Use of metakaolin with a low surface area and rich in quartz and iron as a precursor in the production of structural alkali-activated concrete

• Published in: Construction & building materials Vol. 430; p. 136418
• Main Authors: Silva Neto, J.A., Marçal, N.A., Nóbrega, A.F., Nóbrega, A.C.V., Souza, J.J.N., Malheiro, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 07.06.2024
• Subjects: Alkali-activated concrete. Metakaolin. Low reactivity. Quartz. Iron; Alkali-activated concrete. Metakaolin. Low reactivity. Quartz. Iron
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2024.136418

Pumpable and machineable alkali-activated structural concretes are made using low-reactivity metakaolin with high quartz and iron contents. The effects and interaction of alkaline concentration (NaOH - 8, 10, 12, 14, and 16 M) and ratio of alkaline reagents (Na2SiO3/NaOH - 1.0, 1.5, 2.0, 2.5, and 3.0) on their properties were accessed using 2k complete factorial design. Higher concentrations of alkaline solutions resulted in faster hardening, decreased material deformation, and increased mechanical strength, with higher elastic modulus, lower damping, lower water absorption, and porosity. With time, the elastic modulus increased, and the dynamic damping decreased, suggesting the homogeneous formation of alkaline-activated products, confirming the proper configuration of the hardening process. The factorial design allowed for determining the ideal dosage for producing the material, indicating that the alkaline concentration (NaOH) should be 10 M and the Na2SiO3/NaOH ratio should be 2.5. They analyzed the possible combinations that allowed obtaining a material with adequate characteristics for the structural application. •Obtaining alkali-activated structural concretes with low surface area metakaolin, rich in quartz and iron.•The microstructural analysis showed an ideal alkaline concentration to guarantee the complete dissolution of the aluminosilicates.•The optimized dosage indicated an alkaline concentration (NaOH) of 10 M and a Na2SiO3/NaOH ratio 2.5.