| Sulfoaluminate cement is a energy-saving eco-cement.To achieve scientific,rational and safe use of sulfoaluminate cement based materials,and consequently bring economic and ecological benefits.By means of modern testing methods,the mechanical properties,micro-structures and mechanism of hydration reaction process of limestone-SAC cement gelation system and recycled powder is systematic studied.The study results can provide the theoretical and experimental basis for the performance optimization of materials and the preparation of SAC cement based repair materials.Experimental studies show that:In SAC clinker-gypsum system,gypsum can reduce the setting time of SAC cement and increase the hourly strength of SAC cement.The addtion of gypsum not only significantly influences the formation of hydration products,but also affects the type of hydration products.Different thermal curing system and gypsum content will seriously affect the thermal stability of SAC based materials.In SAC cement early hydration,increasing the amount of gypsum can promote the strength of SAC cement based materials under the 60℃condition.While more than 90℃,it may occur significant delayed ettringite formation（DEF）damage.After 7d ages of SAC cement,increasing the amount of gypsum can promote the growth of the strength of the SAC cement based materials under 60℃and 90℃heat curing conditions.While under120℃heat curing conditions,SAC cement based materials will occur serious DEF damage,and when the amount of gypsum is too high,it will be disrupted in a short period of time.The application of XRD and SEM microscopic test found that AFt is transformed to AFm in SAC cement based materials under 90℃.The phenomenon will cause obvious DEF damage with high amount of gypsum.Limestone powder possesses high hydration activity.It improves properties of the later strength,reduces early heat release and the amount of heat,stabilizing ettringite to reduce volume expansion than quartz powder blended in SAC cement based materials.And hydration degree of limestone powder is low in early hydration,it possesses high hydration activity hydration at the later stage.C4A3 s can produce hemicarbonate to enhance performance of SAC cement based materials with limestone powder.Limestone powder is more beneficial to the thermal stability of SAC cement based materials in different heat curing system.The interfacial transition zone of the loose structure also exists in the SAC cement based materials,and the enrichment of Al（OH）3 gel and AFt crystal is also observed in the interface.a large number of fine acicular ettringite crystals is gathered in sandstone surface,and the limestone is closely combined with the slurry,and no obvious coarse crystal is enriched with its surface.There are apparent hydrate distribution differences between different lithology of aggregate and the bulk cement pastes.Ca,S,Al and other elements in the interface transition zone appeared a certain degree of aggregation.There is obvious phenomenon about the enrichment of Si element and the descent of the content of S element in the interface of limestone aggregate.With the increase of heat treatment temperature,the fluidity and strength of SAC cement mortar mixed with recycled powder are increased at first and then decreased.When the recycled powder with heat treatment of 600℃,the fluidity and strength properties of SAC cement mortar is optimized.With the increase of the content of the recycled powder,the fluidity of SAC cement mortar decreases gradually.Incorporation with certain amount of recycled powder can increase in SAC cement mortar later strength.Recycled powder（600℃）blended in SAC cement will significantly reduce exothermic rate and total quantum of heat in 1-4h hydration.And it can reduce the total heat released of SAC cement.Recycled powder has effect on the variety and amount of the hydration products in SAC cement.Its high activity of CaCO3 can have the early reaction with SAC cement to produce hemicarbonate.Under different heat curing system,the thermal stability of the SAC cement based materials is not obviously affected by the regeneration powder.SAC cement exhibit to be selective on the addtions.the effect of tlithium carbonate which promotes coagulation and 3h strength is better.Boric acid has a significant influence on the coagulation time and early strength of SAC cement.The effect of sodium citrate on the retarding effect of SAC cement is limited,and the 3h strength of SAC cement is not obviously decreased.Types of early strength agent and coagulant will not change hydration products of the SAC cement.By using orthogonal experiment,SAC cement based quick repairing materials is prepared.The performance of its 3h compressive strength can reach 40MPa.And through the mechanism of limestone sand,regeneration powder to optimize the preparation of repair materials,The performance of its 3h compressive strength can reach 45MPa. |
