Impulse Radar used to locate post tensioning tendon ducting to allow for building alterations

Background

The area investigated was a 54m by 6m portion of a bulk goods warehouse floor slab. The slab is reinforced with post tensioned tendons; housed in ducting. Due to the requirement to expand the office floor space, a mezzanine floor was planned for a corner of the warehouse. The envisaged design will require the erection of additional support columns. This will require cutting through the existing slab to allow excavation for the column footings therefore there was a requirement to accurately locate the ducts prior to excavation of the slab to avoid damage and possible loss of load capacity in the slab

Methodology & Equipment

The subsurface investigation technique selected was high frequency impulse radar. Impulse radar is a non-destructive technique that provides reflection imaging of the subsurface of a material. The technique is very effective in the location of tendon ducts with plain slabs or complicated reinforced slab / beam structures as the ducts produce a different signal to surrounding reinforcement and so can be isolated and plotted from the profiles.

Results

The results were presented in a scaled plan drawing giving the exact location of each duct to a tolerance of +/- 10mm and the depth of the duct in the slab relative to the surface.

Images

Figure 1. Plotted Position of Tendon Ducts

Figure 2. Typical Transverse Radar Profile Showing Tendon Location

Figure 3. Typical Longitudinal Radar Profile Showing Slab Construction

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