The effect of water-cement ratio on the macrocell polarization behavior of reinforcing steel embedded in cement mortars was investigated by comparing and analyzing the macrocell polarization ratios and slopes of anodic and cathodic steels. Based on the experimental results, the relationship between macrocell potential difference and macrocell current density was also analyzed, and the mechanism of macrocell polarization affected by water-cement ratio was proposed. The results indicated that the water-cement ratios had little impact on the macrocell polarization ratios of cathode and anode. The lower water-cement ratio could reduce the macrocell current by decreasing the macrocell potential difference and increasing the macrocell polarization resistance of the cathode and anode. 1. Introduction The water-cement ratio (W/C ratio) is one of the important parameters affecting the long-term properties of reinforced concrete. For cement pastes hydrated to the same degree, as the water-cement ratio decreases, the permeability of reinforced concrete decreases as well. The permeability of reinforced concrete is a critical factor limiting the penetration of chloride and the diffusion of carbon dioxide, oxygen, and other aggressive agents and therefore plays an important role in controlling the microcell and macrocell corrosion behaviors of reinforcing steel. According to the study of Arya and Vassie [1], for the same area ratio of cathode to anode, a lower water-cement ratio, and hence lower permeability, could decrease the macrocell current flowing between cathodic steel and anodic steel. This lower current obtained from the lower permeability mix could probably be explained by the higher resistance of concrete and the lower transport rate of oxygen and ferrous ions, producing restrictions to the cathode and anode reaction kinetics. Similar results could be confirmed by the study of Vedalakshmi et al. [2], Hansson et al. [3], and Ohno et al. [4–7]. The results of Raupach [8] indicated that a reduction of the water-cement ratio from 0.6 to 0.5 yielded a further reduction in steel mass loss in the crack zone. This influence was especially pronounced after 24 weeks and then became much smaller after one year, which might be explained by the fact that the period up to depassivation was prolonged by a reduction of the water-cement ratio. However, after the onset of corrosion, the water-cement ratio had only a negligible influence. All these studies as mentioned above only investigated the effect of water-cement ratio on the magnitude of macrocell current and did not
References
[1]
C. Arya and P. R. W. Vassie, “Influence of cathode-to-anode area ratio and separation distance on galvanic corrosion currents of steel in concrete containing chlorides,” Cement and Concrete Research, vol. 25, no. 5, pp. 989–998, 1995.
[2]
R. Vedalakshmi, K. Rajagopal, and N. Palaniswamy, “Longterm corrosion performance of rebar embedded in blended cement concrete under macro cell corrosion condition,” Construction and Building Materials, vol. 22, no. 3, pp. 186–199, 2008.
[3]
C. M. Hansson, A. Poursaee, and A. Laurent, “Macrocell and microcell corrosion of steel in ordinary Portland cement and high performance concretes,” Cement and Concrete Research, vol. 36, no. 11, pp. 2098–2102, 2006.
[4]
Y. Ohno, K. Suzuki, and H. Tamura, “Effect of cover thickness and cracking on corrosion of steel in concrete,” JCA Proceeding of Cement and Concrete, vol. 46, pp. 642–647, 1992 (Japanese).
[5]
Y. Ohno, K. Suzuki, and H. Tamura, “Corrosion of steel in cracked concrete,” in Proceedings of the JCA Proceeding of Cement and Concrete, vol. 47, pp. 504–509, 1993.
[6]
Y. Ohno, K. Suzuki, and H. Tamura, “Corrosion of steel in cracked high strength concrete,” JCA Proceedings of Cement & Concrete, vol. 48, pp. 536–541, 1994 (Japanese).
[7]
Y. Ohno, K. Suzuki, and H. Tamura, “Influence of various parameters on macrocell corrosion of steel in concrete,” in Proceeding of the Cement and Concrete (JCA '95), vol. 46, pp. 726–731, 1995.
[8]
M. Raupach, “Chloride-induced macrocell corrosion of steel in concrete—theoretical background and practical consequences,” Construction and Building Materials, vol. 10, no. 5, pp. 329–338, 1996.
[9]
T. Maruya, H. Takeda, K. Horiguchi, S. Koyama, and K.-L. Hsu, “Simulation of steel corrosion in concrete based on the model of macro-cell corrosion circuit,” Journal of Advanced Concrete Technology, vol. 5, no. 3, pp. 343–362, 2007.
[10]
A. Poursaee, A. Laurent, and C. M. Hansson, “Corrosion of steel bars in OPC mortar exposed to NaCl, MgCl2 and CaCl2: macro- and micro-cell corrosion perspective,” Cement and Concrete Research, vol. 40, no. 3, pp. 426–430, 2010.
[11]
C. Andrade, I. R. Maribona, S. Feliu, J. A. González, and S. Feliu Jr., “The effect of macrocells between active and passive areas of steel reinforcements,” Corrosion Science, vol. 33, no. 2, pp. 237–249, 1992.
[12]
Y.-S. Ji, W. Zhao, M. Zhou, H.-R. Ma, and P. Zeng, “Corrosion current distribution of macrocell and microcell of steel bar in concrete exposed to chloride environments,” Construction and Building Materials, vol. 47, pp. 104–110, 2013.
[13]
Y. Yuan, Y. Ji, and J. Jiang, “Effect of corrosion layer of steel bar in concrete on time-variant corrosion rate,” Materials and Structures, vol. 42, no. 10, pp. 1443–1450, 2009.
[14]
Y. Zou, J. Wang, and Y. Y. Zheng, “Electrochemical techniques for determining corrosion rate of rusted steel in seawater,” Corrosion Science, vol. 53, no. 1, pp. 208–216, 2011.
[15]
Z. L. Cao, M. Hibino, and H. Goda, “Effect of steel surface conditions on the macro-cell polarization behavior of reinforcing steel,” Applied Mechanics and Materials, vol. 584–586, pp. 1771–1779, 2014.
