Suitability of a high-calcium slag for alkali activation, and strength and microstructure of the resultant materials.
Citation:
O. Alelweet, S. Pavia, Suitability of a high-calcium slag for alkali activation, and strength and microstructure of the resultant materials., 1st International Conference on Environmental Science & Green Energy, Clichy, Paris, October 24-26, 2022, G Edwards, 2022Download Item:
OA SP Green E conference Paris.pdf (PDF) 1.461Mb
Abstract:
We study the feasibility of producing building materials by activating an Irish slag with
alkali-metal activators. The slag is highly amorphous and basic (CaO+ MgO/SiO2=1.56), with
CaO/SiO2=1.41 and Al2O3/SiO2=0.34 which evidence high reactivity and potential for alkali activation-AA-. Its chemical composition complies with standard requirements for slags in concretes/mortars/grouts. Devitrification, supported by calorimetry, evidenced that the slag consists of a melilitegehlenite isomorphous solution which denotes high reactivity. The slag was activated with NaOH
and Na2SiO3, both combined and separately, to produce mortars. The mortars achieved reasonable
setting times and workability, and strenght significantly increased between 28 and 270 days. Crack
ing by drying shrinkage, a challenge in AA materials, is hindered by the slag’s high calcium. The
Na2SiO3 + NaOH slag mortars gained the greatest compressive and flexural strengths. Rising the
curing temperature to 60°C, enhanced their strength and microstructure (mainly up to 28 days), and
develops hydrogarnet–gehlenite hydrate cements that may be responsible for the high 270-day
strength (96MPa). Generally, curing at 60°C enhances early strength (3-7 day) but the increase
between 28 and 270 days is not significant, with sometimes lower values than ambient-cured
material (Na2SiO3-activator). An excessive %Na2O by mass of slag is blamed for the low strength
generated by the Na2SiO3 activator (the slag’s high reactivity requires lower %Na2O). The NaOH-activated slags tend to perform best when ambient-cured. An undue high molarity of the NaOH
solution has generated an excessive alkalinity for the highly reactive slag, lowering the strength of
the NaOH-activated slag mortars. The results indicate that the best activator is a combination of
Na2SiO3 and a low molarity (<6M)NaOH.
Author's Homepage:
http://people.tcd.ie/pavias
Author: Pavia, Sara
Other Titles:
1st International Conference on Environmental Science & Green EnergyType of material:
Conference PaperAvailability:
Full text availableLicences: