Effects of ettringite seed on the hydration and properties of supersulphated phosphogypsum-slag cement

Supersulphated phosphogypsum-slag cement (SPPSC), which consist of more than 95% industrial wastes, is regarded as a newly low-carbon emission and green cementitious material. However, extremely slow early strength development of SPPSC restricts its application in practical engineering. In this work, the methods of separation of the nucleation and aging steps were adopted to synthesis ettringite (AFt) seed, and it was used to improve the early hydration progress and properties of SPPSC by acting as nucleation seed. The setting time, compressive strength, autogenous shrinkage and early-age hydration process were tested; behind mechanism was systematically investigated. In addition, anti-carbonization property was also evaluated. These results displayed that the compressive strength enhanced by 25.17 times at 3 days when added 7%AFt; the late compressive strength increased by 152% and 88% compared to benchmark, respectively. The main reasons were that AFt seed speeded up the whole hydration progress via acting as the nucleation seed to promote the formation of ettringite phase in the pore gaps space among the particles rather than on the surface of slag, which could contribute to the further dissolution of slag and result in the production of C-(A)-S-H gel. Furthermore, it shortened the setting time and autogenous shrinkage, refined pore structure and promoted the anti-carbonization property. These results provided the reference for improving the basic performance of SPPSC system.