New insights into the use of glass cullet in cement composites-Long term examinations

Finely ground glass cullet is a very attractive pozzolanic additive, as it is an excellent source of active silica. Moreover, crushed glass is sometimes used due to its aesthetic and decorative qualities. Unfortunately, it is also the source of alkalis. The packaging glass cullet contains even more than 16% alkalis, which are slowly but continuously released into the hydrating system. This could be a reason for the occurrence of ASR in hardened concrete. In this work, OPC mortars containing finely ground glass powder (as a part of the binder) and glass sand (as quartz sand replacement) in various proportions were examined for 10 years. The compressive strength, phase composition, and expansion tests were carried out, along with microstructural observations. Many re-searchers indicated positive effects of the use of glass as a mineral additive, however, the presented long-term results show that the applicability of glass cullet as a mineral additive is disputable. This is the first work that presents the results of 10-year-long examinations of glass-containing mortars. It also shows a new, previously undescribed phenomenon: the glass hydration process has a multistage, not a continuous character.