Study On The Reaction Mechanism Of Ferrochrome Slag-slag Based Geopolymer Solidified Chloride Saline Soil Based On Chloride Constraint

A large number of chlorine saline soils are distributed in the coastal areas of Jiangsu,Shandong,Tianjin,Hebei and Liaoning in China,as well as inland areas such as Xinjiang,Qinghai,Gansu and Inner Mongolia.Due to the poor engineering characteristics such as salt expansion,dissolution and corrosion,there are serious safety hazards in some projects in the coverage area.The use of traditional curing agents such as quicklime and cement to solidify chlorine saline soil is the main treatment method at present.However,the traditional curing agent is difficult to form an effective constraint on the excessive chlorine salt in the chlorine saline soil,and the curing effect is general.Moreover,its preparation cost is high and the carbon emission is large,which is contrary to the national‘double carbon target’.At the same time,the resource utilization rate of bulk solid waste in China is still at a low level.The resource utilization rate of slag is only 69%,and that of high carbon ferrochrome slag is only 10%.The storage of a large amount of solid waste not only occupies land,but also causes serious environmental pollution by leaching of harmful ions.Previous studies have shown that slag-based geopolymers can react with Na Cl to form chloride-containing and insoluble Friedel’s and Kuzel’s salts,which provide strength for solidified soil and form a certain constraint on Na Cl.However,the aluminum phase contained in slag is limited,and it is not enough to completely react Na Cl in saline soil.The high-carbon ferrochrome slag is rich in aluminum phase,and the geopolymer curing agent prepared by compounding it with slag can have better ability to restrain Na Cl.Therefore,on the basis of the‘soil reinforcement’performance of the traditional curing agent,the‘de-salinization’ability is added to directly hit the root cause of the disease of chloride saline soil,solve the problem of curing chloride saline soil,and further improve the level of resource utilization of ferrochrome slag and slag in China.In this paper,Na Cl is regarded as the activator component to study the hydration reaction mechanism of ferrochrome slag-slag geopolymer cementitious material,explore the formation mechanism of its mechanical properties and the improvement method of durability,and optimize the component ratio of cementitious material.Then,the Na Cl component in the cementitious material was removed to make a curing agent for chloride saline soil,which was used to solidify the natural saline soil taken from Lianyungang area.Through the macroscopic tests such as unconfined compressive strength,consolidation content,capillary water absorption,frost resistance,dry-wet cycle,water stability and suspension conductivity of the solidified soil,and the microscopic tests such as Fourier transform infrared spectroscopy,XRD,mercury intrusion and SEM,the reaction mechanism of chromite slag-slag based curing agent to improve saline soil was explored by comparing with the hydration mechanism of chromite slag-slag based geopolymer cementitious material.Finally,in order to verify the adaptability of the curing agent to chloride saline soil with different salinization grades,the curing effect of the self-made chloride saline soil with weak,medium and strong salinization grades was verified,which provided a basis for the industrial application of chromite slag-slag based curing agent.The results show that:（1）Ferrochrome slag-slag based geopolymer cementitious material can react with Na Cl in the composition to form a large number of flake and needle-like Friedel’s salts and AFt crystals.In the sulfate environment,Friedel’s salts are transformed into Kuzel’s salts to provide strength for the matrix,while Kuzel’s salts and AFt are formed with C-A-H as reactants.Ferrochrome slag and slag together provide aluminum phase for hydration reaction,so that more C-A-H gels are generated in cementitious materials,which promotes the formation of Kuzel’s salts.（2）On the one hand,Kuzel’s salt crystals,AFt and C-S-H gel,which are beneficial to the strength of the soil,are generated,and the soil is connected as a whole.On the other hand,the participation of ferrochrome slag promotes the consumption of Cl^-and SO₄^2-,which significantly reduces the content of soluble salt ions in the solidified soil and achieves the purpose of‘desalinization’.In addition,the by-product Na OH generated by the hydration of the curing agent improves the alkalinity of the system and promotes the reaction of active Al₂O₃ and Si O₂ in the soil.（3）Due to the slow hydration reaction of ferrochrome slag in the early stage,the strength of the solidified saline soil is slightly lower than that of the slag-based curing agent at 7 d and 28 d,but the strength can be 4.1%higher than that of the slag-based curing agent after 60 d.In addition,it also has significant advantages over slag-based curing agents in terms of durability.Through the macroscopic properties and durability of solidified soil,the optimal ratio of chromite slag-slag based composite curing agent can be obtained as building gypsum:quicklime:chromite slag/activated object=6:15:30.（4）Compared with cement and lime,the saline soil solidified by ferrochrome slag-slag based composite curing agent not only has high strength,good durability,strong ability to solidify soluble salt ions,but also has low cost.The curing cost of ferrochrome slag-slag based composite curing agent can be 43.67%lower than that of cement curing agent and 37.75%lower than that of lime curing agent.（5）Through the study of adaptability,it is found that ferrochrome slag-slag composite curing agent has obvious effect on saline soil with different salinization grades,among which the curing effect of strong saline soil is slightly lower,but its strength can still meet the requirements of secondary and lower highway subbase in the specification.