Effect of glass powder on microstructure of cement pastes

The effect of glass powder (GP) on the microstructure of cement pastes was studied by using mercury intrusion porosimetry, thermogravimetric and differential thermal analysis, scanning electron microscopy, energy dispersive spectrum analysis and X-ray diffraction techniques. The compressive strength and alkali–silica reaction (ASR) expansion was also tested. The test results indicated that GP can increase the compressive strength of cement pastes and control the ASR expansion of mortars. With the increase in GP content, ASR expansion decreases sharply, although compressive strength decreases a little with a large amount of GP. The characteristic pore sizes decreased with some capillary pores transforming to interstitial pores or gel pores as GP content increased. GP could diminish pore size in cement pastes, which has important significance in improving durability. Incorporating GP in cement-based materials had little effect on the kinds of hydration products, but it significantly affected the amount of hydrates, especially calcium hydroxide. The amount of calcium hydroxide reduces with the increase in curing age and GP content. The microstructure of hardened pastes containing GP was relatively dense with an abundance of calcium silicate hydrate, whose morphology was different from the gel in pure cement systems. This kind of calcium silicate hydrate gel with a low calcium/silicon ratio had a network structure formed by irregular stumpy and lamelliform gel granules. GP has high pozzolanic activity.