GREEN CEMENTITIOUS COMPOSITES OF WASTE GLASS AND LIMESTONE

Investigations were carried out to characterize the reactivity and strength of alternative cementitious composite pastes based on waste glass and limestone activated by NaOH and Na2CO3. The Taguchi method was applied to outline the design of experiments. The parameters considered were the CaO/SiO2 ratio, fraction of preactivated binder, type of alkaline activator, Na2O concentration, water/binder ratio and curing temperature; their effect was analyzed on the compressive strength using signal to noise ratios and mean response data. The experimental results showed that the most effective alkali activator was a mixture of Na2CO3/NaOH that reached 60 MPa after 28 days; while NaOH resulted the least favorable, with 30 MPa. The strength decreased with the increased in CaO/SiO2 ratio. The main reaction products found, by means of X-ray diffractometry, thermal analysis and scanning electron microscopy, in all formulations were: calcium silicate hydrate (C-S-H), a silica gel type phase, and other minor crystalline phases were pirssonite (Na2Ca(CO3)(2)center dot 2H(2)O) and gaylussite (Na2Ca(CO3)(2)center dot 5H(2)O). The optimum strength resulted at CaO/SiO2 ratio of 0.5, preactivation of 40% of the binder with a mixture of Na2CO3/NaOH at about 9% Na2O, a water binder ratio of 0.3 and a curing temperature of 40 degrees C.