Experimental Study On Durability Of Basalt Fiber Reinforced Concrete Under Compound Salt Erosion

Saline soils in southern Xinjiang are widely distributed,with dry climate and large temperature difference between day and night.Soil and underground（surface）water contain a large amount of high concentrations of corrosive ions such as SO₄^2-,Cl^-,Mg²⁺,resulting in many concrete projects in this area suffering from long-term The combined effect of compound salt erosion,freeze-thaw cycle,and dry-wet alternation results in different degrees of corrosion damage to the structure.Basalt fiber,as a new type of green and environmentally friendly fiber material,can effectively improve the mechanical properties and durability of concrete when mixed into concrete.Therefore,the effect of basalt fiber content on the basic mechanical properties of early-age concrete,the coupling effect of compound salt erosion and dry-wet cycle,and the corrosion and deterioration mechanism of basalt fiber concrete under the coupling action of compound salt erosion and freeze-thaw cycle are studied to solve this problem.The durability and disease problems of regional engineering structural concrete have important theoretical and engineering application value.The main findings of this study are as follows:（1）By carrying out the macroscopic mechanical properties of basalt fiber reinforced concrete specimens with different volume dosages（0%,0.1%,0.2%,0.3%,0.4%,0.5%）at different curing ages（3d,7d,28d）Test and microstructure analysis（SEM image）,analyze the distribution characteristics of basalt fibers in concrete,and determine the optimal amount of basalt fibers to improve the early mechanical properties of concrete.The test results show that the incorporation of basalt fiber can effectively improve the early mechanical properties of concrete.The corresponding strength increases of the specimens with 0%fiber content are 23.31%and 34.78%,respectively.When the content of basalt fiber is 0.4%,the improvement effect of concrete flexural strength is the best,and the flexural strength of concrete specimens with 0%content is increased by 12.62%.However,the mechanical properties of the basalt fiber reinforced concrete specimens decreased to varying degrees with the gradual increase of the dosage,indicating that the more the dosage of fibers in the concrete,the better.At the same time,through the SEM scanning electron microscope image observation,it can be seen that the"bridging"effect of the basalt fibers prevents the expansion of micro-cracks in the concrete.When subjected to external loads,the fibers and the cement matrix are jointly stressed.As the load gradually increases,the basalt The fibers are pulled off or pulled out,and the concrete specimen fails immediately.（2）The apparent morphology of basalt fiber reinforced concrete specimens with different dosages（0%,0.1%,0.2%,0.3%）reaching the specified composite salt erosion-dry-wet cycle and composite salt erosion-freeze-thaw cycle times was observed.Mass and dynamic elastic modulus measurement,the relative dynamic elastic modulus and mass loss rate are two indicators to reflect the change law of macroscopic durability performance of concrete specimens.The results show that the addition of basalt fiber can improve the ability of concrete to resist compound salt erosion.When the fiber content is 0.3%,the curve of relative dynamic elastic modulus and mass loss rate of the specimen changes the most stable.（3）Using SEM（scanning electron microscope）,EDS energy spectrum and XRD diffraction to analyze the microscopic morphology and composition of the corrosion products of the composite salt erosion-dry-wet cycle,composite salt erosion-freeze-thaw cycle test,it is concluded that the corrosion of basalt fiber concrete is The products are mostly ettringite（AFt）and gypsum,and with the addition of basalt fiber,the generation of ettringite and gypsum gradually decreases.Adding basalt fiber can reduce the consumption rate of Ca（OH）₂on the surface and inside of concrete.Therefore,the incorporation of basalt fibers can inhibit the formation rate and quantity of corrosion products inside the concrete.（4）Under the combined action of composite salt erosion and dry-wet cycles,the corrosion products（ettringite,gypsum）of the basalt fiber reinforced concrete specimens gradually grow in the internal micro-cracks and spread around the cracks.The expansion pressure generated by the corrosion products leads to the continuous deepening and widening of the original cracks,and at the same time,it causes many new micro-cracks,which makes the compound salt solution more likely to further penetrate into the concrete and cause corrosion damage.Under the action of composite salt erosion-freeze-thaw cycle,the test piece is mainly due to the infiltration of composite salt solution,which causes"frost heave"under the action of freeze-thaw cycle,which destroys the capillary pipes inside the concrete,causing salt frost heave cracking in the concrete and causing structural damage.damage.The damage and destruction of concrete under compound salt erosion is a long-term slow process.Corrosive ions in the solution play a role in interacting with each other inside the concrete,and the damage caused is mainly chemical corrosion damage and salt crystal physical damage.