Ordinary Portland cement has an alkaline chemistry. This high alkalinity attacks reactive silica in the glass, turning it into an expansive gel. This article shows the alkaline silica gel in cement and sodalime glass composite. The inner surface of these glass inclusions is in fact dried out alkaline silica gel.
Most electron microscopes require vacuum in order to prevent the interference of air with the electron beam. However, this vacuum makes it difficult to observe wet specimens since water tends to evaporate as the air pressure in the vacuum chamber decreases. This vacuum is also the reason behind the drying of the alkaline silica gel featured in this article.