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Using MIT Scan-2 for Ev aluatingDowel Bar Placeme nt
Prepared By:
Geoffrey J. Kurgan andH. Thomas Yu
Prepared For:
ND ACPA WorkshopBismarck, ND12 March 2008
MIT Scan-2 Designed specificall y for measuring
dowel bar position and alignment Offers pr actical means of evaluating
dowel placement accuracy
Three Easy Steps to Testing(R) MIT GmbHGostritzer Str. 61-63D-01217 Dresden, GERMANYweb : www.mit-dresden.deemail : [email protected]
Federal Highway AdministrationOffice of Pavement [email protected]. :web : www.fhwa.dot.gov------------------------------------------Date + Time : 26/08/2004 10:09File g:\04_08_26\26081009.hdf------------------------------------------Highway : US 90Direction : EStation No. : 1 + 00Lane : Lane 1Joint : 1Bar type : 454 x 38mmBar spacing : 300 mmConcrete thickness : 280 mm------------------------------------------Bar x-Loca Depth Side Misalignm. BarNo. tion Shift hor. vert. Space
mm mm mm mm mm mm------------------------------------------
1 129 138 54 -19 8 1292 455 146 25 -7 -6 3263 766 148 -2 -3 -10 3114 1071 143 27 0 -2 3055 1379 151 -13 8 12 3086 1690 151 -32 -1 4 3117 1996 148 -19 -3 6 3078 2302 137 10 2 2 3059 2601 140 9 -2 -10 300
10 2908 137 -9 -3 0 30711 3211 141 -17 8 -7 30412 3516 144 -26 2 -2 304
Signal intens ityContour p lot
Horizontalalignment
Verticalalignment
Example Output
Key Acceptance Items
Concrete strength Slab thickness Air content Initial smoothness
Dowel bar alignment
Dowel Alignment
Horizontaltranslation
Plan
Horizontalskew
Plan
Longit udinaltranslation
Plan
Verticaltranslation
Section
Verticaltilt
Section
State Specifications
0
1
2
3
4
5
6
7
8
9
10
5 mm (3/16 in) 6 mm (1/4 in) 10 mm (3/8 i n) 13 mm (1/2 in)
Tolerance on Horizontal or Vertical Misalignement
Num
be
rof
stat
es
So what if dowels are misaligned?
Pav ement damage may resultSpallingCracking
The eff ectiveness of dowel bars may becompromisedLoss of load transfer efficiency (LTE)Premature development of faulting
How bad is bad? – we don’t knowExisti ng specifications maybe too tightComprehensi ve s tudy under way (NCHRP 10-69)
Joint Score for IN1 (Basket)
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
1 3 5 7 911
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
Joint
Jo
int
Sc
ore
IN1 – 5 years old
Joint Score for KS4 (DBI)
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
1 3 5 7 911
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
Joint
Jo
int
Sco
re
KS4, NB I-35 – 6 years ol d
Joint Score for the GA Section (DBI)
0
5
10
15
20
25
30
35
40
45
50
1 2 3 4 5 6 7 8 9 10 11 1 2 13 14 1 5 16 1 7 18 19 2 0 21 2 2 2 3 24 2 6 2 7 28 3 0 32 33 3 5 36 3 7 38 39 4 0 41 42 4 3 44 45 46 47 4 8 49 50
Joint
Jo
int
Sc
ore
30- yr old GA section with extremel y poor dowel alignment
Joint Score for the WA Section (Retrofit)
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
1 3 5 7 911
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
Joint
Jo
int
Sco
re
WA section – 35 yr old pavement; 8 yr old retrofitEffects of Embedment Length (Burnham 1999)
Effects of Dowel Misalignment(Prabhu et al. 2006)
78.8%
14. 2%
3.6%1. 6% 1.8%
72.7%
1 9.2%
5.7%1.7% 0.6%
0%
1 0%
2 0%
3 0%
4 0%
5 0%
6 0%
7 0%
8 0%
9 0%
10 0%
d≤10 10 <d≤15 15<d≤2 0 20 <d≤25 d >2 5
Range of misalignment,mm
Pe
rce
nt
of
ba
rs
Bas ketDBI
Comparis on of DBI and Basket
More critical rangesof misalignment
Typical JointProblemJoints
Use of MIT Scan-2 da ta in optimizingPCC mix for dowel-bar inserter
0%
2%
4%
6%
8%
10%
12%
10<d≤15 15<d≤20 20<d≤25 d > 25
Range of misalign ment, mm
%o
fBar
s
Aug 7Aug 10Aug 12
Dowel Placement Specifications(CPTP Techbrief FHWA-HIF-07- 021)
Ideally , dowel bars should be placed without anyplacement error
There are tolerable lev els of placement errors Stringent (but constructible) requirements should
be specif ied, but allowance should be made f ortolerable errors
Possible Options for CorrectingMisaligned Bars
Cut misaligned bars Retrof it additional dowel bars Remov e and replace slab Full-depth repair
Best approach: don’t create problems
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
1 2 3 4 5 6 7 8 9 1 0 11 12 1 3 1 4 15 16 1 7 1 8 19 20 2 1 2 2 2 3 24 2 5 2 6 2 7 28 2 9 3 0 3 1 32 3 3 3 4 3 5 36 3 7
Joint
Jo
int
Sc
ore
Some misalignments are harmless
0
5
1 0
1 5
2 0
2 5
3 0
3 5
4 0
4 5
5 0
1 3 5 7 911
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
Joint
Jo
int
Sc
ore
Questions?
