Mechanical properties of Halloysites-based and Halloysites-modified slag/fly ash-based geopolymers

Halloysite is an affordable natural mineral clay with a nanotubular structure and surface reactivity, giving it strong industrialization potential. This study investigated how the calcination temperature (0 degrees C-850 degrees C) affected the properties of halloysite and geopolymers derived from calcined halloysite, then as a modified material, the performances of a slag/fly-ash geopolymer with halloysite calcined at different temperatures were compared. Finally, the effects of halloysite curing temperature (20 degrees C-80 degrees C) and mass content (0.25%-1.5 %) on the mechanical properties and microstructure of the slag/fly-ash geopolymer were studied. The results show that the calcination temperature of 750 degrees C was optimal for stimulating the halloysite's activity, leading to the highest compressive strength of 42.7 MPa of the halloysite-based geopolymer. Uncalcined halloysite was the most suitable reinforcement for slag/fly-ash geopolymer because it retains relatively intact tubular structure, and its chemical bonding at the interface with geopolymers ensured good reinforcing properties. The bridging effect derived from tubular structure of halloysite led to a more noticeable enhancement of flexural strength. To prevent agglomeration from too much tubular halloysite, 1.0 % content was found to be optimal. The compressive and flexural strengths reached 62.5 MPa and 3.83 MPa, respectively, which were 9.84 % and 35.8 % higher than that without halloysite. Furthermore, with increasing curing temperature, the strength of the halloysite-modified geopolymer reached its peak at 60 degrees C. For 1.0 % halloysite modified geopolymer, the compressive strength was 87.0 MPa and the flexural strength was 4.56 MPa, respectively, which were 39.2 % and 19.1 % higher than that at the curing temperature of 20 degrees C.