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Effect of Microstructure on Thermal Conductivity of Cement-Based Foam
- Author / Creator
The use of thermal insulation has assumed greater importance amidst rising energy costs, with applications in the resource-rich but climatically harsh regions like Canada’s North. The thermal performance of structural and non-structural components is singularly determined by the thermal properties of the materials used in its construction. The thermal conductivity which is a material’s property is used in designing the insulation. In recent years, the use of cement-based foam has noticeably increased due to its good insulating properties and with potential for utilization of industrial by-products as pozzolanic admixtures.
The microstructure of cement-based foam comprises of two phases i.e. the solid phase and the void phase. The dimension and distribution of the air-void phase are influenced by a change in the overall density or porosity, whereas the properties of the solid phase are affected by the type of mix composition i.e. addition of the pozzolanic admixture, hydration age and moisture content.
This study investigates in detail the influence of air-void parameters and hydrated cement paste on the thermal conductivity of cement-based foam by varying the density and binder types. In the experimental phase, three series of cement-based foams were prepared with cast densities of 800 kg/m3, 600 kg/m3 and 400 kg/m3 respectively. In addition to the reference mix, two mixes were prepared at each cast density containing fly ash, silica fume and metakaolin, where in the cement was replaced 10% and 20% by weight. The result shows that the thermal conductivity was significantly influenced by the change in density and the substitution of admixtures leads to further reduction. This is mainly due to formation of crystalline and amorphous hydrated products, changes to air-void network and water absorptive property. Adding fly ash, silica fume and metakaolin does not significantly influence the of air-void size distribution. However, pore-size of 0.03 mm diameter had the maximum frequency of occurrence for all the mixes. The shape of the majority of the air-voids in all mixes was circular (i.e. spherical).
An empirical thermal conductivity model was developed based on the measurement of the void phase (porosity), substitution ratio of the pozzolanic admixture and the age of the paste. These observations were recorded in the current study for mixes with and without the pozzolanic admixture. For validation, thermal conductivity predictions were examined against other independent databases, reliable and accurate predictions were found.
- Graduation date
- Spring 2015
- Type of Item
- Doctor of Philosophy
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