Experimental Study On Compressive Behavior Of Polypropylene Fiber Lithium Slag Concrete Columns Under The Coupling Of Thermal Cycle And Load

In the northwest cold region,the temperature difference is large,the summer is hot and the winter is cold.The concrete structure will undergo the effect of thermal-cold cycles.Polypropylene fiber can be added into the concrete to toughen and improve its durability.Industrial waste lithium slag is added into concrete to improve its later strength.Most of the reinforced concrete structures in service work under the joint influence of load and external environment.The coupling effect of the two will make the concrete structure degenerate,cause erosion and cracking,and reach the limit state too early.In practical construction engineering,reinforced concrete columns usually bear eccentric compression.Therefore,through indoor simulation of the actual service state and environment of concrete structures,the eccentric compression test of polypropylene fiber lithium slag concrete column(PFRC column)under the coupling action of thermal-cold and load is carried out to study the influence of thermal-cold cycles,fiber content and stress level on the ultimate bearing capacity and deformation capacity of PFRC columns.The main research contents of this paper are as follows.(1)The effects of the number of thermal-cold cycles and fiber content on the mass loss rate and dynamic elastic modulus of PFRC are studied,and the thermal-cold damage mechanism is analyzed.The results show that thermal cycling will cause damage and deterioration to PFRC.With the increase of thermal-cold cycle times,the mass loss rate increases,but the amplitude is very small.The relative dynamic elastic modulus of PFRC decreases obviously after 200 times of thermal-cold cycle.When the fiber content is0.9kg/m~3,the relative dynamic elastic modulus of PFRC is higher than that of other content,the internal damage is the smallest,and the thermal-cold resistance is the best.(2)81concrete blocks were made in the same batch to study the influence of fiber content and thermal-cold cycles on compressive strength,splitting tensile strength,axial compressive strength and stress-strain curve of PFRC specimens.The results show that with the increase of fiber content in the range of 0.9～1.5kg/m~3,the values of mechanical properties decrease.With the increase of thermal-cold cycles,the compressive strength of PFRC decreases,while the splitting compressive strength first increases and then decreases.The peak stress and peak strain of PFRC decrease obviously after 300 thermal-cold cycles.Under the same thermal-cold cycle times,the PFRC with 0.9kg/m~3 fiber has the best thermal-cold durability.(3)Ten corbel columns are designed,and the eccentric compression tests are carried out on PFRC columns under thermal cycling and load to study the influence of different fiber content,thermal-cold cycle times and stress level on the compression of PFRC columns,and whether the PFRC column conforms to the plane cross-section assumption in the process of loading.The results show that the double effects of thermal cycling and load make the mechanical performance of PFRC columns degenerate,and the PFRC column with 300 times of thermal-cold cycle and stress level of 0.35 is the most seriously damaged,with much and dense crack.The bearing capacity of PFRC column decreases with the increase of thermal-cold cycle times.At the same thermal-cold cycle times,the bearing capacity of PFRC column is the lowest at the high stress level of 0.35.The bearing capacity of PFRC columns decreases with the increase of fiber content,but the influence is small.(4)According to the test results,considering the damage of polypropylene fiber reinforced concrete columns caused by thermal-cold environment and load factors.The environmental effect coefficient is introduced to establish the bearing capacity calculation formula of PFRC columns under eccentric compression under the coupling of thermal-cold cycle and load.The calculated values of the model are in good agreement with the experimental values,which can provide theoretical reference for the design and application of fiber reinforced concrete structures in severe cold regions.