Experimental Study On Mechanical Properties Of Rice-Husk-Ash And Rubber Fiber Concrete Under Hygrothermal Environment

In this paper,rice husk ash and rubber particles were prepared by processing waste rice husk and waste rubber tires.Rice husk ash was used to replace cement with equal mass,rubber particles were used to replace sand with equal volume,and toughening material PVA fiber was added to prepare rice husk ash-rubber-fiber concrete（RRFC）.The properties of concrete materials were optimized,and the durability and fatigue resistance of concrete under the influence of multiple factors such as hygrothermal environment,chloride salt erosion and cyclic load were studied.Taking the particle size of rubber particles（factor A）,the content of rice husk ash（factor B）and the content of PVA fiber（factor C）as the test factors,three levels of each factor were set up,and the orthogonal test of three factors and three levels was designed.Based on the static mechanical properties,the optimal ratio was selected,and the dry-wet cycle test and cyclic loading-unloading test were carried out under two solutions at different temperatures.The main research contents include:（1）The results of orthogonal test show that the best mix proportion of RRFC is A2B2C3,and the comprehensive performance is better than other mix proportions,namely the rubber particle size（factor A）is 1-2mm,PVA fiber content（factor B）is1.2kg.m^-3,rice husk ash content（factor C）is 15%.（2）Through the dry-wet cycle test under different environments,it can be seen that the compressive strength of the specimens under dry-wet cycles in different environments generally increases first and then decreases.The compressive strength of the specimens under the chloride solution is lower than that of the clear water solution,and the higher the solution temperature,the more serious the damage of the specimens.（3）Through the constant amplitude cyclic loading-unloading test,it can be seen that the axial peak and residual strain of RRFC specimens increase continuously in the process of repeated loading-unloading,and the increase of axial peak and residual strain in the first 5 cycles is the most obvious.The fatigue failure strength of specimens decreased and gradually stabilized.Compared with RRFC specimens in aqueous solution,the fatigue damage of specimens in chloride solution is more serious,and the fatigue resistance coefficient is lower and its variation is larger.The higher the temperature,the smaller the fatigue resistance coefficient of the RRFC specimen,which is more likely to cause internal fatigue damage of the specimen.（4）Microscopic mechanism analysis shows that the large specific surface area of rice husk ash optimizes the grain composition of RRFC specimens and exerts the filling effect.At the same time,a large amount of highly active Si O₂in rice husk ash reacts with Ca（OH）₂to form C—S—H gel,which improves the density of concrete,reduces the concentration of Ca²⁺,promotes the hydration reaction of cement and makes the whole specimen form a dense structure.The excellent ductility of rubber particles effectively alleviates the damage caused by repeated loading and unloading during cyclic loading and unloading,optimizes the internal stress redistribution of the specimen,and makes RRFC exhibit excellent fatigue resistance.PVA fibers form a random three-dimensional space grid in RRFC specimens,which effectively hinders the migration channel and crack development of chloride ions,prevents the floating of rubber particles,and improves the mechanical properties and fatigue resistance of specimens.