Chemical stability of hollow glass microspheres in cementitious syntactic foams

Recent studies have shown cementitious syntactic foams (CSF) to have great potential as a low density and high strength structural material. However, CSFs are made with hollow glass microsphere (HGM) inclusions and cementitious materials with amorphous silica inclusions such as glass are known to have a potential for the deleterious alkali silica reaction (ASR). In this study, CSFs containing HGMs are tested for ASR expansion and compressive strength along with solid particles of soda-lime and borosilicate glass to compare. Results show that in the 30–90 μm average particle size range, only solid borosilicate particles lead to more than 0.2% expansion of the composite material in an accelerated ASTM C1260 lab test for ASR, which is considered as the limit for deleterious effects. Similarly, compressive strength tests show that only solid borosilicate particles lead to reduced compressive strengths (from ~95 to ~40 MPa) in the long term, while CSFs showed no sign of loss of compressive strength even at extremely alkaline conditions. Scanning electron microscopy investigations suggest that CSFs are safe from ASR expansion of the composite and internal stresses due to their hollow geometry, which provides reservoir space for the alkaline silica gel expansion and mitigates the ASR effects.