Study On Properties Of Concrete With Waste Glass After Exposure To Elevated Temperatures

With the improvement of the living standard of people,the rapid pace of urbanization in China,as well as a variety of buildings are emerging.This has led to an increasing consumption of concrete and a greater demand for sand,gravel and cement,the basic materials of concrete.Therefore,in order to alleviate the various environmental problems that may be caused by the vigorous exploitation of natural resources,waste glass has begun to be recycled as an effective alternative.It not only solves the pollution problem of waste glass,but also relieves the scarcity of natural resources and achieves a sustainable development process.Many scholars both domestic and foreign have concentrated on the normal temperature performance of waste glass concrete,however,little has been done to discuss the elevated temperature performance of waste glass concrete.Therefore,in this study,two types of recycled glass concrete（RGC）were produced using different replacement ratios of crushed glass（CG）and glass powder（GP）to replace coarse and fine aggregates in concrete,respectively:crushed glass concrete（CGC）and glass powder concrete（GPC）.The performance changes of these RGC were investigated at temperatures from 0 to 600°C,containing the mixture of concrete properties in terms of workability,mass loss rate,water content,water sorptivity rate,residual compressive strength and splitting tensile strength,and the microstructure of RGCs after elevated temperatures was observed using Scanning Electron Micrographs（SEM）.The main conclusions were drawn as follows:（1）For the workability,there is no remarkable difference between CGC and control concrete（CC）.In contrast,GPC has better flowability and better workability than CC due to the characteristics of GP with low water absorption and smaller particle size than sand particles.For the appearance changes,the surface color of RGC as a whole shows a process of change from bright to dark to bright as the temperature increases,while more and more holes and cracks appear on the surface of the specimens;（2）As a whole,the mass loss rate of RGC kept the same change trend with CC,increasing with the increase of temperature.It is noteworthy that the mass loss rate of CGC decreases with the increase of CG under the high temperature of 600°C,while the mass loss rate of GPC increases with the increase of GP.The water absorption and water sorptivity rate of GP and CG are always lower than those of CC during the entire warming process due to their features such as impermeability and strong resistance to water penetration;（3）At room temperature,the residual compressive strength of GPC was greater than that of CC,while CGC was lower than that of CC.As the temperature increased,the residual compressive strength of RGC showed a trend of first increasing and then decreasing.The peak of residual compressive strength was attained at 150°C,and compared with CC,CGC and GPC increased by 3.76%～5.05%and 5.52%～5.85%,respectively.When the temperature reaches 450°C,it can be clearly found that the increase of CG and GP content can enhance the residual compressive strength of concrete,and this beneficial effect is more significant at 600°C;（4）The splitting tensile strength of RGC both decreased continuously with the increase of temperature,in which the loss of splitting tensile strength was most obvious in the interval from 300°C to 450°C,up to 38%.When the temperature is up to 600°C,the splitting tensile strength values of both CGC and GPC are higher than those of CC,and increase with the increase of the percentage of replacement,which is the same as the pattern of compressive strength;（5）The excellent high-temperature performance of GPC is derived from the pozzolanic reaction of GP by SEM analysis.This activity is gradually excited with the increase of temperature and reacts with Ca（OH）₂in the matrix to generate more calcium-silicate-Hydrate（C-S-H）gel,which enhances the internal structure of GPC and prevents the thermal decomposition of some Ca（OH）₂,reducing the damages of GPC at elevated temperatures.Meanwhile,CG is not decomposed under high temperature like limestone,which can greatly reduce the volume expansion and slow down the damage of concrete structure by elevated temperature to some extent.