Reactivity of Glass Powder in Aqueous Medium

Recycled glass powder (GP) has recently been widely used as a complementary cementitious material to replace a part of the Portland cement in concrete. However, unlike the chemistry of the Portland cement hydration, more studied and mastered, the mechanism of GP reaction that occurs in-situ during the mixture hydration, is less studied. To overcome this, a first study was focused on the reactivity of the anhydrous glass powder surface over time and its effect on physico-chemical and mechanical properties of concrete. The results showed a very good stability of GP surface. Actually, Portland cement mortars incorporating 20% GP at different ages exhibited the same required properties. The second step, which is the subject of this paper, consists of studying the behavior of GP alone in water and identifying species likely to involve in the hydration reaction in presence of the cement. pH of suspensions and chemical composition of leachates were monitored respectively by pH-meter and inductively coupled plasma mass spectrometry (ICP-MS) as a function of contact time, water-to-solid mass ratio (W/S) and GP particle size. Results reveal an instantaneous increase of pH after mixing GP with water resulting in the passage of surface alkali ions in the solution. Moreover, an enhancement of silicon content in solution is observed suggesting a partial dissolution of the glass network. The dissolution rate increases with increasing W/S ratio and decreasing particle size. Thus, dissolved silica species would react with portlandite from cement hydration explaining good mechanical properties generally observed in concrete containing GP at long term. Accordingly, due to its high amorphous silica content, GP could be an excellent alternative for conventional supplementary cementitious materials such as fly ashes which are not locally available.