| Lithium slag is produced by industrial production of lithium carbonate, belonging to industrial waste residue.It has a wide range of sources and low price. The chemical constitution of lithium slag is very similar to the cement constitution. Lithium slag has good pozzolanic activity. The preparation of concrete with lithium slag instead of cement can not only make full use of industrial waste residue, reduce the environmental pollution of lithium slag, but also enhance the growth of green concrete and environment-friendly society.Simultaneously, with the rapid development of society, the environment is getting worse, the performance of building materials and building structures gradually decline and deterioration,often resulting in insufficient durability of concrete structures, structural damage is serious and can not meet the design requirements. Therefore, many scholars have actively carried out research on the durability of concrete. In order to explore the advantages of lithium slag in concrete, this paper studies the effect of lithium slag as the admixture on the durability of concrete. After a lot of experimental and theoretical analysis, this paper completed the following work:1.Through the orthogonal experiment design, orthogonal analysis method and effect calculation method were used to study the influence of water-cement ratio, lithium slag content and fineness on lithium slag concrete compressive strength, and the best ratio of lithium slag concrete and the optimum content of lithium slag admixture were determined.The results show that the order of effect of each factor on the compressive strength of concrete is water binder ratio> lithium slag content> lithium slag fineness. The compressive strength of lithium slag concrete is basically lower than that of ordinary concrete or its equivalent in the early stage, and its compressive strength in later period is generally larger than that of ordinary concrete. The optimum proportion of lithium slag concrete is as follows:the water to binder ratio is 0.342, the content of lithium slag is 20%, the fineness of lithium slag is about 7.5%. The optimal content of lithium slag is 20%.2.Based on the existing concrete strength model, the prediction model of compressive strength of lithium slag concrete was established by SPSS stepwise regression analysis and non-linear regression method. Then, based on the appraisal index, the best prediction model of compressive strength of lithium slag concrete was established. The results show that the five proposed models have high accuracy, and can predict the compressive strength of lithium slag concrete. Based on the comprehensive evaluation of the root mean square error, the average absolute error and the average absolute percentage error and the R2 value of the model, the nonlinear regression equation of cement strength, binder/water ratio, the dosage of lithium slag and water reducing admixture content as arguments is determined as the best prediction model of compressive strength of lithium slag concrete.3.The effects of lithium slag content and freeze-thaw environment on the frost resistance of concrete were discussed. The freezing and thawing medium is water and salt solution two kinds of medium, lithium slag content includes 0, 20% and 40%. The change law of mass,dynamic elastic modulus and compressive strength of lithium slag concrete under freeze-thaw environment was studied. Combined with scanning electron microscope (SEM), the microstructure of different lithium slag concrete under freezing and thawing cycles was analyzed. The results show that the addition of lithium slag in concrete has a great influence on its mass change and relative elastic modulus under the action of freeze - thaw cycle. The larger the amount of lithium slag is, the more serious the appearance damage is, the worse the frost resistance is. The coupling action of salt solution and freezing thawing will accelerate the corrosion and freeze-thaw damage of concrete. The freeze-thaw resistance of lithium slag concrete in salt solution is lower than that in water, and the freezing resistance of ordinary concrete in water is better than that in salt solution. The addition of lithium slag in concrete has certain influence on the compressive strength of concrete under freezing and thawing, and the content of lithium slag should not be more than 40%. Under the long-term freeze-thaw cycle, the compressive strength of concrete with 20% lithium slag content is the best, and its strength is bigger than that of ordinary concrete. When the content of lithium slag is more than 20%, the compressive strength of lithium slag concrete is reduced and is smaller than that of ordinary concrete. The compressive strength of concrete under the action of freeze-thaw cycle in salt solution is lower than that under freeze-thaw action in water.4.The effects of lithium slag content and carbonization time on the carbonation resistance of concrete were discussed by using the contents of three kinds of 0, 20% and 40%. The changes of mass, dynamic elastic modulus, splitting tensile strength and neutralization depth of concrete were studied. Combined with SEM, the microstructure of different lithium slag concrete under carbonization was analyzed. The results show that the depth of carbonization of concrete is increased with the increase of lithium slag content. However, the 28d carbonization depth of the concrete with 40% lithium slag content is 7.38mm, which is much smaller than the thickness of the protective layer of the reinforced concrete in the general structure design, so the lithium slag concrete has certain carbon resistance. In the project requiring strict carbonization resistance, the lithium slag content should not be too large,should be less than 40%. At the same carbonization stage, the greater the amount of lithium slag, the greater the loss rate of splitting tensile strength of concrete. However, before and after carbonization, the splitting tensile strength of lithium slag concrete is better than that of ordinary concrete. The carbonization time of concrete has a certain influence on the carbonization depth of concrete. The carbonization depth of ordinary concrete and lithium slag concrete has a tendency to increase at the beginning and the middle of carbonation, and the carbonization depth of concrete will gradually stabilize in the later stage of carbonization.5.According to the characteristics of acid rain in Jiangxi, the simulated acid rain solution with different pH value and different SO42- concentration were prepared. The acid rain corrosion test was simulated by indoor wet and dry cycle spray method. And 0, 20% and 40%of the three lithium slag content was used in the test. The effects of lithium slag content, acid rain pH value and SO42- concentration on the corrosion resistance of concrete were discussed.The changes of appearance, quality, compressive strength and neutralization depth of concrete were studied. Combined with scanning electron microscope (SEM), the microscopic analysis was carried out on concrete samples with different lithium slag content in simulated acid rain environment. The results show that the addition of lithium slag to the concrete can reduce the appearance damage of the concrete and reduce the mass loss rate of the concrete under the same simulated acid rain solution erosion condition. The incorporation of lithium slag in concrete can improve the compressive strength of concrete after acid rain corrosion to a certain extent. The larger the amount of lithium slag is, the smaller the compressive strength loss of concrete is. Among them, the strength of lithium slag concrete after acid rain corrosion is larger than that of ordinary concrete under the same acid rain corrosion condition. The neutralization depth of concrete is increased with the addition of lithium slag in the concrete.The greater the lithium slag content, the greater the neutral depth of concrete. However, in the later period of acid rain corrosion, the neutralization depth of lithium slag concrete is stable.The maximum neutralization depth of lithium slag concrete is 2.25mm, which is far less than the protective layer thickness of reinforced concrete. When the acid concentration of SO42-ion is fixed, the smaller the pH, or when the PH value of the acid rain is fixed, the concentration of SO42- ion is large, lithium slag concrete quality loss is more serious, the concrete compressive strength loss rate and the neutralization depth is greater. Under the action of three different simulated acid rain, the maximum neutralization depth of concrete with 20%slag content is only 2.13mm. |
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