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Concrete Durability Testing

Concrete Durability Testing

Corrosion of steel reinforcement remains the greatest threat to the durability of reinforced concrete structures. It has led to massive amounts of of premature replacement and repair. We offer several equipment options for concrete durability testing.

Apart from obvious cases of construction error, corrosion usually occurs when outside influences, mainly chloride ions or carbon dioxide, change the composition of the pore water in the concrete.

This can lead to the creation of electrochemical potentials within the concrete which are the prerequisite for corrosion activity.

Concrete Durability testing kits

We stock both half-cell (corrosion of steel) and resistivity meter (electrical resistivity of concrete) kits.

For best results these items should be used together. They are available as a pair for hire.

Half-CellConcrete Durability testing 2

These specialised tests are widely used to detect the presence of electrical activity associated with reinforcement corrosion.

Measurements are taken using a high-impedance voltmeter of the electrical potential of embedded reinforcement relative to a half-cell placed on the concrete surface. Copper/Copper sulphate and silver/silver chloride cells are the most commonly used.

We stock both simple and more complex kits suited to testing small, isolated areas or large spans (for example a bridge deck or multi storey car park). Simple kits consist of a silver/silver chloride electrode and a digital display, more complex kits such as the Profometer corrosion or Canin + utilise a copper/copper cell solution and are capable of logging results and displaying as contour maps (heat map) as required. Large areas are best covered with a cell wheel.Concrete durability testing 4

Generally if using a copper/copper sulphate electrode the percentage chances of steel being corrosively active is as follows:

-350 to -500mv                   95%

-200 to -350mv                   50%

-200 to less negative          5%

Most erroneous readings are caused by:

  • Poor electrical connection to reinforcing steel
  • Lack of continuity
  • Inadequate surface preparation and wetting
  • Surface carbonation or surface coverings.

A half-cell survey should be carried out alongside a full cover meter/Ferroscan survey, chloride and carbonation sample testing at the highest and lowest potential areas.

Concrete ResistivityWenner method

The time at which corrosion of steel may commence and the rate it may proceed is dependent upon properties of the cement paste and the permeability of the concrete.

Since the electrical conductivity of concrete is an electrolytic process which takes place by ionic movement in the aqueous pore solution of the cement matrix, it follows that a highly permeable concrete will have a high conductivity and low electrical resistance.

Knowledge of the electrical resistance of concrete can provide a measure of the possible rate of corrosion of steel embedded in it.

Concrete resistivity is measured in K ohm cm.Concrete durability testing 5

The probability criteria is as follows:

5 K Ω cm: Very high

5-10 K Ω cm: High

10-20 K Ω cm: Moderate to low

20 K Ω cm: Insignificant

This table is based on a 200 µA current range.

We stock the Proceq Resipod, a 4 probe wenner unit (surface test) and a Scribe DRAM, this requires two holes drilled to approximately 8 mm depth to accommodate the two probe head. Both meters can be supplied with the standard 50 mm probe spacing, if required the Resipod can also be supplied with 38 mm spacing.

Correlations for Resistivity readings can be heavily affected by but not limited to the following:

  • Moisture and salt content
  • Temperature
  • Mix details
  • Electrode spacing (typically 50mm). Results reflect concrete properties to a depth approximately equal to this spacing.
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