高温作用下碳纤维增强混凝土内部孔隙结构与动态力学特性研究

Study on internal pore structure and dynamic mechanical properties of carbon fiber reinforced concrete under high temperature

为研究不同长度(0 mm、3 mm、6 mm、12 mm)碳纤维增强混凝土在高温(25℃、100℃、200℃、400℃)作用下内部孔隙结构变化及动态力学特性,采用核磁共振(NMR)技术分析试件T谱分布及孔隙率变化情况,并利用霍普金森压杆对不同高温作用下混凝土试件开展动态单轴冲击压缩试验,分析碳纤维长度、温度对混凝土动态力学性能的影响。结果表明:纤维长度为6 mm时对混凝土增强效果最好,温度升高会减小试件的强度和质量;碳纤维增强混凝土T谱曲线为双峰型,纤维长度为0 mm时试件T谱峰值最大,孔隙数量最多,纤维长度为6 mm时峰值最低,纤维的掺入能有效减少孔隙数目;随着温度的升高,T谱峰值增高,试件内部孔隙数目随之增加,孔隙率变大,温度效应造成了试件的劣化;碳纤维的掺入能增强试件动态抗压强度,有效减小极限应变,温度的上升会对碳纤维增强混凝土造成损伤,降低其动态抗压强度与应变率效应,DIF随之降低。

In order to study the changes of internal pore structure and dynamic mechanical properties of carbon fiber reinforced concrete with different lengths(0 mm,3 mm,6 mm and 12 mm)under high temperature(25℃,100℃,200℃and 400℃),the Tspectrum distribution,pore diameter and porosity of the specimen were analyzed by nuclear magnetic resonance(NMR),the dynamic uniaxial impact compression tests of concrete specimens under different high temperatures are carried out by using Hopkinson compression bar,and the effects of carbon fiber length and temperature on the dynamic mechanical properties of concrete are analyzed.The results show that when the fiber length is 6 mm,the reinforcement effect of concrete is the best,and the increase of temperature will reduce the strength and quality of specimens.The Tspectrum curve of carbon fiber reinforced concrete is bimodal.When the fiber length is 0 mm,the Tspectrum peak value of the specimen is the largest,the number of pores is the largest,and the peak value is the lowest when the fiber length is 6 mm.The addition of fiber can effectively reduce the number of pores.With the increase of temperature,the peak value of Tspectrum increases,the number of pores in the specimen increases,the porosity increases,and the temperature effect causes the deterioration of the specimen.The addition of carbon fiber can enhance the dynamic compressive strength of specimens and reduce the ultimate strain.The rise of temperature will cause damage to carbon fiber reinforced concrete,reduce its dynamic compressive strength and strain rate effect,and DIF will decrease.