Study On Freeze Resistance Of Coal Gasification Slag Concrete

Sand and gravel aggregate is an indispensable and huge raw material for concrete construction.But the limited availability of river sand makes it urgent to find alternatives in order to ensure infrastructure construction and maintenance.Coal is currently the main energy source in my country,and coal gasification is one of the important processes of coal chemical industry.In this paper,coal gasification slag is added to concrete instead of river sand,and the design of coal gasification slag concrete mix ratio and frost resistance research are carried out.Coal gasification slag(particle size below 4.75mm)replaces river sand to make cement mortar according to the quality of 0%,20%,40%,60%,80%,determines the optimal mix ratio by compressive strength,and tests its drying shrinkage and temperature shrinkage properties.Then carry out coal gasification slag concrete strength test,rapid chloride ion penetration test,rapid freeze-thaw test and rapid salt freeze-thaw test.The results show that the optimal replacement rate of river sand is80%;coal gasification slag concrete can resist chloride ion erosion well,and the frost resistance grade of concrete is F125,which can be used for cement concrete pavement of rural highways,and its mechanical properties meet the requirements of non-standard axle load routes.10 years.By means of microscopic methods XRD,TG,MIP and SEM,the hydration products,bound water content,pore structure and micromorphological changes of coal gasification slag mortar under different substitution rates were compared,and the mechanical properties and freezing resistance mechanism of coal gasification slag concrete were explained.The results show that after the coal gasification slag is added to the concrete,no new hydration products are produced.The further hydration of the cement clinker and the pozzolanic reaction are alternately carried out,which improves the degree of hydration.At the same time,the pozzolanic reaction consumes CH and generates more C-S-H gel.,which is the main reason for the improvement of mechanical properties;the proportion of pore size of coal gasification slag concrete above 50 nm gradually decreases with the substitution rate of coal gasification slag,the chloride ion diffusion coefficient of concrete also gradually decreases,and the resistance to chloride corrosion is enhanced;The frost resistance of coal gasification slag concrete is disadvantageous.The multi-scale simulation software Digimat was used to homogenize the mechanical and thermodynamic parameters of coal gasification slag mortar and ITZ,and Comsol Multiphysics was used to establish a random aggregate concrete freezethaw numerical model under the coupling action of stress field,porous seepage field and temperature field.The temperature field,pore pressure,vertical displacement and Mises stress changes were used to analyze the damage of coal gasification slag concrete after chloride salt freeze-thaw cycles.The results show that the frost resistance of coal gasification slag concrete is slightly worse than that of ordinary concrete;the pore pressure,vertical displacement and Mises stress of salt-freezing damage are all larger than those of water-freezing,and the overall performance deterioration of concrete under salt-freezing is greater than that of water-freezing.The research in this paper shows that the improvement of mechanical properties of coal gasification slag concrete is the result of the combined effect of the increase of cement hydration degree and the reaction of pozzolan,which can be used for cement concrete pavement of rural highways.