We fabricated 50.8-mm cube-shaped samples of metakaolin geopolymer (GP) composites with various additives chosen to increase or decrease the thermal conductivity of the composite. Sodium-based GP (NaGP) and GP composites were more conductive than potassium-based GP (KGP) composites for a given phase fraction of filler, but the maximum amount of filler phase was higher with KGP due to the lower viscosity of the KGP mixture. The highest thermal conductivity achieved was about 8 W/m K by KGP + 44-vol% graphite flakes, whereas NaGP + 27 vol% graphite flakes reached 4.7 W/m K. The thermal conductivity was strongly affected by the moisture remaining in the composite, which appeared to have a greater effect at higher filler content. On the other hand, the size of alumina particles (6, 40, or 120 µm) did not have any apparent effect on thermal conductivity for the same filler content. Larger particles caused less change in mixture viscosity, though, thus permitting incorporation of higher filler phase fractions and therefore higher thermal conductivity.

The incorporation of smart building materials into construction will improve the working life of structures and infrastructure around the globe. Unfortunately, conventional smart building materials are cost-prohibitive because of the self-sensing additives required. Alkali-activated inorganic polymers are a promising low-cost and environmentally friendly alternative that exhibit intrinsic self-sensing properties, without the need for self-sensing additives. An improved methodology has been developed to quantify the self-sensing piezoresistivity of these materials. Experimental measurements reveal a strong intrinsic piezoresistivity up to 12%. The results agree with a first-principles model of the theoretical piezoresistivity of an alkali-activated inorganic polymer from the quantum mechanical perturbation theory. This first-of-its-kind computation provides a mechanistic explanation for the origin of intrinsic piezoresistivity in inorganic polymers.