Measurements of carbonation depth provide an assessment of the extent of alkaline protection provided by the original concrete and the extent to which this has been lost due to atmospheric acidification. Carbonation depths are determined by spraying a freshly cut surface with a phenolphthalein pH indicator per the EN 14630 - 06. The indicator changes colour to magenta when the concrete has high enough alkaline content to passivate the reinforcement.
Locations of areas with low or high passivity protection are presented on CAD drawings. If the minimum depth of cover, the carbonation depth and the age of the structure are known, an estimate can be made for the remaining of the structure.
For chemical analysis, the sample should be at least five times the volume of a large-sized aggregate within the concrete (typically 20-50 g). This can be collected using samples of dust from percussive drilling.
Samples for chloride and sulphate content should be at least 50 g. This can be achieved with a 50 mm diameter core sample. Cores are normally cut into slices to determine the chloride profile (typically 0-10 mm, 10-25 mm, 25-40 mm and 40-60 mm to the approximate depth of the reinforcement). Sulphates typically affect the concrete at the surface therefore two cuts are normally sufficient. Acid soluble chloride and sulphate content by weight are normally determined per the AS 1012.20-1992.
Where large intact samples are required for compression strengths (as per the AS 1012.14) or visual examination, samples are taken using a diamond-tipped coring barrel with water as coolant and flush. The compressive strength testing usually requires at least three core samples for each structure. The minimum core size is 75 mm diameter (depending on the aggregate size) and should have a diameter to length ratio of 1:2. The compressive strength samples are usually checked for mass per unit volume, following the rapid method AS 1012.12.1-1986. Compressive strength is determined under the AS 1012.14-1991. Alternatively, the samples may be wet when preconditioned if the concrete is normally in contact with water.
The cement content can be determined from the soluble silica and calcium oxide content per the AS 2701-2001. These results can then be used to determine the cement content by calculation based on assumed proportions.
The petrographic analysis involves visual examination of a thin section by optical and scanning electron microscope. Testing is performed under ASTM C856.
Data is presented in tables and on CAD drawings where applicable.
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