No abstract

The applicability and efficiency of an alternative for impressed current cathodic protection (CP) for reinforced concrete, based on pulse technology, was investigated. The technique, denoted as pulse CP (pCP), was evaluated on the basis of a comparative analysis to reference (non-corroding), corroding, and conventional CP conditions, in terms of long-term monitoring of electrochemical parameters for the embedded steel with time of corrosion and protection. The hereby reported results are for the total duration of the experiment, i.e., 460 days of conditioning, also presented in comparison with earlier stages. Protection was applied after corrosion was initiated (using corrosion medium of 5% NaCl), at different time intervals (here reported are starting points 60 and 150 days of age). Both CP regimes used current density of 5 or 20 mA/m 2 steel surface. The pulse CP was applied as a pulse-shaped block current (square wave) with the current itself being the feedback control signal, using 12.5-50% duty cycle at 500 Hz to 1 kHz frequency. Under equal environmental conditions and for a comparatively long period of application, the pulse CP was found to perform as effectively as the conventional CP with regard to electrochemical behavior of the steel reinforcement. Furthermore, the pulse CP technique was found to achieve more rapidly the so called ''open circuit potential (OCP) passivity'' as a result of an enhanced ion transport (chloride withdrawal) and more favorable cement chemistry (increased alkalinity around the steel reinforcement).

No abstract

No abstract

When the interfacial transition zone (ITZ) is treated as a separate phase, the ITZ volume fraction plays an essential role in determining the physico-mechanical properties of concrete. The intention of the present paper is to develop a numerical algorithm for the ITZ volume fraction in concrete with spheroidal aggregate particles. By applying a contact function for two spheroidal aggregate particles and introducing periodic boundary conditions, the distribution of spheroidal aggregate particles with various sizes within a cubic element is implemented. The Monte Carlo method is then adopted to evaluate the ITZ volume fraction. After the validity of the developed numerical algorithm is verified with the analytical solution for the ITZ volume fraction in concrete with spherical aggregate particles, the effects of various factors that affect the ITZ volume fraction are evaluated through sensitivity analysis.It is found that the ITZ volume fraction increases with the increase of the ITZ thickness, but decreases with the increase of the maximum aggregate diameter and the aspect ratio of spheroidal aggregate particles. It is also found that the aggregate gradation has a significant influence on the ITZ volume fraction. The paper concludes that the numerical algorithm developed in the paper can predict the ITZ volume fraction with reasonable accuracy.