Hydration And Properties Of Sulfoaluminate Cement Under Minus Temperature

Infrastrucure construction at low temperature or minus temperature in winter is the ordinary process to control construction period.At present,the low-temperature construction in winter can be realized by means of the measures such as warming aggregate in preheating shed,mixing with warm water,increasing the strength with early strength accelerator,insulating slurry during transportation,pouring in warm shedand heating during curing.These methods are cumbersome and require highquality site requirements,which may cause accidents due to inadequate thermal insulation.Accordingly,it is important to develop new cement-based materials that do not need heating and have rapid strength development under minus temperature for winter construction,especially minus temperature construction.In this paper,rapid-hardening calcium sulphoaluminate cement clinker and anhydrite are used to prepare special calcium sulphoaluminate cement.Anhydrous calcium chloride is used to prepare the low freezing point solution.Retarders such as borax and early strength agents such as lithium carbonate are used to adjust workability and strength The effect of minus temperature on the hydration process and microstructure of calcium sulphoaluminate cement was studied,using X-ray diffraction(XRD),scanning electron microscopy(SEM),infrared spectroscopy(IR)and the measurement method of temperature change during hydration.(1)Calcium sulphoaluminate cement can be quickly set and hardened by mixing with calcium chloride solution with a mass fraction of 12.28% and a freezing point of-14 ? at-10 °C.It needs to require retarders because the setting time is too short.Calcium sulphoaluminate cement can be normally set and hardened by mixing with calcium chloride solution with a mass fraction of 18.03% and a freezing point of-23 ? at-20 °C.However,it needs to require early strength agents because the strength is too low.(2)The results showed that the initial and final setting time of pastes respectively prolonged to 25 min and 28 min with 0.6% borax at-10 ?.The 3-day and 28-day strength increased to 38.8 MPa and 51.9 MPa,respectively.The setting time of pastes with sodium gluconate or L(+)-tartaric acid did not extremely change,but the strength of these samples sharply decreased.The retarders reduced the hydration exotherm and affected the formation of ettringite.Borax reduced the volume of ettringite at early ages,while sodium gluconate and L(+)-tartaric acid changed the morphology of ettringite.0.6% borax reduced the production of ettringite in 1 day by 45.9%.The short–column ettringite in samples with sodium gluconate and the needle-like ettringite in samples with L(+)-tartaric acid were detected.(3)The results showed that the initial and final setting time of pastes respectively shortened to 15 min and 33 min with 0.6% lithium carbonate at-20 ?.The 3-day and 28-day strength increased to 9.7 MPa and 38.0 MPa,respectively.Although aluminum sulfate significantly shortened the setting time,it was extremely harmful to strength development.Lithium carbonate and aluminum sulfate both changed the early hydration exotherm,but t had no obvious effect on the morphology of ettringite.(4)According to the formulation of the cementitious material,the concrete was prepared in the winter outdoor environment(mixing and pouring temperature is-9 ?,temperature range between day and night is-9 ??1 ?).The curing method of covering with the wetted material was adopted.The result showed that the grade of strength was high up to C50.