The Problem

The damage to the concrete is initially observed as rust stains and minute cracks. Typically the cracks in the concrete run parallel to the reinforcing steel. This damage is the result of the increase in volume of the reinforcing bar as corrosion forms. This cross-sectional increase in volume acts as a wedge and delaminates the surrounding concrete. The concrete cover will de-bond from the reinforcing steel and can present as highly visible spalls, or the damaged area may remain hidden.

The costs associated with conducting an assessment of any structure are a function of the field survey. Surveying a structure for delaminations is usually one of the first steps taken to evaluate the extent of damage. The results from a delamination study often indicate the need for many more detailed and highly scientific tests. It is important approach the delamination studies with some degree of accuracy.

The Old Method

Until now, the chain drag or good old hammer has been the universally accepted method for detecting delaminations in steel reinforced concrete structures. Listening for the characteristic hollow sound when tapping a delaminated surface, an experienced technician can detect a damaged area. Clearly, there are limitations inherent in the use of the current "technology" used to detect delaminated concrete.

The Solution

The need for an accurate method for non-destructive testing for delaminations in reinforced concrete has led to the development of rotary percussion. Currently accepted in ASTM standard D 4580-86, rotary percussion is a method which uses non-destructive percussion similar to that of hammer tapping, but designed to cover large areas, including vertical and overhead structural elements, more easily and with a greater degree of accuracy.

Rotary percussion was developed out of a need to perform non-destructive sounding studies on overhead structural elements. The device and process are patented and are used to detect delaminated concrete in large top slab applications and in overhead surveys with greater speed and increased accuracy. The design of the tool includes a telescopic extension pole and a precision machined tool head.

The rotary percussion tool, known as the Delam Tool, is easily rolled over the subject area, striking the surface numerous times with 30 percussion points acting as 30 separate hammers. Overhead areas, which are typically out of reach, can be tested in most applications by extending the telescopic pole. The unique design of the pole allows it to remain rigid while fully extended. The tool head can be removed and hand held for close detailed examination. This speeds the entire process and causes far less fatigue than using a hammer or any other percussive device, and eliminates the need for ladders.

Attachments

A set of companion tools which are used with the Delam Tool System makes the process of detecting, marking, measuring and documenting delaminated areas easier, faster and with greater accuracy with its various attachments. When a defective area is identified, a crayon marker attached to the tool head is used immediately to mark the area.

Once the top slab and the overhead structural elements are delineated for delaminations and marked with the attached crayon, the defective areas can be clearly marked with the spray paint tool attachment. After the area has been paint-marked for repair, a measuring wheel can be attached to the extension pole and a precise measurement taken to document the size of the repair area. The wireless headphones mean that work can continue even in the noisiest areas.

Importance of Drummy Testing

It is important to make an accurate assessment of the extent of damaged area not only to maintain structural integrity, but also for the engineer to produce an accurate cost estimate for repair. On structural repair projects the line item most likely to exceed estimated costs is the repair of delaminated concrete due to underestimation of total delaminated areas.