Structural Behaviors Of Prestressed Recycled Aggregate Concrete Composite Floor System

Based on recycled aggregate concrete and prefabricated building technology,this paper proposes a prestressed recycled aggregate concrete composite floor,which consists of a prefabricated prestressed grouted-round-steel tube truss floor and a recycled aggregate concrete layer.The traditional prefabricated component of steel-tube-truss floor is replaced by a grouted-round-steel tube truss floor to improve the flexural rigidity of the floor.And the recycled aggregate concrete is used in this floor to reduce resource consumption.Compared with the traditional composite floor,prestressed recycled aggregate concrete composite floor has a unique structural form and obvious resource saving advantages.In order to promote the application of this kind of prestressed recycled aggregate concrete composite floor,firstly 72 concrete cubes of 100 mm×100 mm×100 mm are designed and manufactured to study the mechanical properties of recycled coarse aggregate concrete,taking into account the replacement rate of recycled coarse aggregate,the content of cementitious materials,the influence of particle shaping and silica fume strengthening.The final research results show that when the amount of cementitious material is 430 kg/m~3,the replacement rate of recycled aggregate is 60%.The 28-day compressive strength of recycled concrete is 90.2%of natural aggregate concrete.This shows that the mechanical properties of composite reinforced recycled concrete are close to natural aggregate concrete.In the experiment of prestressed grouted-round-steel tube truss floor,4 prestressed grouted-round-steel tube truss floors are designed and manufactured.Two kinds of loading methods including concentrated load and uniform load are considered.The cracking load and ultimate load of the prestressed grouted-round-steel tube truss floor under concentrated load,uniform load are obtained.The cracking load and ultimate load of prestressed grouted-round-steel tube truss floor are 12.7kN and 19.8kN respectively,which meet the requirements of load code for construction of prefabricated floor.In the experiment of prestressed recycled concrete composite floor,fourprestressed recycled concrete composite floors are designed and manufactured,considered the different content of recycled coarse aggregate.The cracking load and ultimate load of prestressed recycled concrete composite floor under different replacement rate of recycled coarse aggregate are obtained.The study found that the prestressed recycled concrete composite floor slab with a 60%replacement rate of recycled coarse aggregates develops the deflection faster under the same load and cracked prematurely.The use of composite floors with 60%replacement ratio of recycled coarse aggregate shall be properly avoided in the works.In the experiment of damaged prestressed bottom slab composite floor,three damaged prestressed bottom slab composite floors are designed and manufactured under three different working conditions.It is found that the overall mechanical performance and deformation law of the damaged composite floor have not changed much compared with that of the undamaged composite floor,and even the damaged prestressed composite floor still has a good bearing capacity when the damage reaches the cracking load,which also provides a demonstration for the safety and reliability of this kind of composite floor in the construction stage and normal working stage.Finally,based on the test,the theoretical analysis of the recycled concrete composite floor system is carried out,and the deformation and bearing capacity of the recycled concrete composite floor system are analyzed by the equivalent cross-section method.The maximum error does not exceed 16%,which indicates that the method can better reflect the stress state of the prestressed recycled concrete composite floor system in the construction stage and normal use stage.