Properties of an aged geopolymer synthesized from calcined ore-dressing tailing of bauxite and slag

The strength evolution of a geopolymer synthesized from calcined ore-dressing tailing of bauxite and slag and cured at ambient temperature for 6 years was investigated. Changes in products and microstructure were studied as well. The results indicated that the strength steadily increased from 50.0 MPa at 28 days to 75.0 MPa at 6 years. The hardened samples became more compact with advancing age due to progressive geopolymerization to form the coexisted C-A-S-H and N-A-S-H gels, which explains the lower porosity of the aged geopolymer. An X-ray amorphous phase corresponding to geopolymerization gel was detected in both the early-age and long-term geopolymers, but calcite and natron were present in the aged specimens, indicating that carbonation occurred and the studied geopolymer is vulnerable to carbonation in an atmospheric environment. Despite carbonation, the high stability of the N-A-S-H gels in this relatively low-calcium system and the compact matrix combined to increase the strength.