Research On Water Treatment Sludge Modification And Its Performance And Microstructure Of Cement-based Materials

Along with our country urbanization speed up the pace of construction,the expanding of the city,people,the demand for water is increasing.Therefore,the number of waterworks is increasing constantly,and the sludge produced by waterworks is also increasing dramatically.As a kind of solid waste,water treatment sludge will cause land waste and environmental pollution if it is simply piled up and incinerated without disposal.Therefore,the application of water treatment sludge in cement-based materials is beneficial to the resource utilization of solid waste and the construction of"no waste city".The pozzolanic activity of modified water treatment sludge was studied from different calcination temperature and different calcination time.The strength index method was used to compare and analyze the physical and chemical properties of the modified water treatment sludge before and after modification,and to determine the best calcining system of the water treatment sludge.The effects of different factors such as dosage,fineness,temperature,water-binder ratio and age on the properties of modified water treatment sludge cement based materials were studied.The mechanical properties and drying shrinkage properties of the cement mortar mixed with modified water treatment sludge were studied by testing the compressive resistance,bending resistance and drying shrinkage.By means of scanning electron microscope,X-ray diffraction and nano-indentation,the phase composition,micro-morphology and nano-mechanical properties of the sludge slurry containing modified waterworks were analyzed.Based on the micromechanics of porous media,the properties of cement slurry containing modified water treatment sludge were characterized and its mechanism was analyzed from macroscopic,microscopic and microscopic perspectives.The main conclusions of this paper are as follows:（1）The pozzolana activity test after calcination of water treatment sludge shows that,based on the strength index of cement mortar prepared by different calcining temperatures and different calcining times,the best modification system is that the modified water treatment sludge calcined for 2h at 900℃has the best activity.（2）The strength test results show that under the condition that the water-binder ratio is kept constant,the calcining temperature is 900℃,the dosage is 10%,and the average particle size of the water treatment sludge has the best strength performance.（3）The drying shrinkage results showed that when the sludge powder content of the modified waterworks was 10%,it was beneficial to restrain the drying shrinkage of cement paste,and its final dry shrinkage decreased by 30.9%compared with the reference group.When the content exceeded 20%,the drying shrinkage value of cement paste increased.Cement paste containing modified WTS has a certain linear relationship between drying shrinkage and strength.（4）According to the microscopic test,modified water treatment sludge has a certain microaggregate filling effect.SEM analysis shows that adding a certain amount of modified WTS can improve the internal pores of the structure,and adding10%modified WTS reduces the width of micro-cracks by 10%compared with the reference group.According to XRD analysis,the weakening of Ca（OH）₂crystal front indicates that Ca（OH）₂participates in hydration reaction.Meanwhile,the analysis of nano-indentation test shows that the elastic modulus of cement matrix and interfacial transition zone with 10%modified WTS cement paste are improved to a certain extent.