High strength/density ratio in a syntactic foam made from one-part mix geopolymer and cenospheres

By designing a composite of one-part mix geopolymer and hollow cenospheres, a commercially viable and environmentally-friendly foam was synthesised with a high strength/density ratio. The composite is made of a dry mix powder of geopolymer source materials, sodium silicate alkali activator and cenospheres, which starts to react when mixed with water. As the geopolymer reacts and gains strength over time, the surface of the cenospheres takes part in the reaction and forms a strong bond with the binding matrix. Synchrotron-based Fourier transform infrared microspectroscopy revealed, for the first time, the chemical bonding interaction of the amorphous interfacial layer between the geopolymer and cenospheres. The resulting foam composite gained a strength of 17.5 MPa at a density of 978 kg/m3, which is noticeably higher than that of existing environmentally-friendly lightweight foams made under ambient conditions. The thermal conductivity of the foam was measured to be around 0.28 kW/mK, which is similar to that of foam concrete. This foam produced in this study is found to be lightweight, strong and possess a desirable insulating capacity, while the preparation process of the one-part mix composite is maintained simply by adding water and curing the mixture at an ambient temperature.