Effect of tricalcium aluminate and nano silica on performance of hemihydrate gypsum

In this article, tricalcium aluminate (C3A) was utilized as addition agent for hemihydrate gypsum (HHG) to improve the performance of gypsum pastes, and on that basis, the optimal dosage group of C3A was selected for further study on the composite effect with nano-silica (NS). HHG plasters with 0–5% content of C3A and besides combining 3% C3A with 0.5% NS were made. The macroscopic properties were discussed by testing the compressive strength, setting time, consistency and softening coefficient. The hydration products were described by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and solid state nuclear magnetic resonance (NMR). The microstructure was presented by performing scanning electron microscopy (SEM). Hydration heat evolution process was studied by hydration heat analysis. The results showed that under the effect of C3A, HHG could achieve instant diagenesis, thereby realizing instant solidification, and its compressive strength and water resistance could also be improved to a certain extent; on the basis of C3A, the addition of NS could further optimize these properties. These conclusions were expected to provide reference for promoting the basic performance of HHG.