No abstract

No abstract

Phase Change Materials (PCMs) incorporated into cementitious systems have been well-studied with respect to energy efficiency of building envelopes. New applications of PCMs in infrastructural concrete, e.g., for mitigating early-age cracking and freeze-and-thaw induced damage, have been proposed. Hence this paper develops a detailed understanding of the characteristics of cementitious systems containing two different microencapsulated PCMs. The PCMs are evaluated using thermal analysis, vibrational (FTIR) spectroscopy, and electron microscopy, and their dispersion in cement pastes is quantified using X-ray Computed Microtomography (µCT). The influences of PCMs on cement hydration and pore structure are evaluated. The compressive strength of mortars containing PCMs is noted to be strongly dependent on the encapsulation properties. Finite element simulations carried out on cementitious microstructures are used to assess the influence of interface properties and inter-inclusion interactions.The outcomes provide insights on methods to tailor the component phase properties and PCM volume fraction so as to achieve desirable performance.

No abstract

No abstract

This paper examines the influence of four different porous hosts (lightweight aggregates (LWA)) having different pore structure features, as hosts for phase change materials (PCM). The porosity and absorption capacity of the LWAs significantly influence the composite thermal conductivity. The incorporation of 5% of PCMs by total volume of the cementitious system reduces the composite thermal conductivity by ≥10%. The fact that the inclusions (LWAs) in these composites are by themselves heterogeneous, and contain multiple components (solid phase, PCM, water, and air) necessitate careful application of predictive models. Multi-step Mori-Tanaka mean-field homogenization methods, either based on known microstructural arrangement in the composite, or property contrast between the constituents, are applied to predict the composite thermal conductivity. A microstructural contrast factor is used to account for both the thermal conductivities and the volume fractions of the phases with the highest property contrast. Smaller contrast factors result in improved agreement of the models with the experiments, thereby aiding in the selection of suitable predictive schemes for effective properties of such multi-phase composites.

No abstract

This paper presents a microstructure-guided numerical homogenization technique to predict the effective thermal conductivity of a hierarchical cement-based material containing phase change material (PCM)-impregnated lightweight aggregates (LWA). Porous inclusions such as lightweight aggregates embedded in a cementitious matrix are filled with multiple fluid phases including phase change material to obtain desirable thermal properties for building and infrastructure applications.Simulations are carried out on realistic three-dimensional microstructures generated using pore structure information. An inverse analysis procedure is used to extract the intrinsic thermal properties of those microstructural components for which data is not available. The homogenized heat flux is predicted for an imposed temperature gradient from which the effective composite thermal conductivity is computed. The simulated effective composite thermal conductivities are found to correlate very well with experimental measurements for a family of composites considered in the paper. Comparisons with commonly used analytical homogenization models show that the microstructure-guided simulation approach provides superior results for composites exhibiting large property contrast between phases. By linking the microstructure and thermal properties of hierarchical materials, an efficient framework is available for optimizing the material design to improve thermal efficiency of a wide variety of heterogeneous materials.