Effect of freeze-thaw cycles on the mechanical behavior of geopolymer concrete and Portland cement concrete containing micro-encapsulated phase change materials

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Flame retardancy of rigid polyurethane foams containing thermoregulating microcapsules with phosphazene-based monomers

Thermoregulating microcapsules (MC) with flame-retardant properties were used to produce polyurethane (PU) foams. Thermogravimetric analyses of the microcapsules performed under atmospheric air and nitrogen confirmed that the hexa(methacryloylethylenedioxy) cyclotriphosphazene (PNC-HEMA) monomer raised the amount of residue after exposure to high temperature, proving the formation of a thermally stable char layer. Additionally, the flame-retardant properties of the microcapsules were analyzed by micro-combustion calorimetry (MCC), and the PU foams were tested by both MCC and cone calorimetry. The total heat release and maximum heat release rate were lower for microcapsules containing the flame-retardant PNC-HEMA. The composition of the microcapsules has been proved by MCC and TGA, where the release of the encapsulated phase change material (PCM) occurred at the expected temperature. However, in PU foams, the release of PCM is shifted to higher temperatures. Accordingly, these materials can be considered as an important alternative to commonly used microcapsules containing phase PCMs, where a lower flammability is required for their future application.publishedVersio

Effect of temperature on geopolymer and Portland cement composites modified with Micro-encapsulated Phase Change materials

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Effect of Microencapsulated Phase Change Materials on the Flow Behavior of Cement Composites

Microencapsulated phase change materials (MPCMs) were incorporated into cement pastes of Portland cement (PC). Minislump tests and rheological properties of cement pastes containing three MPCMs with different surfaces (hydrophilic, amphiphilic and hydrophobic) were measured, and the water demand of MPCM in the cement matrix was evaluated. The hydrophilic MPCM was chosen for a more thorough rheological study, since it was found to be more compatible with the cement matrix. The dispersion of a high amounts (45 wt% with respect to the cement content, which corresponds to about 62 vol% of the total solids) of the hydrophilic MPCM in the cement pastes was achieved by optimization of the amount of superplasticizer through rheological measurements. For the viscometer tests, a Power Law model was found to give the best fit to the experimental data. While pastes (with 45 wt% of hydrophilic MPCM) prepared with low superplasticizer contents (<1.2 wt%) were found to be shear thinning, the paste exhibited a shear thickening behavior in the presence of higher amounts of superplasticizer. The shear thickening is probably caused by high water adsorption onto the microcapsules combined with deflocculation of the cement particles at high concentrations of superplasticizer. After the optimization of the superplasticizer content, homogeneous pastes were obtained, where the particles of the hydrophilic MPCM were well dispersed and unaltered after 28 days of hydration.MINECO -BIA2017-82391-R) y I3 (IEDI-2016-0079

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

The effect of microencapsulated phase‐change materials (MPCM) on the rheological properties of pre‐set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s−1. New empirical equations were developed to quantify the time‐dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D‐geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear‐induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.publishedVersio

Thermal analysis of geopolymer concrete walls containing microencapsulated phase change materials for building applications

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Influence of Microcapsule Size and Shell Polarity on the Time-Dependent Viscosity of Geopolymer Paste

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