MEASUREMENTS OF CARBONATION DEPTH
- Assess the extent of atmospheric acidification (or assess concrete passivation protection or the steel)
- Estimate remaining life of a concrete structure
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, in accordance with EN 14630 – 06. The indicator changes colour to magenta when the concrete has high enough alkaline content to passivate the reinforcement.
Data analysis and presentation
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 life of the structure.
- Determine concrete pH profile, chloride profile, sulphate content
- Determine cement content of concrete
- Measure concrete compressive strength
- Provide information on the nature of the coarse and fine aggregates, cement type, cement paste content, water-cement ratio, degree of hydration, voids, carbonation depth and fractures and alkali aggregate reaction products,
For chemical analysis the sample should be at least five times the volume of a large sized aggregate within the concrete (typical 20 – 50 g). This can be collected using samples of dust from percussive drilling.
Samples for a 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 mm – 25 mm, 25 mm – 40 mm and 40 mm-60 mm to approximately the 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 is normally determined in accordance with AS 1012.20,1992.
Where large intact samples are required for compression strengths (as per AS1012.14) 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 (ratios as low as 1:1 is allowed but must be corrected). The compressive strength samples are usually checked for mass per unit volume, in accordance with the rapid method AS 1012.12.1-1986. Compressive strength is determined in accordance with AS 1012.9 -1986 and is usually tested in the dry condition as per precondition AS1012.14 -1991. Alternatively, the samples may be wet preconditioned if the concrete is normally in contact with water.
The cement content can be determined from the soluble silica and calcium oxide content, in accordance with AS 2701 – 2001. These results can then be used to determine the cement content by calculation based on assumed proportions. The minimum sample size is 100 g.
Petrographic analysis involves visual examination of a thin section by optical and scanning electron microscope. Testing is performed in accordance with ASTM C856.
Data analysis and presentation
Data is presented in tables and on CAD drawings where applicable.