The increase in the corrosion rate around a repair area caused by the formation of a galvanic cell between the substrate concrete and the repair mortar is known as the incipient anode. The current study is aimed at investigating the effects of repair dimensions on the corrosion rate of the macrocell created by the patch repair. To do so, repair slabs were manufactured with different repair dimensions and repair mortars containing ordinary Portland cement (OPC), 5% microsilica, and 9% microsilica. The half-cell potential and macrocell current of the experimental specimens were measured, and the electrochemical parameters (i.e., Tafel slope and macrocell corrosion rate) of the repair mortar and the substrate concrete were determined. The effects of repair dimensions and the driving force were evaluated in a wider range using a numerical model. The results showed that compared to OPC, the repair mortar containing 9% microsilica significantly reduced the maximum macrocell corrosion (MMC) and the average macrocell corrosion (AMC) rates. The effects of the repair dimensions are not significant and there is only a slight increase of 30% in the MMC rate when the repair dimension is less than 30 cm, while this rate remains constant in repair dimensions higher than 30 cm. The effect of the repair dimension on the AMC is more significant than its effect on the MMC, i.e., as the repair dimension increases to 100 cm, the AMC increases by at least 130%, and then, it remains constant. Moreover, the reduction in the driving force considerably decreased the MMC and AMC rates.
