Cementitious materials of pozzolanic type prepared from red mud and fly ash with gypsum and portlandite as activators

Cementitious materials of pozzolanic type prepared from red mud and fly ash with gypsum and portlandite as activators

Creators Ikida Ko

Bauxite from Australia contains boehmite which remains intact in the red mud after extraction of alumina. Therefore, this kind of red mud can be used as cementitious mateirals without clinkering process. Gypsum and/or portlandite were added to the red mud as activators. Two series of mixtures were prepared to produce ettringite and/or C_4AH_<13>. These cementitious mixtures called the red mud mixes are hydraulic themselves. Howevr, they are no use as cementitious materials due to the unstable hydration strength. To improve this defect fly ash was introduced to the red mud mixes together with 7 percent extra addition of portlandite to the fly ash. Thus, cementitious materials of pozzolanic type with moderately high strength have been obtained by water curing, resulting compressive strength up to 9.7, 16.4 and 20.1 MPa at 7, 28 and 91-day ages, respectively. Depressions of strength encountered in some specimens especially in air curing have been improved by blending fly ash and more activators. The depressions are closely related to the disintegrations of ettringite, C_4AH_<13> and/or C_4AHCH_<12>.

[ISSN]0386-3433

[NCID]AA0086073X