Phosphorescent-based pavements for counteracting urban overheating – A proof of concept

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New experimental technique to investigate the thermal behavior of PCM/doped concrete for enhancing thermal/energy storage capability of building envelope

Abstract In recent years, the scientific community has profusely investigated the chance of implementing advanced Thermal Energy Storage (TES) systems within building envelope components. In particular, several contributions have focused on the use of Phase Change Materials as passive TES strategies, to increment the thermal buffer potentiality of the building envelope. In this context, this work is focused on the development of a new experimental methodology for testing PCM-doped concrete composites in thermal-energy dynamic conditions. Such method, coupling controlled environmental forcing and transient plane source analysis, can be considered as an effective procedure for testing composite materials with adaptive thermal performance

Using advanced Urban Canopy Models to investigate the potential of thermochromic materials as urban heat island mitigation strategies

Recent trends in urbanization processes are causing serious threats at both local and global environmental scale. Greenhouse gas emissions, heat waves, and the heat island effect are constantly growing in intensity and produce increasing discomfort and health impacts in urban populations. In this context, the building sector is currently developing advanced and adaptive materials for building envelope and paving surface applications characterized by high energy performance and low embodied energy. Most of these innovative materials are firstly analysed at the component scale by means of laboratory investigations, while their effect on the built environment is generally assessed at a later stage, by means of advanced computer simulations in buildings and urban microclimate monitoring or modelling. In this context, this work focuses on the evaluation of the UHI modulation potential of materials with advanced dynamic optical properties, i.e. variable surface albedo, for surface urban canyon applications. Specifically, the Princeton Urban Canopy Model (PUCM) is applied with the aim of investigating the potential of advanced urban roofing material to modulate the urban heat island. The aim is to minimize the heat island in the summer but to let it develop in the winter, using roofing applications characterized by a dynamic temperature-dependent optical behavior. In particular, the effect of thermochromic materials on local energy transport phenomena is assessed and benchmarked against more common cool roof solutions. Results show that the modified UCM can effectively be implemented to represent temperaturedependent albedo variations. Additionally, this study demonstrates that using thermochromic materials produces a smart optical response to local environmental stimuli and allows enhanced short wave solar reflection in summer conditions, reduced reflected solar fraction in winter, and adaptive properties during transition periods

Innovative composite materials with enhanced acoustic, thermal, and optical performance for urban pavements: experimental characterization

Over the last decades, the implementation of innovative multifunctional materials for urban surfaces has produced a variety of paving solutions characterized by self-cleaning, self-healing, electricity conductive, solar reflective, sound absorbent properties and so on. Therefore, a key challenge is nowadays represented by the need for combining multi-physics properties in a single material or system for flooring. The present work concerns the development of a new outdoor paving application with enhanced acoustic, thermal, and optical performance. To this aim, eleven concrete mix-designs were tested. The composites were characterized by different aggregate size, material and additives. The aggregates included in the composite consist of (i) natural stones with different grain size s, (ii) expanded clay aggregates, and (iii) glass fragments. Acoustic, thermal, and optical measurements were performed for each sample. Additionally, a dedicated in-field monitoring campaign was carried out to characterize the albedo under summer boundary conditions. Finally, the thermal behaviour of the samples was tested in an environmental chamber using controlled boundary conditions in terms of temperature, humidity, and radiation. The results demonstrate that bigger grain size presents the best acoustic performance in terms of absorption capability, i.e. absorption coefficient of about 0.9 and 0.8 at 1000 Hz and 500 Hz, respectively. Moreover, the thermal-optical lab and field tests confirm previous literature result s demonstrating that the mix-design with the smaller grain size has the best reflectivity potential

Effect of the curing process on the thermomechanical properties of calcium aluminate cement paste under thermal cycling at high temperatures for thermal energy storage applications

Future perspectives to improve the energy efficiency of concentrating solar power (CSP) plants are focused on increasing temperatures above 600 ◦C. Among the different components of a CSP plant, the thermal energy storage (TES) medium must withstand high operating temperatures. Concrete was identified as an exciting candidate for its mechanical and thermal properties, needing further experimental research about this specific application. A fundamental concrete element is the cement binder, bringing cohesion to the composite components. As a requisite, the cement needs to be heat-resistant, and calcium aluminate cement (CAC) suits this demand. This cement is characterised by curing temperature-driven crystallisation changes, triggering an alteration of material properties. Considering that at 60 ◦C, the metastable hexagonal crystallisation is converted into a stable cubic crystallisation, seven curing cases were proposed in this study. After the curing process, thermo-mechanical properties of calcium aluminate cement paste were tested before and after thermal cycles from 290 ◦C to 650 ◦C. The results showed that, despite thermal cycling, the immediate hydration at 60 ◦C results in a higher thermal conductivity and compressive strength than standard curing at 20 ◦C.novaci´on - Agencia Estatal de Investigaci´on (PID2021-123511OB-C31 - MCIN/AEI/10.13039/501100011033) and by the Ministerio de Ciencia, Innovaci´on y Universidades - Agencia Estatal de Investigaci´on (AEI) (RED2018-102431-T). The authors at University of Lleida would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme. Laura Boquera acknowledgments are due to the PhD school in Energy and Sustainable Development from University of Perugia. Laura Boquera would like to acknowledge the financial support provided by UNIPG –CIRIAF InpathTES project. The authors also thank Ciments Molins industrial that provided the material to make possible this experimental research. Financial support of the UNIPG-CIRIAF team has been achieved from the Italian Ministry of University and Research (MUR) in the framework of the Project FISR 2019 “Eco Earth” (code 00245) that is gratefully acknowledged

Effect of PCM on the Hydration Process of Cement-Based Mixtures: A Novel Thermo-Mechanical Investigation

The use of Phase Change Material (PCM) for improving building indoor thermal comfort and energy saving has been largely investigated in the literature in recent years, thus confirming PCM's capability to reduce indoor thermal fluctuation in both summer and winter conditions, according to their melting temperature and operation boundaries. Further to that, the present paper aims at investigating an innovative use of PCM for absorbing heat released by cement during its curing process, which typically contributes to micro-cracking of massive concrete elements, therefore compromising their mechanical performance during their service life. The experiments carried out in this work showed how PCM, even in small quantities (i.e., up to 1% in weight of cement) plays a non-negligible benefit in reducing differential thermal increases between core and surface and therefore mechanical stresses originating from differential thermal expansion, as demonstrated by thermal monitoring of cement-based cubes. Both PCM types analyzed in the study (with melting temperatures at 18 and 25 ºC) were properly dispersed in the mix and were shown to be able to reduce the internal temperature of the cement paste by several degrees, i.e., around 5 ºC. Additionally, such small amount of PCM produced a reduction of the final density of the composite and an increase of the characteristic compressive strength with respect to the plain recipe.Funding: The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation program under Grant agreement No. 657466 (INPATH-TES) and No. 765057 (SaferUp!). The authors also thank the Microtek Laboratories, Inc. for providing the capsulated materials. The work is also partially funded by the Spanish government (ENE2015-64117-C5-1-R). Acknowledgments: Acknowledgments are due to the “CIRIAF program for UNESCO” in the framework of the UNESCO Chair “Water Resources Management and Culture”. Luisa F. Cabeza would like to thank the Catalan Government for the quality accreditation given to her research group (2017 SGR 1537)