Bond Between Layers

Impact-Echo signals can be used to detect the quality of bond between layers. Where there is good bond the signal will pass across the interface without much distortion and give a full
depth measurement. Conversely, poor and partial bond will reflect some of the signal producing secondary peaks. This technique has been successfully used by our company on shaft and tunnel liners to verify bond quality

Honeycombing

The presence of honeycombing produces characteristic signals which enables the detection of hidden honeycombing. The main characteristic of the signal is the result of the wave energy being scattered by the individual aggregates in the honeycombed region. Because of the accuracy of the instrument, the extent and limits of the honeycombed area is readily defined.

Voids in Grouted Ducts

Impact-echo technology can detect voids in grouted ducts. Where the duct is fully filled, the signal registers the full thickness of the concrete section together with a secondary frequency which indicates the presence of the wire strands. Where the duct is not filled, the impact waves are distorted. This results in a delayed response and an apparent increase in the measured thickness of the web, a characteristic of an empty duct. This technique is also useful to detect the presence of other types of voids within the body of concrete and where required, verify that they have been properly filled.

Detection of Internal Cracks

There are many occasions when the depth of a surface opening crack is required. Current methods usually require a core to be taken at the crack location. Impact-echo technology offers a simple and fast nondestructive technique. The stress waves created by the impact, oscillate between the top and bottom surfaces of the concrete and the bottom of the crack, enabling a trained operator to immediately evaluate the depth of crack. Our company has used this technique to measure the proper formation of cut control joints and depth of shrinkage and structural cracking. A major use of this technique has been to verify proper filling of epoxy resin crack injection

Voids Below Concrete Slabs

Impact-echo technology can be used to detect voids below a concrete slab. A high acoustic impedance at a boundary, such as an air/concrete interface reflects almost all of the impact energy back to the surface. Conversely at a boundary with low acoustic impedance, such as a soil/concrete interface, some or all of the impact energy is lost into the soil. Consequently, the presence of a void below a slab produces a high energy signal response compared to locations supported by the subgrade. This characteristic enables trained specialists to nondestructively detect the presence of voids below slabs-on-grade, behind retaining walls and around tunnel systems, including concrete shafts and drainage systems. This technique has also been used to verify complete filling of the voids before, during and after repair