Research On Mechanical Properties Of Hybrid Fiber Concrete Under Seawater Freeze-thaw Erosion

When concrete materials are used in harsh environments,the durability of concrete materials is becoming increasingly prominent.For the concrete structures in roads,bridges,hydraulics,port engineering and other projects in cold areas,the problem of insufficient durability is mainly due to insufficient resistance to frost and salt corrosion.With the rapid development of fiber materials,the research on high-performance fiber concrete is becoming more and more extensive and in-depth.Under this background and based on the excellent physical and chemical properties of polyvinyl alcohol fiber（PVA）and nano-SiO₂,the basic mechanical properties and freeze-resistant durability of PVA-nano-SiO₂hybrid fiber concrete were explored,and the corresponding freeze-thaw cycle values simulation.The main contents and related achievements of the research in this article are as follows:（1）For C（control group）,P（0.1%PVA）,S（1%nano-SiO₂）,SP1（0.1%PVA and 0.5%nano-SiO₂）,SP2（0.1%PVA and 1.0%nano-SiO₂）,SP3（0.1%PVA and1.5%nano-SiO₂）concrete test group conducts experimental research on the working performance,compressive strength and flexural strength of concrete.Through the test data,it is found that the SP2 test group doped with 0.1%PVA and 1.0%nano-SiO₂has the best compressive and flexural strength improvement effects,which are increased by 11.62%and 16.64%,respectively.（2）Combined with previous researches,the mechanism of PVA fiber and nano-SiO₂on the compression and flexural strength of concrete was analyzed.PVA fiber is mainly explained from the theory of composite materials and fiber spacing,while nano-SiO₂mainly explains its reinforcement mechanism from the aspects of hydration reaction catalytic mechanism and optimization of interface transition zone.（3）The seawater freeze-thaw failure mechanism of PVA and nano-SiO₂concrete is explained from two aspects:freeze-thaw failure is a kind of temperature fatigue failure,internal stress changes with temperature,continuous loading and unloading inside the matrix;salt in seawater The chemical corrosion of cement on the matrix.（4）Through the rapid freeze-thaw cycle test of seawater,the freeze-thaw appearance damage form,quality loss,relative dynamic elastic modulus,and compressive strength evaluation indexes were evaluated.The test found that SP2 with0.1%PVA and 1.0%nano-SiO₂test group had the best frost resistance.After the freeze-thaw cycle,the relative dynamic elastic modulus and compressive strength residual ratio were 70.28%and 77.29%,respectively.It is also found that the quality loss evaluation index is not sensitive to the fiber concrete in this test,and the pros and cons of the freeze resistance of each test group cannot be evaluated.（5）The ABAQUS finite element software was used to simulate the freezing and thawing cycle of the control group C and SP2 concrete,respectively.The temperature field,thermal stress field and compressive strength after freezing and thawing are numerically simulated,and the numerical simulation results are compared with the test,and the error is within 15%.The simulation results are consistent with the test results as a whole.If the SP2 concrete material is further used on the bridge pier in a freeze-thaw environment,the seismic performance of the pier column needs to be clear,therefore,the seismic performance simulation and analysis of ordinary reinforced concrete pier column C（control group）and reinforced fiber concrete pier column SP2（doped with 0.1%PVA and 1.0%nano-SiO₂）after 50 freeze-thaw cycles.The simulation results of seismic performance show that the hysteresis curve area of SP2 pier column is larger than that of C pier column,and the maximum bearing capacity of C and SP2 pier columns are 103.43KN and 119.94KN,respectively,so SP2 reinforced fiber reinforced concrete pier columns have better seismic performance.