Our Rope Access Teams are regularly called to undertake testing and sampling to structures because of the ease in which we can access facades and deliver same day test results.
But why do we take concrete dust samples for testing for chloride-ion content and undertake carbonation tests?
The two main reasons are:
There is an apparent requirement for testing and sampling prior to remediation of distressed facades ie multiple defects are apparent to both the concrete and the underlying re-inforcement (re-bar).
A change of Use or Refurbishment of the building, to make sure the existing building is fit for purpose.
Chloride Sampling
Chloride sampling is mainly carried out on reinforced concrete using test methods described in BS 1881*.
Chloride can be present in the concrete either as added calcium chloride which was used to accelerate the setting time of the concrete or as a contaminant of the aggregate. Post-construction contamination can subsequently permeate the concrete.
Another more recognisable name for calcium chloride – is Salt.
The chloride ions can diffuse through concrete pores in solution form and attack the passive layer protecting the steel reinforcement leading to corrosion…..this can be more apparent on buildings next to large infrastructure such as Seaside locations or motorways where road salts can become airborne.
In chloride contaminated concrete, the chloride concentration can be determined at various depths to determine the likelihood of corrosion of the reinforcing steel, the chloride profile of the concrete is determined by taking dust samples from the following increments of depth.
- 5 to 25 mm
- 25 to 50 mm
- 50 to 75 mm
The first 5 mm of drilled concrete is normally discarded as being non-representative. Sample increments should relate to the determined location of the steel reinforcement.
A single Chloride dust sample can also be obtained whilst undertaking Carbonation Testing.
Carbonation Testing
Carbonation in concrete is measured by applying Phenolphthalein solution to exposed concrete.
In the first instance, a defect survey of the building or structure is carried out using our Rope Access Inspectors; recording distressed areas.
A desktop study is normally used to reference locations on where Carbonation sampling is to be carried out, this is the easiest method of undertaking a survey.
Once locations have been decided on, using a Cover Meter, or rebar locator, which is a gauge that measures the thickness of concrete cover over steel reinforcement bars is used.
The cover meter can tell you the depth of the rebar, the location and orientation of reinforcement bar (rebar) and determine the diameter of the rebar. Once the area that has the lowest concrete cover is recorded, the method we use, is to drill two holes a set distance apart and remove the concrete between them.
Drilling a single hole to a specified depth and performing the test in that location is not recommended. A single drilled hole is a small test area and is at risk of potential contamination. By drilling two or more holes and breaking between them, fresh concrete is exposed providing a more accurate carbonation penetration reading. The number of holes can also be used for sampling concrete for chloride ion content or HAC.
Carbonation testing can also be performed on cores recovered from site by cutting them open in a lab, this also must be done in a controlled manner to avoid any cross contamination from potentially carbonated areas on the surface.
The recommended Phenolphthalein solution to be used is in a 1% mix solution. The Phenolphthalein solution gives a very clear contrast on the concrete. Carbonated areas will remain clear and alkaline, non-carbonated areas will show as pink.
The tests should be carried out at various pre-determined locations across the building substrate, to both good and bad locations. The cover readings at each sample location can then be compared to the measured carbonation depth indications to estimate the extent in which carbonation has reached the re-bar.
The number of holes can also be used for sampling concrete for HAC.
We often provide structural survey and inspection services using rope access methods for Consulting Engineers involved in high level structural assessment for various organisations such as councils, building owners and managers, and maintenance companies requiring statutory routine inspections. Our Rope Access Teams have extensive knowledge in delivering these tests to High Rise Buildings, MSCP, Bridges and in Confined Space areas. We often carry out inspections in Birmingham, London, Manchester and Liverpool.
We can provide a comprehensive report detailing our findings using an online cloud-based service which can allow access to multiple clients at the same time.