Mechanical Properties And Microstructure Of Ultra-high-performance Concrete With Recycled Glasses After Exposure To Elevated Temperatures

Waste glasses(RG)are common solid waste which is very difficult to be degraded naturally.Recycling and utilizing it is good for economic development and environmental protection.At present,concrete with RG,which has widely application prospects,has become the hot research spot in international engineering materials,and it has been applied in the field of traffic engineering.However,there are many studies focused on its mechanical performances at room temperature and few studies on its properties after high temperatures.Based on the study of high-temperature behavior of concrete with RG,the experimental studies were performed on the high-temperature explosive spalling of ultra-high-performance concrete(UHPC)with RG(GUHPC),mechanical properties,microstructure and phase transformation of GUHPC after high temperatures.The main work and results are as follows:The explosive spalling of GUHPC is related to the particle diameter of RG and size of specimens,but not to the composition of RG.With the decrease of the size of RG particles and specimens,the probability of spalling decreased.The critical RG particle size of GUHPC for spalling was 0.15 mm and mixing with RG of 0.08 mm could prevent spalling.The explosive spalling of GUHPC can be attributed to the combined effects of vapor pressure,thermal stress and incompatibility between RG and the matrix.After high temperature test,experiments of compressive and flexural strength of UHPC with different particle sizes or composition RG were performed.The compressive strength and failure modes were not influenced by the composition of RG.After 800 ℃,the failure mode of UHPC with RG was better than that of UHPC without RG.With the increase of temperature,the compressive and flexural strength of GUHPC increased first and then decreased,and the critical temperature was 200 ℃.When the temperature was below 800 ℃,compressive and flexural strength of GUHPC increased as the particle size of mixed RG decreased.After 800 ℃,however,the particle diameter of RG had no significant influence on the strength of GUHPC,and the strength of UHPC with RG was significantly higher than that of UHPC without RG.With the purpose of further researching the effect of RG on high-temperature properties of GUHPC,the residual strength retention and high-temperature reinforcing coefficient of GUHPC were studied and relevant formulas were proposed.The RG powder can improve the high-temperature mechanical properties of GUHPC,especially for 200 ℃and 800 ℃.The experiments of SEM,XRD,and TG–DSC were performed.And the results indicated that the RG powder could improve microstructure of GUHPC due to its pozzolanic activities.In addition,the RG powder could catalyze the pozzolanicreaction of GUHPC,and then strengthen the bonding interface between RG particles and the matrix and improve the shape of hydration products.After 800 ℃,the microstructure of UHPC with RG was more dense than that of UHPC without RG because of pretty heat stability of the glass.Moreover,the mass loss of UHPC without RG at elevated temperatures was higher than that of UHPC with RG.TG–DSC test results suggested that the rate of heat flow of GUHPC was low,which was easy to form temperature gradient and then increased the risk of explosive spalling.