| In the cold area of north of our country,the durability of concrete structure has been deteriorated seriously because of the influence of freeze-thaw for a long time.However,there are few studies on the mechanical properties of concrete after sequential freeze-thaw and high temperature.Scoria aggregate concrete has the advantages of light weight,good heat insulation and heat resistance.However,concrete made by completely replacing natural aggregates with scoria aggregates is often damaged by cracks through the aggregates when under pressure.Scoria aggregate concrete is prone to precipitation and uplift of scoria aggregates during the formulation process,which is detrimental to strength.Based on the present situation,40% scoria aggregate is used to replace natural crushed stone aggregate in equal volume,and 0%,0.5%,1.0% and 1.5% steel fiber are added to make the fiber scoria aggregate concrete and fiber natural concrete.The mechanical properties of fiber reinforced scoria aggregate concrete after freeze-thaw and high temperature were studied fiber reinforced natural aggregate concrete as a control group,providing a theoretical basis for the subsequent application of fiber reinforced scoria aggregate concrete in structures.The specific work is as follows:(1)Freeze-thaw tests of fiber reinforced natural aggregate concrete and fiber reinforced scoria aggregate concrete were conducted.The influence of scoria aggregate and steel fiber content on the frost resistance of concrete was studied by the index of mass loss rate and relative dynamic elastic modulus after freeze-thaw cycle.(2)Five high-temperature tests were carried out on all specimens at 20 ℃,200 ℃,400 ℃,600 ℃ and 800 ℃.The apparent characteristics and mass loss rate of fiber reinforced scoria aggregate concrete specimens before and after freeze-thaw cycle were studied to make a preliminary determination of the fire resistance of fiber reinforced scoria aggregate concrete specimens before and after freeze-thaw cycle.(3)Cubic uniaxial compressive tests,splitting tensile tests and prismatic uniaxial compressive tests were carried out on fiber reinforced scoria aggregate concrete specimens and fiber reinforced natural aggregate concrete specimens after freeze-thaw cycle and high temperature.The cubic compressive strength,splitting tensile strength,stress-strain curve,peak strain and elastic modulus of fiber reinforced scoria aggregate concrete after freeze-thaw cycle and high temperature are investigated in relation to temperature and steel fiber contents.(4)MATLAB was applied to fit the experimental data to obtain equations that can be used to predict the variation of the mechanical properties of scoria aggregate concrete such as cubic compressive strength,splitting tensile strength,modulus of elasticity and peak strain with temperature for each steel fiber contents after freeze-thaw,and to establish a uniaxial compressive constitutive model for fiber scoria aggregate concrete after freeze-thaw cycle and high temperature for each steel fiber contents. |
