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The COVID-19 lockdown in Spain caused abrupt changes for students following the Bachelor's Degree in Civil Engineering at the University of Burgos when face-to-face classes switched to online teaching. The recovery of face-to-face teaching after lockdown meant that classes were taught with obligatory social distancing and the use of masks. Teachers were therefore unable to interact with students closely, to perceive their facial expressions during class, or to conduct group work. The changes to civil-engineering teaching linked to the COVID-19 pandemic and the lessons that civil-engineering teachers learnt from the new teaching scenarios are studied in this paper. The reflections of teachers throughout all three stages of the pandemic (pre-pandemic and lockdown, during lockdown, and post-lockdown), and the qualitative and mixed analysis of their responses to a survey of open-ended questions contributed to the identification of six major lessons: (1) asking questions and using real-time quiz tools enliven classes and help to determine which concepts to emphasize for proper student understanding; (2) autonomous student learning can be promoted through the provision of supplementary documentation and the digitalization of solutions to classroom exercises; (3) virtual site visits and real visual examples interspersed with explanations bring concepts closer to their real applications; (4) the delivery of projects in the form of audio-recorded presentations enable their distribution, so that other students can also learn from them as well as the students who created them; (5) online videoconferences, adapted to the concepts that are addressed, facilitate fast and flexible communication with students; and (6) online continuous-assessment exams can promote better student learning patterns and final-exam preparation. Nevertheless, these six lessons were drawn from the experience of teachers at a small Spanish university where the period of solely online teaching during the COVID-19 pandemic lasted only four months. Thus, it would be interesting to analyze the experience of civil-engineering teachers at larger universities and universities that had longer periods of solely online teaching. A study of the level of implementation of the six aspects when the pandemic is declared over might also be worthwhile. [ABSTRACT FROM AUTHOR]

The modulus of elasticity of a concrete depends on the elastic stiffness of both the cementitious matrix and the aggregate–ITZ system, which includes any slippage mechanisms under loading between the aggregate and the cementitious matrix within the interfacial transition zone (ITZ). A procedure is presented in this paper to estimate the elastic stiffness of an aggregate–ITZ system within a cementitious matrix, by considering the relative volumes and the porosities of the concrete components. The method was validated by determining the elastic stiffness of both the limestone–ITZ and the electric arc furnace slag (EAFS)–ITZ systems when embedded in a slag-based cementitious matrix. The greater stiffness of the EAFS–ITZ system in comparison with the natural aggregate system explained the higher strength and modulus of elasticity of the concrete following additions of EAFS. Moreover, having determined those parameters, the elastic moduli of concretes with a similar cementitious matrix could then be accurately estimated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal damage favored by micro-cracking in ITZ upon addition of coarse RA. • Apparition of thermal micro-cracks arising in pores promoted when adding fine RA. • Effect of coarse RA more negative in SCC under cyclic temperature increases. • Freezing conditions caused a more notable loss of compressive strength of SCC. • Decrease of UPV and density useful as indicators for quantifying thermal damage. 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. [ABSTRACT FROM AUTHOR]

The use of Recycled aggregate (RA) enhances concrete sustainability. If used on an industrial‐scale, structural verification, and testing will be required to confirm that RA concrete can meet relevant industrial standards and the requirements of manufacturers, especially in the precast‐concrete industry. In this paper, an experimental campaign with the participation of a precast‐concrete manufacturer is reported. The objective is to test a self‐compacting concrete (SCC) mix, designed for structural applications, that contains maximum amounts of 100% coarse RA, in order to establish its compliance with the habitual requirements of precast‐concrete manufacturers. Thus, scaled beams (12 × 24 × 180 and 24 × 24 × 130 cm) were subjected to bending, shear‐bending, shear, and long‐term‐deflection tests. In addition, the performance of that SCC mix in the bending and shear‐bending tests was compared with the performance of an SCC mix of similar compressive strength containing 0% coarse RA. In the failure tests, the experimental results were between 1.5 and 3 times higher than the required values. The elastic behavior of both SCC mixes was also very similar in those tests, regardless of the amount of coarse RA, due to the robust design of the water and superplasticizer content of the SCC, which balanced the decreased flowability and the lower compressive strength of SCC that resulted from the additions of coarse RA. The SCC mix with 100% RA showed a lower load‐bearing capacity after failure and narrow compliance margins with the deflection limits of the long‐term‐deflection test. Even though the SCC mix with 100% RA met all the standard technical specifications of the precast‐concrete manufacturer, reference should always be made to the serviceability limit states that are applicable at the time of the structural design phase. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • 19 SCC mixes made with GGBS, recycled aggregates and sustainable aggregate powder. • Comprehensive MCDM analysis with 3 algorithms and 14 scenarios of evaluation. • GGBS only advisable if maximizing short-term flowability and strength. • Limestone fines improved SCC sustainability and behavior versus conventional filler. • Behavior-focused design essential to get green SCC competitive with commercial SCC. [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]

The compressive strength of recycled concrete is acknowledged to be largely conditioned by the incorporation ratio of Recycled Concrete Aggregate (RCA), although that ratio needs to be carefully assessed to optimize the design of structural applications. In this study, Self-Compacting Concrete (SCC) mixes containing 100% coarse RCA and variable amounts, between 0% and 100%, of fine RCA were manufactured and their compressive strengths were tested in the laboratory for a statistical analysis of their strength variations, which exhibited robustness and normality according to the common statistical procedures. The results of the confidence intervals, the one-factor ANalysis Of VAriance (ANOVA), and the Kruskal–Wallis test showed that an increase in fine RCA content did not necessarily result in a significant decrease in strength, although the addition of fine RCA delayed the development of the final strength. The statistical models presented in this research can be used to define the optimum incorporation ratio that would produce the highest compressive strength. Furthermore, the multiple regression models offered accurate estimations of compressive strength, considering the interaction between the incorporation ratio of fine RCA and the curing age of concrete that the two-factor ANOVA revealed. Lastly, the probability distribution predictions, obtained through a log-likelihood analysis, fitted the results better than the predictions based on current standards, which clearly underestimated the compressive strength of SCC manufactured with fine RCA and require adjustment to take full advantage of these recycled materials. This analysis could be carried out on any type of waste and concrete, which would allow one to evaluate the same aspects as in this research and ensure that the use of recycled concrete maximizes both sustainability and strength. [ABSTRACT FROM AUTHOR]

• SCC with RCA subjected to cyclical positive and negative temperature variations. • Remaining strain appeared at sub-zero temperatures. • Deformability reduced with the number of cycles at positive thermal variations. • RCA, especially the coarse fraction, increased SCC deformability. • 1.2·10−5 °C−1 suitable value of thermal expansion coefficient for RCA concrete. Recycled Concrete Aggregate (RCA) has greater elasticity than natural aggregate, due to the presence of adhered hydrated mortar in the coarse fraction, and mortar particles in the fine fraction. To evaluate this aspect under temperature variations, four Self-Compacting Concretes (SCC) made with 100% coarse and/or fine RCA were subjected to cyclical temperature variations between 70 °C and 20 °C and between −15 °C and 20 °C. The addition of RCA, especially in the coarse fraction, increased the thermal deformability, although the difference tended to decrease with the number of cycles, especially in positive temperature variations. This study concludes that the traditional upper limit of the linear thermal expansion coefficient for concrete (1.2·10−5 °C−1) is also suitable when RCA is incorporated. [ABSTRACT FROM AUTHOR]

The use of different types of waste in the manufacture of concrete is increasingly common, due to unabating concerns over climate change and sustainability in the construction sector. It is now widely accepted that the optimal behavior of vibrated concrete produced with the addition of certain wastes can rival the behavior of conventional products. The manufacture of special concretes, such as self-compacting concrete, is also currently under investigation, although the state of knowledge in this field is not so well developed. In this review paper, current and past research articles on the design of self-compacting concrete with recycled concrete aggregate, both by itself and in combination with other wastes, are summarized and assessed. Research is presented into recycled concrete aggregate properties and the mix-design of the self-compacting concretes that contain them, as well as relevant results on the fresh state (workability, rheology), the hardened state (compressive strength, splitting tensile and flexural strength, modulus of elasticity, density, and porosity), durability (resistance to aggressive agents), long-term properties of concrete (shrinkage, creep), and structural elements manufactured with self-compacting concrete containing recycled concrete aggregate. The results under review reaffirm that the incorporation of recycled concrete aggregate can produce a suitable self-compacting recycled concrete, on the basis of careful designs that are essential for successful performance. Image 1 • A careful dosage adjusted to the RCA amount is the key to good flowability. • Mechanical properties of SCC with RCA can be suitable for structural use. • The performance SCC with coarse RCA is better than with the fine RCA fraction. • Permeability and carbonation resistance are worsened with the use of RCA. • The higher amount of RCA implies higher dispersion in the hardened performance. [ABSTRACT FROM AUTHOR]

Electric arc furnace slag (EAFS) and ladle furnace slag (LFS) are by-products of the electric steelmaking sector with suitable properties for use in bituminous mixtures as both coarse and fine aggregates, respectively. In this research, the production of a porous asphalt mixture with an aggregate skeleton consisting exclusively of electric steelmaking slags (using neither natural aggregates nor fillers) is explored. The test program examines the asphalt mixtures in terms of their mechanical performance (abrasion loss and indirect tensile strength), durability (cold abrasion loss, aging, and long-term behavior), water sensitivity, skid and rutting resistance, and permeability. The results of the slag-mixes are compared with a standard mix, manufactured with siliceous aggregates and cement as filler. The porous mixes manufactured with the slags provided similar results to the conventional standard mixtures. Some issues were noted in relation to compaction difficulties and the higher void contents of the slag mixtures, which reduced their resistance to raveling. Other features linked to permeability and skid resistance were largely improved, suggesting that these mixtures are especially suitable for permeable pavements in rainy regions. In conclusion, a porous asphalt mixture was produced with 100% slag aggregates that met current standards for long-lasting and environmentally friendly mixtures. [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]

The manufacture of concrete with Electric Arc Furnace slag as aggregate is known; in this work, fiber reinforcements are added to this concrete. The properties of several mixes, reinforced with 0.6% metallic and 0.4% synthetic fibers in volume, are studied both in the fresh and in the hardened state. Mechanical characterization of the fiber-reinforced concretes showed that they had good compression, flexural and tensile splitting strength. They also showed good toughness, post-cracking behavior, impact strength and tests on their abrasion resistance yielded suitable results. The concrete mixtures were characterized with SEM, to analyze their microstructure and the adherence of fibers. [ABSTRACT FROM AUTHOR]

Four high-workability (pumpable and self-compacting) concrete mix designs are presented that incorporate steelmaking slags with additions of both metallic and polymeric fibers. Electric arc furnace slag (EAFS) as aggregate, and ladle furnace slag (LFS) and ground granulated blast furnace slag (GGBFS) as supplementary cementitious material (SCM) are applied to optimize the sustainability of the mix design. The main variables in the microstructural analysis, the porosity and the pore structure of the hardened mixes, were assessed with 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) observations revealed 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 damage induced by this test decreased the brittle fracture strength of the concrete mixes, although the use of GGBFS and LFS moderated that damage, due to the increased compliance of the cementitious matrix. [ABSTRACT FROM AUTHOR]

The main objective of this work is to produce structural slag mortars of good mechanical strength and workability, while reducing the consumption of Portland clinker, the production of which is a growing source of environmental concern. In this context, the study looks at the preparation of these mortars with steelmaking slags (electric arc furnace slag, ladle furnace slag) in partial substitution of conventional aggregates, and as supplementary cementing materials, and the use of Portland cement that includes a notable proportion of fly-ash. A detailed examination of the characteristics of eight mortar mixes is described. Structural and mechanical analyses are performed on the mixes, to study the role of water-reducer and air-entrainment admixtures; also, shrinkage contraction and other volumetric variations of the mixtures are measured and evaluated. The long-term behavior of these slag mixes appeared acceptable, thereby opening a promising line of work that will eventually establish suitable conditions for their use. The strength-to-weight ratio of these mortars is encouraging although uncertainty persists over the use of air-entrainment admixtures and ladle furnace slag. [ABSTRACT FROM AUTHOR]

• A new approach is presented for determining the diagonal cracking resistance. • The method is not dependent on the subjective visual appraisals of the cracks. • The results are obtained by using conventional measuring instrumentation. • Concrete mixes containing EAF steel slag aggregates have been assessed. 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. [ABSTRACT FROM AUTHOR]

• SCC flowability was maintained by adding fine RCA and adjusting effective w/c ratio. • Up to 50% fine RCA, SCC presented optimal mechanical properties for structural use. • Strength development was slower the higher the fine RCA content. • The addition of fine RCA increased the fracture strain of the SCC. • Adjustment to the theoretical formulas improved by increasing the RCA content. 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%. [ABSTRACT FROM AUTHOR]

Ladle furnace (white or basic) slag is a significant by-product of the steelmaking industry; nowadays the manufacturing process yields two types of basic slag that are either low or high in alumina. The present research focuses mainly on the composition of the high-alumina slag and the reactivity of its compounds such as calcium aluminates, free calcium oxide, and free magnesium oxide, when aged at room temperature and at water steam temperature (accelerated aging). Additionally, a characterization was performed of pastes and masonry mortars that incorporate high alumina ladle furnace slag as a supplementary cementing material in partial substitution of Portland cement in amounts of 10% and 20% by weight. Different properties are studied such as porosity distribution, volumetric stability, mechanical strength and durability, mainly referring to wetting-drying aging cycles. The study concludes that high-alumina ladle furnace slag can induce slight hydraulic reactivity and its partial addition has no negative effect on the fundamental properties of cement masonry mortars. [ABSTRACT FROM AUTHOR]

Estimating the shrinkage of structural concrete is essential to calculate, at the design stage, the stresses that a structure may experience due to this phenomenon. Nevertheless, changes in composition, as well as the use of wastes as raw materials, alter the shrinkage behaviour of concrete and render invalid shrinkage-prediction models from the standards. This paper shows a procedure to estimate the shrinkage of recycled aggregate concrete made with alternative binders. This procedure is based on modifying the shrinkage estimated through the Eurocode 2 or ACI 209.2R models by multiplying it by a partial correction coefficient for every change in concrete composition. The application of this procedure to high-performance and self-compacting concretes made with various contents of recycled aggregate of different maturity, reactive magnesium oxide and ground granulated blast furnace slag showed that it is suitable for estimating long-term shrinkage with maximum deviations of ±10%. However, to obtain an adequate accuracy, it is necessary to bear in mind some tips, such as the need to consider the prediction interactions between the factors, the usefulness of the natural logarithm of the concrete age to improve the estimation accuracy or the convenience of introducing a concrete-age-dependent coefficient to reach accurate shrinkage estimations at early ages. Finally, the partial correction coefficients are found to be of a simpler nature for the ACI 209.2R model, so this model is recommended for predicting the shrinkage of recycled aggregate concrete. • Shrinkage estimation of recycled-aggregate alternative-binder concrete analysed. • ACI 209.2R and Eurocode 2 shrinkage models fitted by partial correction coefficients. • Partial correction coefficients easier to obtain and use for ACI 209.2R model. • Maximum deviations of ±10% when predicting shrinkage of recycled aggregate concrete. • Concrete-age-dependent natural logarithm improved estimations accuracy. [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]