Study On Axial Pressure Properties Of FRP Constrained Biochar Aggregate Concrete

With the acceleration of industrialization and the increase of population,the ecological environment is facing unprecedented challenges.As a kind of organic solid waste,the current stock and future increment of biochar are large.Adopting reasonable recycling technology can not only realize carbon storage but also reduce the consumption of non-renewable resources.Biomass carbon aggregate concrete has the advantage of light weight,but because of its microstructure of high porosity,it has weak strength and poor corrosion resistance.This paper proposes that using FRP to constrain biochar concrete can not only effectively improve the defects of high brittleness and low strength of biochar aggregate concrete,but also improve its ductility and durability.In this paper,the basic properties of biochar are studied first,the trial test of biochar concrete is carried out,the mix scheme to ensure the light weight and strength is proposed,the axial compression test of 30 FRP constrained biochar condensate is carried out,and the corresponding constitutive model is proposed.The results of this research show that: 1.The water absorption process of biochar can be divided into two stages,rapid water absorption stage and slow water absorption stage.The water absorption capacity of biochar is very strong in the first three minutes,reaching 83% of the equilibrium water content.After that,the water absorption capacity becomes weaker and weaker,and the saturated water content is 87%.With the increase of biochar content,the strength of biochar concrete generally decreased and the apparent density decreased.When the carbon content is 50%,the apparent density is 1915g/cm3,reaching the standard of lightweight concrete.2.The ultimate compressive strength of FRP constrained specimens has a great increase compared with that of unconstrained specimens,but the higher the carbon content,the lower the peak stress.The peak strength of unrestrained biochar concrete is much lower than the transition point of stress-strain curve of FRP restrained concrete.The quadratic stiffness of FRP constrained specimens is related to the number of FRP layers.The more the number of FRP layers,the greater the quadratic stiffness.3.FRP is an effective restraint form for biochar concrete.By comparing existing literature models with experimental curves,it is found that these models cannot accurately predict the changes of axial stress-strain curve,peak stress and ultimate strain of FRP confined biochar concrete,especially at the transition zone and inflection point.Based on the stress-strain curve characteristics of the constrained specimens,the stress-strain curve model of FRP constrained biochar concrete is simplified into a reinforced model,and a constitutive model suitable for this experiment is proposed.