The Proper Installation of Strain Gauges on Concrete Surfaces
Installing strain gauges on concrete surfaces does not have to be difficult. Bear in mind three key criteria and the rest will be a cakewalk. Read on to find out what these criteria are and what you have to take into account.
Chosing the Right Strain Gauge
The choice of the right strain gauge depends on the measuring grid length, mainly because it has a decisive impact on the result of the measurement. The strain gauge determines the arithmetic mean of the strain conditions existing under its measuring grid. This factor needs to be taken into account to answer the question regarding the optimum measuring grid length. When a short measuring grid is used to measure the strain on inhomogeneous material such as concrete, partial strains in pebbles or individual sections of the hardened cement paste would be measured. In this case, it is essential to comply with the recommendation to use a measuring grid length five times as long the largest aggregate grain size. Taking this into consideration, HBM provides strain gauges with up to 150mm measuring grid length (for instance HBM 1-LY41-150/120)
Which adhesive is particularly suitable?
What must be considered when preparing the measuring point?
The preparation of concrete bonding surfaces is tailored to the use of X60 superglue and is generally simpler than in the case of metal installations. It is necessary to determine whether the concrete was cast with oiled or dry molds. In the case of the former, the oil-soaked layer must be removed with a grindstone. De-greasing with the help of solvents is not recommended, as the solvent and the dissolved oil will only penetrate deeper into the concrete. If dry molds were used, simply remove the concrete laitance until you reach solid concrete. Grinding is also recommended here to obtain as flat a surface as possible.
Further, carefully blow off the grinding dust with an air pump or with oil and water-free compressed air. Thoroughly seal the pores with X60 adhesive, filling them completely, not just superficially. Smoothen the bonding areas, do not apply a layer. After approximately 30 minutes, a thin aluminum foil can be applied as a barrier layer or, under certain circumstances, the strain gauge can be attached.