Which method employs electrical resistance inside a drilled hole to detect decay?

The method that employs electrical resistance inside a drilled hole to detect decay is known as the Field Ohmmeter. This technique is based on measuring the electrical resistance within the material, which can indicate changes in the structure's integrity, particularly due to decay or deterioration such as wood rot or corrosion in concrete. By drilling a hole into the material and inserting electrodes, the device measures how easily electricity can flow through the material; this resistive measurement can reveal localized areas of decay, providing valuable information for assessing the overall condition of the structure.

Using a Field Ohmmeter is particularly effective because it can provide quantitative data that correlates with the level of decay present. As decay develops, the electrical resistance changes, allowing inspectors to identify potential problem areas within a bridge or other infrastructure.

The other methods listed, such as the Pachometer, Impact Echo Test, and Moisture Meter, each employ different principles and approaches to assess material condition but do not focus on measuring electrical resistance as a means of detecting decay. The Pachometer is typically used for locating reinforcing bars or conduits within concrete, the Impact Echo Test assesses the integrity of concrete by analyzing reflected waves from impacts, and the Moisture Meter, while helpful in determining moisture content, does not measure electrical resistance