Section 188.8.131.52 of the standard SIA 262 states that the tightness of the cover concrete should be checked to assure the durability of a structural member. To achieve this with the air permeability method according to SIA 262/1, the experience gained mainly in the ASTRA-projects and related VSS-reports Nr. 506, 516 (Torrent 1993/1995), Nr. 587 (Brühwiler, 2005) and Nr. 604 (Jacobs, 2006) as well as from the RILEM Technical Committee „Non-Destructive Evaluation Of Cover Concrete“ should be compiled in a SIA-recommendation.
With the SIA-recommendation for the air permeability method according to SIA 262/1 the engineer/owner should obtain clear information about the quality control of structural members, e.g. in relation to the exposure class. Additionally testing laboratories should obtain clear information how to perform and evaluate the measurements.
The main project aims are:
- elaboration of a SIA-recommendation for the determination of air permeability according to SIA 262/1
- Execution of a round robin test on structural concrete members to determine statistical parameters for the air permeability method according to SIA 262/1
This project is mainly based on the recommendations created, so the key result is the final report.
Over 100 construction elements have been examined with the SIA 262/1-E airpermeability
test method in Switzerland. Based on the accumulated knowledge, recommendations for determining the air-permeability are presented. These recommendations cover proposals for the tendering, execution and evaluation of measurements of air-permeability.
When conducting measurements of air-permeability, the required temperature and moisture conditions of the concrete elements must be observed and recorded. On each surface under investigation, 6 measurements of air-permeability are conducted. If not more than 1 result exceeds the proposed limiting values (kTs = 2.0 10-16 m2 for the concrete types C, D and E according to SIA 118/262; kTs = 0.5 10-16 m2 for the concrete types F and G according to SIA 118/262), the surface complies with the requirements. If 2 results exceed the proposed limiting values, then 6 additional measurements should be performed. If not more than 1 of the additional measurements exceeds the limiting value, the surface under investigation complies with the requirements. In case of non conformity, further investigations should be performed or a protective treatment applied to the element(s).
The multiplication of requests to determine the air permeability of cover concrete on structures will eventually lead to changes in the construction process, towards more care being dedicated to the placing and curing of concrete. It will also foster the use of methods to improve the tightness of cover concrete (such as Controlled Permeability Formwork liners or vacuum dewatering) and thus extend the durability of structures.