<b>ABSTRACT</b> </br>

The need to reduce heat-related thermal stress calls for a reassessment of shading in outdoor urban spaces with the aim of achieving more habitable and sustainable cities. In this research, a methodology based on mathematical formulas is presented and applied to determine the most appropriate geometric properties and position of the trees to be planted in an urban canyon, based on its E-W solar orientation and the height of the buildings. The methodology relies on shading the largest possible surface area of the pedestrian zones of a canyon through the appropriate autochthonous tree species, but it also requires a thermal-comfort evaluation of tree transmissivity. The case study is validated in Bilbao, where a combination of measurement and modelling techniques (Solweig model) are used to verify suitable guidelines for urban design. The results will be of interest to architects and city planners for decision-making when integrating trees, so that urban thoroughfare development can improve thermal comfort in actual or new canyons. The methodology could be applied to other climatic regions, although some of the parameters used both for the evaluation of the heat-related critical moments and in the formulas should be adapted.</br>

<b>ACKNOWLEDGEMENTS</b></br>

The authors wish to express their gratitude for funding from UPV/EHU (contract PPGA20/26), SHELTER EU project (GA 821282), and the research groups: IT1314-19 (Basque Government) and GIU19/029 (UPV/EHU).

<b> ABSTRACT </b> </br>

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.

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<b> ACKNOLEDGEMENTS </b> </br>

The authors wish to express their gratitude for funding this research work to the Spanish Ministry of Universities, MInisterio de Ciencia e INNovación (MICINN), Agencia Estatal de Investigación (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 León (BU119P17; UIC-231); European Social Fund (ESF) and Youth Employment Initiative (JCyL) (UBU05B_1274); Sustainable And Resilient ENvironment (<b>SAREN</b>) research group (IT1619-22, the Basque Government); and the University of Burgos [Y135.GI]. Our thanks also go to the companies Chryso Additives and Hormor-Zestoa for their ongoing collaboration with research group members.