Geopolymer concrete for net-zero buildings: Correlating paste chemistry with monolith hygrothermal performance

Geopolymers are among the materials that are being studied for use in Net-Zero Buildings. The main reasons for their popularity are their low embodied energy and capacity to passively control indoor microclimate especially when they are cellular. The performance of cellular geopolymers as passive thermal and moisture regulators depends on their manufacturing parameters. To achieve an optimal design of geopolymers for the desired application understanding the influences of these parameters is crucial. Among these salient parameters are the initial water content and alkalinity of the reaction mixture. The focus of this paper is to investigate the extent of these factors' influence on the thermal, hydric, phase composition, and microstructure of aerated geopolymers. In this study, two groups of samples were prepared by varying initial water content and alkaline molarity of the reaction mix. The results showed that the vapor permeability and moisture effusivity of the samples prepared by adjusting the initial water content showed similar hydric properties. The vapor permeability of the samples measured at 7-75%RH and 7-37%RH vapor pressure gradients are approximate to 3 kg/m.s. Pa and approximate to 2.3 kg/m.s Pa respec-tively. Their moisture buffer capacities are very similar as well (ranging from 4.93 to 5.14 g/ (m2%RH)). The slim differences in hydric properties are attributed to minor differences in porosity, degree of reaction, and porogen decomposition. However, the thermal conductivity and density of the samples increased as the water content is raised. This is because of differences in the amount of water trapped in the interstitial sites of the inorganic polymer. On the other hand, the hygrothermal and physical properties of the three samples prepared at different molarities showed a non-monotonic trend (for instance; Density (g/cm3): 0.50, 0.40, 0.44; Moisture buffer ca-pacity (g/ (m2%RH)): 4.65, 5.65, and 4.79). This is because the fluctuations in alkaline molarity resulted in significant differences in the degree of geopolymerization, carbonation, and porosity of the samples. Despite the differences, all the geopolymers samples showed a potential to efficiently modulate indoor environment compared to conventional building materials.

Automated summary

Geopolymers are materials that show promise for use in Net-Zero Buildings due to their low embodied energy and ability to passively control indoor microclimate. The influences of manufacturing parameters, such as initial water content and alkalinity, on the thermal, hydric, phase composition, and microstructure of aerated geopolymers were investigated. The results showed that these factors affect the properties of the geopolymers, but all the samples demonstrated potential for efficient modulation of indoor environment.