Experimental Study On Mechanical Properties And Durability Of Silica Fume-Glass Fiber Lightweight Aggregate Concrete

The use of industrial waste to replace part of cement to prepare concrete is a sustainable liberation scheme to reduce the exploitation of natural resources and alleviate the pressure on the environment.My country is a big producer of ferrosilicon and industrial silicon.Ferrosilicon production enterprises are mainly concentrated in the underdeveloped northwest provinces,with Inner Mongolia in the first place.The excess production of industrial waste silica fume can not be used reasonably,which is not only wasteful,but also pollutes the local environment.In this thesis,the natural pumice widely distributed in Inner Mongolia is used as the coarse aggregate of lightweight aggregate concrete.Glass fiber and industrial waste silica fume were mixed into lightweight aggregate concrete to prepare silica fume-glass fiber lightweight aggregate concrete.The effects of both on the properties of lightweight aggregate concrete are discussed from the aspects of macroscopic mechanical properties,frost resistance durability,micro pore structure and micro morphology.The main research results are as follows:1.The single addition of silica fume or glass fiber improves the compressive strength and splitting tensile strength of lightweight aggregate concrete in different degrees.The addition of silica fume and glass fiber can significantly improve its mechanical properties.When the content of glass fiber is 0.3kg/m³～0.9kg/m³,the compressive strength and splitting tensile strength first increase and then decrease with the increase of silica fume replacement rate.When the fiber content is 0.6kg/m³ and the silica fume substitution rate is 6%（G0.6S6）,the compressive strength and splitting tensile strength are the largest,which are respectively increased by 21.89%and 53.54%compared with the reference group（G0S0）.Compared with the compressive strength,the synergistic effect of them is more significant in improving the splitting tensile strength and toughness.2.The active effect of silica fume and the filling effect of microaggregate can effectively improve the interfacial transition zone between cement matrix and glass fiber and pumice aggregate,and enhance the interfacial bonding properties.The toughening and crack resistance of glass fiber has been significantly improved,and the utilization efficiency of glass fiber has been effectively improved.At the same time,enhance the strength of pumice aggregate.3.The coupling of silica fume and glass fiber can refine the microscopic pore structure and optimize the pore size distribution of lightweight aggregate concrete.The pore structure of silica fume-fiber lightweight aggregate concrete has obvious multifractal characteristics.The fractal dimensions D₂,D₃ and D₄ respectively reflect the complexity of the pore structure with different pore sizes.There are significant differences in the fractal dimension of each fractal region.The increase of the silica fume substitution rate has a greater impact on the range of change in the fractal dimension D₂,but has less impact on the fractal dimensions D₃ and D₄.At the same time,there is a good correlation between fractal dimensions D₂,D₃ and D₄ and pore characteristic parameters.4.Through the analysis of grey relational entropy,it is found that the main factors affecting the compressive strength of silica fume-glass fiber lightweight aggregate concrete are bound fluid saturation and fractal dimension D₃.On this basis,the prediction model of NSGM（1,3）compressive strength is established.The average relative error between the experimental value and the simulated value and the predicted value is 2.024%and 0.775%respectively,which has high prediction accuracy.5.When the content of glass fiber is 0.6kg/m³ and the substitution rate of silica fume is 6%～9%（G0.6S6,G0.6S9）,the frost resistance is improved obviously.The coupling of silica fume and glass fiber can slow down the pore growth and expansion and reduce the pore connectivity of lightweight aggregate concrete during freeze-thaw cycle,and delay the process of freeze-thaw breakage.The freeze-thaw damage model of Weibull probability distribution was established.6.Under the action of freeze-thaw cycle,the fractal dimensions D₂ and D₃ decrease in different degrees,while the fractal dimension D₄ has no obvious change law and the change range is small.The changing range of fractal dimensions D₂ and D₃ can characterize the damage degree of internal pore structure of concrete to some extent.The greater the variation range of fractal dimensions D₂ and D₃,the more serious the damage degree of internal pore structure.