Research On Hydration Characteristics And Application Of Corundum Dust In Cement-based Materials

Corundum dust is the dust collected by high temperature bag filter in corundum smelting process.The annual production of brown corundum in China is about 3 million tons,and about 210000 tons of corundum smelting dust are produced.At present,the utilization of corundum dust is very little,most of them are only landfilling or hoarding,and the utilization rate is low.Aiming at how to use corundum dust in cement-based composites,the phase composition and characteristics of corundum dust were analyzed by various advanced analysis methods;Then,based on the composition of corundum dust and the excitation mechanism of mineral admixtures,the excitation technology of corundum dust and its reaction characteristics in cement paste are explored;Finally,combined with the characteristics of corundum dust and fly ash,the utilization of corundum dust in cement-based composites was explored by compounding corundum dust-fly ash-cement.The original corundum dust is an alkaline and porous material.The pore size measured by bet is mainly larger than 50nm,the specific surface area is about 6 times of that of P·Ⅱ52.5 cement,and the total pore volume is about 4 times of that of cement.The results show that the original dust has potential activity,and its main components are amorphous spherical glass phase composed of Si,Al,K and O elements,crystalline phase K₂SO₄,crystalline phase Al₂O₃,and a small amount of carbon black particles and carbonate.Most of the potassium salt in the dust can be removed by washing with water after pickling.The corundum dust is not hydrated by itself,and it has high activity after being excited by Ca（OH）₂.After being excited by 10%Ca（OH）₂ and long-term steam curing at 80℃for 7d,the reaction of amorphous glass phase alumina in corundum dust was promoted,and ettringite was found.The hydration process of corundum dust within 72hours is higher than that of grade I fly ash,but lower than that of grade S95 slag powder.When the corundum dust is mixed into cement as admixtures,the conclusions of using hydration heat and resistivity to study the hydration process are basically the same.It was found that corundum dust could promote the early hydration of cement.With the increase of the content of corundum dust from 5%to 50%,the hydration heat of the composite cementitious material system increases gradually before 4 hours of hydration,and the hydration heat of 72 hours first increases and then decreases;Macroscopically,the retarding and compressive strength of the cementitious system will decrease significantly.The setting time will appear inflection point when the dosage is 30%,and the 7d strength will drop to the lowest point when the dosage is 20%.Compared with the fly ash and cement composite cementitious system with the same amount of cement,the hydration process of the corundum dust,fly ash and cement composite cementitious system with 5%corundum dust is slowed down in the early stage（15～20h）,but the hydration exothermic rate of the system is higher than that of the binary system,and the total heat release is higher than that of the binary system after 36～48h,the compressive and flexural strength of the ternary system at 3d,7d and28d increased in varying degrees,and the corundum dust can stimulate the activity of fly ash to a certain extent,while the drying shrinkage of the ternary composite system is reduced at different ages.