Study On Physical And Mechanical Properties Of Fiber Aerogel Concrete

In seasonal frozen soil areas,road gravity concrete retaining wall is susceptible to negative effects of freeze-thaw cycle,and the deterioration of concrete leads to the wall cracks,surface spalling and other diseases.In order to solve the problem of poor thermal insulation of concrete retaining wall in seasonal frozen soil area,a self-insulating concrete material is designed in this thesis to improve the service performance of retaining wall.Due to its very low density and thermal conductivity,the thermal conductivity of aerogel concrete prepared by Si O2 is much lower than that of ordinary concrete.Aerogel concrete is often used as wall insulation material in cold areas,but it is difficult to be used as loadbearing structure due to its insufficient strength.Fiber,as a strengthening and toughening material,can improve the strength of concrete materials.In this study,fibers were selected to be mixed into aerogel concrete to prepare a new type of high-performance thermal insulation concrete material,which can not only bear weight but also meet the requirements of thermal insulation.Based on laboratory tests,this thesis studies the effects of fiber type,fiber length,fiber content and aerogel content on the physical and mechanical properties of cement-based concrete,and analyzes the function mechanism of aerogel and fiber in concrete materials from a microscopic perspective.Finally,the mechanical strength and thermal conductivity of fiber aerogel concrete materials are predicted based on integrated learning method.The main conclusions of this thesis are as follows:(1)With the increase of fiber content and length,the consistency of aerogel concrete mixture gradually increases and the fluidity gradually decreases.The influence degree of different kinds of fiber on the consistency of mix from large to small shows: polyvinyl alcohol fiber > glass fiber > polypropylene fiber > basalt fiber.(2)The effect of fiber on the physical properties of aerogel concrete was studied.After adding glass fiber and basalt fiber,the water absorption and thermal conductivity of the material first decrease and then increase with the increase of fiber content,and gradually decrease with the increase of fiber length.The softening coefficient first increases and then decreases with the increase of fiber content,and gradually increases with the increase of fiber length.With the addition of polypropylene fiber and polyvinyl alcohol fiber,the water absorption and thermal conductivity first decreases and then increases with the increase of fiber and dosage,and first decreases and then increases with the increases of fiber length.The variation of softening coefficient is opposite to the change in water absorption rate.Polypropylene fiber aerogel concrete has low water absorption and good water resistance.The lowest thermal conductivity of polyvinyl alcohol fiber aerogel concrete is 0.786W/(m·K)and 1.056W/(m·K)under dry and saturated conditions,respectively.(3)The influence of fiber on flexural strength and compressive strength of aerogel concrete was investigated.The flexural strength of fiber aerogel concrete increases with the increase of fiber length and dosage of glass fiber and polyvinyl alcohol.With the increase of the length of basalt fiber and polypropylene fiber,flexural strength increases first and then decreases with the increase of fiber content.Among them,polypropylene fiber has the best improvement effect on flexural strength of aerogel concrete.The compressive strength of aerogel concrete increases gradually with the increase of fiber length,and first increases and then decreases with the increase of fiber content.After adding 9mm and 0.6% polypropylene fiber,the aerogel concrete strength has the best lifting effect and the highest 28 d compressive strength is 35.6MPa.SEM scanning electron microscopy showed that there were a lot of hydration products on the surface of hydrophilic fibers.(4)The polyvinyl alcohol fiber aerogel concrete is preferred,and the aerogel content was changed(0～60%)to explore the performance changes of aerogel concrete under the optimal fiber content.With the increase of the aerogel content,the consistency value of the fiber aerogel concrete mixture increases by 21.1%～97.7%.Water absorption increases1.6 ～11.6 times.But the apparent density and softening coefficient decreases gradually.The thermal conductivity decreases sharply with the increase of aerogel content,and the lowest thermal conductivity is 0.407W/(m·K)and 0.226W/(m·K)under saturated and dry conditions,respectively.The strength of the material decreases with the increase of aerogel content.When the aerogel content increases to 60%,the flexural strength decreases by 71.5% and the compressive strength decreases by 76.9%.The analysis of microstructure shows that with the increase of aerogel content,the number of pores in fiber aerogel concrete gradually increases,and the pore size becomes smaller and smaller,which leads to the decrease of mechanical properties and the increase of thermal insulation.When adding 0.6%,9mm long polyvinyl alcohol fiber,50% aerogels,the compressive strength meets the minimum strength(C20)requirements of concrete used for retaining wall in the code,and the thermal conductivity is much lower than that of ordinary concrete.(5)The mechanical properties and thermal conductivity of fiber aerogel concrete were predicted based on ensemble learning.Four models were selected,namely RF,GBDT,XGBoost and LGBM.It was found that GBDT model had the best prediction effect on flexural strength and compressive strength,and RF model had the best prediction effect on thermal conductivity.