Sodalime glass beads are commonly used in cement to make concrete stronger and more durable. The reactive amorphous silica in the glass reacts with the calcium hydroxide crystals in hydrated cement to form calcium silicate hydrate. Calcium silicate hydrate is essentially the strong backbone of concrete.
While glass can be beneficial to concrete, it can also be critically detrimental. The highly alkaline nature of ordinary Portland cement must also be considered before adding highly reactive glass into concrete. Glass, in high pH solutions, will turn into an expansive gel. The expansion, in hardened cementitious composites, will lead to cracking of the material from within. Preventing this expansion is almost impossible. Therefore, care must be taken when fillers for composite materials are chosen.