Abstract
• Microcapsules slow down the reaction of both geopolymer and Portland cement pastes. • Increasing the temperature accelerates the setting times of geopolymer and Portland cement pastes. • Addition of microcapsules reduces the compressive strength. • Enhanced porosity at higher temperatures for both geopolymer and Portland cement. To reduce pollution and global warming, the energy consumption needs to be decreased. Incorporation of Phase Change Materials (PCMs) into building materials can help lower the energy needed to cool and warm buildings, while keeping the indoor temperature at a comfortable level. However, incorporation of PCMs into construction materials alter their performance. In this study, the effect of temperature and addition of two different Micro-encapsulated Phase Change Materials (MPCM) to geopolymer concrete (GPC) and Portland cement concrete (PCC) and pastes was investigated. The samples were examined both below (20 °C) and above (40 °C) the melting points of the PCMs. While the MPCM is not damaged by the alkaline solution, a few microcapsules are broken during the mixing process. Isothermal calorimetry shows that MPCM addition slows down the reaction rate of both geopolymer and Portland cement paste. The setting times were faster when the temperature was increased. The mechanical properties are reduced when MPCM is added to GPC and PCC, although the compressive strength is adequate for building applications. Microstructural studies show more uniform and undamaged edges in the shell-concrete matrix transition zone of GPC than PCC. The samples cured at 40 °C exhibits more air voids in both GPC and PCC than at 20 °C.
Highlights
The production of Portland cement is a major contributor to CO2 emissions [1]
This paper focuses on how Micro-encapsulated Phase Change Materials (MPCM) addition affect the reaction kinetics of the samples, utilizing isothermal calorimetry at both 20 and 40 °C
EDX mapping and scanning electron microscopy (SEM) images of St-DVB-Phase Change Materials (PCMs) after immersion in the alkaline solution are presented at two different magnifications in Fig. 2a and b
Summary
The production of Portland cement is a major contributor to CO2 emissions [1]. Tion is an exothermic reaction that involves dissolution of silicoaluminates in an alkaline solution and provides an amorphous to semi-crystalline three-dimensional network [3]. The aluminosilicate sources can be natural minerals, like kaolinite, metakaolin and clays [2,4] or industrial secondary products such as fly ash (FA), ground granulated blast furnace slag (GGBFS), red mud, and silica fume [5,6,7]. Sodium hydroxide (NaOH), sodium silicate (Na2SiO3), potassium hydroxide (KOH), and potassium silicate (K2SiO3) are commonly used as the alkaline solutions.
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