Key Engineering Materials Vol. 668

Abstract: Nowadays, scientific community is looking for alternatives to reduce the problem of CO₂ emissions, making more sustainable binders and reusing wastes from other industries.In this line, the technology of geopolymers was born, in which, binders based on alkali-activation can be produced entirely or almost entirely from waste materials. In alkali-activation a source of aluminosilicate is dissolved by a highly alkaline solution previous to precipitation reactions that form a gel binder.The use of alumino-silicate minerals such as metakaolin, blast furnace slag and fly ash to produce alkali-activated cements has been extensively studied and it’s increasing the interest in investigating the suitability of using other materials. Different wastes containing silica and alumina, such as hydrated-carbonated cement, glass, fluid catalytic cracking catalyst residues (FCC) have been activated.The aim of this study is to verify if the use of geopolymers is compatible with the manufacturing technology of typical building elements, in this case roof tiles.Mechanical properties of mortars and roof tiles using as source of aluminosilicates FCC have been studied, with different mixtures and variating the proportions of NaOH and waterglass.Compressive strength development was evaluated in mortars cured at 20oC for 7 and 28 days and flexural strength, impermeability and impact resistance were evaluated in roof tiles. The results obtained demonstrated the feasibility on the use of geopolymers in the design of new products with less CO₂ emissions and then the contribution to the sustainability in the construction sector.

Abstract: Many works have shown that metakaolin is very good pozzolanic material for using in lime mortars and Portland cement mortars. Alternatively, many studies also have shown that kaolin wastes, after some treatment, can become a high quality pozzolans. Most of these studies have discussed about the microstructural characteristics and hardened properties of pastes, mortars or concretes mixes containing metakaolin or kaolin wastes cured in moist environment. In this work pastes and mortars made of metakaolin and hydrated lime (L-MK), which the metakaolin was obtained from the kaolin production waste, were assessed in their hardened state. Two curing conditions were considered: dry and moist environment; and three ages of curing (28, 90 and 180 days) were studied. Pastes were assessed by XRD and TG/DTG. In pastes according to the XRD and TG/DTG results, the main hydrated products found were strätlingite, in moist curing, and monocarboaluminate, in dry curing. Properties like flexural and compressive strengths, water absorbed capillarity and loss mass variation were studied in mortars. The results showed that mortars in dry curing presented lower strengths than one in moist curing. In moist curing mortars presented compressive strength values around 12 MPa and in dry curing this value reached 6 MPa. This fact indicate that the strätlingite maybe is responsible for the high strengths in mortars in moist curing when compares with the strengths of mortars cured in dry environment. Further the results showed that mortars in dry curing presented higher water absorbed and mass loss variation than mortars in moist curing.