Experimental Study On Mechanical Properties Of Damaged Concrete

In this thesis, the mechanical properties of pre-damaged concrete under impact load was systematically carried out. The load damages was created by applying different static load on the concrete specimens and the elevated temperature damages was created by exposing the concrete specimens to temperature ranging from room temperatures to as high as 600℃ or 700℃, and then the damage was calibrated with ultrasonic velocity. An Split Hopkinson Pressure Bar (SHPB) was adopted to study the effect of pre-damages (both load damage and elevated temperature damage) on the compressive strengths, stress-strain relationships, energy absorption capacity, dynamic enhancement factor (DIF,dynamic strength-intic strength ratio) and failure modes of concrete.Test results indicated that with the increasing degree of pre-damage, the dynamic compressive strength of concrete specimens decreased till a certain threshold. When the pre-damage was smaller than the threshold, it had little effect on the dynamic compressive strength of concrete. However, the effect would become tremendous when the damage level was beyond the threshold. It was also confirmed that the compressive strength and energy absorption capacity of concrete would increase with increasing strain rate. In addition, the higher water/cement ratio of concrete specimen, the lower dynamic compressive strength. At low strain rate, the strain-rate enhancement effect would counteract the softening effect by temperature; this phenomenon occurred in a specific temperature range. And when at other temperatures, the temperature softening effecting is dominant, compared to the strain rate effect on concrete. An empirical model was proposed to predict the compressive strength of concrete, in which the influences of both pre-damages and strain rate was included. Additionally, the relationship between the splitting tensile strength, dynamic splitting tensile strength and elevated temperature was studied.