Preparation And Hydration Properties Of Belite Sulfoaluminate Cement With Solid Waste

According to statistics,China’s cement output was 2.34×109 tons in 2019,accounting for about 57%of the world’s output.Cement manufacturing is a high consumption and high pollution industry.Mass production of cement causes a lot of natural resource consumption and environmental pollution.At the same time,due to insufficient utilization methods and utilization rates,the stockpiles of coal gangue and carbide slag are increasing year by year,causing serious pollution to the natural environment.If a green cementitious material that can replace ordinary Portland cement can be prepared with coal gangue and carbide slag as the base material,it will greatly improve the utilization rate of calcium carbide slag and coal gangue,and can also reduce the cement industry’s impact on natural resources consumption and environmental pollution.Therefore,this paper studies the feasibility of preparing solid waste-based Belite sulfoaluminate cement with coal gangue and calcium carbide slag as the base material and using a small amount of steel slag,dihydrate gypsum and calcium carbonate in synergy.The main research contents and conclusions are as follows:（1）The calcination system of solid waste-based Belite-sulfoaluminate cement was preliminarily determined by XRD,scanning electron microscope and free calcium oxide determination.The mineral composition analysis of the cement clinker prepared under the calcination system shows that the cement clinker is mainly composed of dicalcium silicate and tetracalcium sulfoaluminate,and contains a small amount of tetracalcium ferric aluminate and anhydrite.Through the test of the working performance of cement,it is found that it has higher early strength and late strength and faster setting time.The compressive strength of Belite-sulfoaluminate cement AFter hydration for 3 days can reach the compressive strength of PC42.5 AFter hydration for 28 days,and the 90-day compressive strength of Belite-sulfoaluminate cement can reach 112 MPa.（2）The hydration characteristics of Belite-sulfoaluminate cement were studied by means of hydration heat,chemically bound water,XRD,TG-DSC,scanning electron microscope and other test methods.It was found that it has the characteristics of fast hydration rate,high calorific value and concentrated in the early stage,and it can still maintain continuous hydration in the later stage of hydration.Hydration products such as silicate gel,single-carbon hydrated calcium sulfoaluminate,feldspar and other hydration products also provide the possibility for the continuous increase of strength in the later stage of hydration.The study also found that the addition of steel slag has a certain influence on the hydration activity of cement,and within a certain dosage range,with the increase of steel slag dosage,the hydration activity of cement increased first and then decreased.The impact of steel slag on cement hydration is mainly concentrated in the early stage of hydration,and the impact on the later stage of hydration is relatively small.（3）Through a systematic study on the formation process of solid waste-based belite-sulfoaluminate cement clinker minerals,it is found that when the calcination temperature is lower than 1100°C,the clinker is mainly composed of free calcium oxide,yellow feldspar,anorthite,calcium aluminate yellow feldspar,dodecyl calcium heptaaluminate,and contains a small amount of dicalcium silicate.When the calcination temperature is in the temperature range of 1100-1200°C,the intermediate minerals in the clinker will decompose or undergo solid-phase reaction with calcium sulfate and free calcium oxide to generate tetracalcium sulfoaluminate and dicalcium silicate.When the calcination temperature is higher than 1200℃,the formation of minerals in clinker is no longer dominated,but the change and development of mineral crystal structure and morphology.With the increase of temperature,the crystal size of dicalcium silicate and tetracalcium sulfoaluminate increases gradually,and the crystal structure also changes continuously.When the calcination temperature reaches 1350℃,the minerals in the clinker will melt and decompose.（4）The carbon emissions and energy consumption of solid waste-based Belite-sulfoaluminate cement and ordinary Portland cement were evaluated based on the life cycle assessment method.The evaluation results show that the solid waste-based Belite-sulfoaluminate cement has obvious advantages in energy saving and emission reduction,and the CO₂ emission reduction is even more than 55%.