Autoclaving cementitious syntactic foams will lead to the accelerated reaction between the highly alkaline sodium hydroxide and the reactive silica in the glass walls of microspheres. Therefore, scientists make use of autoclaving to simulate the longterm behavior of cementitious composites with an autoclave. In this article, the reaction product of glass and sodium hydroxide is seen as a fuzzy dried out gel on the periphery of the microspheres.
The cracks on the walls of the microspheres are proof that glass at high alkalinity turns into an expansive gel. This gel after drying out starts cracking just like dried out mud cracks at a much larger scale.