STUDY OF EARLY HYDRATION OF CEMENT PASTES CONTAINING ALTERNATIVE CALCIUM SULFATE BEARING MATERIALS

The majority of cement plants mainly uses natural gypsum (CaSO₄·2H₂O) to regulate cement setting. The partial or total replacement of gypsum by materials, which contain calcium sulfate, has been instigated either by the increasing availability of low-cost by-products containing calcium sulfate or by the possibility that quarries would mine rock that is a mixture of gypsum and anhydrite. This paper is part of an extent research program aiming to investigate alternative calcium sulfate bearing materials, such as anhydrite and FGD gypsum. These materials have been examined in order to study the influence of their addition in cement physicomechanical properties (compressive strength, setting time). Hydration of cement pastes containing these CSBM was interrupted at specific time intervals within 5 min to 12 hours, and cement-setting reactions were characterized with the use of DTA, isothermal calorimetry and ESEM. In the same time SO₃²⁻, Ca²⁺ and pH of the pore solution were also evaluated. It is concluded that, compared with natural gypsum, FGD gypsum prolongs the dormant period of hydration, while anhydrite accelerates it. Moreover, at a specific hydration time, cements with FGD gypsum seem to form more ettringite than natural gypsum and anhydrite does.

• INTRODUCTION

• EXPERIMENTAL

• RESULTS AND DISCUSSION

• CONCLUSIONS

• ACKNOWLEDGEMENT

• REFERENCES