MIT Scan-2 Using MIT Scan-2 for Evaluating Designed specificall - - PDF document

SLIDE 1

Using MIT Scan-2 for Evaluating Dowel Bar Placeme nt

Prepared By: Geoffrey J. Kurgan and

• H. Thomas Yu

Prepared For: ND A CPA Workshop Bismarck, ND 12 March 2008

MIT Scan-2

 Designed specificall yfor measuring

dowel bar position and alignment

 Offers pr actical means of evaluating

dowel placement accuracy

Three Easy Steps to Testing

(R) MIT Gmb H Gost ritz er Str. 61- 63 D-01 217 Dre sden , GE RMAN Y web : www .mit

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sden .de emai l : mit @mit .tz- dd.d e Fede ral Hig hway Adm inis trat ion Offi ce o f P avem ent Tech nolo gy sam. tyso n@f hwa. dot. gov tel. : web : www .fhw a.do t.go v

• Date + T

ime : 26 /08/ 2004 1 0:09 File g:\ 04_ 08_2 6\26 0810 09.h df

• High

way : US 90 Dire ctio n : E Stat ion No. : 1 + 00 Lane : La ne 1 Join t : 1 Bar type : 45 4 x 38m m Bar spac ing : 30 0 mm Conc rete th ickn ess : 28 0 mm

• Bar

x- Loc a De pth Sid e M isal ign

• m. B

ar No. ti

• n

Shi ft h

• r. ver
• t. S

pace m m mm m m mm mm mm

• 1

12 9 138 5 4

• 19

8 129 2 45 5 146 2 5

• 7
• 6

326 3 76 6 148

• 2
• 3
• 10

311 4 107 1 143 2 7

• 2

305 5 137 9 151

• 1

3 8 12 308 6 169 151

• 3

2

• 1

4 311 7 199 6 148

• 1

9

• 3

6 307 8 230 2 137 1 2 2 305 9 260 1 140 9

• 2
• 10

300 10 290 8 137

• 9
• 3

307 11 321 1 141

• 1

7 8

• 7

304 12 351 6 144

• 2

6 2

• 2

304

Signal intens ity Contour plot Horizontal alignment Vertical alignment

Example Output

SLIDE 2

Key Acceptance Items

 Concrete strength  Slab thickness  Air content  Initial smoothness  Dowel bar alignment

Dowel Alignment

Horizontal translation Plan Horizontal skew Plan Longit udinal translation Plan Vertical translation Section Vertical tilt Section

State Specifications

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 Numberof states

So what if dowels are misaligned?

 Pav ement damage may result

• Spalling
• Cracking

 The eff ectiveness of dowel bars may be

compromised

• Loss of load transfer efficiency(LTE)
• Premature development of faulting

 How bad is bad? – we don’t know

• Existi ng specifications maybe too tight
• Comprehensive study under way (NCHRP 10-69)

SLIDE 3

Joint Score for IN1 (Basket)

5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0

1 3 5 7 9 1 1 1 3 1 5 1 7 1 9 2 1 2 3 2 5 2 7 2 9 3 1 3 3 3 5 3 7 3 9 4 1 4 3 4 5 4 7 4 9

J

• int

Joint Score

IN1 – 5 years old

Joint Score for KS4 (DBI)

5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0

1 3 5 7 9 1 1 1 3 1 5 1 7 1 9 2 1 2 3 2 5 2 7 2 9 3 1 3 3 3 5 3 7 3 9 4 1 4 3 4 5 4 7 4 9

Join t Joint S core

KS4, NB I-35 – 6 years ol d

SLIDE 4

Joint Score for the GA Section (DBI)

5 10 15 20 25 30 35 40 45 50

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 6 2 7 2 8 3 0 3 2 3 3 3 5 3 6 3 7 3 8 3 9 4 0 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 5

Joint Joint Score

30- yr old GA section with extremel y poor dowel alignment

Joint Score for the WA Section (Retrofit)

5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0

1 3 5 7 9 1 1 1 3 1 5 1 7 1 9 2 1 2 3 2 5 2 7 2 9 3 1 3 3 3 5 3 7 3 9 4 1 4 3 4 5 4 7 4 9

Join t Joint S core

SLIDE 5

WA section – 35 yr old pavement; 8 yr old retrofit

Effects 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 Perc ent of bars

Bas ket DBI

Comparison of DBI and Basket

More critical ranges

• f misalignment

SLIDE 6

Typical Joint ProblemJoints

SLIDE 7

Use of MIT Scan-2 data in optimizing PCC 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

% of Bars Aug 7 Aug 10 Aug 12

Dowel Placement Specifications

(CPTP Techbrief FHWA-HIF-07- 021)

 Ideally , dowel bars should be placed without any

placement error

 There are tolerable lev els of placement errors  Stringent (but constructible) requirements should

be specif ied, but allowance should be made f or tolerable errors

SLIDE 8

Possible Options for Correcting Misaligned Bars

 Cut misaligned bars  Retrof it additional dowel bars  Remov e and replace slab  Full-depth repair

SLIDE 9

Best approach: don’t create problems

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 10 1 1 1 2 13 14 1 5 1 6 17 18 1 9 2 21 22 23 2 4 25 26 27 2 8 29 30 31 3 2 33 34 35 3 6 37

Joint Joint Score

Some misalignments are harmless

5 1 0 1 5 2 0 2 5 3 0 3 5 4 0 4 5 5 0

1 3 5 7 9 1 1 1 3 1 5 1 7 1 9 2 1 2 3 2 5 2 7 2 9 3 1 3 3 3 5 3 7 3 9 4 1 4 3 4 5 4 7 4 9

J

• int

Joint Score

SLIDE 10

Questions?