CT Image-based Analysis on the Defect of Polypropylene Fiber Reinforced High-Strength Concrete at High Temperatures

With the application of X-ray computed tomography（CT） technology of C80 high-strength concrete with polypropylene fiber at elevated temperatures, the microscopic damage evolution process observation and image building could be obtained, based on the statistics theory and numerical analysis of the combination of concrete internal defects extension and evolution regularity of microscopic structure. The expermental results show that the defect rate has changed at different temperatures and can determine the concrete degradation threshold temperatures. Also, data analysis can help to establish the evolution equation between the defect rate and the effect of temperature damage, and identify that the addition of polypropylene fibers in the high strength concrete at high temperature can improve cracking resistance.

Experimental study on the time-dependent dynamic mechanical behaviour of C60 concrete under high-temperatures

To study the dynamic mechanical behavior of C 60 concrete at high temperatures,impact tests under different steady-state temperature fields（ 100,200,300,400 and 500 ℃） were conducted under a variety of durations at the corresponding constant high temperature,namely 0,30,60,90 and 120 min,employing split H opkinson pressure bar（ SH PB） system. In addition,the impact tests were also conducted on the specimens cooled fromthe high temperature to the roomtemperature and the specimen under roomtemperature. Fromthe analysis,it is found that C 60 concrete has a time-dependent behavior under hightemperature environment. U nder 100,200,300,400 and 500 ℃ steady-state temperature fields respectively,as the duration at the corresponding constant high temperature increases,the dynamic compressive strength and the elastic modulus decrease but the peak strain generally ascends. After cooling to the roomtemperature,the dynamic compressive strength and the elastic modulus descend as well,but the peak strain increases first and then decreases slightly,when the duration increases. For specimens under and cooled fromthe high-temperature,as the temperature increases,the dynamic compressive strength and the peak strain raise first and then reduce gradually,and the dynamic compressive strength of specimen under high temperature is higher than that of the specimen cooled fromthe same high temperature.

Simulation of the Cracking and Ablation Behavior of Ferrosiliceous and Siliceous Nuclear Sacrificial Concretes

We investigated the simulation of the cracking and ablation behavior of ferro-siliceous and siliceous nuclear sacrificial concretes. To this end, four type of sacrificial concretes were fabricated, i e, the ferro-siliceous（F） and siliceous（S） plain concretes, and the polypropylene fiber reinforced concretes of the above two（FF, SF）. The cracking and ablation behaviors of the sacrificial concretes were investigated by simulation tests, and the simulated elevated temperature was obtained by means of thermite powder. The number and the width of the cracks were compared and the pore size distribution of sacrificial concretes was measured. In addition, the interface and chemical composition of melt at different positions were analyzed, and the ablation depth of the sacrificial concrete crucibles was also measured. It was found that the siliceous concrete shows to be more prone to cracking than the ferro-siliceous concrete due to the higher content of fly ash and lower water to binder ratio; though the ablation depth of siliceous concrete is found to be slightly larger, no clear difference can be detected for the basemat ablation rate.