Evaluation of the properties of a foamed geopolymer developed with different types of metakaolin

Abstract

The physical and mechanical properties of foamed geopolymers were determined. The geopolymers were made with two different metakaolins (from Metacaulim do Brasil -MB, and Pantano Grande/RS -MPG) as precursors, with NaOH and Na 2 SiO 3 as activators, and with the addition of foam, which was produced with the foaming agent diethanolamide of coconut fatty acid with a minimum of 80% concentration. Also, two times (2.5 and 4 h) were used for the calcination of MPG at 750 °C. The results showed that all factors (precursors type, alkali content, silica modulus, and foam content) had a significant influence on the response variables, which presented the following variations: compressive strength of 0.36 to 3.23 MPa; thermal conductivity from 0.22 to 0.42 W/(m.K); saturated bulk density from 1176 to 1364 kg/m 3 ; dry bulk density of 619 to 864 kg/m 3 ; air void from 46.4% to 62.5%; and water absorption from 55.7% to 95.4%. It was also concluded that the precursor type was the factor that had the most influence on the properties of foamed geopolymers, with MPG calcined for 4 h being the best, as greater compressive strength and low thermal conductivity were obtained.

Foamed geopolymers: a review of recent studies

“…[30], [31] Syntactic foams The data gathered in Table 1 not only provides information on the method used for the production of foamed geopolymers but demonstrates and at the same time confirms that still the most popular raw materials that are used as an aluminosilicate source are fly ash, ground granulated blast slag and metakaolin, but sodium hydroxide together with sodium silicate as an alkaline activator. At the same time, the most commonly used the foaming agent is hydrogen peroxide, aluminium powder and different surfactants, which is consistent with the information given in scientific publications about the most popular raw materials [36].…”

Mechanical and Thermal Properties of Geopolymer Foams (GFs) Doped with By-Products of the Secondary Aluminum Industry

“…For this purpose, metakaolin (MK), (Al 2 O 3 40.1 wt.%; SiO 2 : 54.1 wt.%) have been used during the alkaline activation process as precursor materials, using a potassium hydroxide aqueous solution (A) (pH 11) [53,54]. In addition, chopped carbon fibers, which show evidence to increase the mechanical properties of the materials [55], are employed in the REF-2 geopolymer and in the geopolymer foams where aluminum waste materials represent additives for foaming.…”

Influência da quantidade de água na formação de eflorescência em geopolímeros a base de metacaulim

“…O ensaio de DRX foi realizado com um difratômetro (X'pert PRO Multifuncional, PanAlytical) usando radiação CuKα (λ = 1,5418 Å) a 40 kV e 30 mA e irradiações variando de 0 a 90° (2θ), com intervalo de 0,05° para cada 1 s. Na Figura 3 pode ser visualizado o difratograma de raios-X para o metacaulim HP Ultra. ), a qual é benéfica para as reações de geopolimerização, pois aumenta a resistência mecânica da matriz geopolimérica [26,27]. Segundo LONGHI [28], quanto maior for o amorfismo do metacaulim, maior a reatividade, isto é, a maior quantidade de sílica ativa é formada para dissolver em um meio alcalino [29].…”

“…O surgimento de picos entre 600 e 800 cm -1 indica a dissolução de espécies para a formação dos laços próprios da estrutura do geopolímero. Os resultados obtidos estão de acordo com a literatura [27,34,35].…”

“…Os baixos valores de resistência à compressão encontrados podem ser explicados pela reatividade do precursor, isto é, o metacaulim utilizado apresenta baixo amorfismo (73,18%) que implica em menor partículas amorfas utilizadas na geopolimerização. A elevada cristalinidade do metacaulim deve-se possivelmente pela falta de temperatura e/ou tempo de sinterização do caulim [27,40].…”