| Titanium gypsum is an industrial by-product in the process of producing titanium dioxide by the sulfuric acid method.For every ton of titanium dioxide produced,4 tons of solid waste of titanium gypsum can be produced.In 2017,the national titanium dioxide enterprises discharged 22 Mt of titanium gypsum,and the accumulated stock It has exceeded 130 Mt.The comprehensive utilization rate is only 10%,and most of them cannot be used and are piled up or buried,which not only occupies land resources,but also pollutes the surrounding environment.In this study,uncalcined titanium gypsum was used as the main raw material,and a cementitious material was prepared by adding 42.5 ordinary Portland cement,mineral powder,sulfoaluminate clinker,and fly ash,and explored its basic mechanics and most The excellent water-binder ratio,curing method,and grinding fineness affect its performance,and the mechanism of its hydration process is explained through hydration heat test and microscopic test.In addition,certain researches have been made on its durability,such Volume stability,carbonization resistance and sulfate corrosion resistance,etc.Finally,in actual production,the cementitious material is used to replace 42.5 ordinary Portland cement to prepare autoclaved aerated concrete blocks,reaching A3.5B06 qualified product level According to the calculation,it is estimated that it can bring significant economic benefits to the factory.The main conclusions are as follows:(1)In this cementitious material system,its compressive strength increases due to the increase in cement content,and the increase in gypsum content decreases,and the strength of the alkali activator is reduced.The optimal ratio of this material is "Cement 10 %,30% of mineral powder,5% of sulp Hoaluminate clinker,20% of fly ash,35% of titanium gypsum",the 28 d compressive strength of this ratio reaches34.1MPa(2)The optimal water-binder ratio of the titanium gypsum-based composite cementitious material is 0.5.The strength of the standard cured test block is 36.7%lower than that of the sealed cured test block.The curing system is changed.After the test block is formed,it is sealed and cured to 3d and 7d,and then subjected to standard curing to 28 d.The compressive strength is compared with the standard curing condition The time has increased by 17.1% and 29.2% respectively.As the specific surface area of sulp Hoaluminate clinker increases,the standard thick water consumption of titanium gypsum-based composite cementing materials increases,the initial and final setting time is shorter,and the compressive and flexural strength increases.The cementitious material has two hydration heat exothermic peaks with different heights.The first peak is higher and appears at about 2 hours,which is lower than the 42.5 Portland cement exothermic peak,and the exothermic peak appears earlier.(3)The larger the proportion of mineral admixtures of the titanium gypsum-based composite cementitious material,the smaller the volume expansion,the longer the expansion time,and the later volume expansion rate will have a greater development,and the cementitious material will have a volume before 14 days of curing.It swells rapidly and stabilizes after 14 days of curing.The anti-carbonization performance of this cementitious material is worse than that of 42.5 ordinary Portland cement.After 28 days of carbonization,its compressive strength has dropped by43.7% compared to before.The larger the proportion of mineral admixtures,the smaller the amount of titanium gypsum,and the carbonization strength.The larger the value,the smaller the carbonization depth.The cementitious material is more resistant to sulfate erosion than cement.After curing for 28 days in Na2SO4 solution,the compressive strength of mortar test block is slightly higher than curing in water,while42.5 ordinary Portland cement is cured in Na2SO4 solution for 28 days.The strength is reduced by 15.1% compared to the strength of curing in water.(4)Titanium gypsum-based composite cementitious material can replace 42.5ordinary Portland cement to prepare autoclaved aerated concrete,and its molded blocks can meet the requirements of A3.5B06 qualified product level. |
