Study On Dynamic Mechanical Properties Of Cement Mortar Mixed With Fly Ash And Slag After High Temperature

With the acceleration of urbanization in China,concrete structure buildings have sprung up,accompanied by fire and explosion accidents from time to time,greatly reduces structural safety.In combination with China’s"carbon peak,carbon neutral"development goal,in order to reduce CO₂ emissions from cement production and use,common industrial wastes such as fly ash and slag are selected to replace cement.While protecting the environment and reducing the cost of cement-based materials,it can also ensure the dynamic mechanical properties of cement-based materials after high temperatures and improve the structural fire resistance.In this paper,fly ash and slag were used to replace 40%cement content,in which slag content is 0,10%,20%,30%and 40%respectively.The cement mortar specimens of each group were treated at 25℃,100℃,200℃,400℃and 600℃respectively.The dynamic compression and dynamic splitting tensile tests were conducted usingφ50mm separated SHPB device,and the impact pressure was 0.3MPa,0.4MPa and 0.5MPa,respectively.The variation of dynamic compressive strength,dynamic splitting strength,peak strain,and strain rate of cement mortar under the coupling effects of fly ash and slag content,processing temperature,and impact air pressure was studied,as well as the fracture morphological characteristics of specimens,the energy dissipation under dynamic splitting tension is analyzed.The main research contents and conclusions are as follows:（1）Test the static compressive strength of cement mortar with double fly ash slag at room temperature for 3,7,and 28 days.Combined with the dynamic compressive strength analysis for 28 days,the static and dynamic compressive strength of mortar increases with the increase of slag content.The mortar DIF of the test group was greater than that of the control group under the same impact air pressure,and the relationship between DIF and strain rate satisfied a logarithmic function.（2）Dynamic compression tests were conducted on five groups of mortars mixed with different amounts of slag and the control group mortars under different treatment temperatures and different impact pressures.Based on the dynamic compression stress-strain curve,the changes in various dynamic performance parameters were analyzed.Under different working conditions,each group of mortar has a significant strain rate effect.Under the same impact air pressure,the dynamic compressive strength of mortar shows a trend of first increasing and then decreasing with the increase of temperature,with 100℃being a turning point;The peak strain and strain rate increase continuously with the increase of temperature,and the high-temperature softening effect of mortar is stronger than the strain rate effect.The more slag,the better the dynamic mechanical properties of mortar under the same conditions.The dynamic compression crushing morphology is significantly affected by various variables.The higher the processing temperature,the greater the impact pressure,and the less slag content,the more serious the mortar damage.（3）Select mortar mixed with 30-40%slag and control group,and conduct dynamic splitting tensile tests under different impact pressures after being treated at different temperatures.Analyze the energy dissipation of each group of mortar.The dynamic fracturing performance parameters of mortar vary in a similar manner to those under dynamic compression.There is a good linear relationship between incident energy and impact pressure,and the incident energy is not affected by processing temperature changes.The greater the impact air pressure,the greater the strain rate and incident energy,resulting in a continuous increase in dynamic splitting strength.When the temperature exceeds 100℃,both the absorption energy and the energy absorption rate decrease with the increase of temperature.There are also temperature and strain rate effects in the dynamic fracturing failure patterns of mortar.The higher the temperature and strain rate,the larger the number of fragments and the smaller the volume after mortar crushing.From the comprehensive consideration of mechanical properties and resource recycling,adding 10%fly ash and 30%slag is the optimal mixing ratio.Figure 48 Table 17 Reference 82...