Magazine of Concrete Research, 2015, 67(14), 747–761 http://dx.doi.org/10.1680/macr.14.00156 Paper 1400156 Received 25/05/2014; revised 5/11/2014; accepted 22/12/2014 Published online ahead of print 06/02/2015 ICE Publishing: All rights reserved Magazine of Concrete Research Volume 67 Issue 14 Corrosion behaviour of reinforced steel in concrete with ground limestone partial cement replacement Diab, Aliabdo and Mohamed Corrosion behaviour of reinforced steel in concrete with ground limestone partial cement replacement Ahmed M. Diab Professor and Head of Structural Engineering Department, University of Alexandria, Egypt Ali A. Aliabdo Professor, Department of Structural Engineering, University of Alexandria, Egypt Ismail A. Mohamed PhD Student and Assistant Lecturer, Department of Structural Engineering, University of Alexandria, Egypt Corrosion of steel bars embedded in concrete made of Portland cement replaced partially with ground limestone is studied. Three variables are considered: replacement ratios with ground limestone (0, 10, 15, 20 and 25% of cement by weight), level of cement content (300, 350 and 400 kg/m 3 ) and fineness of ground limestone (345, 530 and 720 m 2 /kg). Reinforced concrete specimens are immersed in a 5% sodium chloride solution by weight up to 9 months. The corrosion rate is measured by potentiodynamic polarisation technique. To explain the corrosion behaviour of steel bar embedded in Portland limestone cement concrete, samples are prepared from the same concrete mixes and tested mechanically and physically. X-ray diffraction and thermogravimetric analyses of limestone cement pastes with similar replacement levels are also conducted. The corrosion rate of steel bars embedded in concrete containing ground limestone (530 m 2 /kg or more) is found to decrease with increase of cement replacement ratio up to 25% by weight. The corrosion behaviour of steel bars and the resistivity characteristics of Portland limestone cement concrete are also found essentially to depend on the cement content of the concrete. The corrosion behaviour of steel bars in Portland limestone cement concrete, as well as the compressive strength of the concrete, is found to be strongly associated with the fineness of limestone relative to the fineness of cement. Notation B Stern–Geary coefficient b a anodic Tafel slope b c cathodic Tafel slope C t cement content D density E corr corrosion potential f cu cube compressive strength FM fineness modulus I electrical current i corr corrosion current density P total porosity of concrete R p polarisation resistance R s electrical resistivity of concrete S spacing between electrodes V electrical potential Introduction Corrosion of steel bars of reinforced concrete is one problem that requires a continuous research effort (Erhan et al., 2013; Mohamed and Masayasu, 2006). Corrosion threatens the durabil- ity and safety, reduces the performance and distorts the appear- ance of reinforced concrete structures. The corrosion rate increases with the increase of chloride ions. Therefore, the problem becomes more severe in a marine environment (Cabrera, 1996; Tuutti, 1982). A lot of research has been directed at studying various methods to control the corrosion process, but quality control of the concrete itself is still the most appropriate and the cheapest method to control reinforced steel corrosion (ACI, 2004; Erhan et al., 2013). In other words, the quality of ingredients, water-to-cement (w/c) ratio, type and content of cement in concrete mix, have to be carefully controlled to ensure high corrosion resistance of concrete. The high increase in the price of energy, alongside the high amount of carbon dioxide emitted in the Portland cement industry, has increased the need for a sustainable solution to the corrosion problem (Baron and Dourve, 1987; Bonavetti et al., 2003; Moir, 1994; Thomas et al., 2010). Lately, many countries have made allowance in their standards to replace Portland cement partially with substitute binder materials, such as ground limestone (GLS) (Federica et al., 2014; Kung’u and Mark, 2013). 747