# Cement Pastes with Hygyroscopic Polymeric Additions for Potential Building Applications
###### Abstract  
The development of highly predictive analysis for designing cementitious composite with improved thermal and hygroscopic performance for building and construction poses a significant challenge. To investigate new potential applications, cement pastes have been prepared using a cement, sand, and crystallization admixture, with highly hygroscopic polymer additions (SA-PA) of sodium polyacrylamide and/or recycled polyamide fibers. The porosity evolution was investigated at different curing stages and after heat treatment at 200 \({}^{\circ}\)C, the temperature at which the paste dehydrates quickly without structural changes. Mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), cyclic shear tests, thermal conductivity, and diffusivity measurements were carried out on the cement pastes to assess their microstructure. The behavior of the cement pastes varied with polymer additions and thermal treatments; ka\({}^{-0.5}\) must be maximized in heat storage applications, where a and k are thermal diffusivity and conductivity, respectively. In contrast, the product a\({}^{0.5}\)k\({}^{-1}\) must be maximized in energy-efficient insulation. Cement pastes with SA-PA exhibited the highest values of both 9.191 10\({}^{2}\) m\({}^{-2}\) K\({}^{-1}\) s\({}^{0.5}\) W and 1.088 10\({}^{-3}\) m\({}^{2}\) K s\({}^{-0.5}\) W\({}^{-1}\), respectively. After the thermal treatment at 200 \({}^{\circ}\)C, SA-PA samples maintained the highest heat-storming performance of 6.258 10\({}^{2}\) m\({}^{-2}\) K\({}^{-1}\) s\({}^{0.5}\) W, while the samples with SA-PA and polyamide fibers performed better in energy-efficient insulation, demonstrating performance of 2.552 10\({}^{-3}\) m\({}^{2}\) K s\({}^{-0.5}\) W\({}^{-1}\). These results, discussed in terms of pore size distribution, suggest potential applications in the building field and are valuable for designing plaster and concrete for applications such as thermal and hygroscopic control. p 2024 14 853 202  
The porosity of concrete is mainly due to its cement paste, the binder of coarse aggregates. More frequently, cementitious materials, such as concrete, mortars, or plasters, contain polymeric fibers for structural use [18; 19]: these additions affect the development of porosity. As recalled before, low permeability is linked to an absence of interconnected porosity: the larger the porosity, the greater the interconnectivity. In a previous study [20], a correlation was established between air permeability and the size of pores during the hydration of cement paste and the continuous growth of CSH crystals. Pore size distribution has been associated with water diffusion: the more CSH forms, the more gel pores, the fewer capillary pores, and the greater the strength. Moreover, it was also evidenced that the addition of superabsorbent poly-acrylates (SA-PA), as an internal curing additive [12; 13], modifies the pore size distribution in cement paste; thus, a reduction in the capillary pressure and an improvement in the permeability was obtained. The present study considered the effect of the addition of SA-PA and polyamide fibers (Ny) on the pore size evolution and the thermo-mechanical behavior of cement pastes, prepared using a cement mix containing a crystallization admixture. The latter was a calcium silicate, which hydrates quickly, forming crystalline seeds as nuclei for CSH crystallization and promoting the development of strength [20; 21; 22; 23]. Aging progressively reduces the volume and size of pores; therefore, the presence of highly hygroscopic fibers or additions could induce a different pore distribution. SA-PA and Ny increase liquid permeation resistance because both absorb water, although to a different extent and, when simultaneously present, a mutual strengthening effect on porosity is supposed to occur [14]. Many factors could affect internal pore structures, including thermal treatment.