Experimental Study On The Impermeability Of Multi-scale Polypropylene Fiber Concrete

Impermeability is an important indicator of concrete materials.Many projects often do not reach the design service life due to the infiltration of concrete structures and cause significant economic losses.The impermeability of ordinary concrete is difficult to meet the requirements of strength,applicability and durability of the structure of modern civil engineering under special environmental conditions.Previous studies have shown that the proper amount of fiber in the cement matrix can improve the impermeability of concrete and improve the durability of concrete components.In this paper,three different sizes of polypropylene fibers are mixed into concrete specimens(called multi-size polypropylene fiber concrete)in a certain proportion,and through macroscopic and mesoscopic tests and theoretical analysis,the penetration of fibers and loads on concrete is studied.The law of influence reveals the impermeability mechanism of multi-sized polypropylene fiber concrete.Finally,the prediction model of concrete impermeability was established by using regression analysis of support vector machine.The main research contents and results are as follows:1.Through the test of compressive strength and impermeability of polypropylene fiber reinforced concrete,the effect of fiber on compressive strength and impermeability of concrete was obtained.The results show that: polypropylene fiber can improve the compressive strength and impermeability of concrete;blended thick fiber has better anti-permeability performance than single fiber,and when the total fiber content is the same,the proportion of fine fiber is more.It is beneficial to improve the impermeability of concrete;the multi-size polypropylene fiber concrete has the best impermeability;the strength of polypropylene fiber concrete has a linear function with the logarithm of its permeability coefficient.2.Through the chloride ion permeability test and capillary water absorption test of polypropylene fiber concrete,the effects of factors such as fiber and load on chloride ion diffusion coefficient and capillary water absorption were obtained.The results show that the chloride ion diffusion coefficient and the capillary water absorption of the concrete generally increase with the increase of the load.The stress ratio(the ratio of the load to the ultimate compressive strength)of some specimens is between 0.6-0.8,and the critical stress phenomenon appears;The impermeability of fine fiber is better than that of coarse fiber under the stress level.When the load level exceeds the critical stress,the effect of coarse fiber is more obvious.The impermeability of mixed fiber reinforced concrete is better than that of single fiber reinforced concrete under different stress levels.However,the anti-seepage effect of multi-size polypropylene fiber concrete still performed best.After the unloading,the concrete cracks are closed,and the degree of crack closure is related to the holding time.After the unloading,the permeability of the concrete is lower than that of the load.When the load is 120 minutes and the stress ratio is 0.8,the capillary water absorption after unloading takes up the load.90% or so.3.Through fiber-reinforced concrete NMR and mercury intrusion tests,the effect of fiber and load on the pore structure of concrete was obtained.The results show that the incorporation of fibers can reduce the most probable pore size,critical pore diameter and the proportion of detrimental pores;the mixed fibers have better effect on pore structure than single-doped fibers,multi-size polypropylene fiber concrete has the best pore structure,and the concrete can be the most The pore diameter,critical pore diameter and the proportion of harmful pores increase with the increase of load;when the stress ratio is 0.8,the critical pore size of plain concrete reaches the harmful pore size range,and the proportion of harmful pores is the highest;the incorporation of fiber can relieve the load on the concrete pores.Destruction of the structure,the coarse fibers inhibit the macropores better than the fine fibers,the fine fibers inhibit the micropores better than the coarse fibers,and the multi-sized polypropylene fibers have the best effect on the improvement of the pore structure of the concrete.4.Based on the results of impermeability test,combined with nuclear magnetic resonance,mercury intrusion,and electron microscope scanning tests,the impermeability mechanism of fiber reinforced concrete was obtained.The results show that: after the fiber is incorporated into the concrete,the pore structure of the matrix is improved,the connectivity of the matrix and the proportion of harmful pores are significantly reduced,the toughening and cracking resistance performance is improved,the damage degree of the pore structure of the concrete is alleviated,and the suppression of the micro-pores by the fine fibers is alleviated.The effect is more significant,and the inhibition of macroporous cracks by coarse fibers is greater than that of fine fibers,and there is no definite working area boundary between coarse and fine fibers.Fibers of different sizes can complement each other and act synergistically,inhibiting the generation and development of pores of different diameters and pores at different times,and improving the impermeability of concrete.5.The support vector machine analysis method can use the fiber concrete impermeability test data to establish a multi-factor predictive model of complex nonlinear relationships.The model has high prediction accuracy and good generalization ability.It has been verified that by training the unloaded test data,the impermeability at the time of loading can be predicted more accurately.