Study On Ultra-High Performance Concrete Containing Coarse Aggregate Used In Overlay Of Bridge Deck

Ultra-high performance concrete(UHPC)is a cementitious composite with excellent mechanical properties and durability.Using UHPC can greatly improve the durability of bridge deck pavement,but the high usage cost and significant shrinkage limit its widespread application.However,Ultra-high performance concrete with coarse aggregate(UHPC-CA)can significantly reduce the cost and concrete shrinkage by adding coarse aggregate to replace the amount of cementing material.Based on the close packing theory,this paper designed several groups of ultra-high performance concrete containing crushed pebble aggregate,and studied the effects of different coarse aggregate particle size,coarse aggregate mixing method and steel fiber mixing amount on the workability and mechanical properties of UHPC-CA.Combined with the application background of UHPC-CA used as bridge deck pavement material,the effects of different interface treatment methods and different matrix strength of ordinary concrete(NC)on the bonding mechanical properties and bonding durability of UHPC-CA and NC composite specimens were further studied.The main research contents and conclusions of this paper are as follows:(1)Combined with the minimum water requirement method and Modified Andreasen and Andersen model(MAA model),multiple UHPC-CA groups were designed using the semi-empirical UHPC-CA mix design method to study the effects of different factors on the workability and mechanical properties of UHPC-CA.It was found that after grading optimization,the mechanical properties of UHPC-CA were optimal when coarse aggregate with a maximum particle size of 4.75 mm was added and the steel fiber content was 2%.The fracture characteristics of UHPC-CA were analyzed in combination with DIC.It was found that the addition of steel fiber made the tensile fracture of UHPC-CA change from brittle fracture to ductile fracture.(2)The durability performance of the optimal mix ratio UHPC-CA was studied through experiments on frost resistance,impermeability,and chloride ion permeability.It was found that UHPC-CA had excellent durability,with only 1.1% loss in mass after 150 freeze-thaw cycles;Gradually pressurize to the design maximum water pressure of 1.3MPa,no water seepage at the end was observed;56d electric flux is only 73 C.(3)The splitting tensile test and bending tensile test were conducted on UHPC-CA and NC composite specimens with different adhesive surface treatments and different matrix strengths.It was found that the larger the roughness of the adhesive surface,the higher the splitting tensile strength of the adhesive;The tensile strength of adhesive splitting increases linearly with the increase of NC matrix strength;The flexural and tensile strength of composite specimens with higher interface roughness is higher than that of NC matrix.(4)The Freezing-thaw resistance experiments and Water permeability resistance experiments were conducted on UHPC-CA and NC composite specimens with different adhesive surface treatments.It was found that after 150 freeze-thaw cycles,the splitting tensile strength of each group of specimens decreased significantly compared to before freeze-thaw.The higher the roughness of the adhesive surface,the smaller the impact of freeze-thaw cycles on the splitting tensile strength;The weak impermeability of UHPCCA and NC bonding specimens lies on the bonding surface,and the stronger the bonding,the better the impermeability performance is.