Study On The Composition And Properties Of Titanium-gypsum Based Matrix Composite Cementitious Materials

Titanium-gypsum is used in the process of sulfuric acid production of titanium dioxide,adding limestone（or calcium carbide slag）to neutralize a large number of acidic wastewater and derived industrial by-products.The main chemical composition of Titanium-gypsum and natural gypsum is the same as that of Ca SO₄·2H₂O.However,due to the low grade,high viscosity and high impurity content of Titanium-gypsum,the development of its resource utilization is restricted.The simple stacking and disposal of Titanium-gypsum not only occupies land resources,but also brings huge environmental pressure to enterprises.In view of the difficulties in the current utilization of Titanium-gypsum,this topic carries out the preparation of new cementitious materials by taking Titanium-gypsum as the main raw material and adding an appropriate amount of mineral admixtures and chemical admixtures.The main research contents and achievements are as follows:1.Characterization of basic properties of Titanium-gypsumThe basic properties of Titanium-gypsum were characterized by X-ray fluorescence spectrometer,laser particle size analyzer and X-ray powder diffractometer.The results show that the main phase composition of Titanium-gypsum is Ca SO₄·2H₂O and a small amount of Ca CO3.The grain morphology is mainly rhomboid lamellar,rod columnar and detrital.The main chemical components are SO₃and Ca O;The water content was 16.8%,the p H value was 5.74,the density was 2.31g/cm³,the specific surface area was 1.01m²·g^-1,the median particle size was 17.016μm.2.Study on the composition and properties of Titanium-gypsum slag based cementitious materialsResearch on the composition and properties of"Titanium-gypsum+Slag"and"Titanium-gypsum+Slag+Cement"two and ternary cementitious materials,the main contents include:（1）The effects of different W_（TG）/W_（S）and different cement content on the slurry properties and hardening properties of the system were studied with unaltered Titanium-gypsum as the object.The effects of different water-reducing agents and activators on slurry properties and hardening properties of ternary cementitious materials were studied.The results show that in binary cementitious material system,the compressive strength of the system is the highest when W_（TG）/W_（S）=5:5.In the ternary cementitious material system,when W_（TG）/W_（S）=5:5,the compressive strength of the system with 5%cement is the highest.When the content of polycarboxylic acid water reducer is 0.2%,the matching with the system is better,and the effect of"water reduction enhancement"is better.The effect of salt activator on improving the compressive strength of the system is better than that of alkaline activator,and the addition of 1.0%activator S is the most significant for improving the compressive strength of the system.（2）The effects of different roasting systems,retarders and activators on the slurry properties and hardening properties of ternary cementitious materials were studied with the calcine Titanium-gypsum as the object.The results showed that the compressive strength of the system at different ages was taken as the index to judge the merits of the system of Titanium-gypsum frying.When the Titanium-gypsum was calcine at 180℃for 2h and aged for 7d,the compressive strength of the system was the highest.In order to improve the performance of slurry,it is necessary to add retarder.When the system is mixed with 0.3%tartaric acid,the working performance of the slurry and the compressive strength of the hardened body are the best.The effect of salt activator on improving the compressive strength of the system is better than that of alkaline activator,and the addition of 1.0%activator K is the most significant for improving the compressive strength.Taking the compressive strength of Titanium-gypsum-slag-cement ternary cementitious material as the index to judge the performance of undisturbed Titanium-gypsum and calcine Titanium-gypsum,it can be known that the activity of Titanium-gypsum can be greatly improved by frying.3.Study on the composition and properties of Titanium-gypsum-fly ash based cementitious materialsThe research on the composition and properties of"Titanium-gypsum+Fly Ash"and"Titanium-gypsum+Fly Ash+Cement"binary and ternary cementitious materials system is carried out.The main contents include:（1）The effects of different W_（TG）/W_（F）and different cement content on the slurry properties and hardening properties of the system were studied with unmodified Titanium-gypsum as the object.The effects of different activators on slurry properties and hardening properties of ternary cementified materials were studied.The results show that the test blocks under different W_（TG）/W_（F）conditions almost have no strength in binary cementified material system.In the ternary cementified material system,the compressive strength of the same W_（TG）/W_（F）system shows a trend of increasing with the increase of cement content.For the system with a mixture ratio of W_（TG）:W_（F）:W_（C）=37.5:37.5:25 and a mixture ratio of W_（TG）:W_（F）:W_（C）=60:15:25,the activator C with 1.0%and the activator K with1.5%were the most significant to improve the compressive strength of the system.（2）The effects of different activators on the slurry properties and hardening properties of ternary cementitious material system were studied with the calcine Titanium-gypsum as the object.The results show that for the system with the mixture ratio of W_（TG）:W_（F）:W_（C）=37.5:37.5:25 and the mixture ratio of W_（TG）:W_（F）:W_（C）=60:15:25,the activator S and activator C with the content and type of 0.5%and 1.0%respectively have the most significant effect on improving the compressive strength of the system.Taking the compressive strength of Titanium-gypsum-fly ash-cement ternary cementitious material as the index to judge the performance of unmodified Titanium-gypsum and calcine Titanium-gypsum,it can be known that the activity of Titanium-gypsum can be greatly improved by frying.4.Hydration characteristics and mechanism analysis of Titanium-gypsum composite cementitious materialsBy means of isothermal calorimeter,XRD and SEM,the early hydration characteristics,hydration products and internal microstructure of Titanium-gypsum matrix composite cementitious materials were analyzed and studied.The results show that:（1）With the addition of slag,cement and activator,the induction period of the system is shortened,and the time required to reach the second exothermic peak is advanced,indicating that the hydration reaction rate is accelerated.（2）With the addition of cement and activator,the induction period of the system is shortened and the time required to reach the second exothermic peak is advanced,indicating that the hydration reaction rate is accelerated.According to XRD and SEM analysis,the main hydration products of Titanium-gypsum matrix composite cementitious materials are AFt crystal and C-S-H gels,which are interlinked with unhydrated cementitious material particles to form a relatively compact structure,which makes Titanium-gypsum matrix composite cementitious materials have a high compressive strength.