Activation of mixtures of natural clay and glass cullet rejects

Abstract

Alkaline activation involves a reaction between aluminium silicates and compounds with alkalis or alkaline-earth elements in a caustic environment and under certain thermal and pressure conditions. It has been used in the production of non-structural building materials and in so-called ‘green’ concrete, as products display high mechanical strength, low chemical reactivity and high resistance to fire. Green concrete could be an eco-efficient alternative to concrete made using ordinary Portland cement (OPC), reducing CO2 emissions substantially. The main goal of this work is to test common clays, glass cullet and other industrial wastes as an alternative to the commonly used binders (metakaolin or fly ash) in geopolymers. Optimized formulations show interesting mechanical strength (approaching 20 MPa) after just 48 h of curing. The addition of F-sand as aggregate minimizes the shrinkage upon curing and the amount of activator required, and increases the density/degree of compaction of the bodies, thus improving their mechanical resistance within certain limits. Curing in ambient conditions also has a beneficial affect on the mechanical strength.

Alkali activation of biomass fly ash–metakaolin blends

“…However the ratio of Na 2 O was lower in all the compositions though the biomass fly ash contributed a big portion in it. But this can be easily overtaken by the addition of sodium hydroxide and sodium silicate solution in the mix and it is the prime aim of adding alkali activators [20].…”

“…Some researchers consider that the ratios of the principal components, in the solid precursor, must be situated between 3.3 and 4.5 (SiO 2 /Al 2 O 3 ), 0.20 and 0.48 (Na 2 O/SiO 2 ) and 0.8 and 1.6 (Na 2 O/Al 2 O 3 ) for an effective alkali activation to occur [5,[18][19][20]. Relative molar ratios of the mixture compositions tested are shown in Table 6.…”

Weathering Products of a Dismantled Variscan Basement. Minero-Chemical Proxies to Insight on Cretaceous Palaeogeography and Late Neogene Palaeoclimate of Sardinia (Italy)

“…Finally, the Messinian palaeosols yield Ce anomalies that are generally close to 1 with the exception of sample MP1 (Ce/Ce * = 0.48). The Cretaceous samples instead exhibit a wide range of Ce/Ce * values (0.26-2.63) likely as a consequence of local Eh fluctuations, as supported by the presence of remnants of a reducing humic horizon and oxyhydroxide phases (Braun et al, 1990;Mongelli, 1997;Mameli et al, 2008).…”

Alkali activation of natural clay using a Ca(OH)2/Na2CO3 alkaline mixture

“…Alkali activation of aluminosilicates is a term used to describe synthesis of geopolymers, inorganic polymers or alkali-activated binders in a high-pH environment at relatively low curing temperatures, up to 100°C (Davidovits, 1991;Carvalho et al, 2008;Provis & Bernal, 2014;Esaifan et al, 2015). The mechanical strength (>40 MPa) of the alkali-activated materials with low-energy requirements during production, encouraged extensive research worldwide to use the alkali-activated materials as environmentally friendly alternative building materials to Portland cement (Carvalho et al, 2008;Van Deventer et al, 2012;Provis & Bernal, 2014;Esaifan et al, 2016). The mechanical strength, morphology and physical properties of alkali-activated materials are influenced by several factors such as curing temperature, curing time, and type and concentration of the alkaline activator (Pacheco-Torgal et al, 2014).…”