Experimental Research On Mechanical Properties Of Sea Sand Cementitious Composite Material After High Temperature

Due to the shortage of river sand resources and the long distance transportation to increase the project cost,people in recent years had to turn their more attention to sea sand.The sea sand contains a lot of chloride salts,and chloride ions can reduce the durability of structures.At the same time,the fire is one of the disasters that harms the building structure,even it can endanger the lives and belongings safety.Therefore,it has theoretical and practical significance to study and improve the performance of sea sand cementitious composite materials.In this thesis,sea sand cementitious composite materials are the research object,polypropylene fibers,alkali-resistant glass fibers and mixed fibers are added to the composites to study the effects of chloride ion concentration and fiber on the mechanical properties of cement-based composites after high temperature.And it is used to provide reference for the more extensive research and application of the sea sand building structure in the future.In this thesis,the effects of cement-sand ratio and chloride ions concentration on the mechanical properties of cementitious composite materials at different curing ages were studied.After that,the optimal cement-sand ratio was selected,and the fibers were added to the specimens,the effects of fibers on the mechanical properties of the specimens were researched.Finally,the high temperature tests were designed at four temperatures of 200?,400?,600? and 800?,the flexural strength and compressive strength of the specimens after the different cooling methods were tested.The results showed that the chloride salt had obvious early strong effect,but this enhancement was gradually weakened with the increase of the curing age.At room temperature,the polypropylene fibers could make the mechanical properties down,but alkali-resistant glass fibers and mixed fibers could increase the mechanical properties to varying degrees.The flexural strength and compressive strength of the specimens were decreased after the high temperature,but the compressive strength of certain specimens was weakly increased at 200?.The mechanical properties of specimens which had chloride salts were lower than the chlorine-free salt specimens after the high temperature.As the temperature stress of the specimens increased for the water immersion cooling,in most cases mechanical properties of the natural cooling specimens were higher after high temperature.According to the vapor pressure theory and the results of test,the polypropylene fibers could effectively improve the anti-bursting performance of the specimens at high temperature and increase the residual flexural strength and compressive strength of the specimens after high temperature.The alkali-resistant glass fibers did not improve the compressive strength of the specimens after high temperature,the overall improvement effects of mixed fibers on the mechanical properties of the specimens were good after high temperature,indicating that the two kinds of fiber could take the role with each other.