Study On High Temperature Mechanical Properties Of Fiber Modified Lightweight Aggregate Concrete

Now green low carbon has become the leading direction of the development of China's construction industry,building material is one of the main components of green building,and the traditional concrete accounts for the major part of building materials.Comparing with the traditional concrete which consumes much energy and destroys environment,the lightweight aggregate concrete has the advantages of light weight,high resistance,good fire resistance and good insulation.It not only is a kind of green environmental protection material,but also can reduce the damage to the environment.In recent years,number of fire accidents rise,and that accident damaged materials after high-temperature performance decline in frequent fire accidents is one of the main factors of building structure damage of concrete materials,so one of the main measures in the construction structure of fire rescue is to developed new type concrete material with high temperature resistance.Most lightweight aggregate(such as shale,pumice,perlite,clay ceramsite etc.)is formed by volcanic eruption or artificial high temperature calcinations,so it has a high temperature resistance.Because of the small application of lightweight aggregate concrete in our country,there is a large space for the development of lightweight aggregate.High moisture content of lightweight aggregate concrete which is attributed to lightweight aggregate concrete preparation process and high porosity of light aggregate increases the possibility of the burst of lightweight aggregate concrete at high temperature,and lightweight aggregate concrete has low strength and brittle failure.In view of the above reasons,development and application of lightweight aggregate concrete are restricted.Considering defects of lightweight aggregate concrete,shale ceramsite with high compressive strength and low porosity was used as coarse aggregate in this paper to ensure the strength of lightweight aggregate concrete and reduce the moisture content.High tensile strength and high temperature resistance of basalt fiber,and polypropylene fiber which has light weight and good elasticity were added into lightweight aggregate concrete,the effects on the mechanical properties of lightweight aggregate concrete at room temperature and high temperature of two kinds of fibers were studied in detail in this paper.High temperature image acquisition system took the apparent image of specimen in the high temperature,then the apparent strain was calculated by the digital image correlation method.After data was processed and analysised,the deformation rule of the specimen heated at high temperature was studied macroscopically.The results are as follows.(1)The effect of polypropylene fiber on the toughness of lightweight aggregate concrete is better than that of basalt fiber,and the effect of basalt fiber on the compressive strength,splitting tensile strength and flexural strength of lightweight aggregate concrete is obvious.When content of polypropylene fiber in hybrid fiber is 0.15%,the failure characteristics of hybrid fiber lightweight aggregate concrete specimens are consistent with those of polypropylene fiber reinforced lightweight aggregate concrete.The effect on the compressive strength,splitting tensile strength and flexural strength of lightweight aggregate concrete of hybrid fiber is not obvious.(2)From room temperature to 300?,the compressive strength of each type of lightweight aggregate concrete doesn't change obviously,and the tensile strength decreases with the increase of temperature.At 400?-900?,only one plain light aggregate concrete specimen bursts,which proves that the concrete using shale ceramsite as coarse aggregate has good heat resistance.At 100?-500?,the strength decay rate of polypropylene fiber reinforced lightweight aggregate concrete is slower.At 500?-900?,the residual strength of basalt fiber reinforced concrete is higher than that of polypropylene fiber lightweight aggregate concrete and plain lightweight aggregate concrete.At 100?-900?,the strength decay rate of hybrid fiber reinforced lightweight aggregate concrete is the slowest.(3)At the same time,digital image correlation method and resistance strain gauge were used to measure the elastic modulus of lightweight aggregate concrete at room temperature.The two elastic modulus values which were calculated by two methods are in the same order of magnitude and have similar numberical size.The high temperature image acquisition system took images of specimen in high temperature,then digital image correlation method was used to calculate test images.At the end,real-time strain of the specimen is obtained.In this paper,the lowest strength of fiber reinforced lightweight aggregate concrete which has high temperature resistance is LC30,so it can be applied to the main body structure with high fire resistance requirements.That elastic modulus and strain at high temperature of concrete were measured successfully by digital image correlation method has a certain degree of innovation and practical value.