Study On Basic Mechanical Properties And Carbonization Resistance Of Carya Cathayensis Peel Biochar Concrete

Agricultural,forestry and other industries produce crop straw,fruit shell,fallen leaves and other biomass solid waste quantity is amazing.Pyrolytic technology can transform these biomass solid wastes into biochar with resource utilization benefits,which can be applied to concrete to improve the performance of concrete.In this paper,the biochar made from carya cathayensis peel,a unique agricultural and forestry solid waste in Zhejiang Province,was selected as raw material.The physical properties of the biochar from carya cathayensis peel were studied by means of elemental analysis,SEM analysis and Fourier infrared spectroscopy.Biochar was added to concrete in three forms,namely inorganic filler,mass replacement cement and volume replacement sand,to test the compressive strength and splitting tensile strength of concrete under different biochar addition methods,and to study the influence of different addition methods and different dosage of biochar on the mechanical properties of concrete.The effect mechanism of biochar on concrete strength was analyzed by means of mercury injection(MIP)and scanning electron microscopy(SEM).According to the principle of optimum strength,the optimal addition form of biochar in carya cathayensis peel was determined.The carbonation depth and compressive strength of biochar concrete after carbonation were measured and compared with ordinary concrete.The carbonation depth prediction model of biochar concrete was established by COMSOL software,and the validity of the model was verified according to the test results.Based on this model,the carbonation life of biochar concrete is predicted.The purpose of this study is to propose the applicability of carya cathayensis peel biochar in improving the strength and carbonization resistance of concrete.The research in this paper shows that:(1)It was found that the oxygen/carbon ratio(O/C)of hickory shell biochar was0.18,and its half-life was about 1000 years,showing long-term stability.SEM and water absorption tests show that the biochar has developed pore structure,high specific surface area and strong water absorption,with water absorption up to 108%.(2)When biochar was used as a filler in concrete,the optimal dosage was 2% of cement mass,and the compressive strength and splitting tensile strength were increased by 3.54% and 33.11%,respectively,compared with the control group without biochar;When the dosage exceeds 2%,the strength shows a decreasing trend.When applying this method to concrete,the recommended dosage is not more than 2%of the cement mass.(3)When biochar replaces cement applied to concrete,the compressive strength of biochar concrete is reduced by 6.25% to 26.70% compared with the control group,and the splitting tensile strength is almost the same as that of the control group.The main reason is that the biochar contains few elements that can be used for hydration.Based on this study,it is not recommended to use such biochar as a substitute for cementing materials.(4)When the biochar partially replaced sand by volume percentage for concrete,the biochar sand replacement rate was less than 10%,the compressive strength of concrete increased by 4.1% to 16.66%,and the split tensile strength of biochar concrete increased by 2.36% to 28.72% compared with the control group.When the substitution rate is 5%,the compressive strength and splitting tensile strength are the highest.If biochar is used as a substitute for sand when added to concrete,it is suggested that the replacement rate should be controlled within 10% of the sand volume,and the water reducing agent with a mass of about 3‰ of the cementing material should be added to ensure the workability of the mix.(5)The carbonization test of biochar concrete was carried out.The results showed that the carbonation depth of biochar concrete with 5% and 10% biochar sand replacement rate was lower than that of ordinary concrete at carbonation age of 3d,7d,14 d and 28 d,but the increase of compressive strength of biochar concrete after carbonation was lower than that of ordinary concrete,and the increase gradually decreased with the increase of biochar replacement rate.(6)Based on the experimental results,the relationship between carbonation depth and carbonation time of biochar concrete was analyzed,and the numerical model of carbonation depth of biochar concrete and ordinary concrete was established by using the thin material transfer physical field and convection-diffusion equation in the numerical simulation software COMSOL Multiphysics;Based on the test results,the reliability of the numerical model is verified and the carbonization life is predicted according to the numerical model.The results show that the carbonation life of concrete can be prolonged when the carya cathayensis peel biochar replaces sand with5% volume.The results show that the carbonation life of concrete can be prolonged when the carya cathayensis peel biochar replaces sand with 5% volume.Through this study,the applicability and feasibility of using carya cathayensis peel biochar in concrete to improve the strength and carbonization resistance were clarified.The results of this paper provide a basis for the utilization of this biochar in the field of green building materials.