Key Engineering Materials Vols. 400-402

Abstract: In view of the importance of capillary pores to the physiomechanical properties of cement-based materials, it is essential to determine the volume fraction of capillary pores. The intention of this paper is to present a computer simulation-based method for predicting the volume fraction of capillary pores. By applying the periodic boundary conditions and introducing three physical parameters to quantify the mutual interference between neighboring cement particles, a computer simulation technique for the distribution and hydration of cement particles is described. Based on the simulated microstructure of cement paste, a numerical method is developed for the volume fraction of capillary pores. After verifying the numerical method with the experimental results obtained from the research literature, the effect of the water/cement ratio and the maximum cement diameter on the volume fraction of capillary pores is evaluated in a quantitative manner. It is found that, at a given hydration time, the volume fraction of capillary pores increases with the increase of the water/cement ratio and/or the maximum cement diameter. This paper concluded that the developed numerical method can predict the volume fraction of capillary pores with reasonable accuracy.

Abstract: In this paper, the influence of temperature on the cracking of reinforced concrete frame is studied. Finite element analysis software is used to simulate the concrete cracking. In the modeling process, separate model element of SOLID65+LINK8 is used. Also, the Hongestad model is applied to the stress-strain relation of concrete and the rule of BISO is applied to the stress-strain relation of steel. By comparing the stress and strain of three different structure frames before and after temperature increasing, the extending rules of concrete cracking and the stress character of beam and column are analyzed. It is found that the maximum stress of beam is located in the end of the beam-column joints and the middle of beam under the temperature action. It is suggested that they are caused by moment and axis-force respectively. However, the greatest stress of column is situated at the end of beam-column joints. The reason is that the end of beam-column joints should deform to coordinate the influence of temperature. Thus, greater peak stress is caused. So, the concrete cracking is always distributed in the middle of beam span or beam-column joints, where the position of stress concentrates. In addition, the stress of steel in beams increases greatly under the temperature load, suggesting that the temperature leads to the internal force redistribution in the concrete component and the cracking of component.