounts of fibers and GGBFS should be carefully studied. ; Spanish Ministry of Universities within the framework of the State Program for the Promotion of Talent and its Employability in R + D + i, State Mobility Subprogram, of the State Plan for Scientific and Technical Research and Innovation 2017-2020 [PRX21/00007]; the Spanish Ministry of Universities, MICINN, AEI, EU and ERDF [grant numbers PID2020-113837RB-I00; 10.13039/501100011033; 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, to the University of Burgos [grant numbers SUCONS, Y135.GI] and the University of Padova.

The environmental impact of the building sector is especially relevant during the construction phase. Both the materials and the construction methods that are currently in use must be reconsidered, in order to minimize the environmental impact of concrete-based structures. This research is therefore focused on achieving greener concrete-based building structures. In this context, the feasibility of careful use of materials for concrete manufacture and the use of construction techniques that can facilitate and reduce energy consumption during placement are both studied. To do so, twelve sample beams were prepared using eight different sustainable high-workability structural concretes. The aim was to maximize the use of the by-products that amounted to over 80% of the concrete mass, steelmaking slags, fly ash, and quarry waste, and to employ energy-saving concrete placement techniques. The beams underwent bending tests in which their mechanical behavior and their compliance with the specifications of the most relevant building codes were verified. The results pointed to the feasibility of increased sustainability in the field of building engineering through the suitable use of selected by-products and techniques. ; Spanish Ministry MCI, AEI, EU and ERDF [RTI2018-097079-B-C31; 10.13039/501100011033; FPU17/ 03374]; the Junta de Castilla y Le´on (Regional Government) and ERDF [UIC-231, BU119P17]; Youth Employment Initiative (JCyL) and ESF [UBU05B_1274]; the University of Burgos [grant number SUCONS, Y135.GI], UPV/EHU (PPGA20/26) and, finally, our thanks also go to the Basque Government research group IT1314-19 and likewise to CHRYSO and HORMOR for supplying the materials for research.

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. ; Spanish Ministry MCIU, AEI and ERDF [grant numbers FPU17/03374 and RTI 2018-097079-B-C31]; the Junta de Castilla y León (Regional Government) and ERDF [grant number UIC-231, BU119P17]; the 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.

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.

The feasibility of manufacturing fiber-reinforced concretes of high workability through additions of high volumes of electric arc furnace steel slag is evaluated in this paper, using sustainable binders with ground granulated blast furnace slag and ladle furnace slag as a supplementary cementitious material. An extensive experimental plan is developed to test four (self-compacting and pumpable) concrete mixtures, some reinforced with 0.5% vol. of (metallic or synthetic) fibers, in both the fresh and the hardened state. Very specific mechanical aspects are examined, such as the evaluation of both longitudinal and transversal stress-strain compressive behavior, and the assessment of direct tensile strength through the "dog-bone" test. The results of testing this sustainable concrete design yielded suitable mechanical strengths, and good toughness, ductility and impact strength, among other properties. Good adhesion between the fibers and the cementitious matrix was also evident from the fiber pull-out test results. Finally, the overall results confirmed that the use of electric arc furnace steel slag can make a real contribution to construction-sector sustainability and that the mechanical behavior of these novel concretes meets the basic design requirements for use in real structures. ; Spanish Ministries MCI, AEI, EU and ERDF [RTI2018-097079-B-C31; 10.13039/501100011033; FPU17/03374]; the Junta de Castilla y León (Regional Government) and ERDF [UIC-231, BU119P17]; the Basque Government research group [IT1314-19]; Youth Employment Initiative (JCyL) and ESF [UBU05B_1274]; the University of Burgos [Y135.GI] and the University of the Basque Country [PPGA20/26]. Likewise, our thanks to CHRYSO and HORMOR for supplying the materials used in this research.

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. ; Junta de Castilla y León (Regional Government) for funding the UIC-231 group through project BU119P17 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 Government research group (IT1314-19)