Many defects and non-conformities can be related to the planning and manufacturing process.
A quality control on separately manufactured specimens or on structural members of a structure allows the early detection of non-conformities. Additionally, quality control leads to increased quality awareness. Nowadays destructive tests on the structure, if any, are mainly carried out: The compressive strength and/or tightness of concrete are determined on cores taken from the structural member. Non-destructive tests exist since quite a long time, but are rarely used.
In the framework of this project it was aimed at to clarify the practical applicability of the non-destructive air permeability measurement, which is carried out according to standard
SIA 262/1, annex E.
Further investigation on the applicability of the air permeability measurements for the assessment of the quality of the cover concrete will be carried out.
Application of air permeability measurement on new and old concrete structures; execution of laboratory tests to assess the air permeability measurement; evaluation of methods for the determination of the moisture in concrete; elaboration of a recommendation for the application of field tests.
• Concrete composition: w/c-ratio as well as type of binder (cement type, mineral additions) influence air permeability. Concrete containing Portland limestone cement or Portland cement with a partial replacement by fly ash or silica fume leads to higher air permeability than concrete consisting only of Portland cement.
• Storage conditions: In addition to the concrete composition air permeability is influenced
significantly by the age and the water content of concrete. At low air permeability
an influence of temperature was also found.
• Air permeability measuring method:
o If concrete is very wet, the evaporation of water leads to an apparent high air
o Due to the application of a constant value of 15 Vol.-% of porosity for the calculation
of the air permeability, an air permeability is indicated by the measuring
device, which is approx. half of the literal air permeability of concrete.
• The representative air permeability for concrete should be given by the geometrical
mean and the standard deviation; the data evaluation has to be made with and without
considering extreme values.
The investigations on structural members led to the following conclusions:
• Concrete composition: Air permeability corresponds mainly to the expectations based
on the concrete composition.
• Temperature: Air and concrete temperature should be > 5 °C.
• Moisture content of concrete: The specific electrical resistance should be > 10 - 20
kΩcm or the moisture content, determined by capacitive means, < 5.5 - 6.0 mass-%.
• Age: At the time of measurement, on young structures the concrete should have an
age between approx. 1 - 2 months and approx. ca. 1.5 years.
• Durability: Air permeability indicates durability properties like chloride migration coefficient, carbonation progress and capillary suction of water.
With the experience gained, the introduction of non-destructive permeability is to be prepared as a means of quality assurance in Switzerland in the local market.
The results are expected in the standard SIA 162, 262 and 262/1.