Self-compacting geopolymer concretes: Effects of addition of aluminosilicate-rich fines

The presence of alunimosilicate based fine aggregates (2.5 to 7.5 wt%) effectively acted to densify the microstructure of the interfacial zone with a reduction of pore threshold and mean pore size jointly with change on the fracture mode of the Self-Compacting (SC) geopolymer concretes. From the results, pumice and recycled glass with amorphous structure improved the bi-axial four-point flexural strength from 5 to 8 MPa while semi-crystalline feldspar sludge (nepheline syenite) reached 11 MPa. The formation of additional geopolymer gels were responsible for the strengthening mechanism. The specimens with amorphous fines showed the tendency to delay the desorption in the laboratory conditions indicating the need for a very long curing time for the final consolidation. The semi-crystalline fines -nepheline syenite- appeared appropriate for the design of self-compacting geopolymer concretes due to their bulk composition, capacity to enhance densification and strength with low deformation rate, in a short range of curing together with a high rate of desorption, all important parameters for the prediction of the durability of concretes.