PSI - Issue 64

Irene Palomar et al. / Procedia Structural Integrity 64 (2024) 1435–1443 Irene Palomar et al. / Structural Integrity Procedia 00 (2024) 000 – 000

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1. Introduction Environmental impact and energy efficiency of buildings is a main issue of our urban society. The large amount of resources and energy required for living in cities and the large environmental impacts are far than being sustainable. Accordingly, many public and private efforts are applied to reduce impact and increase efficiency of buildings, considering the life cycle of building materials and products, from production, through shelf life until final disposal and recycling. One promising approach to mitigate building impacts is the use of materials that can improve indoor comfort without requiring external energy supply. Self-modulating materials (SMM) are potential solutions to optimize the energy performance of buildings, by compensating climatic hygro-thermal changes and acting as indoor thermal and moisture buffers, as described in Guardia et al. (2020b) and Rode et al. (2006), respectively. The use of SMM in paste and mortar used as renderings in architectural applications can maximize their efficiency, according to Puentes et al. (2023). Bio-based materials are another opportunity to reduce impact of building materials, as they can be produced from vegetal sources without threatening sustainability. Phase-change materials (PCM) and Superabsorbent polymers (SAP) highlight among bio-based components that can be used to design self-modulating mortars. On one hand, PCM can storage and release thermal energy, modulating heat flow and reducing heating and cooling energy demand, as was pointed out by Cunha et al. (2016) and Guardia et al. (2019, 2020a and 2020b). On the other, SAP can help to achieve suitable indoor conditions as they level air humidity and contribute to an evaporative cooling effect, as described by He et al. (2019) and Fort et al. (2020). Although most nowadays commercial PCM and SAP are derived from crude oil, these polymeric materials can also be made from renewable bio-resources, becoming bio based materials, as reported in Magendran et al. (2019). A specific strategy is required in order to incorporate bio-based components in mortars. The first aspect to consider is the type of binder and the proportion and type of other components, as type and particle grading of aggregates or water to binder ratio, as described in Palomar et al. (2015). Besides, the main requirements in fresh state, setting and hardening process and hardened properties must be defined, as in the case presented in Palomar et al. (2017 and 2023) and Pokorný et al. (2022). Finally, the nature and compatibility of bio-based components with other mortar ingredients must be analyzed, which in many cases makes necessary a pretreatment. This is the case of paraffin or organic wax based PCM, which need to be encapsulated in order to avoid leakage, as described in Guardia et al. (2019). Thermal and moisture transport evaluation of bio-based SMM mortars can be performed using standard test methods, although sometimes the parameters evaluated do not correspond to real-scale situations. To overcome this problem, it is advisable to combine standard tests with other non-standard assessment, as reduced scale climate chamber simulations, according to Guardia et al. (2020b). The aim of the study was to design pervious rendering cement-lime mortars with bio-based components for indoor architectural applications acting as heat and moisture buffer to enhance indoor comfort conditions, delaying the effect of climate fluctuations and the need to activate active air-conditioning systems. 2. Materials and Experimental Program An experimental program to evaluate fresh state and hardened properties of pervious rendering cement-lime mortars with bio-based components for indoor architectural applications was designed according to Figure 1. A reference mortar was designed and modified incorporating PCM and SAP. A set of basic material’s requirements consi dering its application as an indoor building rendering was defined. Construction aspects related to workability and setting and service-life and aesthetic characteristics related to hardened properties were considered. Accordingly, the experimental program included fresh state mortar characterization, early age evolution and hardened microstructural, physical and mechanical parameters were evaluated. Due to the use of lime mixed with cement, a long term characterization was considered. Thermal and moisture transport properties using standard tests and climate chamber simulations were assessed to use the mortar as thermal and moisture buffer architectural rendering.