Chloride diffusivity in flexural cracked Portland cement concrete and fly ash concrete beams

LU Chun-hua(陆春华), CUI Zhao-wei(崔钊玮), LIU Rong-gui(刘荣桂), LIU Qi-dong(刘奇东)

(Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang 212013, China)

Abstract:In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete (PCC) and fly ash concrete (FAC), were tested with various crack widths. Total 14 reinforced concrete (RC) beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing (RCT) method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors k_f and k_w can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.

Key words:flexural cracked concrete; fly ash; chloride dry-wet cycle; equivalent chloride diffusion coefficient