Key Technology And Application Of Artificial Aggregates Prepared From Industrial Titanium Gypsum

As an industrial by-product of titanium dioxide production by sulfuric acid method,titanium gypsum is similar to natural gypsum,and its main component is Ca SO₄·2H₂O.Although it has been applied in cement-based cementitious materials and soil conditioners,due to its high viscosity,low hydration activity,high impurity content and other factors,the degree of resource utilization is limited.Therefore,the disposal of titanium gypsum is still based on simple stacking,occupying a large amount of land resources,and enterprises are also facing huge environmental protection pressure.In order to improve the degree of resource utilization of titanium gypsum,this study used industrial solid waste titanium gypsum as the main raw material,and mixed with a small amount of solid waste admixture,cement,chemical admixture and other mixed to prepare artificial unburned aggregate.The performance test was carried out according to GB/T 17431.2,and the optimal mix ratio of artificial aggregate was obtained by in-depth analysis based on XRD,SEM and other characterization techniques.The prepared artificial aggregate was used to replace natural gravel aggregate with different substitution rates to apply to unburned bricks.The compressive strength,water absorption and pore structure of non-fired brick specimens were tested,and the microscopic morphology of the interface was analyzed by SEM.And 15dry-wet cycle tests were carried out on the non-fired brick specimens to investigate their applicability.The specific research conclusions are as follows.（1）The average particle shape coefficient of the prepared artificial aggregate is 1.0～1.2,and the bulk density is 700～800 kg/m³.According to the specification requirements,it belongs to 800 grade aggregate.（2）Through macro and micro test methods,the cylinder compressive strength of artificial aggregate,the cost of raw materials and the utilization rate of industrial titanium gypsum are taken as control indexes,and the comprehensive evaluation is carried out based on the improved MULTIMOORA method.The optimal basic ratio of artificial aggregate is titanium gypsum:cement:silica fume=70%:20%:10%.On this basis,the enhancement effect of activator on its performance was explored,and the cylinder compressive strength,water absorption and microscopic phase under different activator conditions were tested.It was found that when Na OH:Ca O=1:1 composite was used as activator and the dosage was3%,the comprehensive performance of titanium gypsum artificial aggregate was the best.At this time,the compressive strength of the artificial aggregate cylinder is 12.15 MPa,which has reached the 800-level high-strength aggregate standard（≥6 MPa）,and the internal structure is relatively dense,which meets the requirements of the standard artificial aggregate.（3）The non-fired bricks were prepared by replacing natural gravel aggregate with titanium gypsum artificial aggregate.With the increase of the replacement rate of artificial aggregate,the compressive strength of 7d and 28d ages decreased step by step.When the artificial aggregate completely replaces the gravel aggregate,the 28d non-fired brick specimen has the largest water absorption rate of 10.18%and the strength of 31.40 MPa,which meets the strength grade of’concrete solid brick’GB/T 21144-2007 MU30.The dry-wet cycle test found that the compressive strength loss rate of the specimen increased with the increase of the artificial aggregate replacement rate.When the replacement rate exceeded 50%,the compressive strength loss rate of the specimen exceeded 20%,but there was no slag drop in its appearance.The mass loss rate of the specimens was less than 5%.The porosity of the specimen increases as a whole;among them,the average strength of the K100group with the largest strength loss rate is 27.2 MPa.It is considered that the use of titanium gypsum artificial aggregate to completely replace natural gravel to prepare non-fired bricks has a good application effect.（4）The economic benefit analysis of titanium gypsum artificial aggregate and non-fired brick shows that the actual cost of artificial aggregate is about 329 yuan/ton.Compared with natural gravel aggregate,the cost is higher,but the environmental harm caused by the accumulation of titanium gypsum is reduced.The cost of the prepared non-fired brick is about0.8-0.85 yuan/block,which is greatly reduced compared with the price of 2.0-4.0 yuan/block concrete solid brick.From the perspective of carbon emission benefits,the production of 1 ton of titanium gypsum artificial aggregate CO₂ emissions of about 178.24 kg,the preparation of non-fired brick carbon emissions of 14.14 kg/m³MPa,reducing about 100,000 tons of CO₂emissions.