Transcript Presentation Materials - Iowa State University

SHRINKAGE AND CRACKING BEHAVIOR
OF HPC USED FOR BRIDGE DECK
OVERLAYS
By
Hasitha Seneviratne
Iowa State University, 2013
INTRODUCTION

Objective
To
examine the shrinkage and cracking potential
of HPC concrete overlay mixes
Different cements
 Supplementary materials
 Shrinkage cracking potential

RESEARCH APPROACH
Shrinkage and Cracking Behavior of HPC Used
for Bridge Deck Overlays
Materials
Proportions
Experimental work
εauto
εsh
εring
Modeling
εsh
Creep
σ t ring
σ t creep
E, Fc & Fsplit
Stress analysis
σ Split tensile
σ t =Ec εsh
Cracking Behavior
LITERATURE REVIEW

Types of shrinkage





Effects of constituent materials





Chemical
Autogenous
Plastic
Drying
Cementitious material
Aggregates
Admixtures
Factors affecting restrained shrinkage behavior
Creep prediction models


B3
Modified NCHRP 496 model
LITERATURE REVIEW
Plastic shrinkage
Chemical shrinkage
Autogenous shrinkage
Drying shrinkage
pore
Capillary Force
Water evaporates
Autogenous
shrinkage
Free Shrinkage
Factors affecting shrinkage
Influence on shrinkage
Reference
Cement
C3A, C4AF increases observed
shrinkage
Fly Ash
Reduces autogenous shrinkage
Tazawa
(1997)
Nakarai
(2009)
Slag
No clear evidence of increasing or
decreasing effect, depends on
source and fineness
Whiting
(2000)
Metakaolin
Similar shrinkage to control up to
10% replacement, significant
reduction at 15% replacement
Brooks
(2001)
Cement
Higher fineness cements
increases shrinkage
Deshpande
(2007)
Fly Ash
Reduces free shrinkage
Slag
Fineness influences performance.
Fine ground slag reduces
shrinkage
Metakaolin
Both total and pure free shrinkage
are reduced by metakaolin
Nakarai
(2009)
Jianyong
(2001),
Miyazawa
(2009)
Brooks
(2001)
MATERIALS

Cement
 Type
IP, I/II and I
Fly Ash : Class C Fly Ash (Headwaters Resources)
 GGBFS (Holcim)
 Metakaolin : Davison Catalysts
 Coarse aggregates

 Crushed
Limestone (2 gradations), Crushed Quartzite
Fine aggregates – River Sand
 Admixtures

 Air
Entraining Agent: Daravair 1000, Retarder: Daratard 17,
Mid-range Water Reducer (MRWR): Mira 62, Standard Water
Reducer (NRWR): WRDA 82
MIX PROPORTIONS
EXPERIMENTAL WORK

Test methods of concrete shrinkage




Autogenous shrinkage (ASTM C157)
Free Drying shrinkage (ASTM C157)
Restrained ring shrinkage (ASTM C1581)
Test methods of mechanical properties



Elastic modulus (ASTM C469)
Compressive strength (ASTM C39)
Split tensile strength (ASTM C496)
SUMMARY OF RESULTS

Shrinkage displayed by cements were as follows




Type IP < Type I/II < Type I
Autogenous shrinkage has a high correlation to the amount of
cementitious material
Free shrinkage has a strong linear correlation to the mass loss
Coarser coarse aggregate displayed lesser restrained shrinkage
DISCUSSION
 Strength Parameters






Concrete mixtures with supplementary cementitious material
display late age strength development
Elastic modulus is highly dependent on the amount of
cementitious material used
Fly ash improved the strength parameters
Slag and combination of MK and fly ash had no significant
impact on strength parameters
Combination of fly ash and slag reduced the early age strength
but the strength grew with time.
Split tensile strength was greater with coarser aggregates
while elastic modulus was greater with quartzite.
DISCUSSION
Free drying stress calculated from the Hooke’s law
and the stress calculated for the strain recorded on
the steel ring display a linear relationship.



𝜎𝑓𝑟𝑒𝑒 𝑡 = 𝐸𝑐 𝑡 ∗ 𝜀𝑓𝑟𝑒𝑒 (𝑡) −𝐻𝑜𝑜𝑘𝑒′𝑠 𝑙𝑎𝑤
𝑝 = 𝜀𝑠𝑖 𝐸𝑠
𝜎𝑐 = 𝑝
2 −𝑅 2
𝑅𝑠𝑜
𝑠𝑖
2
2𝑅𝑠𝑜
2 +𝑅 2
𝑅𝑐𝑜
𝑐𝑖
2
2
𝑅𝑐𝑜 −𝑅𝑐𝑖
+𝜈
Ring Stress, psi

1200
1000
800
600
400
200
0
y = 0.3845x + 62.256
R² = 0.69
0
1000
2000
Free Drying Stress, psi
3000
Mix
Average Stress Rate, psi/day
1
2
3
4
5
6
7
8
9
10
11
Total
Strain Rate α,
cementitious
(μstrain/day)
material
content/pcy S1 S2 S3
665
24.0 23.7 24.2
650
19.2 20.6 19.5
575
12.9 16.8 20.7
710
23.8 24.1 27.3
625
26.8 24.7 22.6
825
26.7 28.9 32.2
695
34.2 36.6 37.2
670
22.3 28.5 23.7
590
19.7 29.6 33.0
675
27.2 29.8 27.2
590
24.1 27.8 21.5
40
Cracking
Average
ASTM C 1581
Stress Rate q,
time tr,
Stress
Cracking
(psi/day)
Rank
(days)
Rate, S
Potential
Rating
S1 S2 S3 S1 S2 S3 (psi/day)
- - 24 23 23.6
24
9 Moderate-Low
- - 19.0 20.4 19.2
20
10 Moderate-Low
- - 12.8 16.6 20.5
17
11 Moderate-Low
- 13 17 23.5 36.4 35.8
32
3 Moderate-High
11 - - 26.6 24.5 35.7
25
4 Moderate-High
16 16 18 32.9 37.6 41.5
37
1 Moderate-High
- - 33.8 36.2 36.8
36
2 Moderate-High
- - 22.0 28.2 23.4
25
7 Moderate-High
- - 19.5 29.3 32.7
27
6 Moderate-High
- - 26.9 29.5 26.9
28
5 Moderate-High
- - 23.9 27.5 21.3
24
8 Moderate-Low
35
30
Moderate-high
Moderate-low
25
20
15
Low
10
5
0
6
7
4
10
9
Mix5 ID
8
11
1
2
3
Mix
No.
σfree = E*εfree
σ free/(1+φ) ,psi (σfree/1+φ)/Fsp
(psi)
Peak
Average
Cracking
Cracking
ASTM Cracking
(σring/1+φ)/Fs
Stress Rate,
Potential
Potential
Potential Rating
S (psi/day)
p, (psi/psi)
14 day 28day 14 day 28day 14 day 28day Rank
1
1351
1766
363
513
1.07
1.22
7
Medium
0.77
Medium
23.6
Moderate-Low
2
1350
1656
395
508
1.12
1.19
8
Low
0.56
Low
19.675
Moderate-Low
3
933
1246
243
343
0.71
0.89
11
Low
0.55
Low
16.6
Moderate-Low
4
1441
1876
414
560
1.37
1.74
3
High
1.00
High
31.9
Moderate-High
5
1989
2344
542
678
1.71
1.93
1
High
0.85
High
24.9
Moderate-High
6
1571
2253
516
766
1.32
1.74
2
High
0.89
High
37.3
Moderate-High
7
1647
2028
466
600
1.19
1.36
6
Medium
0.69
Medium
35.6
Moderate-High
8
1297
1744
315
490
1.09
1.37
4
Medium
0.77
Medium
24.5
Moderate-High
9
1238
1539
277
396
0.99
1.03
10
Low
0.60
Medium
27.1
Moderate-High
10
1509
1771
457
558
1.13
1.11
9
Low
0.76
Medium
27.7
Moderate-High
11
1900
2092
479
575
1.29
1.36
5
Medium
0.52
Low
24.2
Moderate-Low



Mixes 4, 5 and 6 have high cracking potential,
Mixes 1, 7, 8, 9 and 10 have medium cracking potential and
Mixes 2, 3 and 11 have low cracking potential
CONCLUSION AND RECOMMENDATION



Concrete mixes with high shrinkage values may not always
crack first and it is the combined effect of shrinkage and
mechanical properties (elastic modulus, creep, and strength)
that determines concrete cracking potential.
20% fly ash which reduces shrinkage and 25% GGBFS which
has little effect on the shrinkage and are recommended to be
used in bridge deck overlay concrete either as singular
replacements or in combination.
Type I/II Cement may be preferred over Type I cement and
Type IP is preferred over Type I/II cement for the consideration
of the shrinkage cracking resistance.
 Type IP < Type I/II < Type I
CONCLUSION AND RECOMMENDATION




Since free drying shrinkage and mass loss have a strong
correlation, mass loss can be used as a good indicator for
free drying shrinkage.
Compressive strength is a good indicator to evaluate elastic
modulus and split tensile strength.
Controlling the paste volume in concrete to maintain
minimum paste volume is highly recommended. Cautions
shall be taken when total cementitious material content in
concrete of over 700lb/ft3 is used for bridge decks.
Results of the finite element analysis reveals that the mixes
would not display cracking within the 56 day period of study.
THANK YOU!
QUESTIONS?