Experimental and theoretical investigation of thermal properties of natural soil based geopolymer composites

Abstract

Geopolymer composites have found numerous thermal management applications in the construction industry due to their low thermal conductivity. In this work, geopolymer foams were produced using natural soil with varying fractions of sodium silicate solution. The extent of geopolymerization was evaluated based on qualitative and X-ray diffraction analyses. Scanning electron microscopy was performed to characterize the shape morphology. Thermal properties were measured using a hot disk analyzer. The effect of shape morphology and porosity on the thermal conductivity of the composites was discussed using several theoretical models. Yan- He, Hamilton-Crosser and geometric mean models showed good comparison with experimental observations. It was revealed that the geopolymerization reactions affect the porosity level, which, in turn, influences the effective thermal conductivity of the medium.

Synthesis of Geopolymer from a Novel Aluminosilicate-Based Natural Soil Precursor Using Electric Oven Curing for Improved Mechanical Strength

“…It may now be noticed that the same sample reached the maximum compressive strength. Since the GPN reaction takes place only on the surface of the NS particles, modifying their texture [ 7 ], the formation of a strong Si-O-X network is completely achieved by a limited amount of SS solution present in the system. The excess amount of SS not only develops an Si-O-X network, but also leads to the formation of a dendritic needle-like weak structure [ 8 ] that has the tendency to fail under compressive loading before transferring the stresses to the Si-O-X network.…”

“…for an initial drying at 70 °C for 24 h. The samples were then oven-cooled and removed from the molds before again being placed in the oven for curing and GPN. During curing, a temperature of 220 °C was maintained for a period of 2 h. This is the most critical step, since GPN reaction takes place at these high temperatures [ 6 , 7 ]. Finally, the GP samples were oven-cooled once again and retrieved for testing.…”

“…Thermal activation around the temperature range of 60–200 °C is often necessary to complete the GPN reaction. The dwell-time at these curing temperatures, however, varies from a few minutes (~5 min) to several hours (~24 h) depending upon the heat source, such as microwave radiation or an electric/gas oven [ 6 , 7 ]. Curing/drying is found to improve the mechanical properties, though it results in the distribution of undesirable porosity throughout the structure [ 8 ].…”