Corrosion behaviour of reinforced steel in concrete with ground limestone partial cement replacement

Abstract

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/m3) and fineness of ground limestone (345, 530 and 720 m2/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 m2/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.