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.

This paper presents a microstructure-guided modeling approach to predict the effective elastic response of heterogeneous materials, and demonstrates its application towards two highly heterogeneous, unconventional structural binders, i.e., iron carbonate and fly ash geopolymer. Microstructural information from synchrotron x-ray tomography (XRT) and intrinsic elastic properties of component solid phases from statistical nanoindentation are used as the primary inputs. The virtual periodic 3D microstructure reconstructed using XRT, along with periodic boundary conditions is used as a basis for strain-controlled numerical simulation scheme in the linear elastic range to predict the elastic modulus as well as the stresses in the microstructural phases. The elastic modulus of the composite material predicted from the microstructure-based constitutive modeling approach correlates very well with experimental measurements for both the materials considered. This technique efficiently links the microstructure to mechanical properties of interest and helps develop material design guidelines for novel heterogeneous composites.

This study reports the influence of inclusion stiffness and its distribution on the stress distributions in the microstructural phases of different cementitious mortars using microstructure-guided finite element simulations. Randomly generated periodic microstructures with single/multiple inclusion sizes and random spatial distribution, subjected to periodic boundary conditions and a strain-controlled virtual testing regime are chosen for final analysis. Numerical simulations reveal: (i) the differences in locations/magnitudes of stress concentrations as a function of inclusion stiffness and size distribution, and (ii) the sometimes detrimental influence of matrix and interface stiffening/strengthening on the overall composite response, leading to material design strategies when non-conventional inclusions are used in cementitious systems for special properties. The constitutive behavior in the linear elastic regime is extracted based on the predicted dominant principal stresses and strains in the representative area element. Thus, in addition to the microstructural phase stresses, this methodology also provides predictions of the composite elastic modulus, which are observed to be more reliable than those obtained from analytical prediction models.

This paper reports the fundamental difference in microstress distributions in traditional hardened cement paste with quartz inclusions and a cement paste with lightweight aggregate (LWA) inclusions using microstructurebased numerical simulation involving finite element method with periodic boundary conditions. Variation of relative stress distributions under varying component material properties and varying microstructural features in both the systems is elucidated for a comprehensive understanding. The presented microstructure-based numerical technique accurately captures the stress concentrations inside microheterogeneous systems, which is otherwise not detectible using analytical homogenization schemes. Numerical simulations reveal that strengthening and stiffening of matrix and interfacial transition zone (ITZ) with silica fume incorporation as cement replacement in LWA incorporated cementitious systems has a detrimental effect in terms of overall strength of the material, contrary to traditional quartz-based cement mortar system. Proper selection of stiffness and strength of LWA inclusions is critical towards performance of such materials. This paper links the microstructure with mechanical behavior of two different microheterogeneous materials and provides valuable input towards material design of such non-traditional cementitious systems with different inclusions.