Presented at the XXIV Nordic Concrete Research Symposium in Stockholm, August 17-19, 2022.

1. Air-entrained concrete: A
comprehensive bridge
inspection program in Finland
Ludovic Fülöp, M. Ferreira, M. Leivo, E. Bohner,
24th NCR Symposium, Stockholm, Aug. 2022
05/09/2022 VTT – beyond the obvious

2. 05/09/2022 VTT – beyond the obvious
 Background and scope
 Inspection and methods
 Results and lessons
 Reflections / Conclusion
Outline

3. 05/09/2022 VTT – beyond the obvious
 News headlines:
• Who pays – and how much?
• A strange case!
• New traffic arrangements
• Etc.
 Excessive air-entrainment (AE)
identified as primary cause.
 Limited inspection (18 bridges),
extended to comprehensive inspection
of 96 bridges by the Finnish Transport
Infrastructure Agency (FTIA).
Background
https://yle.fi/uutiset/3-9020449

4. 05/09/2022 VTT – beyond the obvious
 AE concrete is standard for outdoor
application.
 Purpose of AE to enhance freeze-thaw
resistance against internal cracking
and surface scaling.
 Generally, higher air content means
better performance.
 For cracking the transition is at ~3%
AE, for salt scaling at about 5–6% AE.
Good air distribution is an additional
requirement!
Air- entrainement (AE)
* W.A. Cordon, Freezing and Thawing of Concrete,
American Concrete Institute, 1966.

5. 05/09/2022 VTT – beyond the obvious
 FTIA decided for extensive inspection to determine:
• if excessive AE is present in recently built bridges; threshold of 7.5%
was set for entrapped and entrained air-pores;
• if safety in exploitation of any bridge is in question; the 0.85×fc was set
for in-situ compressive strength;
• if excessive AE is due to a certain technology, substance in the mix or
supplier
• review the quality documents of the bridges and improve procedures.
Overall scope by FTIA

6. 05/09/2022 VTT – beyond the obvious
 Measure air content and characteristic in-situ compressive strength of the
concretes (i.e. direct material sampling) in critical load bearing parts;
 Auxiliary rebound hammer tests. Correlation between compressive strength and
rebound tests, would enable further area to be assessed using only NDE.
 Sampling approach based on EN13791 and (at that time) prEN13791.
 Bridge divided in test regions. Focus on main structural elements (e.g. columns,
main girder, deck).
Technical scope

7. 05/09/2022 VTT – beyond the obvious
 Generally, 8-10 locations are recommended; 15 in this study (i.e. >1500 cores +
rebound).
 Individual review of each bridge at VTT– distribution of samples, minimize stress
& damage, accessibility for coring, repairs etc.
 Inspection document for each bridge. Very prescriptive to enhance uniformity of
the sampling, sample handling etc. 24 hours phone hot-line for advice, questions,
on-the-spot adjustments etc.
 5 inspection packages contracted. Work (e.g. coring, NDE, lab-work etc.) may
further be sub-divided and sub-contracted etc.
Sampling methods

8. 05/09/2022 VTT – beyond the obvious
 Ø80 mm diameter; aggregate size
(Dmax~25 mm) and minimizing rebar
damage.
 Length of 130 or 200 mm, h/Ø=1
cylinders for compressive strength; disks
for porosity.
 Approximate method for porosity, by
water absorption tests according to the
VTT-TEST 385-86 (i.e. follows RILEM
recommendation).
Testing methods

9. 05/09/2022 VTT – beyond the obvious
Findings – increasing AE https://doi.org/10.1016/j.cscm.2022.e01211

10. 05/09/2022 VTT – beyond the obvious
Findings – decreasing safety margin
https://doi.org/10.1016/j.cscm.2022.e01211

11. 05/09/2022 VTT – beyond the obvious
Findings – rebound hammer tests
 Correlation of rebound with strength:
• EN 13791:2007: Direct correlation with
cores (Method I)
• EN 13791:2007: Calibration with cores for
a limited strength range using an
established relationship (Method II)
 Method I validated only for 11 test
regions. The compression strength
using the cores alone is generally
larger.
 Method II very conservative (so in
critical instances like this, it is limited).

12. 05/09/2022 VTT – beyond the obvious
Reflections / Conclusions
 Higher AE drove decrease of safety
margin in recent bridges.
 Safety is ok due to large strength
margin in the concretes. One
problem case found.
 Measures taken by industry/FTIA to
eliminate the issue for the future,
but there ae high-AE bridges in the
inventory.

13. 05/09/2022 VTT – beyond the obvious
 High AE cases could result in stricter monitoring, inspection and/or
maintenance regime by the FTIA.
 Studies to understand the performance of high-AE concrete (i.e. in case re-
evaluation of safety/durability is needed).
 More details and data tables:
Reflections / Conclusions
L. Fülöp, M. Ferreira, E. Bohner, J. Valokoski, J. Vuotari, T. Tirkkonen, Inspection of bridges for effects of
air-entrainment on the porosity and compressive strength of concretes, Case Stud. Const. Mater. 17
(2022) e01211. https://doi.org/10.1016/j.cscm.2022.e01211.
Or email your question to: Ludovic.fulop@vtt.fi