NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

The Romanian Road Administration Experience in The Field Of NDT for Bridges

Cristina ROMANESCU1, Constantin IONESCU2, Rodian SCINTEIE3

1Romanian National Company for Motorways and National Roads, Bucharest, Romania, cristinaromanescu@gmail.com 2"Gh. Asachi" Technical University, Iasi, Romania 3Center for Technical Road Studies and Informatics (CESTRIN)

Abstract In 1993 Romanian National Company for Motorways and National Roads (C.N.A.D.N.R.)

decided to perform quality controls by its own research branch, Center for Technical Road Studies and IT (CESTRIN), for works executed on bridges. Thus, three equipments were purchased: Schmidt hammer, ultrasonic concrete tester and pachometer, allowing CESTRIN to perform tests on road bridges, in a multi-year monitoring process. After 1989 in Romania almost all bridge technical data have been lost, thus leading to errors in rehabilitation designs. In 2009 CESTRIN will be beneficiary of a PHARE Project “Improvement of safety, quality of services and institutional capacity in transport sector”. Thus, new equipments that offer information about road structures and riverbed will fulfill the needs of C.N.A.D.N.R. Our task is to create a relation between degradations and bridge’s actual bearing capacity. These quantifiable disorders must lead to an equation to provide an assessment of structure’s behavior under actual traffic loads. This paper describes actual situation in Romania in the field of NDT of bridges.

Résumé En 1993, la Compagnie Nationale Roumaine pour Autoroutes et Routes Nationales

(C.N.A.D.N.R.) a décidé d'effectuer des études de qualité par son département de recherches, Centre pour les Etudes Techniques de Route et IT (CESTRIN), pour des travaux exécutés sur ouvrages. Ainsi, trois équipements ont été achetés: un Marteau Schmidt, un appareil de contrôle ultrasonique de béton et un pachomètre, permettant au CESTRIN de réaliser des tests sur des ponts, dans un processus de surveillance pluri-annuel. Après 1989 en Roumanie, presque toutes les données techniques des ponts ont été perdues, de ce fait menant à des erreurs dans la conception de réhabilitation. En 2009, le CESTRIN est le bénéficiaire du projet PHARE «Amélioration de la sûreté, de la qualité du service et de capacité institutionnelle dans secteur des transports». Ainsi, nouveaux équipements qui offrent des informations sur des structures de route, et lits de rivières, vont répondre aux les besoins du C.N.A.D.N.R. Notre tâche est de créer une relation entre dégradations et portance réelle des ouvrages. Ces désordres quantifiables doivent mener à une équation pour fournir une évaluation de structure sous charges de la circulation réelle. Cet article décrit la situation actuelle en Roumanie dans le domaine des techniques non destructives appliquées aux ouvrages.

Keywords degradations, bearing capacity, structure assessment, bridge statistical data, case studies

1 Introduction Experimental researches supposed NDT methods applied on different types of concrete

having compression strength between 150 and 400 daN/cm2 both on laboratory specimens and

NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

in situ, on bridges elements. Correlation curves derive from methods as rebound method, pulse velocity method and combined method. These results show the quality of concrete in different structures analyzed along 7 years of work. Compression strength measured is corresponding to 20 cm cubes.

2 Experimental results Between 2001 and 2007 C.N.A.D.N.R. asked CESTRIN to perform NDT tests on

structures located on national roads, both for new bridges and bridges that have been rehabilitated. All tests complied with the Romanian regulation “C26-1985 Nondestructive Testing Norm for Concrete” and also STAS 6652/1-1982 “Nondestructive Concrete Testing. Classifications and general guidelines” until August 2007; presently, SR EN 12504-2:2002 “Testing concrete in structures-Part 2: Non-destructive testing-Determination of rebound number” and SR EN 12504-4:2004 “Testing concrete-Part 4: Determination of ultrasonic pulse velocity” are used. For rebar locator we used BS 1881 part 204 and DIN 1045, as Romania has no regulation. During tests a Schmidt hammer, an ultrasonic concrete tester and a pachometer has been used. Also, auxiliary measuring tools have been used, such as: thermometer, crack scale magnifier, water leveling rule, geometric tools, and rule for measurement of distances. Chosen points for the transducers were optimally arranged within a grid where no rebar can be found so results will not be influenced. Direct wave technique has been used in all studies.

2.1. The year 2001 Objective was to assess quality of concrete and monitoring of following bridges: National

Road (NR) 72A at km 32+860 at Gemenea and NR 1 at km 140+640 at Predeal. At km 32+860 distance between transmitter and receiver was of 18 cm, and at km 140+640 was of 20 cm. If crack depth is bigger than concrete cover, carbon dioxide infiltration to rebar through cracks is thus possible, increasing carbonation risk. Using pachometer rebar path, its diameters and concrete cover were detected. Width of cracks was in all sections of exactly 0.3 mm. Concrete cover varies between 36 and 53 mm.

At km 32+860 as a result of in situ tests the following were established: concrete presents an advanced corrosion condition to entire bottom part of slab on all bridge length (pH = 5.5) and concrete segregation may be observed to beams due to insufficient vibration that occurred in circumstances of limited space and a large number of rebar. The use of big aggregates may be observed, discordant to rebar diameter. High porosity concrete used allowed water and aggressive environment to attack. Both, in cross beams and in beams concrete has its pH = 6, thus favoring rebar corrosion.

Figure 1. Tests that have been performed at Gemenea and Predeal

Rebar section is reduced about 50% to transversal rebar, and longitudinal rebar lowered its diameter by 20% (loosing its alkali properties concrete doesn’t constitute a protection for rebar, thus was heavily corroded; a protective concrete has its pH over 9). Tests using

NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

combined method showed following compression strength: crossbeam 6 in 6th span, between 1st and 2nd beam - 200 daN/cm2 and beam 1 - span 6 - 250 daN/cm2.

For the bridge at km 140+640 as a result of tests the following were established: concrete presents an advanced corrosion condition to all inferior part of slab on all bridge length (pH = 6). Measurements showed that: rebar’s diameters of reinforced slab reduced from φ16 to φ13, from φ 10 to φ 8 and from φ 8 to φ 4.5, so to all types of rebar the section is reduced considerably (by 18.75%, 20%, 43.75%) favoring destruction of slab in several spans; minimum of concrete cover is 21 mm, and maximum of 46 mm, so, in case of beam 1 in 1st span carbonation risk is zero for the moment, of course if water does not infiltrate; minimum of measured crack depth from surface of concrete was of 7.67 cm, and maximum of 11.98 cm.

2.2. The year 2002 Based on inspection forms completed for Suceava National Road Section and South

Bucharest National Road Section an analysis has been done regarding the behavior of bridges depending on geographic area and static scheme. We observed that intervals of quality indexes are comparable in these two areas but for identification of a real technical condition a statistical calculation was necessary. So, we calculated: average quality index per Section Iaverage, absolute deviation of each index εi, squared average deviation of indexes Si and variation coefficient of indexes Ci. Statistical calculation supposing a Gaussian distribution has been done using following formulas:

nII i

average

∑= (1) averageii II −=ε (2) 1

2

−= ∑

nS i

i

ε (3) %100⋅=average

ii I

SC (4)

where Ii represent value of each quality index for each bridge; n-number of simple supported beams bridges for each Section. Thus it became clear that condition of simple supported beams bridges in mountain areas is much worse than in plain areas.

Absolute deviation of indexes

-15

-10

-5

0

5

10

15

20

25

0 5 10 15 20 25

SUCEAVA BUCURESTI SUD

Squared average deviation

-1

0

1

2

3

4

5

6

0 5 10 15 20 25

SUCEAVA BUCURESTI SUD

Variation coefficient

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 5 10 15 20 25

SUCEAVA BUCURESTI SUD Figure 2. Charts for quality indexes for Suceava and South Bucharest Sections

2.3. The year 2003 Laboratory tests were performed on a concrete used in different elements of bridges having

a known compression strength 400 daN/cm2. Objective was to establish precision of compression strength evaluation using those three methods. A 20 cm concrete cube was tested, and obtained compression strength was: 384daN/cm2, 425daN/cm2 and 407daN/cm2, so accuracy was high enough (+6.26%, -4% and +1.75%, an average of 1.34%).

2.4. The year 2004 In many cases cracking of concrete may point out overload condition or weakness due to

various reasons. Width on concrete surface may be determined using simple optical methods. Instead, investigation of its position and depth requires use of special techniques, one of them is ultrasonic testing, cracks filled by air creating a screen that reflects ultrasonic waves.

According to Romanian “Norm for concrete testing using NDT methods C 26-85” depth of crack may calculated as follows:

NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

( )[ ]12

l 2

01 −⋅= tthf (5) where: hf-depth of the crack, in cm, l-distance between two transducers, in cm, t1-time that device shows for section in front of crack, in µs and t0-average time of readings on device between points situated on same distance for sections without cracks, in µs. Crack width and distance between cracks for elements of existing reinforced concrete structures can be calculate using both equations in Romanian regulation STAS 10111-2-87 and EUROCOD 2.

Determination of depth of crack F1 on 1st beam span 1 NR 2 km 179+404 Table 1. Section Time

reading (µs)

Corrected time for etalonation

(µs)

Corrected time for

temperature

Average time for crackless

concrete

Distance between transducers

(cm)

01 tt ( )2

01 tt ( ) 12

01 −tt

( )[ ]12

01 −tt d/2 hf (cm)

1' - 2' 102.3 103.8 104.2 20 1.276 1.629 0.629 0.793 10 7.93 3'- 4' 158.4 159.9 160.5 20 1.966 3.865 2.865 1.693 10 16.93 5'- 6' 109.0 110.5 110.9 20 1.359 1.846 0.846 0.920 10 9.20

I 76.5 78.0 77.8 81.7 II 88.7 90.2 90.0 III 75.9 77.4 77.2 Crack width must be limited not to negatively affect behavior of concrete, reinforced

concrete and pre-stressed concrete bridges in service and not to affect aesthetics. In order to insure a high durability one must take into consideration that reinforcement protection to corrosive actions is influenced only by thickness of concrete cover and its quality, and, mostly by the way crack limitation condition is respected. Investigated bridges were: NR 2 at km 179+404-beam 1 span 1 and NR 2 at km 238+150-2nd abutment.

Crack depth variation diagram on beam 1 span 1 - bridge km at 179+404

-16.93

-9.20

-7.93

-18.00-17.00-16.00-15.00-14.00-13.00-12.00-11.00-10.00-9.00-8.00-7.00-6.00-5.00-4.00-3.00-2.00-1.000.00

Dep

th o

f cra

ck h

f (cm

)

Crack depth variation diagram on beam 1 span 1 - bridge km 179+404

-5.07

-2.22

-7.71

-3.75 -3.97

-1.70

-6.54

-11.13

-6.13

-12.00

-11.00

-10.00

-9.00

-8.00

-7.00

-6.00

-5.00

-4.00

-3.00

-2.00

-1.00

0.00

Cra

ck d

epth

hf (

cm)

Crack depth variation on abutment 2 -

bridge km 238+150

-14.01

-11.13-12.15

-13.63

-10.69

-12.86

-9.41

-7.11

-12.86

-15.00-14.00-13.00-12.00-11.00-10.00-9.00-8.00-7.00-6.00-5.00-4.00-3.00-2.00-1.000.00

Cra

ck d

epth

hf (

cm)

Figure 3. Cracks F1 and F2 on NR 2 km 179+404 and crack F3 at km 238+150

2.5. The year 2005 Objective was a comparison between results obtained using destructive and non-

destructive methods in order to determine the maximum error percent. Three 20 cm cubes and 3 prisms (55x10x10 cm) of B 250 concrete were tested. Pa 35 cement was used with a dosage of 300 kg/m3, river aggregates with a maximum dimension of 41 mm and smaller than 1 mm fractions in a percent of 17,7%. Concrete maturity age is of 48 days. Tested specimens had the following hardening process: 14 days in a dry environment at 20˚C, then 7 days in water at 22˚C, and, in last stage, dry environment at 20˚C.

NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

Figure 4. Laboratory tests on a concrete cube with 250 daN/cm2

Table 2. Rebound number, pulse velocity and compression strength Compression strength with

(daN/cm2) No. Element Rebound

number Pulse

velocity (km/s) Schmidt hammer Ultrasonic Combined

Compression strength at hydraulic press (daN/cm2)

1 Cube 1 38.1 4.09 315 214 286 224 2 Cube 2 40.4 4.10 359 216 310 228 3 Cube 3 40.9 4.08 369 212 315 228 4 Prism 1 - 4.27 - 258 - - 5 Prism 2 - 4.30 - 266 - - 6 Prism 3 - 4.30 - 266 - - Using obtained data values were determined for each non-destructive method as follows:

Table 3. Measured error for each non-destructive method Compression strength using the hydraulic press

(daN/cm2) Schmidt hammer

method Ultrasonic method

Combined method

Average(daN/cm2) 227 348 239 304 Error ±% N/A 53 5 34

2.6. The year 2006 Objective was to assess compression strength for following bridges on NR 15: km

127+737, km 133+958, km 140+888, km 217+424 and km 219+206.

Table 4. Rebound number, pulse velocity and compression strength with SONREB Beam

km 127+737 Beam

km 133+958 Beam

km 140+888 Abutment

km 217+424 Abutment

km 219+206

1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 Rebound number 48.5 48 48.8 44.7 45.5 45.2 48.5 48.1 46.8 44.3 43.8 37.5 31.5 31.7 30.7 Pulse velocity (km/s) 4.09 4.22 4.14 3.94 3.60 3.80 4.16 4.22 4.12 3.14 3.14 3.12 3.32 3.72 3.53 Compression strength (daN/cm2)

390 415 400 328 250 296 400 415 375 160 155 120 115 155 129

150

200

250

300

350

400

450

500

550

30 35 40 45 50

Rebound number

Com

pres

sion

str

engt

h (d

aN/c

m2)

km 127+736 km 133+958 km 140+888km 217+424 km 219+206

50

70

90

110

130

150

170

190

210

230

250

0 1 2 3 4 5

Wave's pulse velocity (km/s)

Com

pres

sion

stre

ngth

(daN

/cm

2)

km 127+736 km 133+958 km 140+888km 217+424 km 219+206

Figure 5. Rebound number/pulse velocity versus compression strength on NR 15

NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

2.7. The year 2007

Objective was to assess concrete quality for following bridges: NR 12B at km 5+033 at Ciresoaia and at km 10+050 at Cerdac. compression strength values for two investigated beams (3 and 5) of the bridge at km 5+033, and two beams (2 and 5) of the bridge at km 10+050 are around 300 daN/cm2, good values for a 59 years old reinforced concrete used to superstructure.

y = 35.887e0.056x

R2 = 0.9996

300

320

340

360

380

400

420

440

39 40 41 42 43 44 45

Rebound number

Com

pres

sion

stre

ngth

(daN

/cm

2)

km 5+033 km 10+050 Average deviation

y = 1.823e1.1585x

R2 = 0.9995

0

50

100

150

200

250

3.85 3.9 3.95 4 4.05 4.1

Wave's pulse velocity (km/s)

Com

pres

sion

str

engt

h (d

aN/c

m2)

km 5+033 km 10+050 Average deviation Figure 6. Rebound number/pulse velocity, compression strength and test points on NR 12B

3 Conclusions One may observe the efficiency and efficacy of using NDT methods versus destructive

methods, fast assessment of bridge elements being a prioritary direction for European road administrators. It is recommended to use NDT for high resistance because errors are considerably smaller. Combined SONREB method gives the best results of compression strength. Because concrete is a complex material interpretation of results may be a challenge for all structural engineers if they do not dispose of a long experience in this field. Non-destructive tests may represent, if properly used, a very important tool in bridge assessments activities and are, for sure, a very useful for determination of relative resistances of concrete in different areas of the same element of a bridge.

References 1. Romanescu, C., Scinteie, R., Padure, V., Padure, M., (2001) “NDT tests of bridges and

time monitoring of rehabilitated bridges” 2. Romanescu, C., Romanescu, C., Padure, M., (2002) “NDT tests and time monitoring of

rehabilitated bridges” 3. Romanescu, C., Scinteie, R., Padure, V., Padure, M., (2003) “NDT tests and time

monitoring of rehabilitated bridges” 4. Romanescu, C., Romanescu, Cl., Padure, M., (2004) “NDT tests and time monitoring of

rehabilitated bridges” 5. Dragomirescu, I., Romanescu, C., Padure M., (2005) “Time monitoring of rehabilitated

bridges using specific methods. Bridges requested by CNADNR” 6. Sandu, L, Romanescu, C., Dragomirescu, I., Padure, M., Istrate G., (2006) “Time

monitoring of rehabilitated bridges using specific methods” 7. Sandu, L, Romanescu, C., Istrate G., (2007) “Time monitoring of rehabilitated bridges

using specific methods. Bridges requested by CNADNR” 8. Migoun, N.P., Novikov, S.A., (2008) “Non-Destructive Testing in Belarus” – 17th World

Conference on Nondestructive Testing, Shanghai, China 9. Shen, G. (2008) “Progress of Nondestructive Testing and Evaluation in China” – 17th

World Conference on Nondestructive Testing, Shanghai, China 10. Klyuev, V.V., Fedosenko, Yu. K. (2008) “50th Anniversary of non-destructive testing in

Russia” – 17th World Conference on Nondestructive Testing, Shanghai, China